Identification of Putative Cellulose Synthase Gene xcsA2 Required for c-di-GMP-Induced Biofilm Formation and Cell Aggregation in Synechococcus elongatus PCC 7942.

Synechococcus elongatus PCC 7942 is a widely used model cyanobacterium for diverse research fields and for bioproduction applications owing to its ease of cultivation, genetic modification, and ability to fix CO2. We found that a laboratory strain of S. elongatus PCC 7942 expressing the ydeH gene from E. coli exhibited pronounced biofilm formation and cell aggregation upon ydeH induction, despite the species rarely showing these phenotypes under standard laboratory conditions. Our findings demonstrate that this strain harbors latent potential for biofilm formation and aggregation through c-di-GMP synthesis, suggesting possible applications in biomass recovery. Further, we identified that xcsA2 (Synpcc7942_2151), a putative cellulose synthase gene containing a PilZ domain that binds c-di-GMP is an indispensable gene in this biofilm-producing phenotype and experimentally confirmed ydeH-induced cellulose-like β-1,4-linked glucans production. Notably, xcsA2 represents the first putative functional cellulose synthase gene involved in biofilm/aggregate formation in S. elongatus and suggests that this organism may serve as a useful platform for bacterial cellulose bioproduction. Overall, discovery of xcsA2 provides a new genetic basis for exploring cellulose synthase evolution in cyanobacteria and specifically opens possibilities for engineering cellulose bioproduction utilizing S. elongatus.