Inhibition of gas vesicle production in Microcyclus aquaticus by L-lysine

The timing and degree of gas vesicle production in Microcyclus aquaticus was affected by nutritional conditions. If 50 μg L-lysine/ml was added to a glucose – mineral salts medium (DM), the organism did not form gas vesicles. This effect was specific for L-lysine, as neither D-lysine nor meso-diaminopimelic acid prevented gas vesicle production. Cells grown in the presence of L-lysine did not contain any immunologically detectable gas vesicle protein, which indicates that L-lysine affects expression of the structural gene for the gas vesicle protein rather than assembly of the protein into gas vesicles. The addition of L-lysine to cultures in DM did not immediately decrease the rate of gas vesicle assembly, nor did the removal of cells from DM plus L-lysine to DM result in immediate gas vesicle production. Gas vesicle production was also affected by the addition of L-threonine or L-cysteine to culture media or by an increase in the medium's ionic strength. These results are discussed in relation to the aspartic acid pathway of amino acid biosynthesis and effects upon the intracellular L-lysine concentration.