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1-Aminocyclopropane-1-carboxylate deaminase (ACCD)-producing rhizobacteria are widely studied as plant growth-promoting rhizobacteria (PGPR) to alleviate a variety of stresses in plants. However, the presence of ACCD-producing rhizobacteria in plants that naturally occur in stressful ecosystems as well as the potential PGPR activity in agriculturally relevant plants has been poorly explored thus far. We isolated and characterized ACCD-producing rhizobacteria from Parastrephia quadrangularis, a native plant from the Andean Altiplano in Chile. The effects of selected ACCD-producing rhizobacteria on biomass and superoxide dismutase (SOD) activity of wheat seedlings subjected to salt stress (0.25 M and 0.45 M NaCl) were also evaluated. Ten out of 30 isolates showed ACCD activity (0.83–3.32 μmol α-ketobutyrate mg−1h−1) and were identified as members of the Enterobacteriales order (mainly Serratia and Klebsiella). The ACCD-producing rhizobacteria also showed salt tolerance (from 2.5 to 7.5% NaCl) and other PGPR traits, such as the production of auxin (from 20.3 to 41 μg mL−1) and siderophores (from 3.35 to 67.7%). Wheat seedlings inoculated with two selected ACCD-producing Klebsiella isolates (8LJA and 27IJA) significantly (P ≤ 0.05) increased the biomass (45–62%) content and SOD activity in roots (18–35%) with and without salt stress. This study demonstrated that PGPR were associated with native plants in the Andean Altiplano and offers a promising potential source of novel PGPR to alleviate salt stress in plants.

Sorption kinetics studies of herbicides, using different models, are an important tool for determining the mechanisms and kinetic parameters that explain the bioavailability and environmental behavior of these compounds. However, little is known about the combined effects of fertilizers and herbicides and how it could modify these processes on the soil. The aim of this study was to evaluate the sorption kinetics of diuron and 2,4-D in an Andisol treated with urea using various kinetic models. The experiments were carried out in batch, independently for each herbicide, with urea application in an equivalent dose of 200 kg N ha−1 and artificial pH modifications. The results showed no differences in sorption kinetics due to urea for diuron; however 2,4-D showed differences with urea and changes in pH conditions. The data fitted well with the pseudo-second-order model (R2 > 0.996), showing a maximum soil adsorption capacity of 11.9, 10.8, and 9.61 mg kg−1 for diuron, 2,4-D, and 2,4-D-urea, respectively. The initial adsorption rate was similar for both herbicides, but a significant increase in the rate constant was observed for 2,4-D at acid pH. We conclude from the Elovich and Weber-Morris models that both herbicides were adsorbed mainly during the first stage, followed by lower adsorption in the slower second stage. According to these models, mass transfer across the boundary layer, and to a lesser degree intraparticle diffusion mechanisms, controlled sorption kinetics for both herbicides. The results suggest that urea application could influence sorption process of acid herbicides for pH changes in soils.

© 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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Plant growth-promoting rhizobacteria (PGPR) naturally occur in the rhizospheres of pasture, but still little is understood regarding how soil agricultural practices affect them. Here, we examined the effects of long-term nitrogen (N) fertilisation on the occurrence of potential culturable PGPR in rhizosphere soils from pastures grown in Chilean Andisols. We also evaluated in vitro the effects of organic acids (citric, malic and oxalic acids), metals (Al and Mn) and N supply (urea and ammonium sulphate) on indole acetic acid (IAA) production and phosphorus (P) liberation by selected strains. Compared with non-N-fertilised pasture, N fertilisation significantly increased (30%) the occurrence of culturable phosphobacteria but decreased (7%) the occurrence of IAA-producing rhizobacteria. Most efficient IAA-producing phosphobacteria were identified as Bacillus, Enterobacter, Pseudomonas and Serratia. At low pH (4.8), the assays showed that the IAA production by Serratia sp. N0-10LB was increased (31–74%) by organic acids. On the other hand, the IAA production by Pseudomonas sp. N1-55PA was increased two- to fivefold by metals. In all strains, the growth and IAA production were significant decreased by 500 μM of Al, except Serratia sp. N0-10LB, suggesting its potential as PGPR for Chilean Andisols. When urea was added as main N source, the bacterial growth and P utilisation significantly increased compared with ammonium sulphate. The influence of environmental factors that are typical of Chilean Andisols on rhizobacterial communities will provide better management practices to enhance their PGPR functions as well as a better selection biofertilisers to be used in Chilean Andisols.

The aim of this work was to study the stabilization of the activity of two commercial microbial phytases (Aspergillus niger and Escherichia coli) after immobilization on nanoclays and to establish optimal conditions for their immobilization. Synthetic allophane, synthetic iron-coated allophanes and natural montmorillonite were chosen as solid supports for phytase immobilization. Phytase immobilization patterns at different pH values were strongly dependent on both enzyme and support characteristics. After immobilization, the residual activity of both phytases was higher under acidic conditions. Immobilization of phytases increased their thermal stability and improved resistance to proteolysis, particularly on iron-coated allophane (6% iron oxide), which showed activation energy (E(a)) and activation enthalpy (ΔH(#)) similar to free enzymes. Montmorillonite as well as allophanic synthetic compounds resulted in a good support for immobilization of E. coli phytase, but caused a severe reduction of A. niger phytase activity.

A novel three-phase solid–gas–liquid bioreactor (SGLB) concept using gaseous alcohol and liquid rapeseed oil with immersed microorganisms overlying a nutrient agar phase (solid) is proposed for biodiesel (fatty acid alkyl esters, FAAE) production based on the high hydrophobicity and negative surface charge showed by the fungi Rhizopus oryzae. This novel bioreactor was thought to increase oil bioavailability and decrease alcohol toxicity for effective microbial growth, reaching high yields of FAAE production without any pretreatment. High growth rates were reached for R. oryzae using a SGLB simultaneously reaching a high FAAE production yield, up to 50% using methanol and up to 70% using ethanol at 144 h of incubation at 20°C. To compare the effect of gaseous alcohol, the same experiments were carried out in a three-phase solid–liquid–liquid bioreactor (SLLB), where the alcohol was added in liquid phase, showing significant R. oryzae growth but no FAAE formation. This suggests that the inhibitory effect of alcohol is more significant in lipase activity than in R. oryzae growth, and the use of alcohol in gaseous phase may decrease both of them. The experimental procedure using SGLB showed that when R. oryzae is maintained alive, it can catalyze at the same time the hydrolysis, esterification and transesterification of triglycerides from rapeseed oil, but its activity strongly depends on the used growth media. Therefore, the application of gaseous alcohol coupled with R. oryzae as immobilized whole cell catalysts may be a potential alternative to the use of commercial lipases for biodiesel production.

The high cost of commercial lipases limits their industrial application in the production of biodiesel or fatty acid methyl esters (FAME). This disadvantage has encouraged the search for lipase-producing microorganisms (LPMs) as potential whole cell catalysts for FAME production. The aim of this study, therefore, was to evaluate innovative procedures for easy selection and testing of LPMs as a low-cost whole cell catalyst, based on catalytic performance, methanol tolerance and physico-chemical cell surface properties. The latter (in particular the cell surface hydrophobicity and charge) were analyzed because of their crucial role in microbial adhesion to surfaces and the concomitant increase in cell immobilization and bioavailability of hydrophobic substrates. Biocatalysis experiments performed in the presence of nutrient, rapeseed oil and methanol were an effective tool for studying and identifying, in just two experiments, the capacity of different LPMs as biocatalysts in organic media, as well as the methanol tolerance of the cell and the lipase. This indicates the potential for using live microorganisms for FAME production. Another finding was that the inhibitory effect of methanol is more significant for lipase activity than LPM growth, indicating that the way in which alcohol is supplied to the reaction is a crucial step in FAME production by biocatalysts. According to these results, the application of these innovative assessments should simplify the search for new strains which are able to effectively catalyze the FAME production process.

Bioaugmentation is a promising technology to clean up sites contaminated with recalcitrant chemicals. White-rot fungi have proven to be effective in the degradation of pentachlorophenol. Here, we report the bioremediation of soil contaminated with pentachlorophenol (PCP) by Anthracophyllum discolor and its impact on the soil microbial community. In this study three types of microcosms were established: fresh soil (C(0)), fresh soil plus wheat straw (WS(0)) and, fresh soil plus wheat straw inoculated with A. discolor (WSAD(0)). Additionally, similar treatments and a control of sterile soil spiked with PCP (C(250), WS(250) and WSAD(250)) were used to evaluate the remediation and adsorption of PCP. The PCP removal, total microbial activity, and enzymatic activities were evaluated. This study also investigated the structure of soil microbial community by denaturing gradient gel electrophoresis (DGGE), identifying some of the dominant bacterial and fungal species. The results showed that PCP was effectively degraded in soils by A. discolor and by indigenous soil microorganisms. The addition of wheat straw increased the PCP degradation and enzymatic activities. Only laccase activity was negatively affected by PCP contamination. The PCP degradation was associated with changes in microbial communities, mainly stimulation of members of bacterial phylum Proteobacteria (Xanthomonadaceae, Burkholderiaceae and Enterobacteriaceae), and fungal phylum Ascomycota and Basidiomycota. This study shows the ability of A. discolor to degrade PCP from contaminated soil, and demonstrates that agricultural residues, such as wheat straw, can be used as growth substrate by microorganisms in PCP-contaminated soil, demonstrating a great potential of autochthonous microorganisms for soil remediation.

article i nfo Atrazine is a commonly used herbicide for maize production in Chile, but it has recently been shown to be ineffective in soils that receive applications of cow slurries generated from the dairy industry. This effect may be caused either by the sorption of the pesticide to organic matter or more rapid degradation in slurry- amended soils. The objectives of this study were to evaluate the effects of cow slurry on atrazine dissipation, the formation of atrazine metabolites and the modification of bacterial community in Andisol. The cow slurry was applied at doses of 100,000-300,000 L ha −1 . After 4 weeks, atrazine was applied to the slurry-amended soils at concentrations of 1- 3m g kg −1 . The amounts of atrazine and its metabolites were determined by high performance liquid chromatography (HPLC). The soil microbial community was monitored by measurement of CO2 evolution and changes in bacterial community using PCR-DGGE of 16S rRNA genes. The results show that cow slurry applications had no effect on atrazine dissipation, which had a half-life of 15- 19 days. The atrazine metabolites were detected after 20 days and were significantly higher in soils amended with the slurry at both 20 and 40 days after application of the herbicide. Respiration rates were elevated after 10 days in all soils with atrazine addition. Both the atrazine and slurry amendments altered the bacterial community structures, indicated by the appearance of specific bands in the DGGE gels after 10 days. Cloning and sequencing of the 16S rRNA genes from the DGGE gels showed that the bands represented various genera of β-proteobacteria that appeared in response to atrazine. According to our results, further field studies are required to explain the lower effectiveness of atrazine in weed control. These studies may include the effect of dissolved organic carbon on the atrazine mobility.