IDENTIFICATION OF VOLATILE FORMS OF METHYL-GROUPS RELEASED BY HALOBACTERIUM-SALINARIUM

Halobacterium salinarium (formerly H. halobium) is a chemotactic and p hototactic archaeon from which volatile methyl groups are released con tinually, a phenomenon related to its sensory system. We found that re leased methyl groups comprised two different chemical species, methano l and methanethiol, the sulfur analog of methanol. Radiolabeling exper iments showed that the methyl groups of both compounds, as well as the sulfur of methanethiol, were derived from methionine but were donated to cellular components and subsequently cleaved to produce the respec tive volatile compounds. Previous work had shown that chemostimuli and photostimuli result in transient increases in the rate of release of volatile methyl groups. We found that these in creases reflected incre ased release of methanol but not of methanethiol. Thus, the methyl gro up chemistry of the H. salinarium sensory system is analogous to the w ell-studied chemotactic system of Escherichia coli. The reactions that result in methanethiol release are of unknown function and have unusu al features. They may involve a methionine-gamma-lyase activity we det ected in H. salinarium. Sulfur derived from methionine was found attac hed to specific proteins in reduction-sensitive disulfide linkages.