EFFECTS OF OSMOLYTE PRECURSORS ON THE DISTRIBUTION OF COMPATIBLE SOLUTES IN METHANOHALOPHILUS-PORTUCALENSIS

The halophilic methanogen Methanohalophilus portucalensis synthesizes three distinct zwitterions, beta-glutamine, N-epsilon-acetyl-beta-lysi ne (NA beta Lys), and glycine betaine, as osmolytes when it is grown a t high concentrations of external NaCl, The selective distribution of these three species was determined by growing cells in the presence of osmolyte biosynthetic precursors, Glycine betaine is formed by the st epwise methylation of glycine, Exogenous glycine (10 mM) and sarcosine (10 mM), although internalized, do not bias the cells to accumulate a ny more betaine, However, exogenous N,N-dimethylglycine (10 mM) is ava ilable to the appropriate methyltransferase and the betaine generated from it suppresses the synthesis of other osmolytes, Precursors of the two zwitterionic beta-amino acids (beta-glutamate for beta-glutamine and alpha-lysine and diaminopimelate for NA beta Lys) have only small effects on beta-amino acid accumulation, The largest effect is provide d by L-alpha-glutamine, suggesting that nitrogen assimilation is a key factor in osmolyte distribution.