Control of a toxic cyanobacterial bloom species, Microcystis aeruginosa, using the peptide HPA3NT3-A2

Lanthanum-modified pyroaurite as a geoengineering tool to simultaneously sink Microcystis cyanobacteria and immobilize phosphorus in eutrophic water

Excessive phosphorus (P) in eutrophic water induces cyanobacterial blooms that aggravate the burden of in-situ remediation measures. In order to ensure better ecological recovery, Flock & Lock technique has been developed to simultaneously sink cyanobacteria and immobilize P but requires a combination of flocculent and P inactivation agent. Here we synthesized a novel lanthanum-modified pyroaurite (LMP), as an alternative for Flock & Lock of cyanobacteria and phosphorus at the background of rich humic acid and suspended solids. LMP shows a P adsorption capacity of 36.0 mg/g and nearly 100 % removal of chlorophyll-a (Chl-a), turbidity, UV254 and P at a dosage (0.3 g/L) much lower than the commercial analogue (0.5 g/L). The resultant sediment (98.2 % as immobile P) exhibits sound stability without observable release of P or re-growth of cyanobacteria over a 50-day incubation period. The use of LMP also constrains the release of toxic microcystins to 1.4 μg/L from the sunk cyanobacterial cells, outperforming the commonly used polyaluminum chloride (PAC). Similar Flock & Lock efficiency could also be achieved in real eutrophic water. The outstanding Flock & Lock performance of LMP is attributable to the designed La modification. During LMP treatment, La acts as not only a P binder by formation of LaPO4, but also a coagulant to create a synergistic effect with pyroaurite. The controlled hydrolysis of surface La(III) over pyroaurite aided the possible formation of La(III)-pyroaurite networking structure, which significantly enhanced the Flock & Lock process through adsorption, charge neutralization, sweep flocculation and entrapment. In the end, the preliminary economic analysis is performed. The results demonstrate that LMP is a versatile and cost-effective agent for in-situ remediation of eutrophic waters.

Spatio-temporal variation of toxin-producing gene abundance in Microcystis aeruginosa from Poyang Lake

Microcystis aeruginosa (M. aeruginosa) causes massive blooms in eutrophic freshwater and releases microcystin. Poyang Lake is the largest freshwater lake in China and has kept a mid-nutrient level in recent years. However, there is little research on microcystin production in Poyang Lake. In this study, water and sediment samples from ten sampling sites in Poyang Lake were collected from May to December in 2020, and from January to April in 2021 respectively. Microcystis genes (mcyA, mcyB, 16 s rDNA) were quantified by real-time fluorescence quantitative PCR analysis, and then the spatial and temporal variation of mcy genes, physicochemical factors, and bacterial population structure in the lake was analyzed. The relationship between the abundance of mcy genes and physicochemical factors in water column was also revealed. Results indicated that the microcystin-producing genes mcyA and mcyB showed significant differences in spatial and temporal levels as well, which is closely related to the physicochemical factors especially the water temperature (p < 0.05) and the nitrogen content (p < 0.05). The abundance of mcy genes in the sediment in December affected the abundance of mcy genes in the water column in the next year, while the toxic Microcystis would accumulate in the sediment. In addition to the toxic Microcystis, we also found a large number of non-toxic Microcystis in the water column and sediment, and the ratio of toxic to non-toxic species can also affect the toxicity production of M. aeruginosa. Overall, the results showed that M. aeruginosa toxin-producing genes in Poyang Lake distributed spatially and temporally which related to the physicochemical factors of Poyang Lake.

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

Harmful algal blooms (HABs) have attracted great attention around the world due to the numerous negative effects such as algal organic matters and cyanobacterial toxins in drinking water treatments. As an economic and environmentally friendly technology, microorganisms have been widely used for pollution control and remediation, especially in the inhibition/biodegradation of the toxic cyanobacterium Microcystis aeruginosa in eutrophic water; moreover, some certain anticyanobacterial microorganisms can degrade microcystins at the same time. Therefore, this review aims to provide information regarding the current status of M. aeruginosa inhibition/biodegradation microorganisms and the acute toxicities of anticyanobacterial substances secreted by microorganisms. Based on the available literature, the anticyanobacterial modes and mechanisms, as well as the in situ application of anticyanobacterial microorganisms are elucidated in this review. This review aims to enhance understanding the anticyanobacterial microorganisms and provides a rational approach towards the future applications.

Primary role of increasing urea-N concentration in a novel Microcystis densa bloom: Evidence from ten years of field investigations and laboratory experiments

A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00-0.20 ± 0.01 mg N l^-1), whereas other factors did not vary significantly. NO₃^--N and urea-N concentrations were higher than the NH₄⁺-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO₃^--N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p < 0.05). Laboratory experiments demonstrated that M. densa cultured with urea-N exhibited a higher maximum cell density (9.8 ± 0.5 × 10⁸ cells l^-1), more cellular pigments for photosynthesis (chlorophyll a and phycocyanin) and photoprotection (carotenoid), and more proteins than those cultured with NH₄⁺-N and NO₃^--N. These results suggested that M. densa cultured with urea-N exhibited preferable growth and physiological conditions. Moreover, M. densa exhibited an increased maximum specific uptake rate (0.93 pg N cell^-1 h^-1) and reduced half-saturation constant (0.03 mg N l^-1) for urea-N compared with NH₄⁺-N and NO₃^--N, suggesting that M. densa preferred urea-N as its major nitrogen source. These results collectively indicated that the increasing urea-N concentration was beneficial for the growth and physiological conditions of M. densa. This study provided ten years of field data and detailed physiological information supporting the critical effect of urea-N on the growth of a novel bloom species M. densa. These findings helped to reveal the mechanism of M. densa bloom formation from the perspective of dissolved organic nitrogen.

Application of a polyethylenimine-modified polyacrylonitrile-biomass waste composite fiber sorbent for the removal of a harmful cyanobacterial species from an aqueous solution

Cyanobacterial harmful algal blooms (Cyano-HABs) in water resources involving algal species such as Microcystis aeruginosa have become a serious environmental issue due to their severely negative effects. In the present study, an adsorption-based strategy was employed to control M. aeruginosa, with industrial waste-derived Escherichia coli biomass valorized to produce polyethylenimine-modified polyacrylonitrile-E. coli biomass composite fiber (PEI-PANBF). PEI-PANBF removed approximately 80% of M. aeruginosa cells from an aqueous solution without causing any cell damage. Interestingly, the thickness of PEI-PANBF had a strong influence on the efficiency of M. aeruginosa cell removal. In addition, PEI-PANBF simultaneously removed M. aeruginosa cells and their toxic secondary metabolite, microcystin-LR, from aqueous media. Thus, our proposed fiber represents a feasible utilization method of industrial waste biomass as a biosorbent for the control of Cyano-HABs.