Influence of mixed antibiotics on Microcystis aeruginosa during the application of glyphosate and hydrogen peroxide algaecides

Antibiotics regulate various physiological functions in cyanobacteria and may interfere with the control of cyanobacterial blooms during the application of algaecides. In this study, Microcystis aeruginosa was exposed to H₂O₂ and glyphosate for 7 d in the presence of coexisting mixed antibiotics (amoxicillin, spiramycin, tetracycline, ciprofloxacin, and sulfamethoxazole) at an environmentally relevant concentration of 100 ng · L^?1. The mixed antibiotics significantly (P < 0.05) alleviated the growth inhibition effect of 15–45 μM H₂O₂ and 40–60 mg · L^?1 glyphosate. According to the increased contents of chlorophyll a and protein, decreased content of malondialdehyde, and decreased activities of superoxide dismutase and glutathione S‐transferase, antibiotics may reduce the toxicity of the two algaecides through the stimulation of photosynthesis and the reduction in oxidative stress. The presence of coexisting antibiotics stimulated the production and release of microcystins in the M. aeruginosa exposed to low concentrations of algaecides and posed an increased threat to aquatic environments. To eliminate the secondary pollution caused by microcystins, high algaecide doses that are ≥45 μM for H₂O₂ and ≥60 mg · L^?1 for glyphosate are recommended. This study provides insights into the ecological hazards of antibiotic contaminants and the best management practices for cyanobacterial removal under combined antibiotic pollution conditions.     

Odorella benthonica gen. & sp. nov. (Pleurocapsales,Cyanobacteria): an odor and prolific toxin producer isolated from a California aqueduct

Pleurocapsales are one of the least understood groups of cyanobacteria in terms of molecular systematics and biochemistry. Considering the high number of cryptic taxa within the Synechococcales and Oscillatoriales, it is likely that such taxa also occur in the Pleurocapsales. The new genus described in our research is the first known pleurocapsalean cryptic taxon. It produces off‐flavor and a large number of bioactive metabolites (n = 38) some of which can be toxic including four known microcystins. Using a polyphasic approach, we propose the establishment of the genus Odorella with the new species O. benthonica from material originally isolated from the California Aqueduct near Los Angeles.     

Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communities

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (∼5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes.
2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species – Aphanizomenon flos-aquae , Anabaena flos-aquae and Microcystis aeruginosa – which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos-aquae . The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology.
3. Standardised concentrations of the hepatotoxic microcystin-LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced.
4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.     

Degradation of Microcystin-RR by Sphingomonas sp. CBA4 isolated from San Roque reservoir (Córdoba – Argentina)

We report the aerobic biodegradation of Microcystin-RR (MC-RR) by a bacterial strain isolated from San Roque reservoir (Córdoba – Argentina). This bacterium was identified as Sphingomonas sp. (CBA4) on the basis of 16S rDNA sequencing. The isolated strain was capable of degrading completely MC-RR (200 μg l⁻¹) within 36 h. We have found evidence that MC-RR biodegradation pathway by this Sphingomonas sp. strain would start by demethylating MC-RR, affording an intermediate product, which is finally biodegraded by this strain within 72 h. Our results confirm that certain environmental bacteria, living in the same habitat as toxic cyanobacteria, have the capability to perform complete biodegradation of MC, leading to natural bioremediation of waterbodies. The bacterium reported here presents genetic homologies with other strains that degrade MC-LR. However, initial demethylation of MC-RR has been not described previously, raising questions on the probable presence of different biodegradation pathways for different MC variants.     

Production of microcystins in calcareous Mediterranean streams: The Alharabe River,Segura River basin in south-east Spain

The development of epilithic cyanobacteria communities in a Mediterranean calcareous stream in the province of Murcia (SE Spain) was studied during the course of one year in an attempt to clarify the environmental variables that influence the production of microcystins. The predominant cyanobacteria were species of Rivularia, which formed conspicuous colonies throughout the year. Seasonally, other species were abundant: Schizothrix fasciculata, Tolypothrix distorta and Phormidium splendidum. All the species collected produced microcystins to a varying degree (up to five varieties), while the benthic community as a whole produced concentrations as high as 20.45 mg m⁻². At the same time, the presence of microcystins dissolved in water was confirmed. Among environmental variables, air temperature and silicate content were positively and strongly correlated with total microcystins, while nitrite, nitrate, orthophosphate, calcium and flow were negatively correlated with them. Dissolved microcystins were negatively correlated with microcystin LR, P.A.R. and total phosphorus and positively with rainfall. The production of microcystin YR seems to be regulated by different factors from those regulating the other main varieties (microcystin LR and microcystin RR). The data obtained indicate that all the tested benthic cyanobacteria produced microcystins in this shallow calcareous stream, which may contribute to their predominance in the prevailing conditions. The accumulation of microcystins in mucilaginous colonies of other groups of algae poses new questions concerning the possible ecological function of these compounds and needs further study.     

Active release of microcystins controlled by an endogenous rhythm in the cyanobacterium Microcystis aeruginosa

The active release of microcystins in cyanobacterium Microcystis aeruginosa (Kützing) Kützing, strain BCCUSP232 was confirmed. The microcystin release is controlled by an endogenous rhythm, pointing to a biosynthetic pattern of toxins in cyanobacteria. Proofing tests for this active release were carried out by experiments at two independent 24 h cycles, light : dark and continuous light (12:12 h) along the exponential growing phase. Cultivation samples at light, temperature and photoperiod controlled conditions were collected in 2‐h intervals. Microcystin concentrations from the pellet aliquots (intracellular microcystin per cell‐quota –IMC) and supernatant (extracellular microcystin per equivalent cell‐quota – EMC) were quantified with enzyme linked immunosorbent assay. The IMC concentrations showed increases and decreases in both cycles. Decreases of IMC clearly demonstrate that the toxin was actively released to the surrounding medium and not by cell lysis. The total microcystins concentrations (IMC and EMC) between the light : dark and continuous light cycles presented similar variations between the same hours.     

基于物种敏感性分布的微囊藻毒素与氮污染水体生态风险评估

应用物种敏感性分布(SSD)方法,可正向和反向评估物种的生态风险及确定保护物种的污染物浓度阈值,为水体生态风险管理提供依据.本文通过采集淡水生物毒性数据,构建SSD方程,在95%物种保护基础上评估微囊藻毒素、氨氮和亚硝态氮对淡水生物的生态风险浓度阈值(HC₅)和复合生态风险,以及不同暴露浓度下的潜在影响比例(PAF).结果表明: 微囊藻毒素对淡水生物的HC₅值为19.22 μg·L^-1,其水生态风险高于氨氮(HC₅ 6583.94 μg·L^-1)和亚硝态氮(HC₅ 334.33 μg·L^-1).不同类别生物对微囊藻毒素和氨氮、亚硝态氮的敏感性随暴露浓度不同存在差异.当微囊藻毒素与亚硝态氮的浓度低于临界浓度125.04、2989.40 μg·L^-1时,甲壳类对微囊藻毒素敏感性高于鱼类,对亚硝态氮敏感性则低于鱼类,而高于临界值其物种敏感性呈相反效应,但氨氮所引起的物种敏感性差异不显著.在代表性水体中,复合生态风险高于单一污染风险,微囊藻毒素、氨氮、亚硝态氮对全部物种的复合潜在影响比例msPAF为2.6%～5.6%,且太湖和红枫湖已超过HC₅生态风险阈值.     

Effects of the microcystin profile of a cyanobacterial bloom on growth and toxin accumulation in common carp Cyprinus carpio larvae

A 12 day growth trial was conducted to compare the effect of the variation in microcystins (MC) composition of two bloom samples of Microcystis aeruginosa on the growth performance and microcystin accumulation in common carp Cyprinus carpio larvae. Two M. aeruginosa natural bloom samples with different MC profiles were collected and larvae were exposed to cyanobacterial cells through their diet. Three diets, a basal control diet and two diets prepared from the basal diet plus the same toxins content (60 ng MC g^?1 diet) of each cyanobacterial bloom, were given at the same ration level to three groups of larvae during the experimental period. Larval mass and standard length from day 9 were significantly different between cyanobacterial treatments and in both cases lower than that of the control. The MC accumulation by larvae, inversely correlated with the growth performance, was also significantly different between cyanobacterial treatments (26·96 v. 17·32 ng g^?1 at the end of the experimental period). These results indicate that MC variants profile may have effects on the toxin uptake and toxicity. To date, this is the first laboratory study to show that fish accumulate MC depending on the toxin profile of the cyanobacterial bloom.     

Comparative study for the effects of variable nutrient conditions on the biodegradation of microcystin-LR and concurrent dynamics in microcystin-degrading gene abundance

Microcystin-LR (MCLR) degradation capability of biofilm was investigated with and without additional nutrients (nitrate, ammonium, peptone and glucose) at concentrations of 100 and 1000 mg L(-1). The MCLR-degradation was stimulated with nitrate and inhibited with other nutrients, except for that glucose of low concentration had no obvious effect. Both stimulatory and inhibitory effects enhanced with increasing concentration of corresponding nutrient. Quantitative polymerase chain reaction (qPCR) indicated that enhanced inhibition in biodegradation correlated to increased inhibition in functional gene (mlrA) abundance, as nutrient concentration increased. Stimulated biodegradation under low nitrate concentration may result from more rapid increase in mlrA gene abundance. These suggested that MCLR-degradation largely depended upon responsible bacterial population, which was affected by population of other bacteria in biofilm according to 16S rDNA-targeting qPCR. However, inhibited mlrA gene abundance implied that the stimulated biodegradation under high nitrate concentration might be involved in the mechanisms not related to MCLRDB population.     

微囊藻毒素生物合成及其检测的分子生物学研究进展

随着世界各地水体富营养化的日益加剧,蓝藻水华的爆发频率越来越高,爆发范围也越来越广,已经成为国内外学者高度关注的重大环境问题。微囊藻水华是淡水水体中危害最严重的一类,特别是在我国巢湖、太湖和滇池等大型湖泊,经常爆发微囊藻水华,给水体生态系统和人类健康带来了巨大的危害。本文简介了微囊藻毒素的化学结构与危害,综述了微囊藻毒素mcy基因簇、Adda生物活性结构以及肽链合成与环化等关键生物合成过程,并重点归纳了聚合酶链式反应(polymerase chain reaction,PCR)、实时定量PCR(real time quantitative PCR detecting system,QPCR)、基因芯片(gene microarray)和变性梯度凝胶电泳(denaturing gradient gel electrophoresis,DGGE)等用于藻毒素检测的分子生物学技术方法,最后对相关研究进行了展望。