Strategies for survival in four peanut Rhizobium spp exposed to saline stress

BUENO MIGUEL; DARDANELLI MARTA; GONZÁLEZ PAOLA S.; WOELKE MARIELA; GHITTONI NORA

Santos Sao Paulo (Brasil)

Simposio; seventh International symposium on Microbial Ecology (ISME-7); 1995

Rhizobia must be able to proliferate in the soil before the legume host can be infected and a successfull symbiosis cambi established. The tolerance to  hypersalinity of rhizobia from different species wass found to vary widely, however, a common strategy for survvival was the  rapid intracellular accumulation of osmolytes (glutamate, trehalose, proline etc). As far as we know , the mechanism for hypersaline adaptation have not been investigate in peanut rhizobia. We analized four rhizobia strains  (ATCC 10317, ATCC 51466, TAL 1000, and USDA 3187) which were  able to nodulate peanut. Bacteria were grown either under basal conditions (1.7 mM  NaCl ), or receiving 10 mM proline. Cellular glucids were obtained and identified by gas chromatography (Hp) and by NMR analyeses (Brucker ). After a more or less prolonged lag each of the four strains grew in the presence of 400 nM  NaCl. In cells from the salt-stressed  bacteria, trehalose was identified as the osmolyte which was accumulated. Similar results were obtained with different carbon sources. Under hypersalinity, exogenously added proline diminished the level of cellular trehalose. In conclucion four peanut rhizobia which were able to grow under saline stress, accumulated trehalose as an endogenous osmoprotectant, while proline was preferred as an exogenous osmoprotectant.