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Bacteria can solubilize phosphorus (P) through the secretion of low-molecular-weight organic acids and acidification. However, the genes involved in the production of these organic acids are poorly understood. The objectives of this study were to verify the calcium phosphate solubilization and the production of low-molecular-weight organic acids by diverse genera of phosphate solubilizing bacterial strains (PSBS); to identify the genes related to the synthesis of the organic acids in the genomes of these strains and; to evaluate growth and nutrient accumulation of maize plants inoculated with PSBS and fertilized with Bayóvar rock phosphate. Genomic DNA was extracted for strain identification and annotation of genes related to the organic acids production. A greenhouse experiment was performed with five strains plus 150 mg dm− 3 P2O5 as Bayóvar rock phosphate (BRP) to assess phosphate solubilization contribution to maize growth and nutrition. Paraburkholderia fungorum UFLA 04–21 and Pseudomonas anuradhapurensis UFPI B5-8A solubilized over 60% of Ca phosphate and produced high amounts of citric/maleic and gluconic acids in vitro, respectively. Eleven organic acids were identified in total, although not all strains produced all acids. Besides, enzymes related to the organic acids production were found in all bacterial genomes. Plants inoculated with strains UFPI B5-6 (Enterobacter bugandensis), UFPI B5-8A, and UFLA 03–10 (Paenibacillus peoriae) accumulated more biomass than the plants fertilized with BRP only. Strains UFLA 03–10 and UFPI B5-8A increased the accumulation of most macronutrients, including P. Collectively, the results show that PSBS can increase maize growth and nutrient accumulation based on Bayóvar rock phosphate fertilization. [ABSTRACT FROM AUTHOR]

Manure-derived biochars have a fertilizer potential as pyrolysis concentrates non-volatile nutrients. The addition of magnesium (Mg) to poultry manure enhances its Mg/Ca ratio and could increase soluble P by phosphate-solubilizing bacteria (PSB). Our objective was to assess the potential of PSB strains to solubilize P from both unenriched and Mg-enriched biochar and to evaluate the growth of maize in an Oxisol fertilized with biochar (100 mg kg−1 total P) to satisfy plant P needs. We examined the strains: Paraburkholderia fungorum UFLA 04–155, Pseudomonas anuradhapurensis UFPI B5-8A, Paenibacillus chondroitinus UFLA 03–116, Acinetobacter pittii UFLA 03–09, and Rhizobium tropici CIAT 899. Biochar was made from poultry manure at temperatures of 350 °C, 500 °C, and 650 °C. Maize growth and P uptake were assessed in plants after 15 and 30 days under greenhouse conditions. The strain P. anuradhapurensis UFPI B5-8A significantly released more P from Mg-biochar (82% of the total P added) than from the unenriched biochar (74% of the total P added). Furthermore, this strain released tartaric and gluconic acids when mixed with the Mg-biochar, whereas malic acid was primarily exuded when applied to unenriched biochar. Similarly, P. anuradhapurensis UFPI B5-8A inoculation or Mg enrichment resulted in a 20% increase in P uptake by maize compared to unenriched biochar. Therefore, a synergistic approach using Mg-biochar and inoculation with PSB increases phosphate availability from poultry manure and maize P use efficiency. [ABSTRACT FROM AUTHOR]

Rhizoctonia solani compromises the production of lima bean, an alternative and low-input food source in many tropical regions. Inoculation of bacterial strains has been used, but research on their biocontrol and growth promotion potential on lima bean is scarce. The objective of this study was to evaluate the effects of inoculation with rhizobacterial strains of the genera Bacillus, Brevibacillus, Paenibacillus, Burkholderia, Pseudomonas, and Rhizobium in combination or not with N2-fixing Rhizobium tropici on the control of damping-off disease and growth promotion in lima bean plants. Greenhouse experiments were conducted to evaluate the inoculation with bacterial strains with biocontrol potential in combination or not with R. tropici in substrate infected with R. solani CML 1846. Growth promotion of these strains was also assessed. Strains of Brevibacillus (UFLA 02-286), Pseudomonas (UFLA 02-281 and UFLA 04-885), Rhizobium (UFLA 04-195), and Burkholderia (UFLA 04-227) co-inoculated with the strain CIAT 899 (Rhizobium tropici) were the most effective in controlling R. solani, reducing the disease incidence in 47–60% on lima bean. The promising strains used in the biocontrol assays were also responsive in promoting growth of lima bean under disease and sterile conditions. A positive synergistic effect of co-inoculation of different genera contributed to plant growth, and these outcomes are important first steps to improve lima bean production. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the resilience of phytophysiognomies under influence of iron mining by assessing the occurrence, diversity, and symbiotic efficiency of native communities of nitrogen-fixing bacteria that nodulate leguminous plants (rhizobia) in soils of an area revegetated with grass after iron mining activities and in the phytophysiognomies in adjacent areas (Canga, Atlantic Forest, Cerrado, and Eucalyptus-planted forest). Experiments for capturing rhizobia through two species of promiscuous plants, siratro (Macroptilium atropurpureum) and cowpea (Vigna unguiculata), were conducted in a greenhouse. The rhizobial strains isolated were characterized phenotypically, genetically (16S rRNA sequencing and BOX-PCR fingerprinting), and regard symbiotic efficiency of biological nitrogen fixation (BNF) compared to mineral nitrogen and reference strains. Cowpea captured a higher density of rhizobia than siratro did. However, most of the strains captured by siratro had greater symbiotic efficiency. The revegetated area proved to be the community most efficient in N2 fixation and was also the most diverse, whereas Canga was the least diverse. For the two trap species, the predominant genus captured in the revegetated area and in the phytophysiognomies was Bradyrhizobium. The greater symbiotic efficiency and the high genetic diversity of the rhizobial community in the revegetated area indicate the effectiveness of the soil rehabilitation process. The revegetated area and the phytophysiognomies proved to harbor strains with high biotechnological potential. Results indicate that the high functional redundancy of this group of bacteria contributes to the resilience of these phytophysiognomies and the revegetated area. [ABSTRACT FROM AUTHOR]

We evaluated the co-occurrence of archaeal taxonomic groups and soil physicochemical characteristics in relation to the structuring of the archaeal community in Amazonian soil under different land use systems. Soil samples were collected in primary forest (PF), secondary forest (SF), agricultural systems (AG) and cattle pastures (PA). Archaeal community composition was revealed based on high-throughput amplicon sequencing of the 16S rRNA gene. The results revealed co-occurrence of archaeal classes, with two groups formed: Thaumarchaeota classes, including South Africa Gold Mine—Group 1 (SAGMG-1), Crenarchaeotic group (SCG) and Crenarchaeota candidate division YNPFFA, with predominance in PF and SF; and Bathyarchaeota_unclassified, Methanomicrobia and Methanobacteria (Euryarchaeota) with the FHMa11 terrestrial group, with predominance in PA. The number of co-occurrences between groups was lower in SF, AG and PA (approximately 30%) than in PF. The qPCR analysis revealed that PF also had the largest number of archaeal representatives. Soil texture may be a limiting factor of interactions between groups since the most representative groups, SAGMG-1 and the SCG (over 20% in all sites), were positively associated with coarse sand, the soil factor most correlated with the groups (33% of the total). These results suggest that interactions between archaeal classes belonging to different phyla may be dependent on the number of individuals in the soil environment. In this context, differences in soil physical structure among the land use systems can reduce the representatives of key groups and consequently the co-occurrence of Archaea, which could compromise the natural dynamics of this complex environment. [ABSTRACT FROM AUTHOR]

We studied the survival of four elite strains of Bradyrhizobium in liquid inoculants with three formulations with exopolysaccharides extracted from other rhizobia genera, and the symbiotic efficiency of these elite strains with soybean and cowpea in a greenhouse. For that purpose, we verified the effectiveness of formulations for maintaining the cell viability of strains by counting the colony-forming units (CFU) per milliliter of the liquid inoculants with formulations after 90 days. For survival of the soybean inoculant strains, 29W and CPAC15, the largest number of CFU (> 1010 mL−1) after 90 days was observed in the PEPS formulation. For the cowpea inoculant strains, INPA3-11B and UFLA3-84, the REPS1 formulation had the largest number of CFU (> 1010 mL−1) after 90 days. The symbiotic efficiency of the PEPS formulation, followed by REPS2, was higher than that shown by the commercial inoculant in soybean. For cowpea, the three formulations with EPS, especially REPS1, showed symbiotic efficiency better than that of the commercial inoculant. [ABSTRACT FROM AUTHOR]

The optimization and sustainability of farming systems are essential. The use of biotechnologies, such as the increase in the density of arbuscular mycorrhizal fungi (AMF) propagules, can be an important technique to maximize the effects of fertilizers and benefit the plant and, consequently, increase the biomass and microbial activity in the soil. This study evaluated the effect of inoculation of native AMF on soil biochemical quality and the yield of different sugarcane (Saccharum species hybrids) cultivars. The experiment was conducted in the field following a randomized block experimental design in 6 × 2 factorial arrangements [sugarcane cultivars (CTC 1, CTC 7, CTC 9, CTC 16, SP89-1115, and RB925345) and inoculation of AMF], in two ratoon crops. The native AMF were inoculated through application of inoculum soil in the planting furrow at the time of sowing the crop. At the end of each ratoon crop, the following traits were evaluated: microbial biomass carbon and nitrogen, soil respiration, enzyme activities (β-glucosidase, urease, phosphatase, and fluorescein diacetate hydrolysis), mycorrhizal colonization and sugarcane yield. The increase in biomass and in microbial activities in relation to inoculation with native AMF led to increases in sugarcane yield, but the more prominent were CTC1, CTC7, and CTC9. The increase in the density of the native AMF by means of inoculation with inoculum soil favored soil biochemical quality and increased the yield of the sugarcane cultivars, regardless of the known yield potential of each cultivar, with reduction in production costs. [ABSTRACT FROM AUTHOR]

Monitoring degraded areas is essential for evaluation of the quality of the rehabilitation process. In this study, we evaluate how the physical and chemical characteristics of the mixture of iron ore tailings with the soil have affected the soil microbial biomass and activity in areas along the Gualaxo do Norte River after the Fundão Dam disaster. Composite soil samples were collected from areas that were impacted (I) and not impacted (NI) by the tailings. The following attributes were evaluated: chemical element content; soil density, porosity, and texture; microbial biomass carbon; basal respiration; and enzyme activity and density of microbial groups (bacteria, actinobacteria, fungi, arbuscular mycorrhizae, phosphate solubilizers, cellulolytic microorganisms, nitrifiers, ammonifiers, and diazotrophs). According to result, the deposition of tailings increased the pH and the soil available P, Cr, Fe, and Mn content and reduced organic matter. The physical and biological attributes were negatively affected, with increases in the silt content and density of the soil, and reduction in macroporosity and in the microbial biomass and activity of the soil (respiration and enzymes) in the impacted area. However, the impacted areas exhibited greater densities of some microbial groups (cellulolytic microorganisms, nitrifiers, and diazotrophic bacteria). Modifications in the organic matter and silt content are the main attributes associated with deposition of the tailings that affected soil microbial biomass and microbial activity. This may affect erosive conditions and the functionality of the ecosystem, indicating an imbalance in this environment. In contrast, the higher density of some microbial groups in the impacted areas show the high rehabilitation potential of these areas. [ABSTRACT FROM AUTHOR]

The nitrogen-fixing bacterial strain UFLA 01-1174T was isolated from nodules of Campsiandra laurilifolia Benth. originating from the Amazon region, Brazil. Its taxonomic position was defined using a polyphasic approach. Analysis of the 16S rRNA gene placed the strain in the Bradyrhizobium genus, the closest species being B. guangdongense CCBAU 51649T and B. guangzhouense CCBAU 51670T, both with 99.8% similarity. Multilocus sequence analysis (MLSA) of recA, gyrB, glnII, rpoB, atpD, and dnaK indicated that UFLA 01-1174T is a new species, most closely related to B. stylosanthis BR 446T (94.4%) and B. manausense BR 3351T (93.7%). Average nucleotide identity (ANI) differentiated UFLA 01-1174T from the closest species with values lower than 90%. The G + C content in the DNA of UFLA 01-1174T is 63.6 mol%. Based on this data, we conclude that the strain represents a new species. The name proposed is Bradyrhizobium campsiandrae, with UFLA 01-1174T (= INPA 394BT = LMG 10099T) as type strain. [ABSTRACT FROM AUTHOR]

In selection of rhizobia, it is important to consider tolerance of the strain to adverse conditions, as well as its symbiotic efficiency and capacity to perform other plant growth-promoting processes. In this study, we evaluated Bradyrhizobium spp. strains from Brazilian soils regarding tolerance to different pH and temperature conditions, inorganic calcium phosphate solubilization capacity, and symbiotic efficiency when inoculated on acacia (Acacia mangium) and velvet bean (Stizolobium aterrimum) in axenic conditions. In each experiment of symbiotic efficiency, 18 strains (including representatives of Bradyrhizobium sp., B. viridifuturi, B. brasilense, B. uaiense, B. stylosanthis, and B. forestalis) were compared to two uninoculated controls, one with low (5.25 mg L−1) and another with high (52.5 mg L−1) concentrations of mineral nitrogen (N), and one inoculant strain [BR 3617 (B. japonicum) in the acacia experiment and BR 2811(B. elkanii) in the velvet bean experiment]. All strains grew at the different pH values tested (4 to 10) and tolerated a wide temperature range (15 to 37 °C) and most of them solubilized inorganic calcium phosphate. Most strains did not nodulate acacia, but were able to promote growth of this species. The UFLA03–268 (Bradyrhizobium sp.) strain was the most efficient in symbiosis with acacia. In the velvet bean experiment, the UFLA03–144 (B. viridifuturi), INPA104A (Bradyrhizobium sp.), and UFLA03-321T (B. brasilense) strains outperformed the other treatments in shoot dry matter production of velvet bean, showing high potential for use as inoculants in this species. Strains representing the five Bradyrhizobium species and Bradyrhizobium sp. were similar or more efficient in shoot nitrogen accumulation (SNA) than the control with mineral N. They also led to 84 (UFLA 04–0212) to 246 (INPA 104A) % increases in SNA compared to inoculation with BR 2811. This study showed an efficient symbiotic relationship between B. viridifuturi, B. brasilense, B. uaiense, B. stylosanthis and B. forestalis and velvet bean. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of Inga edulis trees on soil quality attributes and forage yield and moisture in a pasture field in the county of Carrancas, Minas Gerais, Brazil. Soil samples were collected under the canopy and beyond the canopy projection of five I. edulis trees, at four distances from the tree trunks to beyond the canopy projection, along the radius line. A randomized block design was used, in which five trees represented five blocks and the four distances from the trees corresponded to the treatments. The forage yield and moisture, soil moisture and chemical attributes, density and diversity of arbuscular mycorrhizal fungi (AMF) spores and the presence of nodule-forming nitrogen-fixing bacteria in legumes were evaluated. The statistical analysis was performed using ANOVA and the Scott-Knott test (p = 0.05). No statistical differences between forage yield and moisture were found in the soil under or beyond the canopy projection. The soil quality was elevated, indicated by the improved soil pH, base saturation, sum of bases and effective cation exchange capacity in the samples collected closer to I. edulis. No changes in the density and diversity of AMF spores or in the nodulation and development of inoculated seedlings were observed in soil collected at different distances from the trees. Consequently, I. edulis trees can be intercropped with pasture to increase the soil quality without affecting forage yields. [ABSTRACT FROM AUTHOR]

Soybean (Glycine max L.) is an important legume that greatly benefits from inoculation with nitrogen-fixing bacteria. In a previous study, five efficient nitrogen-fixing bacterial strains, isolated from nodules of soybean inoculated with soil from semi-arid region, Northeast Brazil, were identified as a new group within the genus Bradyrhizobium. The taxonomic status of these strains was evaluated in this study. The phylogenetic analysis of the 16S rRNA gene showed the high similarity of the five strains to Bradyrhizobium brasilense UFLA03-321T (100%), B. pachyrhizi PAC48T (100%), B. ripae WR4T (100%), B. elkanii USDA 76T (99.91%), and B. macuxiense BR 10303T (99.91%). However, multilocus sequence analysis of the housekeeping genes atpD, dnaK, gyrB, recA, and rpoB, average nucleotide identity, and digital DNA–DNA hybridization analyses supported the classification of the group as B. brasilense. Some phenotypic characteristics allowed differentiating the five strains and the type strain of B. brasilense from the two neighboring species (B. pachyrhizi PAC48T and B. elkanii USDA 76T). The nodC and nifH genes' analyses showed that these strains belong to symbiovar sojae, together with B. elkanii (USDA 76T) and B. ferriligni (CCBAU 51502T). The present results support the classification of these five strains as Bradyrhizobium brasilense (symbiovar sojae). [ABSTRACT FROM AUTHOR]

This study describes two Bradyrhizobium strains, UFLA03-164T and UFLA03-153, which share more than 99% sequence similarity of the 16S rRNA with the type strains of 15 species in this genus. The concatenation of three housekeeping genes (recA, gyrB, and dnaK) indicated that both strains formed a single clade separate from known Bradyrhizobium species. B. viridifuturi, represented by SEMIA 690T, is the closest neighboring species (96.2%). Low (< 92%) average nucleotide identity (ANI) was observed between strain UFLA03-164T and any of the closest species on the phylogenetic trees based on concatenated housekeeping genes. The DNA G+C content of UFLA03-164T is 63.25%. Phenotypic characteristics were determined for both UFLA strains. Based on the data, the two strains represent a new species for which the name Bradyrhizobium uaiense is proposed, with UFLA03-164T (= LMG 31509T) as type strain. [ABSTRACT FROM AUTHOR]

Three strains of nitrogen-fixing bacteria isolated from nodules of Inga sp. (INPA54BT) and Swartzia sp. (INPA86A and INPA01-91A) in soils under native forest in the Brazilian Amazon were previously identified as belonging to the Bradyrhizobium genus. In this study, these strains were characterized using a polyphasic approach to establish their taxonomic position. The three strains shared more than 99.5% sequence similarity of the 16S rRNA gene with the type strains of five Bradyrhizobium species (B. japonicum USDA 6T, B. liaoningense LMG 18230T, B. ottawaense OO99T, B. subterraneum 58 2-1T and B. yuanmingense LMG 21827T). However, multilocus sequence analysis of two (recA and glnII) or three (atpD, gyrB, and recA) housekeeping genes indicated that these three strains represent a new Bradyrhizobium species, which is closely related to B. subterraneum 58 2-1T and B. yuanmingense LMG 21827T. DNA-DNA hybridization values between INPA54BT and B. subterraneum 58 2-1T and B. yuanmingense LMG 21827T were only 41.5 and 30.9%, respectively. Phenotypic characterization also allowed the differentiation of the novel species from B. subterraneum 58 2-1T and B. yuanmingense LMG 21827T. In the phylogenetic analysis of the nodC and nifH genes, the three strains showed similar sequences that were divergent from those of type strains of all Bradyrhizobium species. We concluded that these strains represent a novel species, for which the name Bradyrhizobium forestalis is proposed, with INPA54BT (= LMG 10044T) as type strain. The G+C content in the DNA of INPA54BT is 63.7 mol%. [ABSTRACT FROM AUTHOR]

The symbiosis of Leguminosae with arbuscular mycorrhizal fungi (AMF) and N-fixing nodulating bacteria (NFNB) can occur simultaneously, forming a tripartite symbiosis. In particular, AMF can colonize root nodules, although this interaction is not yet well elucidated, especially with regard to nodule activity and to the influence of external factors, such as biostimulants. In this study, we hypothesized that the application of the flavonoid formononetin, used to stimulate root colonization by native AMF, increases the AMF colonization of soybean ( Glycine max) root nodules, especially under low availability of phosphorus (P). To test this hypothesis, we performed a field experiment in randomized blocks in a 4 × 3 factorial design, with 4 treatments of formononetin (0, 0.46, 0.92 and 1.84 g per kg seed) and 3 of P (0, 60 and 120 kg ha) with 5 replicates. Nodules and roots were collected during the R2 stage (full flowering) and evaluated with respect to AMF colonization. Formononetin stimulated mycorrhizal fungi colonization of active nodules, especially when no P was applied, as also observed for AMF root colonization; however, it had no effect with 60 and 120 kg P ha. Thus, the application of formononetin increases surface AMF colonization of active nodules and roots, but its effect disappears with an increase in P and the inactivity of the nodule. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of two rehabilitation systems in sites contaminated by Zn, Cu, Pb, and Cd on biological soil attributes [microbial biomass carbon (C mic), basal and induced respiration, enzymatic activities, microorganism plate count, and bacterial and fungal community diversity and structure by denaturing gradient gel electrophoresis (DGGE)]. These systems (S and S) consisted of excavation (trenching) and replacement of contaminated soil by uncontaminated soil in rows with Eucalyptus camaldulensis planting (S-R and S-R), free of understory vegetation (S-BR), or completely covered by Brachiaria decumbens (S-BR) in between rows. A contaminated, non-rehabilitated (NR) site and two contamination-free sites [Cerrado (C) and pasture (P)] were used as controls. C mic, densities of bacteria and actinobacteria, and enzymatic activities (β-glucosidase, acid phosphatase, and urease) were significantly higher in the rehabilitated sites of system 2 (S-R and S-BR). However, even under high heavy metal contents (S-R), the rehabilitation with eucalyptus was also effective. DGGE analysis revealed similarity in the diversity and structure of bacteria and fungi communities between rehabilitated sites and C site (uncontaminated). Principal component analysis showed clustering of rehabilitated sites (S-R and S-BR) with contamination-free sites, and S-R was intermediate between the most and least contaminated sites, demonstrating that the soil replacement and revegetation improved the biological condition of the soil. The attributes that most explained these clustering were bacterial density, acid phosphatase, β-glucosidase, fungal and actinobacterial densities, C mic, and induced respiration. [ABSTRACT FROM AUTHOR]

Recovery of arsenic contaminated areas is a challenge society faces throughout the world. Revegetation associated with microbial activity can play an essential role in this process. This work investigated biological attributes in a gold mining area with different arsenic contents at different sites under two types of extant revegetation associated with cover layers of the soil: BS, Brachiaria sp. and Stizolobium sp., and LEGS, Acacia crassicarpa, A. holosericea, A. mangium, Sesbania virgata, Albizia lebbeck and Pseudosamanea guachapele. References were also evaluated, comprising the following three sites: B1, weathered sulfide substrate without revegetation; BM, barren material after gold extraction and PRNH (private reserve of natural heritage), an uncontaminated forest site near the mining area. The organic and microbial biomass carbon contents and substrate-induced respiration rates for these sites from highest to lowest were: PRNH > LEGS > BS > B1 and BM. These attributes were negatively correlated with soluble and total arsenic concentration in the soil. The sites that have undergone revegetation (LEGS and BS) had higher densities of bacteria, fungi, phosphate solubilizers and ammonium oxidizers than the sites without vegetation. Principal component analysis showed that the LEGS site grouped with PRNH, indicating that the use of leguminous species associated with an uncontaminated soil cover layer contributed to the improvement of the biological attributes. With the exception of acid phosphatase, all the biological attributes were indicators of soil recovery, particularly the following: microbial carbon, substrate-induced respiration, density of culturable bacteria, fungi and actinobacteria, phosphate solubilizers and metabolic quotient. [ABSTRACT FROM AUTHOR]