Abstract
Confocal and scanning electron microscopic observations have previously shown the strong bacterial association of Microcystis aeruginosa cells on their surfaces. DNA-based analyses of the associated bacterial communities were carried out using two M. aeruginosa strains grown in the laboratory and eight newly collected cyanobacterial bloom samples. M. aeruginosa was the most predominant species (66–100%) within the phylum Cyanobacteria. Rhizobium, Hydrogenophaga and Brevundimonas species were commonly found, and Flavobacterium species were present in all the cyanobacterial bloom samples. In total, 396 colonies from various samples were screened, revealing that most culturable bacteria belonged to the class Alphaproteobacteria (19%) including Rhizobium, Brevundimonas, and Porphyrobacter species. The genetic variation among the M. aeruginosa strains and different habitat conditions may have led to the presence of distinct bacterial populations among the tested samples. Among all the tested seven culturable isolates, Rhizobium sp. MK23 showed the best growth-promotion effect on the axenic M. aeruginosa strains. H2O2 was observed to be produced during the growth of M. aeruginosa PCC7806 under light conditions, this strain was more resistant to H2O2 when associated with Rhizobium sp. MK23. Our data suggested that Rhizobium species along with other associated bacteria might help the growth of M. aeruginosa by decomposing H2O2 under the aerobic growing conditions.
Highlights
Confocal and scanning electron microscopic observations have previously shown the strong bacterial association of Microcystis aeruginosa cells on their surfaces
This study examined the bacterial species that are associated with the phycospheres of 10 bloom-forming ten Microcystis aeruginosa
The temperature ranged from 31.0 °C [at Daecheong lake (DC) sample] to 33.0 °C [at Hapcheon Changnyeong barrage (HC) sample] among the sample locations (Table 1, Fig. S1)
Summary
Confocal and scanning electron microscopic observations have previously shown the strong bacterial association of Microcystis aeruginosa cells on their surfaces. In our growth experiments, which were performed using a PhotoBiobox, the optimum light and temperature conditions were different for four cyanobacterial bloom samples (Fig. S6). The 16S rRNA gene sequencing revealed a high similarity of >99% among the Microcystis species in all the samples, and this observation suggested that the 16S rRNA analysis alone was not enough to distinguish the genotypes of M. aeruginosa strains.
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