To better understand the global effects of "natural" lesions in genes involved in the pyruvate metabolism in Mycobacterium bovis, null mutations were made in the Mycobacterium tuberculosis H37Rv ald and pykA genes to mimic the M. bovis situation. Like M. bovis, the M. tuberculosis ⌬pykA mutant yielded dysgonic colonies on solid medium lacking pyruvate, whereas colony morphology was eugonic on pyruvate-containing medium. Global effects of the loss of the pykA gene, possibly underlying colony morphology, were investigated by using proteomics on cultures grown in the same conditions. The levels of Icd2 increased and those of Icl and PckA decreased in the ⌬pykA knockout. Proteomics suggested that the synthesis of enzymes involved in fatty acid and lipid biosynthesis were decreased, whereas those involved in -oxidation were increased in the M. tuberculosis ⌬pykA mutant, as confirmed by direct assays for these activities. Thus, the loss of pykA from M. tuberculosis results in fatty acids being used principally for energy production, in contrast to the situation in the host when carbon from fatty acids is conserved through the glyoxylate cycle and gluconeogenesis; when an active pykA gene was introduced into M. bovis, the opposite effects occurred. Proteins involved in oxidative stress-AhpC, KatG, and SodA-showed increased synthesis in the ⌬pykA mutant, and iron-regulated proteins were also affected. Ald levels were decreased in the ⌬pykA knockout, explaining why an M. tuberculosis ⌬pykA ⌬ald double mutant showed little additional phenotypic effect. Overall, these data show that the loss of the pykA gene has powerful, global effects on proteins associated with central metabolism.Comparison of the genome sequences of Mycobacterium bovis and Mycobacterium tuberculosis revealed Ͼ99.95% identity at the nucleotide level; however, these pathogens differ in terms of host tropism, phenotype, and virulence (16). Eleven regions of difference (RD) were observed in the M. bovis genome (2 to 12.7 kb) compared to M. tuberculosis, while one region deleted from M. tuberculosis was present in M. bovis (5,16). In addition to the RDs, there are over 2,400 single nucleotide polymorphisms (SNPs) between M. tuberculosis and M. bovis (16). Some SNPs cosegregate with regions of deletions or other genetic markers (5); one such SNP is in the pykA gene, which cosegregates with the RD9 deletion. This SNP results in an inactive pyruvate kinase (PykA) being produced due to a Glu220Asp mutation (20). Glu220 is in the active site of the enzyme (21, 24), and its substitution results in complete loss of the enzyme activity in M. bovis (20). Thus, the pykA SNP explains one of the classic distinctions between M. bovis and M. tuberculosis, namely, the requirement for pyruvate. Neither glycerol, the preferred carbon source for isolation of tubercle bacilli, nor glucose support the growth of M. bovis when they are not supplemented with pyruvate (38), due to the inactive pyruvate kinase.On the routinely used Middlebrook 7H11 agar, containing glycerol and ol...