RESUMO
Microcystins are produced by multifaceted organisms called cyanobacteria, which are integral to Africa's freshwater environments. The excessive proliferation of cyanobacteria caused by rising temperature and eutrophication leads to the production and release of copious amounts of microcystins, requiring critical management and control approaches to prevent the adverse environmental and public health problems associated with these bioactive metabolites. Despite hypotheses reported to explain the phylogeography and mechanisms responsible for cyanobacterial blooms in aquatic water bodies, many aspects are scarcely understood in Africa due to the paucity of investigations and lack of uniformity of experimental methods. Due to a lack of information and large-scale studies, cyanobacteria occurrence and genetic diversity are seldom reported in African aquatic ecosystems. This review covers the diversity and geographical distribution of potential microcystin-producing and non-microcystin-producing cyanobacterial taxa in Africa. Molecular analyses using housekeeping genes (e.g., 16S rRNA, ITS, rpoC1, etc.) revealed significant sequence divergence across several cyanobacterial strains from East, North, West, and South Africa, but the lack of uniformity in molecular markers employed made continent-wise phylogenetic comparisons impossible. Planktothrix agardhii, Microcystis aeruginosa, and Cylindrospermopsis raciborskii (presently known as Raphidiopsis raciborskii) were the most commonly reported genera. Potential microcystin (MCs)-producing cyanobacteria were detected using mcy genes, and several microcystin congeners were recorded. Studying cyanobacteria species from the African continent is urgent to effectively safeguard public and environmental health because more than 80% of the continent has no data on these important microorganisms and their bioactive secondary metabolites.
RESUMO
Microcystins (MCs) are hepatotoxic secondary metabolites produced by several genera of cyanobacteria. Human exposure routes include drinking contaminated water and consuming contaminated fish, vegetables, crops, and even food supplements that contain cyanotoxin. This study investigated the presence of MCs in a stream with a long history of use as a source of water for irrigation farming. To establish the risk of a lack of monitoring programs, we studied MCs contamination of irrigated vegetables. Toxin levels in the water were generally <0.05 µg L-1 in all the investigated stations. Total microcystin concentrations in spinach (0.306 µg Kg-1 upstream and 0.217 µg Kg-1 downstream), lettuce (0.085 µg Kg-1 upstream and 0.462 µg Kg-1 downstream), carrot (0.050 µg Kg-1 downstream and 0.116 µg Kg-1 downstream), cabbage (0.014 µg Kg-1 upstream and 0.031 µg Kg-1 downstream), tomatoes (0.233 µg Kg-1 upstream), and bitter leaf (0.460 µg Kg-1 upstream and 0.050 µg Kg-1 downstream) collected in March were higher than the levels detected in samples of the same vegetables collected in April. These results highlight Nigeria's severe public health problem, especially in regions with long dry season spells. The level of MCs contamination of irrigated vegetables implies a potential for chronic exposure and associated health challenges.
