GLYCINE BETAINE TRANSPORT IN A HALOTOLERANT CHROMATIUM SPECIES

The addition of 1 mM glycine betaine to the growth medium of Chromatiu m sp. NCIMB 8379 relieved growth inhibition caused by exposure to supr a-optimal NaCl concentrations. Intracellular glycine betaine concentra tions were dependent upon the NaCl concentration of the growth medium up to 3 M exogenous NaCl. Kinetic data for the accumulation of [methyl -C-14]-glycine betaine demonstrated that Chromatium sp. NCIMB 8379 pos sesses a constitutively expressed active transport system for glycine betaine. The transport system was saturable with respect to glycine be taine concentration and exhibited typical Michaelis-Menten type kineti cs: K-m = 24 mu M, V-max = 306 nmol min(-1) mg protein(-1) at an exter nal NaCl concentration of 1 M. The rate of glycine betaine transport d ecreased progressively with increasing growth medium NaCl concentratio n. This transport system may represent an adaptive response to growth in high osmolarity environments in this halotolerant isolate, allowing accumulation of glycine betaine from the external cell environment or recycling synthesised glycine betaine which has passively diffused fr om the cell.