Is a Plasmid(s) Involved in the Toxicity of Microcystis Aeruginosa?

Abstract

Toxicity of Microcystis aeruginosa has been observed in various impoundments in South Africa. The symptoms of toxicity (i. e. swollen livers and short survival times) as well as the polypeptide nature of the toxin are similar to those reported elsewhere. In nature, the level, as well as the presence/absence of toxicity, is highly variable. Plasmids have been demonstrated in a number of blue-green algal species. The origin of toxicity in M. aeruginosa is as yet poorly understood. Plasmids are known to be involved in toxin production in certain bacteria, therefore the possibility of plasmid involvement in the toxicity of M. aeruginosa is under investigation. Laboratory cultures of a toxic strain of M. aeruginosa (WR 70) were supplemented by various concentrations of agents known either to eliminate plasmids (e. g. acridine orange) or to select for plasmid-free cells (e. g. sodium dodecyl sulphate) in bacteria. Toxicity of the cultures was monitored by intraperitoneal injection of disrupted cells into mice. It was found that cultures of toxic M. aeruginosa became non-toxic after growth in suitable concentrations of acridine orange, streptomycin, sodium dodecyl sulphate and chloramphenicol. These results indicate a possibility of plasmid involvement in the toxicity of M. aeruginosa (WR 70).