Methionine supplementation exacerbates the growth phenotype of the ∆ MMP16 mutant in the absence of coenzyme M (CoM).

A) Illustration of proposed CoM and homocysteine biosynthesis by MMP16 and L-ASST, respectively, in M. acetivorans. The schematic for L-ASST includes the NIL and CBS domains that are hypothesized to undergo product inhibition by methionine and S-adenosyl methionine, respectively. B) In the ∆ MMP16 mutant the loss of the primary CoM synthase necessitates a secondary route for CoM production, possibly through L-ASST. C) Exogenous supplementation of methionine could lead to an increase in its intracellular concentration and potentially decrease L-ASST activity post-translationally via the NIL and/or CBS domains. If L-ASST compensates for MMP16 in its absence, this would lead to an incidental reduction in CoM biosynthesis and an exacerbation of the growth defect of ∆ MMP16 in the absence of exogenous CoM. D) Growth rates of ∆ MMP16 cultures in triplicate in minimal media with varying concentrations of methionine, with and without 1 µ M CoM (** p < 0.01, Student’s t-test). Error bars represent standard deviations of three replicate cultures.