Abstract
The effects of temperature and light intensity on Microcystis aeruginosa PCC 7806 growth and mcyB transcripts (as a function of microcystin biosynthesis) were investigated at the logarithmic and stationary growth phases. The expression of the mcyB gene-one of the microcystin biosynthetic genes-under different treatments was quantified using real-time PCR. The results showed that cell number increased at 25 degrees C with all light treatments. A significant positive correlation (P=0.060) between mcyB transcripts and cell number was found, indicating the presence of coupling between toxin biosynthesis and growth. The results also revealed that both temperature and growth phase were significantly correlated with the number of mcyB transcripts (P=0.005 and 0.036, respectively), with at least 67% of the variation attributable to these two factors alone. On the other hand, the effect of the range of light intensities tested was overly non-significant. Application of high light intensity, above saturation point for a prolonged period, was inhibitory to transcription of the mcyB gene. Maximum mcyB transcript number was attained during stationary phase of a Microcystis culture grown at 25 degrees C under medium light intensity. The high level of mcyB transcription during stationary phase indicates an increase in the biosynthesis of microcystin. This possibly indicates the role of the toxin as an alarming chemical that cells would release upon lysis/death.