Seasonal Dynamics of Microcystis spp. and Their Toxigenicity as Assessed by qPCR in a Temperate Reservoir

António Martins,Ana Regueiras,Cristiana Moreira,Vitor Vasconcelos,Micaela Vale,Marisa Freitas,Agostinho Antunes

doi:10.3390/md9101715

António Martins, Ana Regueiras + Show 5 more

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https://doi.org/10.3390/md9101715

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Journal: Marine Drugs	Publication Date: Sep 29, 2011
Citations: 69	License type: CC BY 3.0

Affiliation: University of Porto, Polytechnic Institute of Porto

Abstract

Blooms of toxic cyanobacteria are becoming increasingly frequent, mainly due to water quality degradation. This work applied qPCR as a tool for early warning of microcystin(MC)-producer cyanobacteria and risk assessment of water supplies. Specific marker genes for cyanobacteria, Microcystis and MC-producing Microcystis, were quantified to determine the genotypic composition of the natural Microcystis population. Correlations between limnological parameters, pH, water temperature, dissolved oxygen and conductivity and MC concentrations as well as Microcystis abundance were assessed. A negative significant correlation was observed between toxic (with mcy genes) to non-toxic (without mcy genes) genotypes ratio and the overall Microcystis density. The highest proportions of toxic Microcystis genotypes were found 4–6 weeks before and 8–10 weeks after the peak of the bloom, with the lowest being observed at its peak. These results suggest positive selection of non-toxic genotypes under favorable environmental growth conditions. Significant positive correlations could be found between quantity of toxic genotypes and MC concentration, suggesting that the method applied can be useful to predict potential MC toxicity risk. No significant correlation was found between the limnological parameters measured and MC concentrations or toxic genotypes proportions indicating that other abiotic and biotic factors should be governing MC production and toxic genotypes dynamics. The qPCR method here applied is useful to rapidly estimate the potential toxicity of environmental samples and so, it may contribute to the more efficient management of water use in eutrophic systems.

Highlights

Blooms of toxic cyanobacteria are a growing problem in freshwater ecosystems due to water quality degradation caused by eutrophication [1,2]
60 μS/Cm (July 1) to 155 μS/Cm (October 28) (Table 1). pH and temperature followed approximately the same pattern both presenting a peak at August 12, and declining in the following sampling dates
Some previous reports have showed a close relationship between the occurrence of certain toxic genotypes and MC net production [38], and that it is possible to infer MC concentrations from Microcystis cell numbers [39], correlations between MC levels and toxic genotypes numbers are often difficult to obtain [26,40]

Summary

Introduction

Blooms of toxic cyanobacteria are a growing problem in freshwater ecosystems due to water quality degradation caused by eutrophication [1,2]. Toxic blooms pose significant health risks to water users and may prevent its recreational use [3]. Microcystins (MCs) are the most prevalent cyanobacterial hepatotoxins in freshwaters and are produced mainly by strains of Anabaena, Microcystis and Planktothrix [4,5,6]. In Portugal, the occurrence of cyanotoxins is well documented, with MCs being the most prevalent [7,8], and MC-LR, MC-RR, and MC-YR as the dominant variants. Microcystis aeruginosa, M. wesenbergii, Anabaena flos-aquae, A. scheremetievi and Aphanizomenon flos-aquae, are the dominant toxic cyanobacteria species in most of the water bodies [7,8,9]

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