BdlA, a Chemotaxis Regulator Essential for Biofilm Dispersion in Pseudomonas aeruginosa

Abstract

Multiple environmental cues have been shown to trigger biofilm detachment, the transition from surfaceattached, highly organized communities known as biofilms to the motile lifestyle. The goal of this study was to identify a gene product involved in sensing environmental cues that trigger biofilm dispersion in Pseudomonas aeruginosa. To do so, we focused on novel putative chemotaxis transducer proteins that could potentially be involved in environmental sensing. We identified a locus encoding such a protein that played a role in detachment, as indicated by the observation that an isogenic mutant biofilm could not disperse in response to a variety of environmental cues. The locus was termed bdlA for biofilm dispersion locus. The BdlA protein harbors an MCP (methyl-accepting chemotaxis protein) domain and two PAS (Per-Arnt-Sint) domains that have been shown to be essential for responding to environmental signals in other proteins. The dispersiondeficient phenotype of the bdlA mutant was confirmed by treatment with the biocide H 2 O 2 and by microscopic observations. The dispersion response was independent of motility. bdlA mutant biofilms were found to have increased adherent properties and increased intracellular levels of cyclic di-GMP (c-di-GMP). Our findings suggest that BdlA may be a link between sensing environmental cues, c-di-GMP levels, and detachment. Based on our findings, a possible involvement of BdlA in a signaling cascade resulting in biofilm dispersion is discussed.

Energy Taxis Drives Campylobacter jejuni toward the Most Favorable Conditions for Growth

“…Mutations of chemotaxis-like proteins have recently been observed to alter surface structures of A. brasilense (7), while the MCP-homologous protein BdlA of Pseudomonas aeruginosa is known to be involved in biofilm dispersion (35). However, examination of C. jejuni's aggregation and biofilm formation showed no significant difference between the mutants and the wild-type strain (results not shown), indicating that the impaired invasion of the four tlp mutants was not caused by major modifications of global surface structures.…”

Sticky Situations: Key Components That Control Bacterial Surface Attachment

“…First described to control extracellular cellulose biosynthesis in Acetobacter xylinum, high c-di-GMP levels are now known to correlate with the motile-sessile transition in several microorganisms (32, 69, 112, 136-138, 142, 152). Modulation of c-di-GMP has furthermore been linked to biofilm dispersion (9,50,112,152), a mechanism used by biofilm bacteria to successfully transition to the planktonic growth state (140). C-di-GMP production and degradation are controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), respectively, with overexpression of these enzymes generally causing global effects.…”

Dispersion by Pseudomonas aeruginosa requires an unusual posttranslational modification of BdlA

“…In contrast, dispersion is the terminal stage of biofilm development, during which bacteria evacuate a mature biofilm and transition to a planktonic state. Biofilm dispersion can be induced by a variety of environmental cues, including changes in growth medium composition, pH, oxygen, and carbon concentrations, exposure to heavy metals and nitric oxide, exposure to the polysaccharide degrading enzyme dispersin B, and self-synthesized signaling molecules such as cis-2-decenoic acid (1)(2)(3)(4)(5)(6)(7)(8)(9). Dispersed cells are characterized by distinct gene expression and protein production patterns and increased susceptibility to antimicrobial agents compared with their sessile counterparts (2,(10)(11)(12).…”

“…The notable exception is the P. aeruginosa chemotaxis transducer protein BdlA. BdlA was identified in a mutant screen with inactivation of bdlA rendering P. aeruginosa biofilms dispersion deficient in response to various environmental cues (4) and nitric oxide (14). The protein lacks the typical domains required for c-di-GMP modulation, but instead harbors a signal transduction/methyl-accepting chemotaxis (TarH/MCP) domain and two PAS domains (Fig.…”

“…Regulation of biofilm dispersion has also been linked to the modulation of the intracellular signaling molecule cyclic di-GMP (c-di-GMP), high levels of which promote sessile growth, and low levels correlate with planktonic existence. Several proteins associated with dispersion have been shown to possess cdi-GMP-modulating activity (1)(2)(3)(4)14). These include the phosphodiesterases (PDEs) RbdA and DipA, which promote the return to free-swimming growth by reducing cellular c-di-GMP levels (15,16).…”