ORGANIC OSMOLYTES IN AEROBIC-BACTERIA FROM MONO LAKE, AN ALKALINE, MODERATELY HYPERSALINE ENVIRONMENT

The identity and concentrations of intracellular organic solutes were determined by nuclear magnetic resonance spectroscopy for two strains of aerobic, gram-negative bacteria isolated from Mono Lake, Calif, an alkaline, moderately hypersaline lake, Ectoine (1,4,5,6-tetrahydro-2-m ethyl-4-pyrimidincarboxylic acid) was the major endogenous solute in b oth organisms, Concentrations of ectoine varied with external NaCl lev els in strain ML-D but not in strain ML-G, where the level was high bu t invariant from 1.5 to 3.0 hi NaCl. Hydroxyectoine also occurred in s train ML-D, especially at elevated NaCl concentrations (2.5 and 3.0 M) , but at levels lower than those of ectoine, Exogenous organic solutes that might occur in Mono Lake were examined for their effects on the de novo synthesis of ectoine, Dimethylsulfoniopropionate (DMSP) (0.1 o r 1 mM) did not significantly lower ectoine levels in either isolate, and only strain R-IL-G showed any capacity for DMSP accumulation, With nitrogen limitation, however, DMSP (0.1 mM) substituted for ectoine i n strain ML-G and became the main organic solute. Glycine betaine (GB) was more effective than DMSP in affecting ectoine levels, principally in strain ML-D. Strain ML-D accumulated GB to 50 or 67% of its organi c solute pool at 2.5 M NaCl, at an external level of 0.1 or 1 mM GB, r espectively, Strain ML-D also accumulated arsenobetaine, The methylate d zwitterionic compounds, probably metabolic products of phytoplankton (DMSP and GB) or brine shrimps (arsenobetaine) in Mono Lake, may func tion as osmolytes for indigenous bacteria when present at high concent rations or under conditions of nitrogen limitation or salt stress.