Background Harmful cyanobacterial blooms have attracted wide attention all over the world as they cause water quality deterioration and ecosystem health issues. Microcystis aeruginosa associated with a large number of bacteria is one of the most common and widespread bloom-forming cyanobacteria that secret toxins. These associated bacteria are considered to benefit from organic substrates released by the cyanobacterium. In order to avoid the influence of associated heterotrophic bacteria on the target cyanobacteria for physiological and molecular studies, it is urgent to obtain an axenic M. aeruginosa culture and further investigate the specific interaction between the heterotroph and the cyanobacterium. Results A traditional and reliable method based on solid-liquid alternate cultivation was carried out to purify the xenic cyanobacterium M. aeruginosa FACHB-905. On the basis of 16S rDNA gene sequences, two associated bacteria named strain B905–1 and strain B905–2, were identified as Pannonibacter sp. and Chryseobacterium sp. with a 99 and 97% similarity value, respectively. The axenic M. aeruginosa FACHB-905A (Microcystis 905A) was not able to form colonies on BG11 agar medium without the addition of strain B905–1, while it grew well in BG11 liquid medium. Although the presence of B905–1 was not indispensable for the growth of Microcystis 905A, B905–1 had a positive effect on promoting the growth of Microcystis 905A. Conclusions The associated bacteria were eliminated by solid-liquid alternate cultivation method and the axenic Microcystis 905A was successfully purified. The associated bacterium B905–1 has the potentiality to promote the growth of Microcystis 905A. Moreover, the purification technique for cyanobacteria described in this study is potentially applicable to a wider range of unicellular cyanobacteria.

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In order to avoid the influence of associated bacteria on the target cyanobacteria for physiological and molecular studies, a traditional and reliable method based on solid-liquid alternate cultivation is carried out to purify the non-axenic cyanobacterium Microcystis aeruginosa FACHB-905. On the basis of 16S rDNA gene sequences, two associated bacteria named strain B905-1 and strain B905-2, are identified as Pannonibacter sp. and Chryseobacterium sp. with a 99% and 97% similarity value, respectively. To better investigate the general interaction between the bacterium and the cyanobacterium, the effect of strain B905-1 on the axenic cyanobacterium M. aeruginosa FACHB-905A is studied. Results indicate that the axenic M. aeruginosa FACHB-905A could not form colonies on BG11 agar medium without the addition of strain B905-1, while it grows well in BG11 liquid medium. Although the presence of B905-1 was not indispensable for the growth of M. aeruginosa FACHB-905A, B905-1 had a positive effect on promoting the growth of M. aeruginosa FACHB-905A. The purification technique for cyanobacteria described in this study is potentially applicable to a wider range of filamentous cyanobacteria.

Background: Harmful cyanobacterial blooms have attracted wide attention all over the world as they cause water quality deterioration and ecosystem health issues. Microcystis aeruginosa associated with a large number of bacteria is one of the most common and widespread bloom-forming cyanobacteria that secret toxins. These associated bacteria are considered to benefit from organic substrates released by the cyanobacterium. In order to avoid the influence of associated heterotrophic bacteria on the target cyanobacteria for physiological and molecular studies, it is urgent to obtain an axenic M. aeruginosa culture and further investigate the specific interaction between the heterotroph and the cyanobacterium.Results: A traditional and reliable method based on solid-liquid alternate cultivation is carried out to purify the xenic cyanobacterium M. aeruginosa FACHB-905. On the basis of 16S rDNA gene sequences, two associated bacteria named strain B905-1 and strain B905-2, are identified as Pannonibacter sp. and Chryseobacterium sp. with a 99% and 97% similarity value, respectively. The axenic M. aeruginosa FACHB-905A (Microcystis 905A) is not able to form colonies on BG11 agar medium without the addition of strain B905-1, while it grows well in BG11 liquid medium. Although the presence of B905-1 is not indispensable for the growth of Microcystis 905A, B905-1 has a positive effect on promoting the growth of Microcystis 905A. Conclusions: The associated bacteria are eliminated by solid-liquid alternate cultivation method and the axenic Microcystis 905A is successfully purified. The associated bacterium B905-1 has the potential to promote the growth of Microcystis 905A. Moreover, the purification technique for cyanobacteria described in this study is potentially applicable to a wider range of unicellular cyanobacteria.