Adherence of Aeromonas veronii, Shigella flexneri and Escherichia fergusonii with Microcystis-dominated bloom relates to their ability to utilize chitin

Abstract

The study was undertaken to size-fractionate the bacterial population associated with Microcystis blooms of an eutrophic lake. Two bacterial cultures were isolated from the particulate-bound fraction, and biochemical tests, phylogenetic analysis and homology of 16S rRNA gene sequences revealed their high similarity with Aeromonas veronii and Shigella flexneri. Another isolate with characteristics resembling Escherichia fergusonii was obtained in phytoplankton-free water samples. Since these three cultures were enriched on chitin-selective medium, their capability to utilize chitin as a sole C source was examined. The in vivo chitinase activity (as µg N‑acetyglucosamine produced min^–1 mL^–1 culture) was 82.1, 28.5 and 18.5 for A. veronii, S. flexneri and E. fergusonii, respectively. The corresponding N‑acetylglucosamine accumulation in medium was 421, 288 and 122 µg mL^–1. There was also a gradation in growth indices in the three bacteria, which corresponded to their chitin utilization ability. Notwithstanding differences in chitinase activity, the three strains utilized almost equally the exogenous N‑acetylglucosamine. We propose that chitinase activity may have a role in affinity of the particular bacterial cell to phytoplankton extracellular polymeric substances and therefore, adherence ability.