Use of microorganisms for reducing the level of trimethylamine in a human body cavity, in particular for the treatment of trimethylaminuria or of bacterial vaginosis and the prevention of cardiovascular diseases

A method for reducing or suppressing trimethylamine (TMA) present in a human cavity in a human patient in need thereof, comprising:

• administering an effective amount of a composition containing a methanogenic Archaea the RNA 16S of which is coded by the DNA sequence SEQ ID NO:
• 11 or 12, a methanogenic Archaea comprising a gene coding for a TMA methyltransferase of sequence SEQ ID NO:
• 1 or 2, or a methanogenic Archaea containing a TMA methyltransferase of sequence SEQ ID NO:
• 1 or 2, wherein said TMA methyltransferase is capable of reducing or suppressing TMA in said cavity through metabolizing TMA in the presence of hydrogen in said human cavity, and
• having the methanogenic Archaea delivered into the human cavity which is the intestine which comprises microbial flora able to produce said TMA, wherein said methanogenic Archaea is a methanogenic Archaea that when present in the intestine has a TMA metabolism, wherein said methanogenic Archaea produces TMA methyltransferase and metabolizes intestinal TMA in the presence of H2, and
• whereby said TMA present in the intestine is metabolized in the intestine to methane and TMA is reduced or suppressed in the intestine and in the liver.