Seasonal dynamics and toxicity of Cylindrospermopsis raciborskii in Lake Guiers (Senegal, West Africa)

Abstract

Cylindrospermopsis raciborskii is a toxic bloom-forming cyanobacterium that occurs at tropical and temperate latitudes. Despite several reports from Africa, no data were previously available about its dynamics or toxic potential there. We therefore carried out a 1-year survey of the dynamics of C. raciborskii in the main water reservoir in Senegal, Lake Guiers. Cylindrospermopsis raciborskii never formed a bloom in this lake during the period studied, but was dominant during the dry season. The only observed bloom-forming species was a diatom, Fragilaria sp., which displayed a seasonal pattern contrary to that exhibited by C. raciborskii. Principal component analysis applied to environmental and phytoplankton data showed that high C. raciborskii biomasses were mainly related to high temperature and water column stability. Tests for C. raciborskii species-related toxicity and/or toxin synthesis were performed on 21 isolated clones. All the strains isolated tested negative in mouse toxicity bioassays, toxin analysis (MS/MS) and tests for known cylindrospermopsin genes (ps, pks). The limited number of isolates studied, and the occurrence of toxic and nontoxic clones in natural cyanobacterial populations, mean that we cannot conclude that there is no C. raciborskii-associated health risk in this drinking water reservoir.

Tropical cyanobacterial blooms: a review of prevalence, problem taxa, toxins and influencing environmental factors

“…6). Some studies have found that higher temperatures favour Cylindrospermopsis blooms (Bouvy et al, 2000;Huszar et al, 2000;Saker and Griffiths, 2001;Berger et al, 2006;Dufour et al, 2006;Ghosh et al, 2008;Figueredo and Giani, 2009), while high total nitrogen concentration may not be as important for Cylindrospermopsis bloom occurrence, due to the fact that Cylindrospermopsis are nitrogen-fixing (Bouvy et al, 1999;Rustadi et al, 2002;Gondwe et al, 2007;Khuantrairong and Traichaiyaporn, 2008). Comparing this outcome to temperate areas, Cylindrospermopsis blooms in France are similarly affected by high temperature (Briand et al, 2002).…”

“…Nitrogen-fixing species were found to be bloom-forming during the dry season, due to strong thermal stratification and water column stability (Sprober et al, 2003). Since nitrogen fixing genera such as Anabaena and Cylindrospermopsis are able to fix atmospheric nitrogen for growth, these genera are able to compete in conditions of lower nitrogen, for example, after a long period of stratification (Khuantrairong et al, 2008;Bormans et al, 2004;Hawkins and Griffiths, 1993;Hawkins, 1985;Saker and Griffith, 2001;Komarek and Kling, 1991;Okechukwu and Ugwumba, 2008;Berger et al, 2006;Dufour et al, 2006;Gondwe et al, 2007;Branco and Senna, 1994;Bouvy et al, 1999;Bouvy et al, 2003;Vieira et al, 2005;Vieira et al, 2003). Some studies documented Microcystis blooms in the wet season due to elevated nutrient levels in the various water bodies, occurring after periods of heavy rainfall (Ochumba and Kibaara, 1989;Makahant et al, 1998;Salonen et al, 1999;Arfi et al, 2001;Kitaka et al, 2002;Wang et al, 2002;Welker et al, 2004;Sekandende et al, 2005;Meesuko et al, 2007;Krishnan, 2008;Onyema 2010;Sitoki et al, 2012).…”

“…The only species recorded was Cylindrospermopsis raciborskii; however, only strains from ponds in Nigeria were found to produce cylindrospermopsin (Odokuma and Isirima, 2007). Strains from Kazinga Channel, Uganda and Lake Guiers, Senegal were isolated and tested for toxins by LC-MS and mouse bioassay respectively, but were not found to produce any cylindrospermopsin and saxitoxins (Lake Guier isolates) (Haande et al, 2008;Berger et al, 2006).…”

Initial growth phases of two bloom-forming cyanobacteria (Cylindrospermopsis raciborskiiandPlanktothrix agardhii) in monocultures and mixed cultures depending on light and nutrient conditions

“…Neither strain (PMC702.10 and PMC 684.10) was toxic. The detection of genes involved in toxin production was checked by PCR on fresh samples using primers targeting the mcy A, mcy B and mcy E genes for MCs and on ps and pks genes for CYN (according to Berger et al, 2006). No PCR product was obtained.…”

Cyanobacteria and microcystin contamination in untreated and treated drinking water in Ghana

“…These are two large geographical areas with 26 countries and nearly half a billion inhabitants, where Central Africa is represented by nine countries populated by approximately 155 mil people, and West Tropical Africa by 17 countries with a combined population of about 344 mil people (UNSD, 2014). Toxic or potentially toxic cyanobacterial blooms seem to occur frequently in this geographical area (Addico et al, 2006(Addico et al, , 2009(Addico et al, , 2017Akin-Oriola et al, 2006;Berger et al, 2006;Haande et al, 2007;Mhlanga et al, 2006;Odokuma and Isirima, 2007). Nevertheless, MCs in this region have been so far reported from Nigeria (Chia et al, 2009a(Chia et al, , 2009bChia and Kwaghe, 2015) and detected in water reservoirs Brimsu, Kwanyarko, Kpong and Weija in Ghana (Addico et al, 2006;Addico et al, 2017).…”