Detergent‐induced cell aggregation in subpopulations of Pseudomonas aeruginosa as a preadaptive survival strategy

Abstract

During growth of Pseudomonas aeruginosa strain PAO1 with the toxic detergent SDS, a part of the population actively formed macroscopic cell aggregates while the other part grew as freely suspended cells. The physiological function of aggregation for growth with SDS was investigated. Three mutants growing with SDS without aggregation were isolated: the spontaneous mutant strain N and two mutants with transposon insertions in the psl operon for exopolysaccharide synthesis. SDS-induced aggregation in strain N but not in a pslJ mutant was restored by complementation with two genes encoding diguanylate cyclases responsible for synthesis of cyclic-di-guanosine monophosphate (c-di-GMP). By expressing a c-di-GMP-specific phosphodiesterase SDS-induced aggregation of strain PAO1 was reduced. Upon exposure to SDS in the presence of the uncoupler carbonyl cyanide chlorophenylhydrazone, the aggregating strains had ca. 500-fold higher survival rates than the non-aggregating strains. Co-incubation experiments revealed that strain N could integrate into aggregates of strain PAO1 and thereby increase its survival rate more than 1000-fold. These results showed that SDS-induced aggregation involved c-di-GMP signalling with the psl operon as a possible target. Cell aggregation could serve as a pre-adaptive strategy ensuring survival and growth of P. aeruginosa populations in environments with multiple toxic chemicals.

Cyclic di-GMP: a second messenger required for long-term survival, but not for biofilm formation, in Mycobacterium smegmatis

“…During stationary phase, M. smegmatis forms clumps that increase in size during prolonged starvation, and these may promote survival (Smeulders et al, 1999). Similarly, P. aeruginosa forms cell aggregates to survive in the presence of the toxic detergent SDS, and formation of these aggregates is directly linked to levels of c-di-GMP (Klebensberger et al, 2007). In our experiments, we observed increased levels of c-di-GMP in stationary phase, and this suggests that this second messenger is important in adaptation, survival and persistence.…”

Nickel Promotes Biofilm Formation by Escherichia coli K-12 Strains That Produce Curli

“…Aminoglycoside antibiotics have been shown to induce E. coli and P. aeruginosa biofilm formation (27). Powerful detergents that disrupt biological membranes, such as sodium dodecyl sulfate or bile salts, also stimulate biofilm formation in Pseudomonas aeruginosa (35), Vibrio cholerae (30), and Bacteroides fragilis (50). Therefore, we suggest that induction of the biofilm mode of growth could be the early response of bacteria to biocides, allowing the concomitant development of an antibiotic-and metal-resistant phenotype.…”

“…However, neither MlrA nor the two nickel-sensing dedicated regulators in E. coli, namely NikR (17) and RcnR (36), were shown to be involved in the induction of csgB or cgsD by nickel (our personal data). Induction of biofilm formation by sodium dodecyl sulfate and aminoglycosides was shown to involve cyclic di-GMP (c-di-GMP) signaling (27,35). This bacterial second messenger controls lifestyle choices in bacteria, such as a commitment to sessile life or virulence (12), and it is antagonistically controlled by diguanylate cyclases (GGDEF proteins) and phosphodiesterases (EAL proteins).…”

Nitric Oxide Signaling inPseudomonas aeruginosaBiofilms Mediates Phosphodiesterase Activity, Decreased Cyclic Di-GMP Levels, and Enhanced Dispersal

“…The purified PCR products of bdlA, fimX, morA, and rocS1 were digested with SalI, SpeI-PstI, BamHI-HincII, and BamHI-HincII, respectively, and the correct-sized fragments were gel purified and cloned into the respective restriction sites of the suicide vector pKnockout-G (59) before transformation into Escherichia coli XL1-Blue (Stratagene). The resulting suicide vectors pKO[bdlA], pKO[fimX], pKO[morA], and pKO[rocS1] were transferred in strain PAO1 by biparental mating, with E. coli strain S17-1 as a donor, as described previously (27). Correct chromosomal insertion of the vectors was confirmed by PCR with appropriate primer pairs (see Table S1 in the supplemental material).…”