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.

Suqin Wang,Jun Zuo,Peng Chen,Siyu Yang,Chenlin Hu,Nanqin Gan,Lirong Song

doi:10.3390/microorganisms9081594

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.

Highlights

The control of harmful cyanobacterial blooms might become more challenging in the future, because it is widely confirmed that cyanobacterial blooms are gradually increasing in frequency, magnitude, and duration on a global scale owing to progressive eutrophication, rising atmospheric CO2 levels, and global warming [3,4]
An indigenous algicidal bacterium, Paenibacillus amylolyticus bacillus amylolyticus strain SJ-73, was isolated from the sediments sampled from Taihu strain SJ-73, was isolated from the sediments sampled from Taihu Lake
SJ-73 was demonstrated to have no adverse impact on green algae. These to results have no adverse impact on green algae. These results showed the promising potential of strain SJ-73 in controlling multi-species cyanobacterial blooms with a negligible influence on green algae

Summary

Introduction

Cyanobacterial blooms can have long-term negative impacts on water-quality and ecosystem health, such as increasing water turbidity, diminishing dissolved oxygen, smothering fish, producing unpleasant odor compounds, and excreting various cyanotoxins [1,2]. The control of harmful cyanobacterial blooms might become more challenging in the future, because it is widely confirmed that cyanobacterial blooms are gradually increasing in frequency, magnitude, and duration on a global scale owing to progressive eutrophication, rising atmospheric CO2 levels, and global warming [3,4]. Microorganisms 2021, 9, 1594 paid to Microcystis spp. because of their extreme abundance, frequent bloom occurrence, and capacity to produce microcystins (MCs), which are the most commonly reported and problematic cyanotoxins worldwide [5]. The World Health Organization established a guideline of 1 μg/L for the highest acceptable concentration of microcystin LR (MC-LR) in drinking water [6]

Methods

Discussion

Conclusion