Influence of Indole and Mixed Culture Growth on Pseudomonas Aeruginosa Biofilm Structure
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When microorganisms are studied within their natural environments, they are not commonly found as single species. Microbes are usually found as clusters or multitudes of aggregates within surface-attached biofilm communities. The discovery of this sessile lifestyle has had a resounding effect on the scientific community and the approach toward studying anti-microbial resistance (AMR). Past studies showed that quorum sensing (QS) mutants of Pseudomonas aeruginosa, unable to produce N-acylated homoserine lactone (AHL) signals had altered biofilm structure. During mixed culture growth of P. aeruginosa with Escherichia coli, we found that E. coli production of the organic compound, indole, inhibited AHL-regulated genes in P. aeruginosa. The current study was conducted to see if mixed culture growth of P. aeruginosa with indole-producing E. coli affected biofilm structure. Two wt Pseudomonas aeruginosa strains, PA14 and PAO1 were co-cultured with wt Escherichia coli BW25113 (indole producing), and E. coli tryptophanase mutant tnaA (non-indole producing). Comparably, exogenous indole was added in multiple concentrations (mM) in an effort to monitor the response of the P. aeruginosa strains. P. aeruginosa pqs mutant strains where also studied to see if indole induced similar effects in a non-AHL mediated QS system. At lower concentrations (0.1mM), indole induced a spike in growth rates and genes geared toward virulence mechanism of P. aeruginosa. In contrast, higher concentrations (0.5, 1mM), overall induced downregulation of virulence mechanisms controlling pyocyanin, rhamnolipids, and elastase production, inhibiting quorum sensing.