Light and electron microscope assessment of the lytic activity of Bacillus on Microcystis aeruginosa
During the screening of lytic bacteria, plaques were obtained on Microcystis lawns. In the plaques, at least five distinct morphotypes of bacteria were found. The plumb rod-shaped bacilli were the most abundant and were found aggregated around unhealthy Microcystis cells and were the probable cause of deflation and lysis. These bacteria may have utilized the cyanobacteria cell contents as their nutrient source. In contrast to the control areas, the cyanobacteria cells were healthy and did not show any visible distortion of cell structure. The presence and possible role of the free-bacteria, that is, bacteria that were not attached or associated with the cyanobacteria in the plaque is not clear. Maybe their function is to scavenge the skeletal remains of Microcystis cells. Bacillus mycoides B16 were found to have a lytic effect on Microcystis cells. Scanning electron micrographs (SEM) images of B. mycoides B16 did not reveal any unique attachments that may have allowed them to adhere to Microcystis cells. The Microcystis cells were exposed to copper, B. mycoides B16 and Triton X-100, in order to ascertain the level of cell membrane damage. The membrane cell damage was most severe with copper stripping the entire Microcystis cell membrane leaving a honeycomb skeletal structure and B. mycoides B16, leaving perforations on the cell membrane. The electron microscopy observations appeared to reveal at least two mechanisms of Microcystis lysis (contact and parasitism). The light and electron microscope (LEM) observations did not reveal any endoparasitism of B. mycoides B16 or Bdellovibrio-like behaviour.
Key words: Microcystis, mechanism of lysis, Bacillus mycoides B16, photosynthesis, copper.