Abstract
Frequent harmful cyanobacteria blooms limit the sustainable development of aquaculture. Algicidal bacteria can efficiently control harmful algae without secondary pollution. The algicidal bacteria CZBC1 can lyse Oscillatoria spp. and other harmful cyanobacteria, but its effector mechanism and algicidal threshold are unknown. In this study, we examined the algicidal effect of CZBC1 on O. chlorina, O. tenuis, and O. planctonica by microscopic enumeration and scanning electron microscopy observation. Then, we examined the alginolytic effects of CZBC1 (concentrations 103–106 colony forming units (cfu)/mL) on these three species (concentrations 103–106 cells/mL) to determine the effective concentrations of CZBC1 for Oscillatoria spp. alginolysis. Results showed that CZBC1 can directly lyse O. chlorina and O. tenuis but indirectly lyse O. planctonica. When the initial concentration of CZBC1 was 106 cfu/mL, alginolytic effects were high for all three species at all concentrations, and the alginolytic rate could reach 100% in 3–9 days. When the initial concentration of CZBC1 was lower (103 cfu/mL), its inhibitory effects were delayed by 2–5 days, but the cell counts were significantly decreased compared with the control, evidencing significant alginolysis. In addition, the higher the concentration of the algicidal bacteria suspension, the more significant the alginolytic effects. Our results indicate that CZBC1 has different alginolytic mechanisms for O. chlorina, O. tenuis, and O. planctonica, and that different initial concentrations of CZBC1 have different alginolytic effects on these algal species.
Highlights
Eutrophication of water bodies, frequent cyanobacteria blooms, and other environmental problems have greatly affected the natural environment and severely hindered the sustainable development of aquaculture (Cao et al 2014b; Sun et al 2017)
The cell counts of both species started to decrease in the bacterial suspension groups (Oc-B and Ot-B), where O. chlorina cells died by day 4 and O. tenuis cell count on day 7 was 5 × 105 cells/mL
Reports on direct alginolysis include myxobacteria that directly contact and lyse cyanobacteria such as Anabaena, Microcystis, Aphanizomenon, and Oscillatoria species, as well as other microalgae (Peterson et al 1993); bacteria belonging to the genera Cytophaga and Saprospira that contact and lyse dinoflagellates and diatoms
Summary
Eutrophication of water bodies, frequent cyanobacteria blooms, and other environmental problems have greatly affected the natural environment and severely hindered the sustainable development of aquaculture (Cao et al 2014b; Sun et al 2017). The alginolytic mechanisms of algicidal bacteria usually involve both direct and indirect alginolysis. The former refers to algicidal bacteria coming into direct contact and actively attacking algal cells or even invading algal cells to destroy their cell structure and lysate microalgae. The latter refers to indirect attacks on the host, which mainly involve competing for limiting nutrients, forming biofilms, or releasing specific or non-specific extracellular substances for alginolysis (Guan et al 2014; Li et al 2015). The initial concentrations of algicidal bacteria determine alginolytic results, and determining the most effective initial concentration is important for the industrial application of algicidal bacteria
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