Exploiting interspecies interactions in a Corynebacterium-Shewanella co-culture improves succinic acid production.

Anaerobic production of succinic acid in Corynebacterium glutamicum is often constrained by metabolic imbalances and by-product formation. In this study, an engineered co-culture system was developed by pairing C. glutamicum with the electroactive bacterium Shewanella oneidensis to enhance succinic acid biosynthesis through interspecies interactions. The optimized co-culture achieved a succinic acid yield of 0.169 g/g, representing a 45.65% increase compared to monoculture, without markedly altering glucose consumption. Screening of five redox-active compounds identified riboflavin as the most effective additive, and supplementation with 0.1 mM riboflavin further improved production performance. To reduce carbon loss to competing pathways, the lactate dehydrogenase gene (ldhA) in C. glutamicum was deleted, generating a lactate-deficient strain (K1) in which lactate formation was completely abolished. The engineered strain maintained enhanced succinic acid production in the co-culture system, reaching a yield of 0.686 g/g, and exhibited up to a 23.4% increase in yield during extended fermentation compared to monoculture. Transcriptomic analysis revealed that co-culture induced global metabolic reprogramming in C. glutamicum, including reinforcement of the electron transport system, redistribution of carbon flux toward the reductive TCA pathway, and suppression of succinic acid -consuming pathways. Overall, this study demonstrates an effective co-culture strategy for improving succinic acid production and provides insights into the role of interspecies interactions in metabolic regulation.