Our transcriptomic data suggest that the pel and psl polysaccharides may be important constituents of the extracellular matrix of drip-flow biofilms while alginate is unimportant (Figure learn more 6A). The rank of the cdrA gene, a recently described adhesin that interacts with the psl polysaccharide [54], was not much different in drip-flow biofilms and planktonic comparators. Figure 6 Comparison of transcript ranks for

selected genes involved in synthesis of extracellular polysaccharides (A) and production of pili (B). Symbols correspond to individual data sets as given in Table 1. An asterisk next to a data point indicates a statistically significant difference between the indicated data set and the combined data of three standard comparator data sets (see Materials and Methods for specifics). Genes associated with the elaboration of type IV pili were strongly expressed in drip-flow biofilms (Figure 6B). This has led us to speculate that these extracellular proteinaceous appendages contribute to the

mechanical stability of this website the biofilm rather than motility, perhaps by binding to extracellular DNA [55, 56]. Transcriptional profiling – independent identification of upregulated genes in biofilms All of the preceding analyses were predicated using a priori identification of a set of genes associated with discrete physiological conditions. The comparison of transcript ranks can also be used to identify genes that are differentially Selleck 5-FU regulated between the drip-flow biofilm data set and planktonic comparator data sets. Table

3 reports the 100 genes that ranked more highly in the drip-flow biofilm than in the comparator data set, by fold-changes in rank ranging from 8 to more than 100. Some of the salient features of this list are genes associated with oxygen limitation (27 genes), copper stress (12 genes), bacteriophage Pf1 (10 genes), denitrification (8 genes), ethanol metabolism (4 genes), and three genes involved in type IV fimbrial biogenesis. Seven of the genes listed in Table 3 (PA0200, PA0409, PA0713, PA1174, PA3309, PA3572, PA5446) appear on the consensus list of gene transcripts upregulated in P. aeruginosa biofilms reported by Patell et al [7]. Biological basis of biofilm antibiotic tolerance P. aeruginosa strain PAO1 formed biofilms in the drip-flow reactor that were poorly killed by tobramycin or ciprofloxacin. This result is concordant with many previous investigations of antibiotic susceptibility of P. aeruginosa biofilms developed in other in vitro systems [12, 13, 43, 57–82]. A plausible and long-standing explanation for reduced antibiotic susceptibility in biofilms is that nutrient limitation leads to slow growth or stationary phase existence for many of the cells in a biofilm, reducing their antimicrobial susceptibility [63, 83–85]. This mechanism is consistent with all of our data.