Quorum sensing by N-acylhomoserine lactones is not required for Aeromonas hydrophila during growth with organic particles in lake water microcosms

Abstract

It was investigated whether quorum sensing (QS) mediated by N-acylhomoserine lactones (AHLs) was important for heterotrophic bacteria from the littoral zone of the oligotrophic Lake Constance for growth with organic particles. More than 900 colonies from lake water microcosms with artificial organic aggregates consisting of autoclaved unicellular algae embedded in agarose beads were screened for AHL-production. AHL-producing bacteria of the genus Aeromonas enriched in the microcosms but AHLs could not be detected in any microcosm. To test for a potential function of AHL-mediated QS, growth experiments with the wild type and an AHL-deficient mutant of Aeromonas hydrophila in lake water microcosms were performed. Growth of both strains did not differ in single cultures and showed no mutual influence in co-cultures. In co-cultures with a competitor bacterium belonging to the Cytophaga-Flavobacterium group, growth of both A. hydrophila strains was reduced while growth of the competitor bacterium was not affected. Exogenous AHL-addition did not influence growth of the Aeromonas strains in any microcosm experiment. These results showed that AHL-mediated QS was not required for A. hydrophila during colonization and degradation of organic particles in lake water microcosms, suggesting that cell-cell signalling of heterotrophic bacteria in oligotrophic waters relies on novel signal molecules.

Evidence of distinct pathways for bacterial degradation of the steroid compound cholate suggests the potential for metabolic interactions by interspecies cross‐feeding

“…For investigating whether cholate‐degrading bacteria are present in the selected freshwater habitats, we set up quantitative enrichment cultures with cholate as carbon and energy source. To increase the probability of obtaining different bacterial strains, we set up enrichment cultures from decimally diluted environmental samples, and we used a HEPES‐buffered mineral medium, with which relatively high cultivation efficiencies of limnic bacteria had been obtained earlier (Bussmann et al ., ; Styp von Rekowski et al ., ). These enrichment cultures became turbid within 1–5 days.…”

“…Bacterial strains were typed by sequence analysis of their 16S rRNA gene and database analysis as describedpreviously (Styp von Rekowski et al ., ). GenBank accession numbers are listed in Table .…”

Seasonal growth potential of rare lake water bacteria suggest their disproportional contribution to carbon fluxes

“…They were enriched in nutrient additions in autumn, but not during spring or summer in eutrophic Lake Mendota (Newton and McMahon, ), and only at times of lowest phytoplankton biomass in a boreal lake (Peura et al ., ). Aeromonas hydrophila (Gammaproteobacteria) , known for its chitinolytic activity (Jagmann et al ., ), was readily enriched in freshwater microcosms amended with algal‐derived particles, but lost in direct competition assays against a strain affiliated with CF (Styp von Rekowski et al ., ). Thus, there are indications that the growth of opportunistic pelagic GAM is induced by recycled or allochthonous DOM sources and, to a lesser extent, also by phytoplankton exudates, but that they might be outcompeted by other taxa during algal blooms.…”

Interactions of bacteria with different mechanisms for chitin degradation result in the formation of a mixed-species biofilm

“…strain 4D9. Previously, we reported that strains of Aeromonas and of the Cytophaga / Flavobacterium group were dominant in the same enrichment cultures, in which the microbial communities of the littoral zone of the oligotrophic Lake Constance had been supplied with artificial organic particles as substrate (Styp von Rekowski et al ., ). Thus, members of these bacterial groups coexist in the same environment.…”