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Biological control of <i>Microcystis</i> dominated harmful algal blooms

RJ Gumbo
G Ross
ET Cloete


Freshwater resources are now threatened by the presence and increase of harmful algal blooms (HAB) all over the world. The HABs are sometimes a direct result of anthropogenic pollution entering water
bodies, such as partially treated nutrient-rich effluents and the leaching of fertilisers and animal wastes. The impact of HABs on aquatic ecosystems and water resources, as well as their human health
implications are well documented. Countermeasures have been proposed and implemented to manage HABs with varying levels of success. The use of copper algicides, though effective in managing HABs, often results in negative impacts such as copper toxicity and release of microcystins into surrounding water after cyanobacterial lysis. Biological control of HABs presents a possible solution. Predatory
bacteria that have been isolated as potential biological control agents include members of the Bacteroides-Cytophaga-Flavobacterium, ranging from Bacillus spp. to Flexibacter spp., Cytophaga and
Myxobacteria. Various mechanisms of predation have been proposed, including; physical contact between prey and predator, release of extracellular substances, entrapment of prey by the predator
followed by antibiosis and endoparasitism or ectoparasitism of the host by the predator. Despite an increasing amount of work being done in this field, research is usually limited to laboratory cultures;
assessment of microbial control agents is seldom extrapolated to field conditions.