Coexistence of two d-lactate-utilizing systems in Pseudomonas putida KT2440

Summary It is advantageous for rhizosphere‐dwelling microorganisms to utilize organic acids such as lactate. Pseudomonas putida KT2440 is one of the most widely studied rhizosphere‐dwelling model organisms. The P. putida KT2440 genome contains an NAD‐dependent d‐lactate dehydrogenase encoding gene, but mutation of this gene does not play a role in d‐lactate utilization. Instead, it was found that d‐lactate utilization in P. putida KT2440 proceeds via a multidomain NAD‐independent d‐lactate dehydrogenase with a C‐terminal domain containing several Fe‐S cluster‐binding motifs (Fe‐S d‐iLDH) and glycolate oxidase, which is widely distributed in various microorganisms. Both Fe‐S d‐iLDH and glycolate oxidase were identified to be membrane‐bound proteins. Neither Fe‐S d‐iLDH nor glycolate oxidase is constitutively expressed but both of them can be induced by either enantiomer of lactate in P. putida KT2440. This study shows a case in which an environmental microbe contains two types of enzymes specific for d‐lactate utilization.