Catalyzes the condensation of pyruvate and acetyl-coenzyme A to form (R)-citramalate. Makes part of the main pathway for isoleucine biosynthesis in G.sulfurreducens, i.e. the citramalate-dependent pathway. acetyl-CoA + H2O + pyruvate = (3R)-citramalate + CoA + H(+) Amino-acid biosynthesis; L-isoleucine biosynthesis; 2-oxobutanoate from pyruvate: step 1/3. Cells lacking this gene show a great reduction in citramalate synthase activity and are capable of growth in the absence of isoleucine, whereas mutants lacking both cimA and the threonine ammonia-lyase tcdB are auxotrophs for isoleucine. Belongs to the alpha-IPM synthase/homocitrate synthase family.