Search for: All records

ABSTRACT Despite the significant presence of plant-derived tricarboxylic acids in some environments, few studies detail the bacterial metabolism oftrans-aconitic acid (Taa) and tricarballylic acid (Tcb). In a soil bacterium,Acinetobacter baylyiADP1, we discovered interrelated pathways for the consumption of Taa and Tcb. An intricate regulatory scheme tightly controls the transport and catabolism of both compounds and may reflect that they can be toxic inhibitors of the tricarboxylic acid cycle. The genes encoding two similar LysR-type transcriptional regulators, TcuR and TclR, were clustered on the chromosome withtcuAandtcuB, genes required for Tcb consumption. The genetic organization differed from that inSalmonella entericaserovar Typhimurium, in whichtcuAandtcuBform an operon with a transporter gene,tcuC. InA. baylyi,tcuCwas not cotranscribed withtcuAB. Rather,tcuCwas cotranscribed with a gene, designatedpacI, encoding an isomerase needed for Taa consumption. TcuC appears to transport Tcb andcis-aconitic acid (Caa), the presumed product of PacI-mediated periplasmic isomerization of Taa. Two operons,tcuC-pacIandtcuAB, were transcriptionally controlled by both TcuR and TclR, which have overlapping functions. We investigated the roles of the two regulators in activating transcription of both operons in response to multiple effector compounds, including Taa, Tcb, and Caa.IMPORTANCEIngestion of Taa and Tcb by grazing livestock can cause a serious metabolic disorder called grass tetany. The disorder, which results from Tcb absorption by ruminants, focuses attention on the metabolism of tricarboxylic acids. Additional interest stems from efforts to produce tricarboxylic acids as commodity chemicals. Improved understanding of bacterial enzymes and pathways for tricarboxylic acid metabolism may contribute to new biomanufacturing strategies.