Simultaneous Removal of the Freshwater Bloom-Forming Cyanobacterium Microcystis and Cyanotoxin Microcystins via Combined Use of Algicidal Bacterial Filtrate and the Microcystin-Degrading Enzymatic Agent, MlrA

Abstract

Freshwater cyanobacterial blooms (e.g., Microcystis blooms) constitute a major global environmental problem because of their risks to public health and aquatic ecological systems. Current physicochemical treatments of toxic cyanobacteria cause the significant release of cyanotoxin microcystins from damaged cells. Biological control is a promising eco-friendly technology to manage harmful cyanobacteria and cyanotoxins. Here, we demonstrated an efficient biological control strategy at the laboratory scale to simultaneously remove Microcystis and microcystins via the combined use of the algicidal bacterial filtrate and the microcystin-degrading enzymatic agent. The algicidal indigenous bacterium Paenibacillus sp. SJ-73 was isolated from the sediment of northern Lake Taihu, China, and the microcystin-degrading enzymatic agent (MlrA) was prepared via the heterologous expression of the mlrA gene in the indigenous microcystin-degrading bacterium Sphingopyxis sp. HW isolated from Lake Taihu. The single use of a fermentation filtrate (5%, v/v) of Paenibacillus sp. SJ-73 for seven days removed the unicellular Microcystis aeruginosa PCC 7806 and the native colonial Microcystis strain TH1701 in Lake Taihu by 84% and 92%, respectively, whereas the single use of MlrA removed 85% of microcystins. Used in combination, the fermentation filtrate and MlrA removed Microcystis TH1701 and microcystins by 92% and 79%, respectively. The present biological control thus provides an important technical basis for the further development of safe, efficient, and effective measures to manage Microcystis blooms and microcystins in natural waterbodies.

Algicidal interaction between Paenibacillus polymyxa MEZ6 and microalgae

“…can efficiently lyse several tested cyanobacterial strains (Wang et al, 2021). That same strain had only a minor inhibitory effect on the eukaryotic microalgae Chlorella and Tetradesmus (Wang et al, 2021).…”

“…For example, P. polymyxa E681 can produce fusaricidin analogues with a selective growth inhibition activity towards Microcystis aeruginosa (Ko et al, 2019), and an isolate Paenibacillus sp. SJ‐73, which is highly similar to P. amylolyticus based on its 16S rRNA gene, can efficiently lyse several tested cyanobacterial strains (Wang et al, 2021). That same strain had only a minor inhibitory effect on the eukaryotic microalgae Chlorella and Tetradesmus (Wang et al, 2021).…”

“…SJ‐73, which is highly similar to P. amylolyticus based on its 16S rRNA gene, can efficiently lyse several tested cyanobacterial strains (Wang et al, 2021). That same strain had only a minor inhibitory effect on the eukaryotic microalgae Chlorella and Tetradesmus (Wang et al, 2021). In comparison, our P. polymyxa MEZ6 exhibits high lysing activity against several eukaryotic algae, which provides a unique algicidal microbial resource and clearly extends our understanding of the interactions between Paenibacillus members with other micro‐organisms.…”

Recent Advances in the Research on the Anticyanobacterial Effects and Biodegradation Mechanisms of Microcystis aeruginosa with Microorganisms

“…With the addition of fermentation filtrate (5%, v/v) of Paenibacillus sp. SJ-73, the Fv/Fm values of M. aeruginosa PCC7806 and M. aeruginosa TH1701 dramatically decline from 0.52 and 0.29 to 0 [95]; similarly, it is only 0.08 (14.3% of the initial value) for M. aeruginosa FACHB-905 after being treated for 24 h by the fermentation filtrate (5%, v/v) of Raoultella sp. S1 [23].…”

“…The variations of cyanobacterial energy kinetics have also been evaluated by Chl fluorescence parameters, such as the maximum photochemical quantum yield of PS II (Fv/Fm), the effective quantum yield (Φe), and the maximum electron transport rate (ETRmax) [41,95]. With the addition of fermentation filtrate (5%, v/v) of Paenibacillus sp.…”