Differential inhibition and stimulation of extracellular matrix components in Escherichia coli biofilms by a polyketide metabolite

BURALLI, BAUTISTA; CORDISCO ESTEFANÍA; SERRA, DIEGO

Chapadmalal

Congreso; XVIII Congreso Argentino de Microbiología General; 2023

Sociedad Argentina de Microbiología General SAMIGE

Biofilms are multicellular communities that bacteria form by embedding themselves in anextracellular matrix (ECM) composed of polymeric fibers. Due to their tolerance toantibiotics, biofilms promote the persistence of infections. An example of this is urinary tractinfections caused by Escherichia coli. Recognizing the need for solutions to combat biofilmbased infections in general, and of E. coli in particular, we focused on the search forcompounds that can interfere with the production of the major ECM components of E. colibiofilms: amyloid fibers, known as curli, and phosphoethanolamine (pEtN)-cellulose fibers.To do this, we conducted pairwise interactions on agar plates involving macrocolonybiofilms of E. coli strains with varying capacities to produce curli and/or pEtN-cellulose,along with microorganisms that generate metabolites potentially capable of interfering withthe synthesis of both ECM components. For this approach, we supplemented the agarmedium with Congo Red and Coomassie Blue (CR/CB), two dyes that enable the in situstaining of curli and pEtN-cellulose within macrocolony biofilms, imparting distinct colortonalities. Our results demonstrated a potent inhibition of curli fiber synthesis inmacrocolonies of an E. coli strain exclusively capable of producing this component, whenexposed to the soil microorganism Bacillus subtilis. Curli inhibition was detected by the lossof CR/CB staining and by the absence of curli-dependent morphology of the macrocolonywhen they grew in proximity to B. subtilis. Additionally, our studies revealed that thisinhibitory effect is attributed to a polyketide (PK) metabolite. Interestingly, we also observedthat B. subtilis not only fails to inhibit the synthesis of pEtN-cellulose in macrocolonies of E.coli strains capable of producing both curli and pEtN-cellulose, or solely pEtN-cellulose, butrather, it stimulates the production of pEtN-cellulose. Remarkably, this stimulatory effectoccurs independently of CsgD, the regulator that controls the biosynthetic pathways of bothpEtN-cellulose and curli. This was evidenced when macrocolonies of an E. coli ΔcsgDstrain, deficient in CsgD, exhibited a significant increase in pEtN-cellulose production wheninteracting with B. subtilis. We found that this increase in pEtN-cellulose did not occur whenE. coli ΔcsgD interacted with the B. subtilis strain deficient in the synthesis of the curliinhibitory PK metabolite, indicating that this compound is in turn responsible for the inducingeffect on pEtN-cellulose. In conclusion, we found that B. subtilis produces a PK metabolitethat inhibits amyloid curli, the primary ECM component in E. coli biofilms, while conversely,stimulates the synthesis of pEtN-cellulose, the second ECM component. These resultssuggest that when curli production is inhibited, E. coli tries to compensate for this loss byinducing the synthesis of the second ECM component through a new regulatory pathwayindependent of CsgD.