Transcriptome analysis of Pseudomonas aeruginosa biofilm development: anaerobic respiration and iron limitation

Abstract

In nature, bacteria are able to form complex surface-attached communities called biofilms. Microbial biofilms pose a particular problem in many human infections because of an inherent tolerance to antimicrobial agents and host immune killing and clearance. We have used complementary DNA (cDNA) microarray technology to identify Pseudomonas aeruginosa genes that are differentially expressed in growing and developing biofilms. Our study shows that, when compared with planktonic bacteria, gene expression profiles of biofilm cells have the highest resemblance to the profiles of stationary-phase cells. We suggest that the process of biofilm development involves a series of adaptive responses including those to anaerobic and iron-limitation stresses, rather than being associated with a unique biofilm developmental program. Mapping of quorum-sensing regulated genes in a P. aeruginosa biofilm identified a set of N-acyl homoserine lactone (AHL)-dependent genes that are exclusively expressed in sessile cells. One of these genes, pvdQ, encodes an AHL acylase that degrades long-acyl but not short-acyl AHLs. This result may provide an explanation for the previous finding that the level of long-acyl AHLs is greatly reduced in P. aeruginosa biofilm cells as compared with their planktonic counterparts. Furthermore, we present evidence that quorum sensing is participating in the control of iron-limitation responses in the biofilm cells.

Quorum sensing inhibitors: a bargain of effects

“…This gene confers higher tolerance to the antibiotic tobramycin at least in one P. aeruginosa isolate, PA14 (Mah et al, 2003). However, it is not differently expressed in biofilm cells of P. aeruginosa PAO1 (Hentzer et al, 2005) and cannot therefore be a general mechanism for tobramycin tolerance. Perhaps surprisingly, QS has also been found to be involved with the tolerance of biofilms to antimicrobial compounds.…”

“…Deeper in the layers of the biofilm, where oxygen and nutrients are limited, the bacteria grow either slowly or not at all. In fact, a recent transcriptome analysis performed at different stages during biofilm development and maturation demonstrated that the bulk of biofilm cells, as judged from their gene expression profiles, must have adopted stationary-phase physiology (Hentzer et al, 2005). This explains, at least in part, why most antimicrobials which target active, growing cells are unable to fully eradicate the bacterial biofilms (Campanac et al, 2002;Drenkard, 2003;Lewis, 2001;Teitzel & Parsek, 2003).…”

The clinical impact of bacterial biofilms

“…B) Transcriptomic studies of global gene-expression in P. aeruginosa biofilms indicate adaptation of both physiology and biochemistry of biofilm growing bacteria compared to planktonic growing bacteria [21][22]. When the pattern of gene expression during biofilm growth is investigated, the results indicate that the bacterial cells mostly resemble planktonically growing bacteria in the stationary growth phase in which bacteria exhibit low metabolic activity.…”

“…When the pattern of gene expression during biofilm growth is investigated, the results indicate that the bacterial cells mostly resemble planktonically growing bacteria in the stationary growth phase in which bacteria exhibit low metabolic activity. Furthermore, there is upregulation of genes which are necessary for anaerobic growth [21].…”

P. aeruginosa Biofilms in CF Infection

“…The CF lung provides a particularly attractive environment for P. aeruginosa colonization and chronic lung infection and is the major causative agent of morbidity and mortality in CF patients [16]. Biofilms are now thought to be involved in 65-80% of all microbial infections [17,18].…”