Increased transcripts of the dnaK locus genes in Methanosarcina mazei S-6 exposed to supraoptimal concentrations of ammonia

The effect of supraoptimal concentrations of ammonia on cell growth and stress genes of the dnaK locus was investigated in Methanosarcina mazei S-6, a methanogen important for anaerobic digestion in bioreactors. When the concentration of NH4Cl was increased 25 times above the optimal for growth, the lag phase lengthened, growth occurred at a decreased rate, and a stress response was induced - the transcripts from the stress genes grpE, dnaK, and dnaJ increased, whereas that of the adjacent genes orf11-trkA decreased.

In contrast, a 10-fold elevation of the NH4Cl 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.