Medium-chain dehydrogenase/reductase and aldo-keto reductase scavenge reactive carbonyls in Synechocystis sp PCC 6803

Reactive carbonyls (RCs), which are inevitably produced during respiratory and photosynthetic metabolism, have the potential to cause oxidative damage to photosynthetic organisms. Previously, we proposed a scavenging model for RCs in the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803). In the current study, we constructed mutants deficient in the enzymes medium-chain dehydrogenase/reductase (Delta MDR) and aldo-keto reductase (Delta AKR) to investigate their contributions to RC scavenging in vivo. We found that treatment with the lipid-derived RC acrolein causes growth inhibition and promotes greater protein carbonylation in Delta MDR, compared with the wild-type and Delta AKR. In both Delta MDR and Delta AKR, photosynthesis is severely inhibited in the presence of acrolein. These results suggest that these enzymes function as part of the scavenging systems for RCs in S. 6803 in vivo.