A Molecular biological characterisation of Microcystis Aeruginosa Kutz. Emend Elenkin

Abstract

Microcystis aeruginosa Kutz. emend Elenkin is a cyanobacterial species which is sometimes found to be toxic. The most common toxin is a hepatotoxin but other toxins are also produced. The purpose of this study was to study the possibility of plasmid involvement in toxin production by M. aeruginosa. Curing experiments gave no clear answer to this question. The lysis of cells grown in tap water- and deionised water-based media was studied. Both types of cells were refractile to common methods of lysis, with growth conditions having a profound effect on this refractility. A grinding.method gave the highest yield of DNA but this did not exceed 25 %. Relatively high levels of nuclease were found but these could be inhibited by the use of diethyl pyrocarbonate or EDTA. A single contaminating bacterial species was found, which was not identified. The bacterium produced Slow Death Factor and did not contain plasmid DNA. Mass lyses, using methods tested in small scale lyses, yielded plasmid DNA from M. aeruginosa WR70. The mol % G+C of the different DNA's was determined, with the plasmid and M. aeruginosa having similar mol % G+C's (39,57 and 39,25 respectively). The bacterium had a G+C content of 60,54 which was similar to that found for a second band in lysates of M. aeruginosa (61,89). The latter DNA's were probably from the same organism. Electron microscopy of the plasmid DNA revealed the presence of two plasmids which had molecular masses of 2,05 Md and 5,02 Md respectively. From this study no definite conclusion can be drawn as to whether or not plasmids are involved in the toxicity of M. aeruginosa WR70, but the finding that strain WR70 contains at least one plasmid which is not present in the non-toxic strain PCC 7005 may be an indication of this possibility.