Effect of common bean (Phaseolus vulgaris L.) on the community composition of ammonia-oxidizing bacteria in soil previously cultivated with Medicago sativa

The community composition of ammonia-oxidizing bacteria (AOB) was studied during four stages of plant development in soil cultivated with Phaseolus vulgaris in comparison to unplanted soil, using an alfisol previously harboring the legume Medicago sativa. Denaturing gradient gel electrophoresis (DGGE) patterns of 16S rRNA gene and clone libraries of the same gene suggested that bacteria related to Nitrosospira cluster 3 were dominant in both planted and unplanted soil. Bacteria related to Nitrosomonas cluster 8 (Nitrosomonas communis cluster) were found at all times in planted soil, but appeared only randomly in unplanted soil. Analysis of PCR products of the gene encoding the alpha-subunit of ammonia monooxygenase (amoA) by DGGE and clone libraries only detected Nitrosospira cluster 3-like organisms, but failed to detect sequences related to Nitrosomonas. The results suggest that P. vulgaris does not affect the dominant members of AOB communities (Nitrosospira cluster 3), but could have an effect on the prevalence of Nitrosomonas cluster 8 in this type of legume-planted alfisol

Composition of diazotrophic bacterial assemblages in bean-planted soil compared to unplanted soil

The effect of common bean (Phaseolus vulgaris L.) on the composition of nitrogen fixing bacterial assemblages in soil was studied by comparing planted and unplanted soil. The community composition was studied by terminal restriction fragment length polymorphism (T-RFLP) of the nitrogenase reductase gene (nifH ). Principal component analysis (PCA) of T-RFLP profiles showed the separation of profiles from planted and unplanted soil. Terminal restriction fragments (T-RFs) corresponding to rhizobial bacteria were identified preferentially in planted soil; however most nifH T-RFs in soil could not be assigned to T-RFs simulated from a database of known diazotrophs. To specifically study rhizobial bacteria in the soil and nodules, PCR products from the alpha subunit of the nitrogenase enzyme (nifD) were analyzed by denaturing gradient gel electrophoresis (DGGE). DGGE results showed the specific stimulation of the rhizobial microsymbionts in planted soil

Phototrophic bacteria dominate consortia, potentially to remove CO2 and H2S from biogas under microaerophilic conditions

The use of microbial consortia to remove contaminants in industrial systems and in natural environments could be an alternative to the use of unique strains of microorganisms, since microbial consortia have greater robustness to environmental fluctuations. However, it is necessary to evaluate the relationship between the genetic structure and functionality of the consortia. In this work, the functional and structural stability over time of two bacterial consortia (C5 and C6) with the potential to remove CO2 and H2S from biogas was evaluated. Both consortia decreased the dissolved CO2 by over 30% at the end of the incubation period, but C5 presented shorter removal kinetics (3.9 days) than C6 (6.4 days). Additionally, a chemical oxidation of H2S could have occurred in the microcosms. Moreover, both consortia presented a stable genetic structure, measured by terminal restriction fragment length polymorphism profiles of the 16S rRNA gene, characterized by high homogeneity and prevalence of the genus Rhodopseudomonas throughout the incubation period, and an increasing abundance of Xanthobacter during the exponential phase of the growth curve in C5, which would account for the functionality of the consortia.FONDEF Project D07 I-100

Genetic diversity of Rhizobium present in nodules of Phaseolus vulgarisL. cultivated in two soils of the central region in Chile

tAlthough Phaseolus vulgaris L. is native from the Americas and is currently cultured in diverse areas, verylittle is known about the diversity of symbiotic nitrogen fixing Rhizobium (mycrosymbiont) in many ofthose cultures. Therefore, the aim of this study was to assess the genetic diversity of Rhizobium presentin nodules of P. vulgaris in the central region of Chile. A method to extract DNA from surface-sterilizednodules was applied to two populations of the same seed variety grown in different fields. The 16SrRNA and nifH genes were amplified directly from the DNA extracted. DGGE analysis and clone librariesshowed a restricted genetic diversity of the microsymbiotic populations that nodulate P. vulgaris. Bothmolecular markers revealed the presence of a microsymbiont closely related to Rhizobium etli in all theplants from the soils studied, indicating that the populations of Rhizobium sp. nodulating P. vulgaris inthe central region of Chile displayed an extremely low genetic diversity. The level of genetic diversityin microsymbiont populations in plants grown in soils with different origin suggested that other factorsrather than the indigenous soil rhizobial populations play a major role in the selection of the symbioticpartner in P. vulgaris

<em>Peltigera frigida</em> lichens and their Substrates reduce the influence of forest cover change on phosphate solubilizing bacteria.

Phosphorus (P) is one of the most critical macronutrients in forest ecosystems. More than 70 years ago, some Chilean Patagonian temperate forests suffered wildfires and the subsequent afforestation with foreign tree species such as pines. Since soil P turnover is interlinked with the tree cover, this could influence soil P content and bioavailability. Next to soil microorganisms, which are key players in P transformation processes, a vital component of Patagonian temperate forest are lichens, which represent microbial hotspots for bacterial diversity. In the present study, we explored the impact of forest cover on the abundance of phosphate solubilizing bacteria (PSB) from three microenvironments of the forest floor: Peltigera frigida lichen thallus, their underlying substrates, and the forest soil without lichen cover. We expected that the abundance of PSB in the forest soil would be strongly affected by the tree cover composition since the aboveground vegetation influences the edaphic properties; but, as P. frigida has a specific bacterial community, lichens would mitigate this impact. Our study includes five sites representing a gradient in tree cover types, from a mature forest dominated by the native species Nothofagus pumilio, to native second-growth forests with a gradual increase in the presence of Pinus contorta in the last sites. In each site, we measured edaphic parameters, P fractions, and the bacterial potential to solubilize phosphate by quantifying five specific marker genes by qPCR. The results show higher soluble P, labile mineral P, and organic matter in the soils of the sites with a higher abundance of P. contorta, while most of the molecular markers were less abundant in the soils of these sites. Contrarily, the abundance of the molecular markers in lichens and substrates was less affected by the tree cover type. Therefore, the bacterial potential to solubilize phosphate is more affected by the edaphic factors and tree cover type in soils than in substrates and thalli of P. frigida lichens. Altogether, these results indicate that the microenvironments of lichens and their substrates could act as an environmental buffer reducing the influence of forest cover composition on bacteria involved in P turnover

Water Deficit as a Driver of the Mutualistic Relationship between the Fungus Trichoderma harzianum and Two Wheat Genotypes▿

The aim of this study was to assess the occurrence of mutualistic interactions between the fungus Trichoderma harzianum and two wheat genotypes, Triticum aestivum cv. Talhuén and T. turgidum subsp. durum cv. Alifén, and the extent to which water deficit affected these interactions. Two wheat genotypes were cultivated in the presence or absence of T. harzianum and in the presence or absence of water deficit. T. harzianum was in turn cultivated in the presence or absence of wheat plants and in the presence or absence of water deficit. To evaluate the plant-fungus interactions, the root volume, dry biomass, and fecundity of wheat were determined, as was the population growth rate of the fungus. Trichoderma harzianum exerted a positive effect only on plants subjected to water deficit. The population growth rate of T. harzianum was negative in the absence of wheat plants and reached its highest level in the presence of plants under conditions of water deficit. These results confirm the occurrence of a mutualistic interaction between wheat and T. harzianum and show that it is asymmetric and context dependent