Gene expression in Pseudomonas aeruginosa biofilms

Abstract

Bacteria often adopt a sessile biofilm lifestyle that is resistant to antimicrobial treatment. Opportunistic pathogenic bacteria like Pseudomonas aeruginosa can develop persistent infections. To gain insights into the differences between free-living P. aeruginosa cells and those in biofilms, and into the mechanisms underlying the resistance of biofilms to antibiotics, we used DNA microarrays. Here we show that, despite the striking differences in lifestyles, only about 1% of genes showed differential expression in the two growth modes; about 0.5% of genes were activated and about 0.5% were repressed in biofilms. Some of the regulated genes are known to affect antibiotic sensitivity of free-living P. aeruginosa. Exposure of biofilms to high levels of the antibiotic tobramycin caused differential expression of 20 genes. We propose that this response is critical for the development of biofilm resistance to tobramycin. Our results show that gene expression in biofilm cells is similar to that in free-living cells but there are a small number of significant differences. Our identification of biofilm-regulated genes points to mechanisms of biofilm resistance to antibiotics.

Why are bacteria refractory to antimicrobials?

“…However, mutational analysis and gene expression studies of genes that encode known drug efflux pumps indicated that this is not necessarily the case [30,32]. A comparison of the RNA expression profiles from P. aeruginosa planktonic cultures and biofilms identified several candidate genes that may contribute to the antibiotic resistance phenotype of biofilm cells [33]. For example, increased expression of the tolA gene is hypothesized to alter the structure of lipopolysaccharides in the outer membrane, making it more difficult for aminoglycoside antibiotics, such as tobramycin and gentamicin, to enter the cell.…”

Phage-induced lysis enhances biofilm formation in Shewanella oneidensis MR-1

“…However, the nature of the signals that trigger the prophages to enter the lytic cycle during biofilm formation in S. oneidensis is thus far unknown. Notably, phage genes have been shown to be strongly upregulated in biofilms of several bacterial species (Whiteley et al, 2001;Ren et al, 2004;Domka et al, 2007). It remains to be shown whether phage induction in S. oneidensis MR-1 is a direct response to surface attachment and/or nutrient limitations as indicated by cell lysis occurring in planktonic cultures in late exponential phase and whether the prophages are also involved in the dispersal of S. oneidensis biofilms.…”

High-Resolution Visualization ofPseudomonas aeruginosaPAO1 Biofilms by Freeze-Substitution Transmission Electron Microscopy

“…These features were surprising since we often naturally assume that many biofilm cells would be under nutrient limitation (no matter the flow rate) and, accordingly, the cells should not look so healthy. Yet studies do suggest strong metabolic activity (57), and recent DNA microarray studies reveal ribosomal gene expression to be upregulated in P. aeruginosa, Escherichia coli, and B. subtilis biofilms versus their planktonic counterparts (60,62,69).…”