Lysine-2,3-aminomutase and β-lysine acetyltransferase genes of methanogenic archaea are salt induced and are essential for the biosynthesis of Nε-acetyl-β-lysine and growth at high salinity

The compatible solute N-epsilon-acetyl-beta-lysine is unique to methanogenic archaea and is produced under salt stress only. However, the molecular basis for the salt-dependent regulation of N-epsilon-acetyl-beta-lysine formation is unknown. Genes potentially encoding lysine-2,3-aminomutase (abl4) and beta-lysine acetyltransferase (ablB), which are assumed to catalyze N-epsilon-acetyl-beta-lysine formation from alpha-lysine, were identified on the chromosomes of the methanogenic archaea Methanosarcina mazei Gol, Methanosarcina acetivorans, Methanosarcina barkeri, Methanococcus jannaschii, and Methanococcus maripaludis. The order of the two genes was identical in the five organisms, and the deduced proteins were very similar, indicating a high degree of conservation of structure and function. Northern blot analysis revealed that the two genes are organized in an operon (termed the abl operon) in M. mazei Go1. Expression of the abl operon was strictly salt dependent. The abl operon was deleted in the genetically tractable M. maripaludis. Deltaabl mutants of M. maripaludis no longer produced N-epsilon-acetyl-beta-lysine and were incapable of growth at high salt concentrations, indicating that the abl operon is essential for N-epsilon-acetyl-beta-lysine synthesis. These experiments revealed the first genes involved in the biosynthesis of compatible solutes in methanogens.