Diguanylate cyclase Dgc1 synthesizes c-di-GMP and modulates WL gum exopolysaccharide production in Sphingomonas sp....

Diguanylate cyclase (DGC) synthesizes c-di-GMP, an important second messenger that regulates exopolysaccharide production in many bacteria. WL gum is a commercially important exopolysaccharide produced by Sphingomonas sp. WG, however, the DGCs that modulate its biosynthesis remain unidentified. The function of Dgc1 was investigated through heterologous expression and gene deletion. In vitro assays showed that Dgc1 catalyzes c-di-GMP synthesis with a specific activity of 13.7 U/mg. Deletion of dgc1 reduced intracellular c-di-GMP levels by 94% in vivo. Importantly, WL gum production in the Δdgc1 strain reached only 79% of the wild-type yield after 84 h of cultivation, accompanied by lower viscosity and decreased viscoelastic properties of WL gum. Integrated transcriptomic, proteomic, and enzymatic activity analyses revealed that dgc1 deletion redirected carbon flux toward central metabolism, disturbed energy metabolism, and altered protein secretion systems, thereby diminishing WL gum synthesis. These findings establish Dgc1 as a DGC that significantly contributes to global c-di-GMP pools and positively modulates WL gum production in Sphingomonas sp. WG, though it is neither the sole nor primary regulator of this process. The results provide a valuable reference for understanding c-di-GMP dynamics and its indirect impact on WL gum production. However, the absence of chromosomal in situ complementation precluded a definitive causal conclusion, constituting a key limitation of the present study.