Changes in the cellular content of trehalose in four peanut rhizobia strains cultured under hypersalinity

The adaptation to saline stress was examined in four Rhizobium strains which nodulate Arachis hypogaea (peanut). When cultured on basal yeast extract-mannitol liquid medium (1.7 mM NaCl), the strains ATCC 10317, ATCC 51466, and TAL 1000 behaved as fast-growers, while the strain USDA 3187 behaved as slow-grower. After a prolonged lag time, the four strains were able to grow under hypersalinity, albeit at a reduced rate. The slow-grower was less salt-tolerant than the fast-growers. On the other hand, the disaccharide trehalose was identified in the four strains by gas chromatography and by C-13-NMR spectroscopy. Strains ATCC 10314 and ATCC 51466 contained negligible amounts of trehalose, while strains TAL 1000 and USDA 3187 accumulated significant quantities of the disaccharide. Under hypersalinity, fast-growers increased the cellular content of trehalose, regardless of the carbon source mannitol, sucrose, or lactose; when cultured with mannitol as the carbon source, the slow-grower also increased the accumulation of cellular trehalose. When cultured with trehalose as the carbon source, the increase of NaCl in the growth medium did not change the cellular trehalose content in the strain ATCC 10317, but the accumulation of the disaccharide decreased in the strains TAL 1000 and USDA 3187. Results were correlated with changes in the metabolism of trehalose in peanut rhizobia exposed to hypersalinity.