Bacterial exopolysaccharide and biofilm formation stimulate chickpea growth and soil aggregation under salt stress

To compensate for stress imposed by salinity, biofilm formation and exopolysaccharide production are significant strategies of salt tolerant bacteria to assist metabolism. We hypothesized that two previously isolated salt-tolerant strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) have an ability to improve plant growth, These strains can form biofilm and accumulate exopolysacharides at increasing salt stress. These results showed that bacteria might be involved in developing microbial communities under salt stress and helpful in colonizing of bacterial strains to plant roots and soil particles. Eventually, it can add to the plant growth and soil structure. We investigated the comparative effect of exopolysacharide and biofilm formation in two bacterial strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) in response to varying salt stress. We found that biofilm formation and exopolysaccharide accumulation increased at higher salinity. To check the effect of bacterial inoculation on the plant (Cicer arietinum Var. CM-98) growth and soil aggregation, pot experiment was conducted by growing seedlings under salt stress. Inoculation of both strains increased plant growth at elevated salt stress. Weight of soil aggregates attached with roots and present in soil were added at higher salt concentrations compared to untreated controls. Soil aggregation was higher at plant roots under salinity. These results suggest the feasibility of using above strains in improving plant growth and soil fertility under salinity.

Bacterioplankton abundance, biomass and production in a Brazilian coastal lagoon and in two German lakes

The bacterioplanktonic abundance, biomass, and production within a tropical lagoon (Cabiúnas, Brazil) and two temperate lakes (Stechlin and Dagow, Germany) were compared. Bacterial abundance and production were significantly different among the three water bodies. The lowest bacterial production ( 0.8mug C l-1 d-1) was observed in the tropical Cabiúnas Lagoon despite its higher mean temperature and dissolved organic carbon concentration. Highest bacterioplankton abundance ( 2.6 x 10(9) cells l-1) and production ( 68.5mug C l-1 d-1) were measured in eutrophic Lake Dagow. In oligotrophic Lake Stechlin, the lowest bacterial biomass ( 48.05mug C l-1) was observed because of lower bacterial biovolume ( 0.248mum³) and lower bacterial abundance. Bacterial populations in the temperate lakes show higher activity (production/biomass ratio) than in the tropical lagoon. The meaning of isotopic dilution and leucine incorporation by non-bacterial micro-organisms were evaluated in the oligotrophic temperate system. Leucine uptake by non-bacterial micro-organisms did not have significant influence on bacterial production