Microcystis aeruginosa and M. wesenbergii Were the Primary Planktonic Microcystin Producers in Several Bulgarian Waterbodies (August 2019)

Maya Stoyneva-Gärtner,Blagoy Uzunov,Georg Gärtner,Mariana Radkova,Mariya Mitreva,Jean-Pierre Descy,Katerina Stefanova,Vera Pavlova

doi:10.3390/app11010357

Abstract

The rising interest in harmful cyanoprokaryote blooms promotes an increase of phycological and ecological research on potentially toxic species and their hazardous substances. The present study aimed to identify the main microcystin (MC) producers and their contribution to the phytoplankton of shallow waterbodies in Bulgaria, applying different methods. The sampling was performed in August 2019 in nine lakes and reservoirs, two of which (reservoirs Kriva Reka and Izvornik 2) were studied for the first time. The high contribution of cyanoprokaryotes to the total species composition and phytoplankton abundance was proved by light microscopic (LM) observations and HPLC analysis of marker pigments. The LM identification of potential MC-producers was supported by PCR amplification of mcyE and mcyB genes. The MCs amounts, detected by HPLC-DAD, varied by sites with a range from undetectable concentrations to 0.46 µg L−1 with only one recorded variant, namely MC-LR. It was found only in the reservoirs Mandra and Durankulak, while toxigenic MC-strains were obtained by PCR from five more waterbodies. Both LM and PCR demonstrated that the MC-producers were Microcystis aeruginosa and M. wesenbergii, despite their occurrence in low amounts (<0.5–5% of the total biomass) when filamentous cyanoprokaryotes dominated.

Highlights

During the last decades many countries throughout the world experienced incidences related with mass developments of both marine and freshwater toxic algae [1,2]
With this paper we demonstrate the role of two Microcystis species identified by light microscopic (LM) and PCR, namely M. aeruginosa and M. wesenbergii, as primary MCproducers in the studied shallow water bodies with high total cyanoprokaryote contribution to phytoplankton species composition and biomass dominated mainly by filamentous heterocytous taxa
The only exception was the relatively low amount (18%) of cyanoprokaryotes in the coastal lake Durankulak, where, according to the LM observations, they were represented by high cell numbers, but large centric diatoms the genus Cyclotella dominated by biomass

Summary

Introduction

During the last decades many countries throughout the world experienced incidences related with mass developments of both marine and freshwater toxic algae [1,2]. These harmful algal blooms, formed by eukaryotic algae (commonly abbreviated as HABs) or by cyanoprokaryotes/cyanobacteria (known as CyanoHABs, or CHABs) are anticipated to expand their distribution, promoted mainly by global warming, population growth and increasing nutrient loading [1,3,4,5]. Many questions related to the taxonomy, ecology, distribution and toxicity of some important bloom-causative cyanoprokaryotes are still awaiting their answers. There is evidence that higher concentrations of nutrients may promote toxic genotypes and MC production [5,12]

Results

Discussion

Conclusion