Methyl mercaptan production by periodontal bacteria.

Oral malodour is principally caused by volatile sulphur compounds (VSC) such as hydrogen sulphide, methyl mercaptan and dimethyl sulphide. Methyl mercaptan is highly toxic, and its presence within a periodontal pocket suggests involvement in the induction and/or progression of periodontal disease. Methyl mercaptan is produced from L-methionine by L-methionine- alpha -deamino- gamma -mercaptomethane-lyase (METase). METase catalyses the alpha,gamma-eliminating reaction of L-methionine, which results in the release of alpha-ketobutyrate, methyl mercaptan and ammonia. Although methyl mercaptan is produced by a variety of microorganisms, Porphyromonas gingivalis is considered to be the most potent producer. METases of P. gingivalis have been characterised and the genes responsible for their production, the mg/genes, have been sequenced. To ascertain the role of METase in P. gingivalis pathogenicity, a METase-deficient mutant strain (M1217) from P. gingivalis strain W83 was engineered. Only 7.7% of the mice infected with W83 survived 4 days after subcutaneous injection, whereas 36% of the mice infected with M1217 survived over the same time period. Many papers have reported the periodontal pathogenesis of VSC. It has been argued that methyl mercaptan may play a significant role in the pathogenicity of P. gingivalis.