7-Mercaptoheptanoylthreonine phosphate substitutes for heat-stable factor (mobile factor) for growth of Methanomicrobium mobile.

Methanomicrobium mobile requires a heat-stable factor present in ruminal fluid and in boiled cell extract from Methanobacterium thermoautotrophicum for growth. By comparing the growth of M. mobile with boiled cell extract with that observed with various methanogenic cofactors, we found that 7-mercaptoheptanoylthreonine phosphate (HS-HTP) supported sustained growth of M. mobile, at an optimal concentration of 100 microM. No derivatives or possible biosynthetic precursors of HS-HTP could replace HS-HTP as the sole source of growth factor. Results suggest that the growth requirement might be satisfied by 7-mercaptoheptanoic acid plus a second, unidentified heat-stable factor.