Cyanobacterial community and microcystin production in a recreational reservoir with constant Microcystis blooms

Cyanobacterial blooms are increasing worldwide favored by eutrophic conditions of aquatic ecosystems associated with climatic perturbations. Generally, inland lentic systems are more susceptible to the development of harmful blooms. In the Salto Grande Reservoir (Brazil), Microcystis is the most common bloom-forming genus along with a wide range of co-occurring and less-known cyanobacteria taxa. The cyanobacterial community and microcystin production were studied in Salto Grande Reservoir applying biological, toxicological, and molecular approaches. Thirteen cyanobacterial strains belonging to eight genera were isolated and taxonomically investigated based on morphological traits and phylogenetic analyses of their 16S rRNA gene sequence. The morphotypes identified were, in general, in agreement with their phylogeny. The presence of non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) was investigated using PCR gene amplification, which were detected in 76.9 and 84.4% of the strains, respectively. Positive enzyme-linked immunosorbent assays (ELISA) reactions for microcystins were obtained only from the strain Leptolyngbya sp. CENA129. ELISA and high-performance liquid chromatography (HPLC) analyses of the environmental water samples showed the highest microcystin concentration during the dry and rainy seasons, respectively. This study highlights that microcystin production must be suspected in benthic forms as well as in genera that are morphologically similar but belonging to other evolutionary lineages.