Polyketide synthase likely involved in the biosynthesis of a polymethyl-branched fatty acid (PMB-FA) that might only be produced during host infection. Is required for the full virulence of M.tuberculosis during host infection. Lipid metabolism; fatty acid biosynthesis. Homodimer. Is expressed in bacteria grown axenically (7H9 medium) and inside macrophages. Is organized in a condensing KS-AT and a modifying DH-PsiKR-ER-KR region, followed by a flexibly tethered ACP domain. Disruption of this gene causes no major change in the fatty acid and lipid contents of the mutant strain in vitro; the mutant produces all the major methyl-branched fatty acid containing lipids, including DIM, in similar amounts to the wild-type strain. The replication of this mutant is unaffected in mouse bone-marrow macrophages. However, the mutant strain displays severe growth defects in mice, since it multiplies much less extensively than does the parental strain during the acute phase of infection in the lungs and spleen of mice infected via the respiratory route.