Seasonal dynamics of microcystins and microcystin-producing Microcystis populations in three water bodies in Mozambique

Seasonal dynamics of Microcystis spp with or without microcystin-producing genes were monitored in Pequenos Libombos dam, Nhambavale Lake and Chòkwé irrigation channels, located in Southern Mozambique. Water samples and environmental parameters (pH, surface temperature, and turbidity) were collected monthly from September 2009 to July 2010. The number of microcystin-synthethase (mcyB) and phycocyanin (PC) gene copies from Microcystis spp was quantified using qPCR. Microcystis PC and mcyB gene copies were measured throughout the study period in the sampling areas, and the non-microcystin-producing strains were predominant. Microcystin-producing copy numbers of Microcystis spp (mcyB) were abundant during the bloom season, reaching the highest levels in January 2010 at Pequenos Libombos dam and Chòkwé irrigation channels. Microcystin (MC) concentrations exceeded the WHO guideline of 1 µg/L for drinking water in some water samples (44 µg/L). Changes in microcystin profiles were observed during the different seasons and between the water bodies. MC-LR, -RR, -YR, RY, -LA, -[Dha7]-LR, and -[Asp3]-LR were detected in water samples by LC–MS/MS. Generally, MC-LR was the most dominant variant (77% of samples). Considering that Pequenos Libombos dam provides drinking water for the capital Maputo City, these results suggest the need of further studies to evaluate the human health risk associated with MC occurrence.