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© 2020 by the authors., Intercropping could increase the capacity of crops to use soil resources. The aim of this study was to investigate the effects of lupin/wheat intercropping on soil properties, grain yield and nutrient uptake at different plant densities. Lupin and wheat were grown under field conditions as monocrops and intercrops. Soil nutrient availability and relative abundance of functional genes (acdS, phoD, phoC and nifH) were evaluated. The results obtained indicate that the cropping system had a significant effect (p < 0.001) on N and P availability. Lupin monocrop led to significantly higher N availability compared to intercrop. Intercropping resulted in significantly lower Olsen-P and K in soil concentrations compared to monocropping. No significant differences were observed in enzyme activity, except for phosphatase, which was 152% greater in the treatments at high plant density. Foliar nutrients were significantly higher in intercropping compared to monocropping. Acid phosphatase gene phoC was more abundant than the alkaline phosphatase gene phoD, which plays a more relevant role in acidic Andisols. The results confirm that N and P mobilization can improve nutrient absorption on wheat. When intercropped, lupin had positive effects on wheat due to its P mobilization capacity, while no effects were observed on lupin.

The El Tatio Geyser Field (ETGF), located in Northern Chile, is the main geyser field in the southern hemisphere. Despite this, details of its microbial ecology are still unknown. Here, we briefly report on the composition and predicted functions of the bacterial community in spouting pool sediments from the ETGF as revealed by high-throughput sequencing of 16S rRNA genes. Results of this analysis showed that while there were differences in richness and diversity between samples, bacterial communities were primarily dominated by the phyla Proteobacteria, followed Firmicutes, Bacteroidetes, Acidobacteria, and Chloroflexi. Analyses of predicted functional activity indicated that the functions were mostly attributed to chemoheterotrophy and aerobic chemoheterotrophy, followed by sulfur (respiration of sulfur compounds and sulfate) and nitrogen (nitrate reduction, respiration of nitrogen and nitrate) cycling. Taken together, our results suggest a high diversity in taxonomy and predictive functions of bacterial communities in sediments from spouting pools. This study provides fundamentally important information on the structure and function predictive functions of microbiota communities in spouting pools. Moreover, since the ETGF is intensively visited and impacted by tens of thousands of tourists every year, our results can be used to help guide the design of sustainable conservation strategies.

Biochar (BC) is gaining attention as a soil amendment that can remediate metal polluted soils. The simultaneous effects of BC on copper (Cu) mobility, microbial activities in soil using metallophytes have scarcely been addressed. The objective of this study was to evaluate the effects of biochar BCs on Cu immobilization and over soil microbial communities in a Cu-contaminated soil evaluated over a two-year trial. A Cu-contaminated soil (338mgkg -1 ) was incubated with chicken manure biochar (CMB) or oat hull biochar (OHB) at rates of 1 and 5% w/w. Metallophyte Oenothera picensis was grown over one season (six months). The above process was repeated for 3 more consecutive seasons using the same soils. The BCs increased the soil pH and decreased the Cu exchangeable fraction Cu by 5 and 10 times (for OHB and CMB, respectively) by increasing the Cu bound in organic matter and residual fractions, and its effects were consistent across all seasons evaluated. BCs provided favorable habitat for microorganisms that was evident in increased microbial activity. The DHA activity was increased in all BC treatments, reaching a maximum of 7 and 6 times higher than control soils in CMB and OHB. Similar results were observed in microbial respiration, which increased 53% in OHB and 61% in CMB with respect to control. The BCs produced changes in microbial communities in all seasons evaluated. The fungal and bacterial richness were increased by CMB and OHB treatments; however, no clear effects were observed in the microbial diversity estimators. The physiochemical and microbiological effects produced by BC result in an increase of plant biomass production, which was on average 3 times higher than control treatments. However, despite being a metallophyte, O. picensis did not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments. Refereed/Peer-reviewed

Genome analyses are being used to characterize plant growth-promoting (PGP) bacteria living in different plant compartiments. In this context, we have recently isolated bacteria from the phyllosphere of an Antarctic plant (Deschampsia antarctica) showing ice recrystallization inhibition (IRI), an activity related to the presence of antifreeze proteins (AFPs). In this study, the draft genomes of six phyllospheric bacteria showing IRI activity were sequenced and annotated according to their functional gene categories. Genome sizes ranged from 5.6 to 6.3 Mbp, and based on sequence analysis of the 16S rRNA genes, five strains were identified as Pseudomonas and one as Janthinobacterium. Interestingly, most strains showed genes associated with PGP traits, such as nutrient uptake (ammonia assimilation, nitrogen fixing, phosphatases, and organic acid production), bioactive metabolites (indole acetic acid and 1-aminocyclopropane-1-carboxylate deaminase), and antimicrobial compounds (hydrogen cyanide and pyoverdine). In relation with IRI activity, a search of putative AFPs using current bioinformatic tools was also carried out. Despite that genes associated with reported AFPs were not found in these genomes, genes connected to ice-nucleation proteins (InaA) were found in all Pseudomonas strains, but not in the Janthinobacterium strain.

Chile is among the largest avocado producers worldwide; however, currently, its production has diminished mainly attributed to abiotic stresses such as drought and soil salinity. Here, we evaluated the contribution of halotolerant bacterial consortia to water shortage and salt stress tolerance of avocado seedlings ( Persea americana Mill.) under field conditions. Inoculation trials were conducted in a commercial nursery to study the effects of two endophytic (C1 and C2) and two rhizosphere (C3 and C4) halotolerant bacterial consortia on growth, biomass, superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS) of avocado seedlings under salt (2% NaCl) stress and water shortage (50% less irrigation). Ours results revealed that avocado inoculation with C4 significantly ( P ≤ 0.05) increased aerial and root length; aerial and root fresh weight and chlorophyll content of salt-stressed seedlings; and the aerial length and root fresh weight of seedlings under water shortage. Similarly, the C4 significantly ( P ≤ 0.05) increased SOD activity in leaves of both the control and seedlings grown under salt stress and water shortage and also decreased TBARS content in leaves of control plants and of seedlings grown under salt stress. Whereas, C3 increased significantly ( P ≤ 0.05) aerial and root length and root fresh weight of salt-stressed seedlings; and also increased the trunk diameter and chlorophyll content of seedlings under water shortage. Similarly, C3 significantly ( P ≤ 0.05) stimulated SOD activity of leaves as compared to the control seedlings and also reduced the TBARS content of leaves and roots of avocado seedlings under salt stress. In contrast, the endophytic consortia were less efficient than rhizosphere consortia. Thus, C1 only increased the trunk diameter and chlorophyll content of salt–stressed seedlings and C2 increased the chlorophyll content of avocado seedlings under water shortage. Our study showed the favorable effect of bacterial inoculation on avocado nursey in nursery conditions under water shortage and salt stress, and identified consortia that potentially could be used as avocado biofertilizers.

Several studies have demonstrated the relevance of endophytic bacteria on the growth and fitness of agriculturally-relevant plants. To our knowledge, however, little information is available on the composition, diversity, and interaction of endophytic bacterial communities in plants struggling for existence in the extreme environments of Chile, such as the Atacama Desert (AD) and Patagonia (PAT). The main objective of the present study was to analyze and compare the composition of endophytic bacterial communities associated with roots and leaves of representative plants growing in Chilean extreme environments. The plants sampled were: Distichlis spicate and Pluchea absinthioides from the AD, and Gaultheria mucronata and Hieracium pilosella from PAT. The abundance and composition of their endophytic bacterial communities was determined by quantitative PCR and high–throughput sequencing of 16S rRNA, respectively. Results indicated that there was a greater abundance of 16S rRNA genes in plants from PAT (1013 to 1014 copies g−1 DNA), compared with those from AD (1010 to 1012 copies g−1 DNA). In the AD, a greater bacterial diversity, as estimated by Shannon index, was found in P. absinthioides, compared with D. spicata. In both ecosystems, the greater relative abundances of endophytes were mainly attributed to members of the phyla Proteobacteria (14% to 68%), Firmicutes (26% to 41%), Actinobacteria (6 to 23%) and Bacteroidetes (1% to 21%). Our observations revealed that most of operational taxonomic units (OTUs) were not shared between tissue samples of different plant species in both locations, suggesting the effect of the plant genotype (species) on the bacterial endophyte communities in Chilean extreme environments, where Bacillaceae and Enterobacteriacea could serve as keystone taxa as revealed our linear discriminant analysis.

Rivers are important ecosystem services providers in southern Chile; however, the microbiology of most rivers are understudied. This is particularly true for phosphorus (P) recycling by bacterial activity. Here, we studied the physicochemical properties, P contents, phosphomonoesterase (Pase) activities, and bacterial Pase genes (phoD, phoC, and phoX) in Chilean river sediments (Imperial and Tolten rivers, Chile) collected in sites with less and more degrees of anthropogenic influence during the summer and winter seasons. The richness, diversity, composition, and predicted function of the bacterial communities were addressed, as well as the spatiotemporal relationships among P-associated parameters and bacterial communities. Our results showed spatiotemporal variations, highlighting higher values of the temperature, conductivity, nutrients (C, N, P), Pase activity, and Pase genes in sediments collected in sites more anthropogenized during summer. In contrast, higher richness, diversity, and abundance of total bacteria were found in sediments collected in winter. The phylum Proteobacteria and heterotrophy were the most relatively abundant bacterial taxa and predicted function, respectively. The differentiation among winter and summer sediments was also revealed and the relationships between bacterial community and P-associated parameters were confirmed. Our analysis also highlighted the positive relationship between Pase genes with Gemmataceae, Xanthomonadaceae, and Chitinophagaceae families, and between Pase activity and Po with Chromatiaceae and Desulfobacteraceae families. This study represents an initial investigation aimed to unravel the compositions and relationships of bacterial communities with P recycling in these sediments, which are threatened by anthropogenic activity (e.g., agriculture, industry, cities, etc.). This information may be used in the design of countermeasures to prevent deterioration of Chilean rivers, which are relevant as ecosystem service providers.

The effects of arbuscular mycorrhizal (AM) inoculation on prokaryote abundance within the maize rhizosphere and hyphosphere, and retention of nutrients were investigated. Maize plants were grown in pots with a membrane located at a soil depth of approximately 16 cm that allowed growth of fungal hyphae above and below the membrane, but did not allow growth of roots below the membrane. As expected, mycorrhizal inoculation significantly increased the contents of soil organic matter, Total Kjeldahl Nitrogen (primarily organic N), and Mehlich 1 phosphorus relative to the non-inoculated control. Copy numbers of 16S rRNA genes were significantly higher in the mycorrhizal compartments relative to non-mycorrhizal controls. Bacterial ammonia monooxygenase (AOB) genes, but not archaeal monooxygease genes (AOA), were significantly higher in planted treatments with and without addition of mycorrhizae, indicating that mycorrhizae stimulate prokaryotic growth and bacterial nitrification. The ecological relevance of increased NOx-N resulting from the growth of AOB in inoculated soils is not clear; however, increased mobility of NOx-N over NH4 + could result in a competition between leaching loss and increased uptake by mycorrhizae.

Rhizobacterial communities may play a crucial role in phosphorus (P) nutrition of plants. However, our knowledge of how P fertilization modulates rhizobacterial communities in crops and pastures is still poor. Here, we investigated the effect of P addition (phosphate [PHO] and phytate [PHY]) on the composition of total bacterial communities and alkaline phosphomonoesterases (APase)-harboring bacterial populations in the rhizosphere microsites (root tip [RT] and mature zone [MZ]) of L. perenne. Sizes and diversities of bacterial communities were studied by 454-pyrosequencing of 16S rRNA genes, denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR). Our results suggested that phosphorus addition induces significant changes in the rhizobacterial community composition. Despite that pyrosequence analysis showed that members of the Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in all sampled rhizosphere microsites, differences in the relative abundances of some bacterial genera were detected (e.g., Arthrobacter and Acidothermus). Greater richness in rhizosphere microsites of plants supplied with PHY compared with PHO were revealed. With respect to APase-harboring bacterial populations, DGGE (phoD gene) showed significant differences between microsites supplied with PHO, PHY and controls. qPCR (16S rRNA genes, phoD and phoX) showed significantly greater abundances of bacteria and APase genes in RT than in MZ microsites. This study contributes to our understanding of the effect P fertilization on rhizobacterial community compositions of pastures grown in Chilean Andisols.

Chile is topographically and climatically diverse, with a wide array of diverse undisturbed ecosystems that include native plants that are highly adapted to local conditions. However, our understanding of the diversity, activity, and role of rhizobacteria associated with natural vegetation in undisturbed Chilean extreme ecosystems is very poor. In the present study, the combination of denaturing gradient gel electrophoresis and 454-pyrosequencing approaches was used to describe the rhizobacterial community structures of native plants grown in three representative Chilean extreme environments: Atacama Desert (ATA), Andes Mountains (AND), and Antarctic (ANT). Both molecular approaches revealed the presence of Proteobacteria, Bacteroidetes, and Actinobacteria as the dominant phyla in the rhizospheres of native plants. Lower numbers of operational taxonomic units (OTUs) were observed in rhizosphere soils from ATA compared with AND and ANT. Both approaches also showed differences in rhizobacterial community structures between extreme environments and between plant species. The differences among plant species grown in the same environment were attributed to the higher relative abundance of classes Gammaproteobacteria and Alphaproteobacteria. However, further studies are needed to determine which environmental factors regulate the structures of rhizobacterial communities, and how (or if) specific bacterial groups may contribute to the growth and survival of native plants in each Chilean extreme environments.

Bacterial alkaline phosphomonoesterases (APases) are relevant for organic phosphorus (Po) recycling in many soils. However, the abundance and diversity of bacterial APase in the rhizospheres of native plants are poorly known, particularly in extreme environments. In this research work, we studied the composition of total and APase-harboring bacterial communities, abundances of selected APase genes (phoD and phoX), and APase activities in rhizosphere soils from native plants grown in extreme environments of northern (Atacama Desert), central (Andes volcano; Quetrupillan and Mamuil Malal) and hot spring (Liquine), and southern polar (Patagonia and Antarctic) regions of Chile. Differences in the composition of bacterial communities in the rhizosphere soils were revealed by denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR) of 16S ribosomal RNA (rRNA), phoD, and phoX genes. In general, the significant lowest bacterial diversities, APase gene abundances, and APase activities were observed in rhizosphere soils from Atacama Desert, whereas the highest values were observed in rhizosphere soils of Patagonia. In addition, APase gene abundances were positively correlated among them and with APase activity of rhizosphere soils, but negatively correlated with phosphorus (P) availability in rhizosphere soils. Although bacterial APases were observed in all studied rhizosphere soils, their relevance to soil Po recycling in soils of extreme environments remains unclear and further studies are needed.

Harmful algae blooms (HABs) cause acute effects on marine ecosystems due to their production of endogenous toxins or their enormous biomass, leading to significant impacts on local economies and public health. Although HAB monitoring has been intensively performed at spatiotemporal scales in coastal areas of the world over the last decades, procedures have not yet been standardized. HAB monitoring procedures are complicated and consist of many methodologies, including physical, chemical, and biological water sample measurements. Each monitoring program currently uses different combinations of methodologies depending on site specific purposes, and many prior programs refer to the procedures in quotations. HAB monitoring programs in Chile have adopted the traditional microscopic and toxin analyses but not molecular biology and bacterial assemblage approaches. Here we select and optimize the HAB monitoring methodologies suitable for Chilean geography, emphasizing on metabarcoding analyses accompanied by the classical tools with considerations including cost, materials and instrument availability, and easiness and efficiency of performance. We present results from a pilot study using the standardized stepwise protocols, demonstrating feasibility and plausibility for sampling and analysis for the HAB monitoring. Such specific instructions in the standardized protocol are critical obtaining quality data under various research environments involving multiple stations, different analysts, various time-points, and long HAB monitoring duration.

Soil microorganisms are important mediators of carbon cycling in nature. Although cellulose- and hemicellulose-degrading bacteria have been isolated from Algerian ecosystems, the information on the composition of soil bacterial communities and thus the potential of their members to decompose plant residues is still limited. The objective of the present study was to describe and compare the bacterial community composition in Algerian soils (crop, forest, garden, and desert) and the activity of cellulose- and hemicellulose-degrading enzymes. Bacterial communities were characterized by high-throughput 16S amplicon sequencing followed by the in silico prediction of their functional potential. The highest lignocellulolytic activity was recorded in forest and garden soils whereas activities in the agricultural and desert soils were typically low. The bacterial phyla Proteobacteria (in particular classes α–proteobacteria, δ–proteobacteria, and γ–proteobacteria), Firmicutes, and Actinobacteria dominated in all soils. Forest and garden soils exhibited higher diversity than agricultural and desert soils. Endocellulase activity was elevated in forest and garden soils. In silico analysis predicted higher share of genes assigned to general metabolism in forest and garden soils compared with agricultural and arid soils, particularly in carbohydrate metabolism. The highest potential of lignocellulose decomposition was predicted for forest soils, which is in agreement with the highest activity of corresponding enzymes.

Phosphobacteria, secreting organic acids and phosphatases, usually favor plant performance in acidic soils by increasing phosphorus (P) availability and aluminum (Al) complexing. However, it is not well-known how P-deficiency and Al-toxicity affect the phosphobacteria physiology. Since P and Al problems often co-occur in acidic soils, we have therefore proposed the evaluation of the single and combined effects of P-deficiency and Al-toxicity on growth, organic acids secretion, malate dehydrogenase (mdh) gene expression, and phosphatase activity of five Al-tolerant phosphobacteria previously isolated from ryegrass. These phosphobacteria were identified as Klebsiella sp. RC3, Stenotrophomona sp. RC5, Klebsiella sp. RCJ4, Serratia sp. RCJ6, and Enterobacter sp. RJAL6. The strains were cultivated in mineral media modified to obtain (i) high P in absence of Al–toxicity, (ii) high P in presence of Al–toxicity, (iii) low P in absence of Al–toxicity, and (iv) low P in presence of Al–toxicity. High and low P were obtained by adding KH2PO4 at final concentration of 1.4 and 0.05 mM, respectively. To avoid Al precipitation, AlCl3 × 6H2O was previously complexed to citric acid (sole carbon source) in concentrations of 10 mM. The secreted organic acids were identified and quantified by HPLC, relative mdh gene expression was determined by qRT-PCR and phosphatase activity was colorimetrically determined using p-nitrophenyl phosphate as substrate. Our results revealed that although a higher secretion of all organic acids was achieved under P–deficiency, the patterns of organic acids secretion were variable and dependent on treatment and strain. The organic acid secretion is exacerbated when Al was added into media, particularly in the form of malic and citric acid. The mdh gene expression was significantly up–regulated by the strains RC3, RC5, and RCJ6 under P–deficiency and Al–toxicity. In general, Al–tolerant phosphobacteria under P deficiency increased both acid and alkaline phosphatase activity with respect to the control, which was deepened when Al was present. The knowledge of this bacterial behavior in vitro is important to understand and predict the behavior of phosphobacteria in vivo. This knowledge is essential to generate smart and efficient biofertilizers, based in Al–tolerant phosphobacteria which could be expansively used in acidic soils.

Phytases are enzymes involved in organic phosphorus cycling in nature and widely used as feed additives in animal diets. Thermal tolerance is a desired property of phytases. The objectives of this study were to screen and characterize bacterial phytases from Chilean hydrothermal environments. In this study, 60% (30 of 63) of screened thermophilic (60 °C) isolates showed phytase activity in crude protein extracts. The characterization of phytase from two selected isolates (9B and 15C) revealed that both isolates produce phytases with a pH optimum at 5.0. The temperature optimum for phytate dephosphorylation was determined to be 60 and 50 °C for the phytases from the isolates 9B and 15C, respectively. Interestingly, the phytase from the isolate 15C showed a residual activity of 46% after incubation at 90 °C for 20 min. The stepwise dephosphorylation of phytate by protein extracts of the isolates 9B and 15C was verified by HLPC analysis. Finally, the isolates 9B and 15C were identified by partial sequencing of the 16S rRNA gene as members of the genera Bacillus and Geobacillus, respectively.

Phosphorus (P) is an essential macronutrient for plant growth and is therefore an important component of agricultural fertilizers, especially for P–deficient soils. As a more environmentally friendly alternative to P–fertilization, phosphobacteria are regularly being proposed as bio–inoculants for plants that are cultivated in P–deficient soils. Although it is known that phosphobacteria inoculation can influence the growth and P nutrition of the host plant, the underlying responses at the molecular level have to date, not been fully elucidated. Here, we evaluated the single and combined effects of a phosphobacteria consortium inoculation and triple superphosphate fertilization on the biomass, P content, anti–oxidant capacity and phosphate–transporters genes of Lolium perenne. Plants were grown over 45 days in presence and absence of P–fertilization and phosphobacteria inoculation in two soils with different P bio–availabilities. Our results reveal that irrespective of P–availability in soils, the phosphobacteria inoculation provides an ‘enhancement effect’ of the P–fertilization on the development, nutrition and the alleviation of oxidative stress, in L. perenne. This was evidenced by higher biomass, increased P content, and lower cellular damage in tissues of the inoculated plants. The inoculation with phosphobacteria decreased the relative gene expression of superoxide dismutase isoforms in tissues of fertilized plants grown in the P–deficient soil. In addition, phosphobacteria inoculation was also associated with a lower relative expression of phosphate–transporter genes of P–fertilized plants. Therefore, instead of being an alternative to P–fertilization, phosphobacteria could rather be a promising complement to P–fertilization in P–deficient soils and potentially reduce fertilizer application rates. Based on our findings, an explicatory model of plant–soil–phosphobacteria interactions on the regulation of anti–oxidant and phosphate–transport capacities in P–deficient, is proposed.

Fil: Briceno, Gabriela. Universidad de la Frontera. Nucleo Cientifico y Tecnologico en Recursos Naturales; Chile

Phytases of different origin were covalently bound onto Fe3O4 magnetic nanoparticles (12 nm). Binding efficiencies of all three phytases were well above 70% relative to the number of aldehyde groups available on the surface of the magnetic nanoparticles. Temperature stability for all three phytases was enhanced as a consequence of immobilisation, whereas pH dependence of enzyme activity was not affected. Maximum catalytic activity of the immobilised phytases was found at 60°C (rye), 65°C (Aspergillus niger) and 70°C (Escherichia albertii). The immobilised enzymes exhibited the same excellent substrate specificities and unique myo-inositol phosphate phosphatase activities as their soluble counterparts. However, the catalytic turnover number dropped drastically for the immobilised phytases. The amount of the desired partially phosphorylated myo-inositol phosphate isomer could be easily controlled by the contact time of substrate solution and immobilised enzymes. The immobilised phytases showed a high operational stability by retaining almost full activity even after fifty uses.

The effect of nitrogen (N) and phosphorus (P) fertilization on composition of rhizobacterial communities of volcanic soils (Andisols) from southern Chile at molecular level is poorly understood. This paper investigates the composition of rhizobacterial communities of two Andisols under pasture after 1- and 6-year applications of N (urea) and P (triple superphosphate). Soil samples were collected from two previously established sites and the composition of rhizobacterial communities was determined by denaturing gradient gel electrophoresis (PCR-DGGE). The difference in the composition and diversity between rhizobacterial communities was assessed by nonmetric multidimensional scaling (MDS) analysis and the Shannon-Wiener index. In Site 1 (fertilized for 1 year), PCR-DGGE targeting 16S rRNA genes and MDS analysis showed that moderate N application (270 kg N ha(-1) year(-1)) without P significantly changed the composition of rhizobacterial communities. However, no significant community changes were observed with P (240 kg P ha(-1) year(-1)) and N-P application (270 kg N ha(-1) year(-1) plus 240 kg P ha(-1) year(-1)). In Site 2 (fertilized for 6 years with P; 400 kg P ha(-1) year(-1)), PCR-DGGE targeting rpoB, nifH, amoA and alkaline phosphatase genes and MDS analysis showed changes in rhizobacterial communities only at the highest rate of N application (600 kg N ha(-1) year(-1)). Quantitative PCR targeting 16S rRNA genes also showed higher abundance of bacteria at higher N application. In samples from both sites, the Shannon-Wiener index did not show significant difference in the diversity of rhizobacterial communities. The changes observed in rhizobacterial communities coincide in N fertilized pastures with lower soil pH and higher pasture yields. This study indicates that N-P application affects the soil bacterial populations at molecular level and needs to be considered when developing fertilizer practices for Chilean pastoral Andisols.

Cereal crops grown in southern Chilean Andisol provide suboptimal levels of this metalloid for human diet. Certain rhizosphere microorganisms, such as rhizobacteria and arbuscular mycorrhizal fungi can increase the selenium uptake in plants. The purpose of this study was to evaluate selenium acquisition by wheat plants through the co-inoculation of native selenobacteria strains (Stenotrophomonas sp. B19, Enterobacter sp. B16, Bacillus sp. R12 and Pseudomonas sp. R8), both individually and in mixture, as selenonanosphere source with one arbuscular mycorrhizal fungus (Glomus claroideum). Total selenium content in plant tissues and substrate was analyzed. According to our results, significant higher selenium content was found in inoculated plants in comparison to uninoculated controls (P ≤ 0.05). Independently of fungal presence, selenium content in grain from plants inoculated with Enterobacter sp. B16 (236 mg kg−1) was higher than the rest of the strains (116–164 mg kg−1). However, when plants were co-inoculated with a mixture of selenobacteria strains and G. claroideum, selenium content in grain was 23.5% higher (725 mg kg−1) than non-mycorrhizal plants (587 mg kg−1). The results suggest a synergistic effect between the selenobacteria mixture and G. claroideum associated to major biodiversity and demonstrate a great potential of these rhizosphere microorganisms for biofortification of cereals and its derivates., This study was supported by CONICYT Postdoctoral scholarship 3130542 and FONDECYT 1100625 of the Chilean Government. J.J. Acuña is thankful for the financial support of CONICYT through the Doctoral Fellowship Program. M.A. Jorquera also acknowledges financial support by FONDECYT 1120505.

Phytase-producing bacteria (PPB) is being investigated as plant growth promoting rhizobacteria (PGPR) to improve the phosphorus (P) nutrition and growth of plants grown in soil with high phytate content. Phytate is dominant organic P forms in many soils and must be hydrolyzed to be available for plants. Indian mustard (Brassica juncea) is a plant with economic importance in agriculture and phytoremediation, therefore biotechnological tools to improve growth and environmental stress tolerance are needed. In this study, we isolated and characterized PPB from Himalayan soils and evaluated their effect on growth and P uptake by B. juncea under greenhouse conditions. Sixty five PPB were isolated and based on phytate hydrolysis, three efficient PPB were chosen and identified as Acromobacter sp. PB-01, Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13. Selected PPB showed ability to grow at wide range of pH, temperature and salt concentrations as well as to harbour diverse PGPR activities, such as: solubilization of insoluble Ca-phosphate (193-642 μg ml(-1)), production of phytohormone indole acetic acid (5-39 μg ml(-1)) and siderophore. Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13 showed 50 and 70 % inhibition of phytopathogen Rhizoctonia solani, respectively. Greenhouse potting assay also showed that the bacterization of B. juncea seeds with Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13 significantly increased the biomass and P content in 30 days old seedlings. This study reveals the potential of PPB as PGPR to improve the growth of B. juncea.

The role of gut microbiota in the development of metabolic illnesses has been abundantly demonstrated. Recent studies suggest that gut microbiota alterations may also be related to the development of hypercholesterolemia. Therefore, we aimed to assess differences in the gut bacterial community profiles between hypercholesterolemic subjects and controls. Thirty cases diagnosed with hypercholesterolemia and 27 normocholesterolemic controls were included. A fasting whole blood sample was obtained to determine the lipid profile. In parallel, stool samples were collected and total DNA was isolated to assess the bacterial community profiles by denaturing gradient gel electrophoresis (DGGE). In addition, the Richness, Shannon-Weaver, and Simpson indexes were used to evaluate the richness and diversity of bacterial communities. As expected, serum concentrations of total cholesterol, triglycerides, and LDL-cholesterol were significantly higher in the cases compared with controls. Moreover, DGGE analysis showed a lower richness and diversity of bacterial communities in hypercholesterolemic subjects. In conclusion, our results showed differences in the profiles of bacterial communities between hypercholesterolemic subjects and controls, suggesting a possible role of the gut microbiota in the development of hypercholesterolemia.

In Chilean volcanic soil, crop production often is limited by a combination of the low available P and high concentration of toxic aluminum (Al). In this study we aimed to isolate Al-tolerant plant-growth-promoting bacteria from the rhizosphere and the endosphere of ryegrass grown in acidic Chilean volcanic soil in order to characterize a bacterial consortium capable of contributing to alleviation of Al 3+ toxicity and supporting plant growth in Andisol. Five strains, i.e. Klebsiella sp. RC3, Stenotrophomonas sp. RC5, Klebsiell a sp. RCJ4, Serratia sp. RCJ6 and Enterobacter sp. RJAL6, were selected based on their capacity to tolerate high Al concentration (10 mM) and to exhibit multiple plant-growth-promoting traits (P solubilization, indole acetic acid production, 1-aminocyclopropane-1-carboxylate deaminase activity, and exudation of organic acid anions and siderophores). Based on the results, we can suggest that selected bacteria could alleviate Al stress by forming Al 3+ -siderophore complexes. The plant-growth-promoting potential of the bacterial consortium was confirmed in an assay with ryegrass plants. In the treatment with cattle dung manure, the consortium promoted plant growth and the phosphatase activity in the rhizosphere soil. Increased phosphatase activity coincided with elevated P concentration in shoots. Our results suggest that a combination of native Al-tolerant bacteria and cattle dung manure is effective in decreasing Al toxicity and promoting plant growth in Andisols of southern Chile.

Plant growth-promoting rhizobacteria (PGPR) are studied as complements/alternatives to chemical fertilizers used in agriculture. However, poor information exists on the potential of PGPR from undisturbed ecosystems. Here, we have evaluated the plant growth-promoting (PGP) effect of rhizobacterial consortia from undisturbed Chilean arid ecosystems (Consortium C1) and agro-ecosystems (Consortium C2) on plant biomass production. The PGP effects of C1 and C2 were assayed in wheat seedlings (Triticum aestivum L.) grown in pots under growth chamber conditions and in pots placed in an open greenhouse under natural conditions, using two different Chilean Andisols (Piedras Negras and Freire series) kept either at 30 or 60% of their maximum water holding capacity (MWHC). PGP effects depended on the soil type, MWHC and the growth conditions tested. Although both consortia showed PGB effects in artificial soils relative to controls in growth chambers, only C1 provoked a PGP effect at 60% MWHC in phosphorus-poor soil of the 'Piedras Negras' series. At natural conditions, however, only C1 exhibited statistically significant PGP effects at 30% MWHC in 'Piedras Negras', yet and most importantly allowed to maintain similar plant biomass as at 60% MWHC. Our results support possible applications of rhizobacterial consortia from arid ecosystems to improve wheat growth in Chilean Andisols under water shortage conditions.Wheat seedling inoculated with rhizobacterial consortia obtained from an undisturbed Chilean arid ecosystem showed improved growth in phosphorus-poor and partly dry soil. Arid ecosystems should be considered in further studies as an alternative source of microbial inoculants for agro-ecosystems subjected to stressful conditions by low nutrients and/or adverse climate events.

Ice-binding proteins (IBPs), such as antifreeze proteins (AFPs) and ice-nucleating proteins (INPs), have been described in diverse cold-adapted organisms, and their potential applications in biotechnology have been recognized in various fields. Currently, both IBPs are being applied to biotechnological processes, primarily in medicine and the food industry. However, our knowledge regarding the diversity of bacterial IBPs is limited; few studies have purified and characterized AFPs and INPs from bacteria. Phenotypically verified IBPs have been described in members belonging to Gammaproteobacteria, Actinobacteria and Flavobacteriia classes, whereas putative IBPs have been found in Gammaproteobacteria, Alphaproteobacteria and Bacilli classes. Thus, the main goal of this minireview is to summarize the current information on bacterial IBPs and their application in biotechnology, emphasizing the potential application in less explored fields such as agriculture. Investigations have suggested the use of INP-producing bacteria antagonists and AFPs-producing bacteria (or their AFPs) as a very attractive strategy to prevent frost damages in crops. UniProt database analyses of reported IBPs (phenotypically verified) and putative IBPs also show the limited information available on bacterial IBPs and indicate that major studies are required.

Organic wastes rich in phosphorus (P) are considered an alternative to decrease the dependence on chemical P fertilization in crops and pastures. Microbial inoculants are being studied as a tool to increase plant P availability in organic wastes. In this study, we explore the effect of inoculation with Bacillus sp. MQH-19 (a native phytase-producing bacterium) on the release of inorganic phosphorus (Pi) in cattle manure with low available P but a high total P content. Bacteria inoculation resulted in a higher release of Pi (8% in NaHCU3 and 13% in NaOH-EDTA extracts) compared with that of uninoculated manure (0.7% in NaHCU3 and 0.1% in NaOH-EDTA extracts). However, a greater amount of Pi was released in inoculated manure supplemented with phytate (47% in NaHCU3 and 117% in NaOH-EDTA extracts) compared with that of uninoculated manure supplemented with phytate (30% in NaHCU3 and 15% in NaOH-EDTA extracts). In addition, the use of denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR) revealed that the bacterial community structure in manure was affected by inoculation and that the prevalence of Bacillus sp. MQH-19 decreased during incubation (6 days). This study demonstrates that Pi availability in cattle manure can be increased by phytase-producing bacteria inoculation. Phytase-producing bacteria inoculation might represent an attractive strategy to increase P availability in agricultural wastes, which are used as organic fertilizers in crops and pastures.

Chlorpyrifos (CP) is a widely used agricultural insecticide that is hazardous to both the environment and human health. Therefore, it is an essential to develop approaches to remove this compound from contaminated soils, water and sediments. In this study, actinobacteria were isolated from an agricultural soil that had received continuous applications of CP. Four strains were selected as a result of their tolerance to 50 mg L -1 of CP in agar plate and they were identified as Streptomyces sp. based on 16S rDNA. According to relationship of CP degradation and microbial growth studies, two isolates were selected and were named Streptomyces sp. strain AC5 and Streptomyces sp. strain AC7. The strains were cultivated in liquid medium with CP at concentrations of 25 mg L -1 and 50 mg L -1 for 72 h. The results indicated that both strains were able to rapidly degrade CP with about 90% degradation after 24 h of incubation. A different pattern of CP degradation was observed when its main metabolite, 3,5,6-trichloro-2-pyridinol (TCP) was monitored. A maximum concentration of 0.46 mg L -1 of TCP was produced by Streptomyces sp. strain AC5 and its concentration decreased as a function of time. In contrast, TCP production by Streptomyces sp. AC7 increased over time from 1.31 mg L -1 to 4.32 mg L -1. CP degradation was associated to microbial growth of the strains, pH modification, glucose consumption and organic acids excretion in the liquid medium. This work constitutes one of the few reports of Streptomyces as CP-degraders. Given the high CP degradation observed here, the Streptomycetes strains show a good potential as CP-degrading actinobacteria. Fil: Briceño, G.. Universidad de la Frontera; Chile Fil: Fuentes, María Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucuman. Planta Piloto de Procesos Industriales Microbiologicos; Argentina Fil: Palma, G.. Universidad de la Frontera; Chile Fil: Jorquera, M. A.. Universidad de la Frontera; Chile Fil: Amoroso, Maria Julia del R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucuman. Planta Piloto de Procesos Industriales Microbiologicos; Argentina Fil: Diez, M. C.. Universidad de la Frontera; Chile

Despite the fact that murta infusions have been used to treat gut/urinary infections by native Chileans for centuries, the mechanisms promoting such effects still remain unclear. As a first attempt to unravel these mechanisms, human fecal samples were incubated in a medium containing water extract of murta leaves (ML) and the growth of different bacterial groups was evaluated. Control incubations were made in media containing fructooligosaccharides (FOS) and glucose as a carbon source. Phenolic compounds in the ML extract, likely promoters of bioactivity, were identified by HPLC-DAD-MS(n) . Concentrations (log₁₀ CFU/mL) of bifidobacteria and lactobacilli in media containing the extract and FOS were 7.33 ± 0.05/4.95 ± 0.20 and 6.44 ± 0.22/6.05 ± 0.06, respectively. Clostridia, anaerobes and Enterobacteriaceae grew to a similar extent in media containing murta extract and FOS. In vitro tests (disk diffusion) showed that Gram-positive (Bacillus and Paenibacillaceae) and Gram-negative (Enterobacteriaceae) bacteria isolated from fecal samples were sensitive to both water and 50/50 ethanol/water extracts of ML (28.4 μg gallic acid equivalents). At this concentration, the antimicrobial activity of ML extracts was significantly (P0.05) lower than that of penicillin (10 U), whereas the difference between activity of ML extracts and gentamicine (10 μg) was no significant (P0.05). No evidence of dependency between the antimicrobial activity of ML extracts and the enzymatic capability of the sensitive strains was found.

Phytate is one of the most abundant sources of organic phosphorus (P) in soils, but must be mineralized by phytase-producing bacteria to release P for plant uptake. Microbial inoculants based on Bacillus spp. have been developed commercially, but few studies have evaluated the ecology of these bacteria in the rhizosphere or the types of enzymes that they produce. Here, we studied the diversity of aerobic endospore-forming bacteria (EFB) with the ability to mineralize phytate in the rhizosphere of pasture plants grown in volcanic soils of southern Chile. PCR methods were used to detect candidate phytase-encoding genes and to identify EFB bacteria that carry these genes. This study revealed that the phytate-degrading EFB populations of pasture plants included species of Paenibacillus and Bacillus, which carried genes encoding β-propeller phytase (BPP). Assays of enzymatic activity confirmed the ability of these rhizosphere isolates to degrade phytate. The phytase-encoding genes described here may prove valuable as molecular markers to evaluate the role of EFB in organic P mobilization in the rhizosphere.

During organic wastes degradation, P is transformed which may affect its availability. In this study, the dynamics of P and the occurrence of phytate-utilizing bacteria (PUB) were evaluated during aerobic degradation of dairy cattle dung in laboratory-scale reactors for 105 d. The results showed an increase of water-soluble inorganic P (Pi) (from 570 to 1890 mg kg(-1)) and biomass P (from 390 to 870 mg kg(-1)) during the initial 40 d. After this period, water-soluble Pi remained constant (around 1500 mg kg(-1)) and biomass P decreased (around 220 mg kg(-1)) probably due to the decrease of easily available C in dung. Under the acidic conditions in the first 20 d there was an increase in concentration of Al (25 mg kg(-1)) and Fe (27 mg kg(-1)) ions. These ions were no longer detectable in the alkaline conditions occurring after 40 d. In the same period, the Ca concentration increased (from 1170 to 2370 mg kg(-1)) and chemical speciation revealed permanent association of Ca ions with Pi. Sequential P fractionation showed a decrease of organic P in NaHCO(3), NaOH and HCl fractions and an increase of residual P (25-52% with respect to total P). Analysis by (31)P NMR also showed a decrease (from 14% to 1.6%) of phytic acid content during final experimental period (60 and 105 d). The bacteriological analysis revealed various PUB involved in degradation of the dung. Two morphotypes, genetically characterized as Enterobacter and Rahnella, which were dominant under higher content of residual P, showed strong utilization of phytate in vitro.

Phytases are a group of enzymes capable of releasing phosphate from phytate, one of the most abundant forms of organic phosphate in the natural environment. Phytases can be found in many organisms; in bacteria, they are particularly described in g-proteobacteria. In recent years, bacterial phytases have been isolated, characterized and proposed as potential tools in biotechnology. Microbial phytases have been applied mainly to animal (swine and poultry) and human foodstuffs in order to improve mineral bioavailability and food processing. Here, we summarize the current knowledge of bacterial phytases and phytase-producing bacteria, as well as their potential biotechnological applications, including new fields poorly explored, such as fish nutrition, environmental protection and plant nutrition. Despite the recognized importance in biotechnology, information on bacterial phytases and phytase-producing bacteria is clearly limited and major efforts are required to improve the knowledge of phytases present in bacteria and their utilization.

The aim of this study was to evaluate the influence of urea fertilizer and pH on the sorption process of two acidic herbicides, flumetsulam (2',6'-difluoro-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonanilide) and MCPA (4-chloro--tolyloxyacetic acid), on an Andisol. Urea reduced the adsorption of MCPA but not that of flumetsulam. The Freundlich parameter of MCPA decreased from 8.5 to 5.1 mg L kg. This finding could be attributed to an increase in dissolved organic C due to an initial increase in soil pH for urea application. The higher acidic character of MCPA compared with that of flumetsulam produced a greater hydrolysis of urea, leading to a further pH increase. A marked effect of pH on the adsorption of both herbicides was observed. The organic C distribution coefficient () values for flumetsulam were in the range of 74 to 10 L kg, while those of MCPA were in the range of 208 to 45 L kg. In the kinetic studies, the pseudo-second-order model appeared to fit the data best ( > 0.994). The initial adsorption rates () ranged from 20.00 to 4.59 mg kg h for flumetsulam and from 125.00 to 25.60 mg kg hfor MCPA. Both herbicides were adsorbed rapidly during the first stage of the sorption process, and the rates of sorption were dependent on pH. The application of the Elovich and Weber-Morris models led us to conclude that mass transfer through the boundary layer and, to a lesser degree, intraparticle diffusion were influenced by the chemical character of the herbicide. These results suggest that urea application could increase leaching of acid herbicides in soils.

Large amounts of urea and various herbicides are applied to Chilean Andisols by farmers; however, how different herbicide types affect bacterial communities in urea-fertilized soils remains unknown. In this study, the effect of post-emergent herbicides (MCPA, flumetsulam, fluroxypyr, triclopyr, clopyralid and picloram) on total bacterial (TB) and ammonia-oxidizing bacteria (AOB) communities was investigated in a urea-fertilized soil microcosm using denaturing gradient gel electrophoresis at days 1 and 15 of incubation. The residual concentrations of herbicides in microcosm soils were measured by high-performance liquid chromatography. Differences in bacterial communities were analyzed and visualized with non-metric multidimensional scaling. All of the tested herbicides decreased in microcosm soils, reaching 46–98% of dissipation at 15 days. Changes in the TB and AOB communities were variable, depending on the urea and herbicide dosage, herbicide type and sampling time. Under the recommended dose of urea (570 mg kg−1 soil), soils that were treated with MCPA and triclopyr showed significant changes in TB and AOB community structures compared to control soils at both sampling times. When a 2-fold-higher recommended dose of urea (1140 mg kg−1 soil) was applied, the TB communities were mainly affected by flumetsulam and picloram at both sampling times. Changes in the AOB communities were mainly observed in soils that were treated with MCPA and fluroxypyr under both urea doses. This study determined which herbicides (and doses) significantly affect the bacterial communities in urea-fertilized soils. This evidence can be very useful when management practices are being designed, revised and/or established in Andisols.

A study was conducted with the aim of evaluating the genetic diversity of alfalfa rhizobia isolated from volcanic soils in southern Chile and their ability to establish an effective symbiosis with alfalfa. Rhizobial strains isolated from nodules were identified and selected based on PCR analyses and acid tolerance. Symbiotic effectiveness (nodulation and shoot dry weight) of acid-tolerant rhizobia was evaluated in glasshouse experiments under acidic conditions. The results revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules with a high genetic diversity at strain level grouped in three major clusters. There was a close relationship (r 2 = 0.895, P ≤ 0.001, n = 40) between soil pH and the size of rhizobial populations. Representative isolates from major cluster groups showed wide variation in acid tolerance expressed on buffered agar plates (pH 4.5–7.0) and symbiotic effectiveness with alfalfa. One isolate (NS11) appears to be suitable as an inoculant for alfalfa according to its acid tolerance and symbiotic effectiveness at low pH (5.5). The isolation and selection of naturalized S. meliloti strains with high symbiotic effectiveness under acidic conditions is an alternative approach to improving the productivity of alfalfa and for reducing the application of synthetic fertilizers in Chile.

Kinetic studies of pesticides in soil are of great importance to know the processes and parameters that govern their fate in the environment. The aim of this study was to evaluate the influence of pH on the kinetic sorption process of four acidic herbicides, clopyralid, fluroxypyr, picloram and triclopyr on an Andisol, characterized by high organic matter content and acidic pH. The pseudo-second-order model appeared to fit the data better than other models (R² > 0.999). All herbicides were adsorbed rapidly during the first stage, but their adsorption was affected by pH and their chemical nature. The initial rate of reactions strongly decreased by increasing pH. The initial adsorption rates (h) and the sorption capacity of the herbicides showed the following order: fluroxypyr > triclopyr > picloram > clopyralid. At pH 4.0 the maximum amounts of fluroxypyr, triclopyr, picloram, and clopyralid adsorbed were respectively 75.2, 69.7, 40.5 and 11.7 %. The application of Elovich and Weber-Morris models suggests that mass transfer through the boundary layer and to a lesser degree intra-particle diffusion, control sorption kinetics, which appeared to be influenced by pH and chemical nature of the herbicides. The results obtained in this work suggest that soil pH and acidic character of herbicides could strongly affect the bioavailability of these herbicides on soil and their potential leaching.

Plasmid-mediated conjugation is an important mechanism through which bacteria establish new genetic traits in the environment. Here we used a combination of direct viable counting (DVC), fluorescence in situ hybridization (FISH), and green fluorescent protein (GFP) gene expression to estimate plasmid transfer frequencies (TFs) on nutrient-limited media at the single cell level. Conjugation experiments on nutrient-rich and -limited media were carried out using Pseudomonas fluorescens as a donor of a broad-host-range plasmid (RK2) tagged with the GFP gene and P. putida as the recipient. FISH-GFP and DVC-FISH-GFP allowed for the accurate detection of donor, recipient and transconjugants by fluorescence microscopy. The TFs obtained by these culture-independent approaches were 1 to more than 3 orders of magnitude higher than those determined by selective plate-counting. Lower and variable TFs obtained by selective plate-counting emphasize the importance of culture-independent approaches in plasmid transfer studies. The application of DVC before FISH-GFP on nutrient-limited medium produced elongated and/or fattened cells and resulted in a better fluorescence signal in target bacteria cells and better accumulation, maturation and fluorescence-emission of GFP within transconjugant cells, facilitating the detection and identification of cells compared with FISH-GFP alone. The DVC-FISH-GFP could be useful for other conjugation studies using bacteria with low metabolic activity under oligotrophic/stressful conditions or studies which require a precise determination of plasmid transfer events during short-term conjugation experiments.

The management of bacterial loading in intensive aquaculture systems is often a key factor in the success of larval cultures, particularly in molluscan hatcheries. Vibrio spp. have often been cited as affecting scallop larvae cultures. Bacteriological studies employing emergent molecular methods may now be of use in molluscan hatcheries to monitor the abundance of total and non-culturable Vibrio spp. In this study, the fluorescence in situ hybridization (FISH) technique with 16S rRNA-targeted oligonucleotide probes was used to quantify the presence of γ-Proteobacteria and Vibrio spp. in the bacterioplankton associated to mass larval cultures in six commercial hatcheries in two geographic regions of northern Chile. Results showed an average of 58% (Region III) and 38% (Region IV) of total cell counts could be detected by hybridization by using probe for domain Eubacteria. Use of the probe for γ-Proteobacteria showed averages between 21% and 28% in these regions, and use of the probe for Vibrio spp. detected percentage between 0.6% and 17%. Direct counts by fluorescence compared with viable plate counts suggested low culturability of the bacterioplankton. Results obtained from the different sampling areas did not reveal a characteristic pattern for each geographic region, nor by culture company. However, some differences were noted between companies with healthy larval cultures and one company which was experiencing mass larval mortalities, emphasizing the relevance of the bacterioplankton in scallop cultures.

Despite the recognized interest in Antarctic bacteria, the relationship between bacteria and Antarctic plants has scarcely been studied. Studies have demonstrated that bacteria in the phyllosphere may contribute to plant growth, but their role in native plants, such as Antarctic vascular plants living in hostile environments, is still unknown. Here we explore the bacterial community structure associated with the phyllosphere of Deschampsia antarctica, and evaluate the presence of ice recrystallization inhibition (IRI) activity in crude protein extracts from phyllosphere culturable bacteria. Denaturing gradient gel electrophoresis analysis (16S rRNA genes) showed significant differences in the total bacterial community of eight sampled plants; however, members of Pseudomonadales (Pseudomonas and Psychrobacter) and Rhizobiales (Agrobacterium and Aurantimonas) orders were dominant in all of the analyzed samples. Use of enterobacterial repetitive intergenic consensus polymerase chain reaction technique also revealed a high (>76 %) genetic diversity in 265 isolates from the phyllosphere. With respect to IRI activity, 32 isolates (21 %) showed IRI activity in crude protein extracts from cold-acclimated bacterial cultures, and 5 isolates (3 %) showed IRI activity in crude protein extracts from nonacclimated cultures.

Cereal production in southern Chile is based on volcanic soils (Andisol) that are phosphorus (P) deficient for plant nutrition. Phytate-mineralizing rhizobacteria (PMR) have been suggested as soil inoculants to improve P uptake and growth of plants cultivated in P-deficient soils. In this study, a greenhouse experiment was conducted to investigate the effects of inoculation with PMR ( Bacillus sp. N1-19NA, Enterobacter sp. N0-29PA, Pseudomonas sp.N1-55PA and Serratia sp. N0-10LB) on biomass and P uptake of cereal plants (wheat, oat and barley) grown in a Chilean Andisol with out P fertilization. Results showed that inoculation with Enterobacter sp. N0-29PA significantly ( P ≤0.05) increased the biomass and Puptake of oat plants. Changes in rhizosphere properties as soil enzyme activities (acid phosphatase and urease), and auxin production potential were also produced by Enterobacter sp. N0-29PA inoculation. Despite the possible value, Enterobacter sp. N0-29PA as a soil inoculant for P-deficient soils, other PMR assayed did not consistently enhanced biomass and P uptake of plants. In addtion, polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) combined with non-metric multidimensional scaling (nMDS) analysis revealed that PMR inoculation induced changes in rhizobacterial community composition, suggesting that PMR application substantially modify the microbiological characteristics of rhizosphere. However, long-term studies at field level are still needed to practical use of PMR as inoculants in Chilean Andisols.

The scallop Argopecten purpuratus is one of themajor resources of commercial importance in Chilean aquaculture. One of themajor limiting factors for the culture of this species has been mass mortalityoccurring during production of juvenile “seed” organisms where massmortality of veliger larvae has been attributed to the presence of pathogenicbacteria in scallops and hatchery systems. Bacteriological studies havedemonstrated that in addition to bacterial pathogens, beneficial bacterialspecies capable of improving scallop larval survival may also be isolated fromscallops and hatchery systems. Research has been carried out on thedetermination of the feasibility of implementing beneficial bacteria in thecontrol of culture pathogens, thus reducing the need for chemotherapeuticmethods. The present review analyzes bacteriological research data on thedifferent roles of bacteria associated with scallop culture and discussesrecentdata on the implementation of beneficial bacteria in biological control ofpathogens in larval mass cultures of Argopectenpurpuratus.

A marine vibrio (strain C33) having inhibitory effects on the growth of the pathogen Vibrio anguillarum-VAR was isolated from seawater used in mass culture of the north-Chilean scallop Argopecten purpuratus. This bacterial isolate demonstrated broad inhibitory activity on several bacterial strains, including some pathogenic vibrios. Ethyl acetate extracts of extracellular products of strain C33 were separated by thin layer chromatography (TLC), and three fractions thus obtained were found to have antimicrobial activity when tested using microplate bioassays. One of the fractions (A2) having marked antimicrobial activity, was further purified using TLC and analyzed by IR spectrophotometry and NMR'H and was characterized on a preliminary basis as an aliphatic hydroxyl ether. This compound demonstrated bacteriostatic activity against the important marine pathogens Vibrio parahaemolyticus and V. splendidus, and as discussed in the paper, may be useful in developing natural strategies for the control of pathogens in mass cultures of Argopecten purpuratus and possibly other molluscs affected by these bacteria.

Plant growth promoting bacteria and nitrogen-fixing bacteria (NFB) used for crop inoculation have important biotechnological potential as a sustainable fertilization tool. However, the main limitation of this technology is the low inoculum survival rate under field conditions. Microencapsulation of bacterial cells in polymer matrices provides a controlled release and greater protection against environmental conditions. In this context, the aim of this study was to isolate and characterize putative NFB associated with lupin nodules and to evaluate their microencapsulation by spray drying. For this purpose, 21 putative NFB were isolated from lupin nodules and characterized (16S rRNA genes). Microencapsulation of bacterial cells by spray drying was studied using a mixture of sodium alginate:maltodextrin at different ratios (0:15, 1:14, 2:13) and concentrations (15 and 30 % solids) as the wall material. The microcapsules were observed under scanning electron microscopy to verify their suitable morphology. Results showed the association between lupin nodules of diverse known NFB and nodule-forming bacteria belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Bacteroidetes. In microencapsulation assays, the 1:14 ratio of sodium alginate:maltodextrin (15 % solids) showed the highest cell survival rate (79 %), with a microcapsule yield of 27 % and spherical microcapsules of 5–50 µm in diameter. In conclusion, diverse putative NFB genera and nodule-forming bacteria are associated with the nodules of lupine plants grown in soils in southern Chile, and their microencapsulation by spray drying using sodium alginate:maltodextrin represents a scalable process to generate a biofertilizer as an alternative to traditional nitrogen fertilization.

In this study, we isolated putative plant-growth-promoting endophytic bacteria from selenium-supplemented wheat grown under field conditions. These bacterial strains belonged to Bacillus, Paenibacillus, Klebsiella, and Acinetobacter genera and showed genetic similarly with rhizospheric bacteria isolated in the same Andisol soil and with other endophytic strains previously reported. Strains isolated from selenium-supplemented wheat were highly tolerant to elevated selenium concentration (ranged from 60 to 180 mM), and showed potential plant-growth-promoting capabilities (auxin and siderophore production, phytate mineralization, and tricalcium phosphate solubilization). In addition, some strains like Acinetobacter sp. (strain E6.2), Bacillus sp. (strain E8.1), Bacillus sp., and Klebsiella sp. (strains E5 and E1) inhibited the growth of Gaeumannomyces graminis mycelia in vitro at 100, 50, and 30 %, respectively. These endophytic microorganisms would be useful for dual purposes: selenium biofortification of wheat plants and control of G. graminis, the principal soil-borne pathogen in volcanic soils from southern Chile., This study was supported by the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) postdoctoral scholarship N° 3130542 and CONICYT regular project N° 1100625 by the Chilean Government.

Soil microorganisms with phytase- and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activities are widely studied as plant growth-promoting rhizobacteria (PGPR). Here, we explored the bacterial community structure and occurrence of putative PGPR in plants grown in agro-ecosystems and undisturbed ecosystems from northern, central, and southern Chile. Total rhizobacterial community structure was evaluated by denaturing gradient gel electrophoresis, and dominant bands present in diverse ecosystems were sequenced. Significant differences in total bacterial communities were shown with some bacterial orders (Enterobacteriales, Actinomycetales, and Rhizobiales) being highly similar to both ecosystems. Twenty-nine putative PGPR, showing phytate- and ACC-degrading activities and production of auxin, were selected from across the sites. Based on 16S rRNA gene sequencing, the putative PGPR were characterized as Enterobacteriales (Enterobacter, Serratia, Pantoea, Rahnella, Leclercia), Pseudomonas, and Bacillus, consistent with previously reported PGPR and endophytic bacteria. Beta-propeller phytase genes with similarity to Bacillus were also identified. PGPR from agro-ecosystems appeared to show higher auxin production compared to those from undisturbed ecosystems. This study demonstrates that putative PGPR are widely distributed across Chilean soils. Further understanding of their contribution to the growth and adaptation of plant hosts to local soil conditions may provide opportunity for development of new PGPR in Chilean agriculture.

The aim of this work was to evaluate the treatment of cattle manure with phytases stabilized in allophanic nanoclays as a potential novel phosphorus (P) biofertilization technology for crops grown in volcanic soils (Andisol). Furthermore, because the optimal pH for commercial phytase catalysis does not match the natural pH of manure, a complementary experiment was set up to evaluate the effect of manure inoculation with an alkaline phytase-producing bacterium. Finally, phytase-treated soil, manure, and soil–manure mixtures were evaluated for their P-supplying capacity to wheat plants grown under greenhouse conditions. Treating cattle manure with phytases stabilized in nanoclays resulted in a significant (P ≤ 0.05) increase of inorganic P in soil extracts (NaOH-EDTA and Olsen). The use of phytase-treated cattle manure increased dry weights by 10 % and the P concentration by 39 % in wheat plants grown under greenhouse conditions, which is equivalent to a P fertilizer rate of about 150 kg of P per hectare. The inoculation of cattle manure with β-propeller phytase-producing bacteria led to an ∼10 % increase in inorganic P in the manure extracts. However, applying inoculated manure to soil did not significantly increase wheat yield or P acquisition responses. Our results suggest that the novel approach of incubating cattle manure with phytases stabilized in nanoclay enhances the organic P cycling and P nutrition of plants grown in P-deficient soils.

Management of soils to facilitate plant beneficial microbial interactions requires basic knowledge of the species composition and microbial community structures in the plant rhizosphere. Here, we examined composition of bacterial communities associated with rhizosphere microsites located at the root tips and mature root zones of Lolium perenne when grown in Chilean ash-derived volcanic soils (Andisols: Freire and Piedras Negras soil series). Community structures were analyzed by pyrosequencing of 16S ribosomal RNA (rRNA) genes followed by in silico analysis for phylogenetic assignments (MOTHUR and Visualization tool for Taxonomic Compositions of Microbial Community (VITCOMIC)). Analysis of the community structure revealed significant differences in community structures in relation to the soil series, which differed particularly in the relative abundance of Cyanobacteria and Firmicutes. However, no significant differences were observed with respect to root microsite location in the same Andisol series. Predominant taxa included members of the Proteobacteria, Actinobacteria, and Acidobacteria. Analysis by VITCOMIC showed that dominant bacterial groups comprised only 5 to 10 % of the total bacterial community and the remaining majority of bacteria included low-abundant taxa (Fusobacteria, Thermotogae, Lentisphaerae, Tenericutes, Deferribacteres Spirochaetes, Planctomycetes, Thermotogae, and Deinococcus-Thermus), most of which have not been previously reported or associated with the plant rhizosphere according to GenBank database. The results indicate that most of bacteria in the Chilean Andisols have not been described to the rhizosphere plants and their functional traits are still largely unknown.