cdGMP stimulates F. novicida biofilm formation. (A) F. novicida strains U112 (WT), KKF457 [Δ(FTN0451-0456)], KKF535 (cdgB), KKF538 (cdgA), and KKF539 (cdgA cdgB), either with no plasmid (−) or carrying plasmid pKEK1524 (cdgB) or pKEK1525 (VCA0956), were assayed for biofilm formation as described in Materials and Methods. **, P < 0.005; ***, P < 0.0005. (B) F. novicida strains U112 (WT) and KKF552 (qseB), either with no plasmid (−) or carrying plasmid pKEK1524 (cdgB) or pKEK1525 (VCA0956), were assayed for biofilm formation. ***, P < 0.0005.