Figure 6. GudB-GltAB interaction is important for biofilm formation.

a) Representative images of biofilms of wild-type and mutant B. subtilis strains on glutamate-glycerol (MSGG) agar medium, monitored over a period of ~7 days. As indicated by their knockouts, both Glt subunits (GltA and B), and GudB, are essential for wild-type like biofilm morphology b) Comparision of biofilm formation by wild-type and mutants expressing GltA under an IPTG-induced promoter, at varying IPTG concentrations (0–100 μM). Wild-type (i-iii); IPTG-induced GltA plus GudB (iv-vi), or RocG (vii-ix); IPTG-induced inactive GltA mutant, GltAB^C1A plus GudB (x-xii), or with RocG (xiii-xv). Wild-type GltAB and the GltAB^C1A were expressed from an IPTG-inducible hyperspank promoter, while GudB and RocG were under gudB’s promoter. Wild-type’s biofilms are not affected by the presence of IPTG (i-iii). The strain expressing GltAB from an IPTG-induced promoter forms altered biofilms with no IPTG (iv), wild-type-like biofilms with low concentration of IPTG (v), while overexpression resulted in biofilms similar to those of the ΔgudB strain (vi). Co-expression of RocG and GltAB resulted in biofilms with no wrinkles (vii-ix). Expression of the inactive GltAB^C1A with GudB restores the morphology of the biofilm’s interior, in an IPTG-dependent manner (x-xii); in contrast, co-expression of GltAB^C1A with RocG does not (xiii-xv). The scale bars in all images correspond to 4 mm. Magnified sections are shown in the last column of panel b. c-e) A summary of the biofilm disruption phenotypes and a proposed model that accounts for them (see text). The biofilm images correspond to the following images from b: iii (c), xii (d) and xv (e).