Bacillus subtilis is the model for the study of Gram-positive sporulation, an important example of prokaryotic cell differentiation. Despite the fact that B. subtilis was one of the first organisms whose genome was fully sequenced, only about 40% of the proteins encoded by this comparatively small genome have been biochemically characterized in vitro. It is perhaps even more surprising that some major metabolic pathways which likely supply energy and carbon during sporulation remain biochemically unstudied as well. We therefore still do not fully understand the metabolism necessary to complete the process of sporulation. The mother cell metabolic gene (mmg) operon, which is expressed during sporulation, encodes a likely fatty acid metabolic pathway and also a methylcitric acid cycle. The protein products of these genes have never been biochemically characterized, and our work has so far demonstrated that the mmg fatty acid pathway operates only in a catabolic direction.