Roles of aconitase in growth, metabolism, and morphological differentiation of Streptomyces coelicolor

The studies of aconitase presented here, along with those of citrate syntha se, were undertaken to investigate the role of the tricarboxylic acid (TCA) cycle in Streptomyces coelicolor development. A single aconitase activity (AcoA) was detected in protein extracts of cultures during column purificat ion. The deduced amino acid sequence of the cloned aco.-l. gene constituted the N-terminal sequence of semipurified AcoA and was homologous to bacteri al A-type aconitases and bifunctional eukaryotic aconitases (iron regulator y proteins). The fact that an acoA disruption mutant (BZ4) did not grow on minimal glucose media in the absence of glutamate confirmed that this gene encoded the primary vegetative aconitase catalyzing Bur through the TCA cyc le. On glucose-based complete medium, BZ4 had defects in growth, antibiotic biosynthesis, and aerial hypha formation, partially due to medium acidific ation and accumulation of citrate. The inhibitory effects of acids and citr ate on BZ4 were partly suppressed by buffer or by introducing a citrate syn thase mutation, However, the fact that growth of an acoA citA mutant remain ed impaired, even on a nonacidogenic carbon source, suggested alternative f unctions of AcoA, Immunoblots revealed that AcoA was present primarily duri ng substrate mycelial growth on solid medium. Transcription of acoA was lim ited to the early growth phase in liquid cultures from a start site mapped in vitro and in vivo.