Microcolonies, quorum sensing and cytotoxicity determine the survival of Pseudomonas aeruginosa biofilms exposed to protozoan grazing

Abstract

This study was based on the hypothesis that biofilms of the opportunistic pathogen Pseudomonas aeruginosa are successfully adapted to situations of protozoan grazing. We tested P. aeruginosa wild type and strains that were genetically altered, in structural and regulatory features of biofilm development, in response to the common surface-feeding flagellate Rhynchomonas nasuta. Early biofilms of the wild type showed the formation of grazing resistant microcolonies in the presence of the flagellate, whereas biofilms without the predator were undifferentiated. Grazing on biofilms of quorum sensing mutants (lasR and rhlR/lasR) also resulted in the formation of microcolonies, however, in lower numbers and size compared to the wild type. Considerably fewer microcolonies than the wild type were formed by mutant cells lacking type IV pili, whereas no microcolonies were formed by flagella-deficient cells. The alginate-overproducing strain PDO300 developed larger microcolonies in response to grazing. These observations suggest a role of quorum sensing in early biofilms and involvement of flagella, type IV pili, and alginate in microcolony formation in the presence of grazing. More mature biofilms of the wild type exhibited acute toxicity to the flagellate R. nasuta. Rapid growth of the flagellate on rhlR/lasR mutant biofilms indicated a key role of quorum sensing in the upregulation of lethal factors and in grazing protection of late biofilms. Both the formation of microcolonies and the production of toxins are effective mechanisms that may allow P. aeruginosa biofilms to resist protozoan grazing and to persist in the environment.

Grazer-induced toxin formation in dinoflagellates: a transcriptomic model study

“…Inducible defences have been found in widely different organisms from prokaryotes (Patterson & Bolis, 1997;Matz et al, 2004) to diatoms (Lu¨rling & Van Donk, 2000), ciliates (e.g. Hammill et al, 2009) and various green, red and brown macroalgae (Toth & Pavia, 2007), but investigations into the transcriptomic changes associated with induced chemical defences have largely been restricted to angiosperm model organisms (Arimura et al, 2000;Reymond et al, 2004;De Vos et al, 2005).…”

Relative importance of evolutionary dynamics depends on the composition of microbial predator–prey community

“…To this end, all bacterial selection lines (eight clones from each) were grown individually with every predator species they had been exposed to during the selection experiment. Briefly, all protist measurement plates were inoculated with 20 μl of ancestral stock protist (approximately 100 cells ml − 1 ), and after 48 h of co-cultivation at 22°C, bacterial defence was determined as the amount of bacterial biofilm biomass; previous studies have shown that bacteria use biofilm aggregation as a size-dependent defence mechanism against protist predators (Matz et al, 2004;Friman and Laakso, 2011;. Bacterial biofilm growth was measured by adding 50 μl of 1% crystal violet solution to microplate wells and rinsed off with distilled water after 10 min.…”

The role of quorum sensing signalling in EPS production and the assembly of a sludge community into aerobic granules

“…This is in contrast to their planktonic single species population counterparts commonly studied in laboratory conditions. The formation and dispersal of structured bacterial biofilms or aggregates occur in response to a range of environmental cues and signals, such as changes in nutrient concentrations, oxygen, temperature, as well as chemicals and predatory stresses (Bassler et al, 1993;Matz et al, 2004;McDougald et al, 2011;Mitri et al, 2011). In many cases, the signal transduction pathways, the associated changes in gene expression and the involvement of second messenger systems have also begun to be unravelled (Barraud et al, 2009;Petrova and Sauer, 2012).…”