Cyanobacterial blooms in China:ecology,toxicity,and treatment

Cyanobacterial blooms are one of the major threats to the health of aquatic ecosystems,and are increasing globally due to the synergistic eff ects of human activities and global climate change.The 7^(th) National Cyanobacteria Bloom Forum was successfully held in May 28-30,2021 in Guiyang,Guizhou Province,China.The forum established a platform for exchanging views on the concerns of cyanobacterial blooms from Chinese researchers,lake managers,and treatment engineers.This special issue,“Cyanobacterial blooms in China:ecology,toxicity,and treatment”in Journal of Oceanography and Limnology,presents a collection of 14 papers on the physiological features and the infl uence on their concurrent aquatic biology of diff erent cyanobacterial groups.

Investigation on cyanobacterial production of the proposed neurotoxinβ-N-methylamino-L-alanine(BMAA)

β-N-methylamino-L-alanine(BMAA)is an environmental neurotoxin thought to be produced by cyanobacteria.However,the cyanobacterial origin of BMAA remains controversial.The detection method and culture conditions of cyanobacteria are often cited as factors behind the discrepancy of published results.We showed previously that BMAA was highly toxic to the cyanobacterium Nostoc PCC 7120,and it is taken up via an amino acid transport system.Using a mutantΔnatAΔbgtA deficient in amino acid transport as a genetic control,we show here that BMAA taken up from the medium can be detected quantitatively at a threshold similar to,or below those reported,but was undetectable in the mutant.The BMAA isomer,2,4-diaminobutanoic acids(DAB),but not BMAA,could be detected in cell free extracts of Nostoc PCC 7120.Long-term(20 days)diazotrophic growth or nonlimiting supply of phosphate,conditions reported to enhance BMAA synthesis,did not lead to the detection of BMAA.An UPLC-MS/MS signal with a similar retention time to BMAA was found after prolonged diazotrophic incubation,but did not have fragment ions of BMAA after further analysis.When extended to 29 different cyanobacterial strains and 6 natural cyanobacterial bloom samples,none of them was found to produce BMAA.The cytotoxicity of BMAA to cyanobacteria,and the lack of a cellular protective mechanism against such toxicity,contradict the presence of a BMAA synthesis pathway in these organisms.More specific methods for BMAA detection in vivo need to be developed to clarify the cyanobacterial origin of BMAA.

Seasonal dynamics of water bloom-forming Microcystis morphospecies and the associated extracellular microcystin concentrations in large,shallow,eutrophic Dianchi Lake

The increasing occurrence of Microcystis blooms is of great concern to public health and ecosystem due to the potential hepatotoxic microcystins （MCs） produced by these colonial cyanobacteria. In order to interpret the relationships between variations of Microcyst/s morphospedes and extracellular MC concentrations, the seasonal dynamics of phytoplankton community composition, MC concentrations, and environmental parameters were monitored monthly from August, 2009 to July, 2010. The results indicated that Microcystis dominated total phytoplankton abundance from May to December （96%--99% of total biovolume）, with toxic Microcystis viridis and non-toxic Microcystis wesenbergii dominating after July （constituting 65%- 95% of the Microcystis population）, followed by M. viridis as the sole dominant species from November to January （49%--93%）. Correlation analysis revealed that water temperature and nutrient were the most important variables accounting for the occurrence ofM. wesenbergii, while the dominance ofM. viridis was related with nitrite and nitrate. The relatively low content of MCs was explained by the association with a large proportion of M. viriclis and M. wesenbergii, small colony size of Microcystis populations, and low water temperature, pH and dissolved oxygen. The extracellular MC （mean of 0.5 ± 0.2 μg/L） of water samples analyzed by enzyme-linked immunosorbent assay （ELISA） demonstrated the low concentrations of MC in Dianchi Lake which implied the low potential risk for human health in the basin. The survey provides the first whole lake study of the occurrence and seasonal variability of Microcyst/s population and

Microcystin-degrading bacteria affect mcy D expression and microcystin synthesis in Microcystis spp

Cyanobacterial blooms occur increasingly often and cause ecological,economic and human health problems worldwide.Microcystins（MCs）are the dominant toxins produced by cyanobacteria and are implicated in epidemic disease and environmental problems.Extensive research has been reported on the various regulating factors,e.g.,light,temperature,nutrients such as nitrogen and phosphorus,p H,iron,xenobiotics,and predators,that influence microcystin（MC）synthesis,but little is known about the effects of cyanobacteria-associated bacteria on MC synthesis.A considerable number of studies have focused on interactions between Microcystis species and their associated bacteria.In this study,we evaluated the effects of MC-degrading bacteria（MCDB）on MC synthesis gene mcy D expression and MC synthesis in axenic strain PCC7806,non-axenic strain FACHB905,and colony strain FACHB1325 of Microcystis by quantitative real-time polymerase chain reaction（RT-PCR）assay and enzyme-linked immunosorbent assay（ELISA）.We demonstrate for the first time that MCDB can induce and up-regulate the MC production and transcriptional response of the mcy D gene of toxic Microcystis.On day 4 of the culturing experiment,the intracellular MC concentration and transcriptional response of mcy D of FACHB1325 were up-regulated 1.9 and 5.3-fold over that of the control,and for FACHB905 were up-regulated 1.8 and 4.2-fold over that of the control,respectively.On day 10,the transcriptional response of mcy D was up-regulated 21.3-fold in PCC7806.These results indicate that there are interactions between toxic Microcystis and MCDB,and MCDB may play a role in regulating mcy D expression in toxic Microcystis.