Summary Microcystis is a cosmopolitan genus of cyanobacteria and occurs in many different forms. Large surface blooms of the cyanobacterium are well known in eutrophic lakes throughout the globe. We evaluated the role of microcystins (MCs) in promoting and maintaining bloom‐forming cell aggregates at environmentally relevant MC concentrations (0.25–10 µg l−1). MCs significantly enhanced Microcystis colony sizes. Colonial diameters in microcystin‐RR (MC‐RR)‐treated cultures (at 1 µg l−1) were significantly larger than control colonies, by factors of 1.5, 2.6 and 2.7 in Microcystis wesenbergii DC‐M1, M. ichthyoblabe TH‐M1 and Microcystis sp. FACHB1027 respectively. Depletion of extracellular MC concentrations caused Microcystis colony size to decrease, suggesting that released MCs are intimately involved in the maintenance of Microcystis colonial size. MC‐RR exposure did not influence Microcystis growth rate, but did significantly increase the production of extracellular polysaccharides (EPS). In addition, MC‐RR exposure appeared to trigger upregulation of certain parts of four polysaccharide biosynthesis‐related genes: capD, csaB, tagH and epsL. These results strongly indicate that induction of polysaccharides by MC‐RR was the major mechanism through which MCs enhanced colony formation in Microcystis spp. Cellular release of MCs, therefore, may play a key role in the persistence of algal colonies and the dominance of Microcystis.
Investigations on the extracellular polymeric substances (EPS) are crucial for better understanding the growth and proliferation of cyanobacterium . In this study, a combined approach of fractionation procedure and parallel factor (PARAFAC) analysis were applied to characterize the EPS of a. Physicochemical analysis showed that the contents of polysaccharides in EPS matrix were higher than those of proteins, regardless of the differences in growth phases and nutritional levels in medium. Organic matters were mainly distributed in the tightly bound EPS (TB-EPS) fraction during the exponential growth phase, whereas they sharply released to the soluble EPS (SL-EPS) and loosely bound EPS (LB-EPS) fractions at the decay period. Fluorescence excitation–emission matrix (EEM) was applied to characterize the specific compositions in EPS matrix, and all the fluorescence EEM spectra collected could be successfully decomposed into a four-component model by PARAFAC analysis. Component 1 [excitation/emission (Ex/Em) = 220/340], component 2 (Ex/Em = 280/340) and component 3 [Ex/Em = (200, 220, 270)/296] were attributed to protein-like substances, while component 4 [Ex/Em = (250, 340)/438] belonged to humic-like substances. Pearson correlation analysis demonstrated that tryptophan-like substances in the LB-EPS and TB-EPS fractions were positively correlated with growth, whereas in the SL-EPS fraction, tryptophan-like as well as humic-like substances were associated with the growth of . The scientific implication for growth and proliferation, based on the results of fractionation procedure and EEM-PARAFAC analysis, was also presented. ► Fractionation procedure and PARAFAC analysis were combined to characterize EPS of . ► Organic contents and compositions exhibited obvious difference among EPS fractions. ► One humic-like and three protein-like components were identified from EPS fractions. ► Tryptophan-like rather than tyrosine-like substances were correlated with the growth of . ► The results were beneficial for insights into the EPS role on growth and proliferation.
Blooms of toxic cyanobacteria such as periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of isolated from a wastewater treatment lagoon, and two other algal strains, and sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the . For , for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: > > sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons. ► Ultrasonication gives greater growth inhibition of cyanobacteria than of green algae. ► Ultrasonication gives highest algal cell reduction rate within initial 5 min ► Microcystin level can be controlled by varying ultrasonication conditions. ► Ultrasonication can selectively inactivate cyanobacteria in wastewater lagoons.
Algal blooms are a seasonal problem in eutrophic water bodies, and novel approaches to algal removal are required. The effect of hydrodynamic cavitation (HC) on the removal of was investigated using a laboratory scale device. Samples treated by HC were subsequently grown under illuminated culture conditions. The results demonstrated that a short treatment with HC could effectively settle naturally growing without breaking cells. Algal cell density and chlorophyll-a of a sample treated for 10 min were significantly decreased by 88% andv 94%, respectively, after 3 days culture. Various HC operating parameters were investigated, showing that inhibition of growth mainly depended on treatment time and pump pressure. Electron microscopy confirmed that sedimentation of algae was attributable to the disruption of intracellular gas vesicles. Damage to the photosynthetic apparatus also contributed to the inhibition of algal growth. Free radicals produced by the cavitation process could be as an indirect indicator of the intensity of HC treatment, although they inflicted minimal damage on the algae. In conclusion, we suggest that HC represents a potentially highly effective and sustainable approach to the removal of algae from water systems.
Summary Cyanobacterial blooms have disrupted the efficient utilization of freshwater worldwide. A new freshwater bacterial strain with strong algicidal activity, GLY‐2107, was isolated from Lake Taihu and identified as Aeromonas sp. It produced two algicidal compounds: 2107‐A (3‐benzyl‐piperazine‐2,5‐dione) and 2107‐B (3‐methylindole). Both compounds exhibited potent algicidal activities against Microcystis aeruginosa, the dominant bloom‐forming cyanobacterium in Lake Taihu. The EC50 values (concentration for 50% maximal effect) of 3‐benzyl‐piperazine‐2,5‐dione and 3‐methylindole were 4.72 and 1.10 μg ml−1 respectively. Based on a thin‐layer chromatography biosensor assay and ultra‐performance liquid chromatography‐coupled high resolution‐tandem mass spectrometry (UPLC‐HRMS/MS), the N‐acyl homoserine lactone (AHL) profile of strain GLY‐2107 was identified as two short side‐chain AHLs: N‐butyryl‐homoserine lactone (C4‐HSL) and N‐hexanoyl‐homoserine lactone (C6‐HSL). The production of the two algicidal compounds was controlled by AHL‐mediated quorum sensing (QS), and C4‐HSL was the key QS signal for the algicidal activity of the strain GLY‐2107. Moreover, 3‐methylindole was found to be positively regulated by C4‐HSL‐mediated QS, whereas 3‐benzyl‐piperazine‐2,5‐dione might be negatively controlled by C4‐HSL‐mediated QS. This study suggests that a QS‐regulated algicidal system may have potential use for the development of a novel control strategy for harmful cyanobacterial blooms.
The use of allelochemicals has been proved an environmentally friendly and promising method to control harmful algal blooms. This study was conducted to explore the application potential of ( ) extracts in ( ) control for the first time. Four treatments with extractions (25 mg L , 50 mg L , 100 mg L , and 200 mg L respectively) and a control group were built to investigate the effects of on the growth, cellular microstructure and cell viability, physiological changes, and release of extracellular matters. Results showed that the cell density of was effectively inhibited by extract, and the inhibition rates were dose-dependent within 5 d. Especially for the treatment with 200 mg L of extract, the inhibitory rates remains above 90% after 5 d exposure. In addition, effectively decreased the amount of extracellular cyanotoxin microcystins and destroyed the photosynthesis-related structure of algae cell during the experimental period. The results demonstrated the extracts can be used as an effective and safe algicide to control algal blooms. However, it must be noted that specific compounds responsible for algicidal effect should be isolated and identified to explore inhibition mechanism of in future study.
Formation of carbonaceous disinfection by-products (C-DBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), chloral hydrate (CH), and nitrogenous disinfection by-products (N-DBPs), including haloacetonitriles (HANs) and trichloronitromethane (TCNM) from chlorination of , a blue–green algae, under different conditions was investigated. Factors evaluated include contact time, chlorine dosages, pH, temperature, ammonia concentrations and algae growth stages. Increased reaction time, chlorine dosage and temperature improved the formation of the relatively stable C-DBPs (e.g., THM, HAA, and CH) and TCNM. Formation of dichloroacetonitrile (DCAN) followed an increasing and then decreasing pattern with prolonged reaction time and increased chlorine dosages. pH affected DBP formation differently, with THM increasing, HKs decreasing, and other DBPs having maximum concentrations at certain pH values. The addition of ammonia significantly reduced the formation of most DBPs, but TCNM formation was not affected and 1,1-dichloropropanone (1,1-DCP) formation was higher with the addition of ammonia. Most DBPs increased as the growth period of algal cells increased. Chlorination of algal cells of higher organic nitrogen content generated higher concentrations of N-DBPs (e.g., HANs and TCNM) and CH, comparable DCAA concentration but much lower concentrations of other C-DBPs (e.g., THM, TCAA and HKs) than did natural organic matter (NOM).
The effect of temperature (26 °C, 28 °C, 30 °C and 35 °C) on the growth of native CAAT-3-2005 and the production of Chlorophyll-a (Chl-a) and Microcystin-LR MC-LR) were examined through laboratory studies. Kinetic parameters such as specific growth rate (μ), lag phase duration (LPD) and maximum population density (MPD) were determined by fitting the modified Gompertz equation to the strain cell count (cells mL ). A 4.8-fold increase in μ values and a 10.8-fold decrease in the LPD values were found for growth when the temperature changed from 15 °C to 35 °C. The activation energy of the specific growth rate (Eμ) and of the adaptation rate (E /LPD) were significantly correlated (R = 0.86). The cardinal temperatures estimated by the modified Ratkowsky model were minimum temperature = 8.58 ± 2.34 °C, maximum temperature = 45.04 ± 1.35 °C and optimum temperature = 33.39 ± 0.55 °C. Maximum MC-LR production decreased 9.5-fold when the temperature was increased from 26 °C to 35 °C. The maximum production values were obtained at 26° C and the maximum depletion rate of intracellular MC-LR was observed at 30–35 °C. The MC-LR cell quota was higher at 26 and 28 °C (83 and 80 fg cell , respectively) and the MC-LR Chl-a quota was similar at all the different temperatures (0.5–1.5 fg ng ). The Gompertz equation and dynamic model were found to be the most appropriate approaches to calculate growth and production of MC-LR, respectively. Given that toxin production decreased with increasing temperatures but growth increased, this study demonstrates that growth and toxin production processes are uncoupled in . These data and models may be useful to predict bloom formation in the environment.
is a notorious cyanobacterial genus due to its rapid growth rate, huge biomass, and producing toxins in some eutrophic freshwater environments. To reveal the regulatory factors of interspecific competition between toxic and non-toxic , three dominant strains were selected, and their photosynthesis, population dynamics and microcystins (MCYST) production were measured. The results suggested that nitrogen-limitation (N-limitation) had a greater restriction for the growth of toxic than that of non-toxic , especially when cultured at high light or high temperature based on the weight analysis of key factors. Comparison of photosynthesis showed that low light or N-rich would favor the competitive advantage of toxic while high light combined with N-limitation would promote the competitive advantage of non-toxic , and these two competitive advantages could be further amplified by temperature increase. Mixed competitive experiments of toxic and non-toxic were conducted, and the results of absorption spectrum (A /A ) and PCR (real-time quantitative PCR) suggested that the proportion of toxic and the half-time of succession process were significantly reduced by 69.4% and 28.4% (p < 0.01) respectively by combining N-limitation with high light intensity than that measured under N-limitation condition. N-limitation led to a significant decrease of MCYST cellular quota in biomass, which would be further decreased to a lower level by the high light. Based on above mentioned analysis, to decrease the MCYST production of blooms, we should control nutrient, especial nitrogen through pollutant intercepting and increase the light intensity through improving water transparency.
Se laden freshwater algae that enter the Salton Sea with river water pose ecorisks to wildlife in the lake by transferring selenium (Se) to higher trophic levels. The aim of this study was to investigate impacts of Se on , widely distributed in freshwater bodies, and its relationship with toxicity, such as microcystins and Se residues. When supplied with selenite, the 96 h-IC was calculated 2.60 mg Se/L. However, these inhibitory effects did not extend to microcystin production, and the extracellular fraction significantly increased with selenite as well as sulfate. As assimilated selenite very efficiently, 97% of the removed Se was through accumulation, compared to 3% via volatilization, raising a concern about ecotoxicity caused by the remaining Se in the algae. The XAS analysis suggests the dominant Se species accumulated in the algal cells was elemental Se (81%), which is relatively nonbioavailable to aquatic organisms. We further investigated the potential fate of Se carried into the Salton Sea by with river water. Under hypersalinity stress, the biomass Se and intracellular microcystins were released and reduced by 47% and 74%, respectively, resulting in the increasing levels of Se and microcystins in the water column. CuSO was then applied as an algaecide to prevent from entering the lake. The results indicate a similar response to that under hypersalinity stress: the volatilization process was blocked and the Se and microcystins were released from the damaged algal cells in the presence of CuSO , further raising toxicity levels by 8% and 60%, respectively, in the water column within 24 h. Overall, the coexistence of selenite and in river waters might negatively impact aquatic ecosystems of the Salton Sea and further research is required on how to harvest Se from to protect local wildlife.