Aerobic L-tartrate Utilization by Bacillus Isolates

Microbial utilization of uncommon C4 dicarboxylate L-tartrate is largely anaerobic, with aerobic L-tartrate utilization known for few bacterial species including Rhodopseudomonas sphaeroides and Pseudomonas putida. Aerobic L-tartrate-utilizing microbes could be industrially relevant owing to the efficient nature of the bioprocess and catalytic versatility of tartrate dehydrogenase (TDH) responsible for aerobic catabolism of L-tartrate. Present work involves isolation and characterization of Bacillus strains capable of aerobic L-tartrate utilization and its correlation with occurrence of TDH activity. Two out of 37 isolates, IC1-G and IC1-Y were identified as Bacillus megaterium spp. showing efficient aerobic growth, utilizing ~3.7 and 2.8 mM L-tartrate respectively at the end of 48 h. Several organic acids possibly including oxalic, succinic and citric acids were secreted as by-products of L-tartrate metabolism. Utilization of L-tartrate directly correlated with induction of TDH activity by ~3.2 and 5.2 folds in IC1-G and IC1-Y respectively, when grown in presence of L-tartrate as compared to when grown on citrate. Overall, this study contributes Bacillus as only the third genus capable of aerobic, TDH mediated L-tartrate utilization. These Bacillus isolates thus offer potential targets to develop an industrially relevant bioprocess and biocatalyst.