INCREASED TRANSCRIPTS OF THE DNAK LOCUS GENES IN METHANOSARCINA-MAZEIS-6 EXPOSED TO SUPRAOPTIMAL CONCENTRATIONS OF AMMONIA

The effect of supraoptimal concentrations of ammonia on cell growth an d stress genes of the dnaK locus was investigated in Methanosarcina ma zei S-6, a methanogen important for anaerobic digestion in bioreactors . When the concentration of NH4Cl was increased 25 times above the opt imal for growth, the lag phase lengthened, growth occurred at a decrea sed rate, and a stress response was induced - the transcripts from the stress genes grpE, dnaK, and dnaJ increased, whereas that of the adja cent genes orf11-trkA decreased. In contrast, a 10-fold elevation of t he NH4Cl concentration, which had only a slight stimulating effect on the stress genes, augmented the orf11-trkA transcript. These findings show that ammonia at certain levels is a cell stressor for M. mazei S- 6.