PEANUT RHIZOBIA UNDER SALT STRESS - ROLE OF TREHALOSE ACCUMULATION INSTRAIN ATCC-51466

Strain ATCC 51466, a motile peanut Rhizobium sp., showed patterns of u tilization of diverse carbon sources characteristic of fast growers. B acteria had periplasmic neutral glucans with molecular weight close to 3000. When the extracellular concentration of NaCl was raised to 400 mM, the lag phase of the culture was prolonged about threefold and the generation time was increased almost twice. The changes in growth beh avior of salt-stressed bacteria were accompanied by the full suppressi on of periplasmic oligoglucans and the accumulation of cellular trehal ose. Almost identical changes in cell-associated oligoglucans were obs erved after exposing peanut Rhizobium sp. strain ATCC 10317 to hypersa linity. When the osmotic pressure of the medium was augmented by the a ddition of either 200 mM mannitol or 16% (w/v) polyethylene glycol, ce lls of strain ATCC 51466 contained decreased levels of oligoglucans an d accumulated trehalose. On the other hand, the content of cellular tr ehalose increased throughout logarithmic and stationary phases of grow th of strain ATCC 51466 in a medium supplemented with 400 mM NaCl. Whe n bacterial cultures were shifted from hypersaline to basal media, oli goglucans were the only oligosaccharides detected. The addition of 10 mM proline to bacteria grown under hypersalinity led to a 50% decrease in the level of trehalose and to the accumulation of oligoglucans. Th e addition of 10 mM glycine betaine to bacteria grown under hypersalin ity also produced accumulation of oligoglucans, but the level of treha lose did not decrease. The results presented here are consistent with a role for trehalose as a compatible solute in peanut Rhizobium ATCC 5 1466, and they suggest that exogenously added proline may act as a com patible solute in preference to trehalose.