Soybean Inoculated With One Bradyrhizobium Strain Isolated at Elevated [CO2] Show an Impaired C and N Metabolism When Grown at Ambient [CO2]

Soybean (Glycine max L.) future response to elevated [CO2] has been shown to differ when inoculated with B. japonicum strains isolated at ambient or elevated [CO2]. Plants, inoculated with three Bradyrhizobium strains isolated at different [CO2], were grown in chambers at current and elevated [CO2] (400 vs. 700 ppm). Together with nodule and leaf metabolomic profile, characterization of nodule N-fixation and exchange between organs were tested through 15N2-labeling analysis. Soybeans inoculated with SFJ14-36 strain (isolated at elevated [CO2]) showed a strong metabolic imbalance, at nodule and leaf levels when grown at ambient [CO2], probably due to an insufficient supply of N by nodules, as shown by 15N2-labeling. In nodules, due to shortage of photoassimilate, C may be diverted to aspartic acid instead of malate in order to improve the efficiency of the C source sustaining N2-fixation. In leaves, photorespiration and respiration were boosted at ambient [CO2] in plants inoculated with this strain. Additionally, free phytol, antioxidants, and fatty acid content could be indicate induced senescence due to oxidative stress and lack of nitrogen. Therefore, plants inoculated with Bradyrhizobium strain isolated at elevated [CO2] may have lost their capacity to form effective symbiosis at ambient [CO2] and that was translated at whole plant level through metabolic impairment.

Cross-Feeding Among Soil Bacterial Populations: Selection and Characterization of Potential Bio-inoculants

The biological nitrogen fixation constitutes a strategy to accelerate soil reclamation and the symbiotic systems Rhizobium-legume is the major N2-fixing in which the enzyme carboxymethyl cellulase plays a key role. As many rhizobia species are cellulase negative, the association with cellulolytic bacteria can be a strategy for the recovery of degraded ecosystems. It has been hypothesized that the sharing of resources should mostly be prevalent among phylogenetically and metabolically different species. Accordingly, twenty-seven actinobacteria isolates from Actinobacteria phyla and twenty-six rhizobia isolates from Proteobacteria phyla were selected from the bacterial collection of the Laboratory of Environmental Microbiology of the Federal University of Ceará. The presence of cellulolytic activity was observed for the rhizobia isolates at 28 °C and for actinobacteria isolates at 28, 39, 41, 43 and 45 °C. Rhizobia isolates deficient in cellulase and actinobacteria isolates with enzymatic activity detected at higher temperature were selected and characterized. The antagonism between isolates of two groups was tested and the pairs antagonistic were eliminated. The cross-feeding test between actinobacteria and rhizobia isolates was realized in a chemically defined medium containing carboxymethyl-cellulose as the only carbon and energy source. Growth of rhizobia strains in 50% of the pairwise indicated that the cellulose hydrolyzed by actinobacteria was used as substrate for the growth of the rhizobia. The Bradyrhizobium strain R10 associated with Streptomyces strains A09 and A18 and Nocardia A11 are promissory inoculants for recovery of semi-arid regions.

Growth stimulation of clusterbean (Cyamopsis tetragonoloba) by coinoculation with rhizosphere bacteria and Rhizobium

Clusterbean [Cyamopsis tetragonoloba (L.) Taub.] is an important commercially utilizable crop grown in arid zone of India. Microorganisms present in the rhizosphere of this crop produce various plant growth-promoting substances and enhance the availability of nutrients to the plants. Therefore, fifty five bacterial isolates obtained from the rhizosphere of clusterbean were explored for beneficial characteristics. Twenty rhizobacterial isolates produced indole acetic acid ranging from 3.9 to 24.7 μg/mL. Only six isolates HCS7, HCS19, HFS7, HFS9, HFS10 and HFS12 showed d-aminolevulinic acid production varying from 1.3 to 7.0 μg/mL. Fourteen isolates showed solubilization of potassium on mica containing Aleksandrov medium plates. Stimulation of root and shoot growth of clusterbean seedlings on water agar plates was observed by inoculation of eleven rhizobacterial isolates at 5 and 10 days of growth whereas some isolates showed stunting effect on the growth of shoot and root as compared to uninoculated seedlings. At 60 days of plant growth, inoculation of Bradyrhizobium strain GSA11 and Rhizobium strain GSA110 showed significant nodulation and their inoculation resulted in 141.94 and 151.43% gains in shoot dry weight, respectively under chillum jar conditions. Coinoculation of Bacillus isolate HCS43 with Rhizobium strain GSA110 formed 48 nodules/plant and plant dry weight was enhanced by 190.09% in comparison to uninoculated control plants.