Abstract
BackgroundHarmful 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.ResultsA 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.ConclusionsThe 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.
Highlights
Harmful cyanobacterial blooms have attracted wide attention all over the world as they cause water quality deterioration and ecosystem health issues
Isolation and purification of the axenic culture M. aeruginosa 905 and 907 samples were curated by the Freshwater Algae Culture Collection of Institute of Hydrobiology (FACHB) as xenic consortia comprised of one M. aeruginosa strain and its associated heterotrophic bacteria
It is obvious that the heterotrophs colonies were much bigger than the cyanobacterium colonies, indicating the heterotrophs were grew much better compared with cyanobacterium
Summary
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. Gao et al BMC Biotechnology (2020) 20:61 phytoplankton benefits from bacterial products such as nutrients, whereas bacteria profit from phytoplankton products such as extracellular polymeric substances [4]; (ii) bacteria and phototrophic phytoplankton form an antagonism relationship that the growth of phytoplankton is restricted or inhibited by bacteria through algalbacterial/cyanobacterial-bacterial contact mechanism (direct interaction) or secretion of the extracellular antialgal/anticyanobacterial substances (indirect interaction) [5, 6] and (iii) bacteria and phototrophic phytoplankton form a commensal relationship that bacteria are loosely associated with phytoplankton and may promote the growth and photosynthesis without having any negative effect, while phytoplankton grows well without the associated bacteria [7, 8]. In order to avoid the influence of heterotrophs for physiological and molecular studies, the purification of the axenic cyanobacterium (bacteria-free) is especially important as well as the understanding of its responses to the heterotrophs
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