Occurrence of microcystin‐producing cyanobacteria in Ugandan freshwater habitats

Abstract

Microcystins (MCs) are cyclic heptapeptides that are the most abundant toxins produced by cyanobacteria in freshwater. The phytoplankton of many freshwater lakes in Eastern Africa is dominated by cyanobacteria. Less is known, however, on the occurrence of MC producers and the production of MCs. Twelve Ugandan freshwater habitats ranging from mesotrophic to hypertrophic conditions were sampled in In order to identify the MC-producing organism in the water samples (i), the conserved aminotransferase domain part of the mcyE gene that is indicative of MC production was amplified by general primers and cloned and sequenced, and (ii), genus-specific primers were used to amplify the mcyE gene of the genera Microcystis, Anabaena, and Planktothrix. Only mcyE genotypes that are indicative of Microcystis sp. were obtained via the environmental cloning approach (337 bp, 96.1%-96.7% similarity to the Microcystis aeruginosa strain PCC7806). Accordingly, only the mcyE primers, which are specific for Microcystis, revealed PCR products. We concluded that Microcystis is the major MC-producer in Ugandan freshwater.

Phosphorus enrichment and carbon depletion contribute to high Microcystis biomass and microcystin concentrations in Ugandan lakes

“…For all of the study lakes included in the current study (with the exception of Lake Nkuruba), Okello et al (2010) observed a strong positive relationship between MC cell quota and the proportion of the mcyB genotype in the Microcystis population. As such, it is likely that much of the difference in cell quota between sites may be attributable to differences in the genotypic composition of Microcystis (and the resulting capacity for MC production).…”

“…There is also evidence that buoyancy-regulating cyanobacteria can access CO 2 by rising to surface waters (Paerl 1988). Based on Okello and Kurmayer (2011), pH in our study lakes is often above 8 or even 9, suggesting that CO 2 availability is quite low. Furthermore, phytoplankton from many of these lakes (particularly where cyanobacterial biomasses were high) were strongly 13 C enriched, which indicates reduced isotopic discrimination during photosynthesis under CO 2 -limited conditions as well as possible cyanobacterial use of bicarbonate as a C source.…”

“…Presence of MC has been reported for Lakes Victoria and Edward as well as for several smaller Ugandan lakes (Sekadende et al 2005;Okello et al 2009;Poste et al 2011). To assess the biological and environmental controls on MC concentrations in tropical lakes, six Ugandan lakes known to have substantial cyanobacteria populations, including the tropical Great Lakes Victoria and Edward, as well as four smaller Ugandan lakes-Lake George, Lake Mburo, and the crater lakes Saka and Nkuruba ( Fig.…”

“…1). Meanwhile, Lake Mburo lies within Lake Mburo National Park and is an important source of drinking water for wild game and supports a large population of hippopotamuses (Hippopotamus amphibius; Nyakoojo and Byarujali 2010).…”

Detection, identification and toxigenicity of cyanobacteria in New Zealand lakes using PCR-based methods

“…In addition to PCR, other molecular methods that have been employed in the past to detect and discriminate between toxic cyanobacteria using mcy genes include Southern hybridisation, dot blot hybridisation, denaturing gradient gel electrophoresis (DGGE), restriction fragment length polymorphism (RFLP), cloning and sequencing (Dittmann & Bo¨rner 2005;Kim et al 2010;Okello et al 2009). In the absence of other genera-specific primers (apart from Microcystis and Anabaena), some of these procedures (e.g.…”