Catalyzes the acetylation of beta-lysine to N6-acetyl-beta-lysine, a compatible solute produced by methanogenic archaea that helps cells to cope with salt stress. (3S)-3,6-diaminohexanoate + acetyl-CoA = (3S)-6-acetamido-3-aminohexanoate + CoA + H(+) Transcription is induced at high salt concentrations. Forms part of an operon with ablA. Belongs to the acetyltransferase family.