Ecological and molecular investigations of cyanotoxin production

This study investigates the effect of mercury contamination on the culturable heterotrophic, functional and genetic diversity of the bacterial community in soil. The changes in diversity were monitored in soil microcosms, enriched with 25 &mgr;g Hg(II) g(-1) soil, over a period of 3 months. The culturable heterotrophic diversity was investigated by colony morphology and colony appearance on solid LB medium. Functional diversity was analysed as sole carbon utilisation patterns in ECOplates. Genetic diversity was measured as bands on denaturing gradient gel electrophoresis (DGGE) gels obtained by purification of total soil DNA and amplification of bacterial 16S rDNA fragments by polymerase chain reaction. Concentrations of bioavailable and total mercury were measured throughout the experiment. The effect on the culturable heterotrophic and genetic diversity was very similar, showing an immediate decrease after mercury addition but then slowly increasing throughout the entire experimental period. Pre-exposure levels were not reached within the time span of this investigation. The DGGE band pattern indicated that a shift in the community structure was responsible for recovered diversity. When analysed by Shannon-Weaver indices, functional diversity was found to increase almost immediately after mercury addition and to remain at a level higher than the control soil for the rest of the experiment. The fraction of culturable heterotrophic bacteria increased from 1% to 10% of the total bacterial number as a result of mercury addition, and the mercury-resistant population increased to represent the entire heterotrophic population.     

Investigation of microcystin removal from eutrophic surface water by aquatic vegetable bed

In southern China, many freshwater ecosystems, including lakes, rivers and reservoirs, are eutrophic. The nutrient loading coupled with year-round warm weather favors the growth of cyanobacteria, several of which can produce cyanotoxins, especially the potent liver toxins called microcystins, which are often detected in eutrophic drinking water sources. For purifying raw water used as source of drinking water treatment plants, an aquatic vegetable bed (AVB) experiment had been carried out in a hypertrophic waterfront of Lake Taihu, China, since October 2002. AVB was a simplification of the nutrient film technique (NFT) used to produce vegetables, which requires large quantities of water and nutrients. The average removal rates of total microcystin-RR and microcystin-LR were 63.0% and 66.7%, respectively. This study indicated that Ipomoea aquatica was able to absorb microcystins by using enzyme-linked immunosorbent assay (ELISA), and that the roots absorbed more toxins than leaves and stems. We used fluorescence in situ hybridization (FISH) to analyze the density of microcystin-degrading bacteria in AVB sediment. Two species of microcystin-degrading bacteria were detected, which indicated that microcystin bio-degradation processes did occur in AVB. Protozoa and metazoa were abundant in the rhizosphere. Aspidisca sp., Vorticella sp., Philodina sp., and Lecane sp. were the dominant species. The predation function of protozoa and metazoa had a positive effect on removal of cyanobacteria and microcystins.     

Rapid quantification of mcyB copy numbers on dry chemistry PCR chips and predictability of microcystin concentrations in freshwater environments

Microcystin-producing cyanobacteria cause serious water quality problems worldwide, which has led to growing pressure for more intensive monitoring. Molecular biology methods that are based on identification and enumeration of biosynthetic genes, such as quantitative PCR, show promise in this respect. To be practical in a wide range of settings, these methods need to be usable also by laboratory personnel who do not have previous experience in PCR setup. Here we present a real-time quantitative mcyB dry chemistry PCR assay capable of identifying the three globally most common microcystin-producing cyanobacterial genera, Anabaena, Microcystis and Planktothrix. It minimizes the amount of liquid handling and avoids direct contact with the PCR reagents at the time of analysis. Large quantities of virtually identical chips can be manufactured, improving the comparability of results. Using the dry chemistry PCR chips, freshwater environmental samples from Finnish and Estonian lakes, rivers and reservoirs were analyzed for mcyB. The chip format was found to be highly suitable for water sample analysis due to its ease-of-use, good sensitivity and amplification efficiency. Significant positive correlation (Spearman's rank correlation, ρ > 0.66, P < 0.001) was observed between combined mcyB copy numbers from Microcystis, Anabaena, Planktothrix and total microcystin concentrations, regardless of the method used to measure the toxins (ELISA or LC–MS). Positive correlations were observed also for single lakes.     

水环境中微囊藻毒素的生物降解

微囊藻毒素在水环境中的生物降解是决定其环境归趋和影响其毒性的重要因素。本文综述了水细菌、鱼类、水生植物、水生无脊椎动物、浮游动物等水生生物对微囊藻毒素生物降解方面的研究进展。目前报道的微囊藻毒素降解菌有鞘氨醇单胞菌、铜绿假单胞菌和青枯菌。鞘氨醇单胞菌和铜绿假单胞菌分别以微囊藻毒素酶和碱性蛋白酶降解毒素,青枯菌降解机理未明;而鱼类、水生植物、水生无脊椎动物、浮游动物等水生生物主要通过谷胱甘肽S-转移酶催化形成低毒性的微囊藻毒素-谷胱甘肽结合物进行转化。本文还对水环境微囊藻毒素的生物修复方式进行了初步的探讨。     

Combining national and state data improves predictions of microcystin concentration

Data collected from lakes at national (regional) scales and state (local) scales can provide different insights regarding relationships between environmental factors and biological responses, and combining these two types of data can potentially yield more precise and accurate understanding of ecological phenomena. National data can include many measures, cover large spatial areas, and span broad environmental gradients. Because of these characteristics, analyses of these data can yield accurate estimates of relationships among different lake characteristics. However, the number of samples in a national data set that is available for estimating a relationship specific to waterbodies within a smaller region, like a single state, is limited. Conversely, state monitoring data provide intensive sampling of lakes within a smaller area, but these data span a narrower range of conditions and may only include a subset of relevant measurements. Here, a Bayesian network model is described that represents the causal linkages between observations of chlorophyll a concentration, cyanobacterial biovolume, and microcystin concentration. This network model was fit to national data and provided a context for modeling observations of chlorophyll a and microcystin collected from lakes in Iowa. Using the knowledge inherent in the national network model improved the accuracy of predictions of microcystin concentrations in Iowa compared to a model based only on Iowa data.