Relative Effects of Varying Light Conditions on the Growth of Toxic and Non-Toxic Strains of <i>Microcystis aeruginosa</i>

Abstract

Harmful algae bloom constitutes a major problem facing water bodies particularly fresh and marine water system. Microcystis aeruginosa represents a major causative organism found in the water. Light plays a major role in the growth and variation of M. aeruginosa in water. What is still inadequate, is the data on the effects of different light conditions on the growth of Microcystis aeruginosa. In this study, two strains of Microcystis aeruginosa PCC 7806 (toxic strain) and PCC 7005 (non-toxic strain) were exposed to varying light intensities at 0, 30, 60, 120, 300, 350 µMol photon m −2 •S −1 to measure their growth and pigmentation. This study observed similarities in growth and pigmentation between toxic strain (PCC 7806) and non-toxic (PCC 7005) strain. Also, at short exposure to light, Toxic strain was seen to be better tolerant of light than non-toxic strain, with non-toxic strain showing better ability to recover from light stress after twenty days of culture. These findings suggest that Toxic strain (PCC 7806) and Non-toxic strain (PCC 7005) of M. aeruginosa respond similarly with respect to growth but differ in their light retention capacity over time and this could be useful in predicting the possible conditions of algal bloom.

Effects of Varying Temperature on the Growth Rate of Toxic and Non-Toxic Strains of <i>Microcystis aeruginosa</i>

“…The growth rate indicated that toxic strain (PCC 7806) shows growth at both 5˚C and 10˚C but the growth was seen to be slow compare to the Non-toxic strain (PCC 7005) where growth was a little faster, this growth response could be due to differences in their photosynthetic and respiratory abilities. Optimum growth for both strains was seen at 22˚C as seen in Figure 1(a) and Figure 1(b), this is also in line with the results obtained for chlorophyll a content and carotenoids contents below, which are photosynthetic pigments supporting growth, this agrees with the work described by [24] in his study on the interdependence between light and the growth of Microcystis aeruginosa (РСС 7806).…”

“…Chlorophyll a content was determined with the absorbance value from the UV-spectrophotometer. Carotenoid concentrations were estimated using the same extract but with absorbance measured at 480 nm [24].…”

“…Cells in major quadrants were counted under the microscope and the cell numbers from 4 major quadrants was averaged. The cell number per ml was calculated applying the formula [24].…”