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 ΔpykA 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 ΔpykA knockout. Proteomics suggested that the synthesis of enzymes involved in fatty acid and lipid biosynthesis were decreased, whereas those involved in β-oxidation were increased in the M. tuberculosis ΔpykA 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 ΔpykA mutant, and iron-regulated proteins were also affected. Ald levels were decreased in the ΔpykA knockout, explaining why an M. tuberculosis ΔpykA Δald 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.