The deficiency of methylglyoxal synthase promotes cell proliferation in Synechocystis sp. PCC 6803 under mixotrophic conditions.

Methylglyoxal synthase (MGS), which converts dihydroxyacetone phosphate to methylglyoxal (MG), is found in only prokaryotes. Synechocystis sp. PCC 6803 possesses the gene sll0036, which encodes MGS. To clarify the biological function of MGS, we constructed a gene-disruption strain of Synechocystis sp. PCC 6803. Expression analysis showed that MG metabolic genes (sll0036, sll0067, and slr1167) were upregulated under photoautotrophic conditions compared to mixotrophic conditions. The sll0036-deficient strain (Δ0036) exhibited a higher growth rate than the wild-type (WT) strain under mixotrophic conditions, whereas no significant difference was observed under photoautotrophic conditions. When cells were cultured in a medium supplemented with sorbitol or mannitol instead of glucose, the growth enhancement observed in the Δ0036 strain disappeared. This suggests that the difference in growth between Δ0036 and WT is influenced by glucose-related metabolism rather than osmotic stress. MG contents were found to be decreased in the Δ0036 strain compared to WT under mixotrophic conditions. This suggests that the reduction of MG level might activate the cell proliferation of Synechocystis sp. PCC 6803 under mixotrophic conditions.