Consequences of impaired microcystin production for light-dependent growth and pigmentation of Microcystis aeruginosa PCC 7806

Abstract

Microcystis aeruginosa PCC 7806 produces potent inhibitors of eukaryotic protein phosphatases called microcystins, whose function to the organism is presently unknown. Mutants with impaired microcystin biosynthesis should provide a useful tool for investigations of microcystin function. This study has focussed on the comparison of growth and pigment content of strain PCC 7806 and its mcyB 3 mutant deficient in microcystin biosynthesis, under semicontinuous culture conditions. Both wild-type and mutant are characterised by a very low light demand and low-maximum specific growth rates in comparison to other Microcystis strains studied. While growth of wild-type and mutant were similar under different light conditions, the mutant cells showed significantly higher specific absorbances in the range of photosynthetic active radiance 420^700 nm, under light-limiting conditions. The mutant cells possess lower contents of chlorophyll a, L-carotene, zeaxanthin and echinenone under light limitation and of myxoxanthophyll under saturated light conditions. Though microcystins are clearly not essential for growth, the observed effects of the mutation are a first indication of their involvement in intracellular processes. ß

An active photosynthetic electron transfer chain required for mcyD transcription and microcystin synthesis in Microcystis aeruginosa PCC7806

“…The data also showed that mcyD transcripts initially increased when cells were transferred from 16 to 400 lmol photons m -2 s -1 (from low light to very high light) but decreased after 2 h (Kaebernick et al 2000). M. aeruginosa PCC7806 is a strain very sensitive to light, with saturating light intensities of about 32 lmol photons m -2 s -1 (Hesse et al 2006). Our study, using real time RT-PCR, shows that the increase not only occurs in light-saturating conditions, but mainly on transits to non saturating light conditions, 28 mol photons m -2 s -1 .…”

Effects of nutrient and light availability on production of bioactive anabaenopeptins and microviridin by the cyanobacterium Planktothrix agardhii

“…Different types of oligopeptides may therefore well be able to replace each other indicating a linked function. This may also be an explanation for the observation that the knock-out of individual oligopeptides has no obvious consequence for the growth of cyanobacteria (Hesse et al, 2001;Repka et al, 2004).…”

Investigating factors affecting growth and cellular mcyB transcripts of Microcystis aeruginosa PCC 7806 using real-time PCR

“…Similarly, Wiedner et al (2003) reported that intracellular microcystin content showed a significant linear positive correlation with growth rate under PAR (photosynthetically active radiation)-limited growth conditions but not under PAR-saturated growth conditions. It is worthy mentioning that the light saturation point for M. aeruginosa PCC 7806 is 32 µmol photon m −2 s −1 (Hesse et al 2001), which implies that, beyond this point, microcystin does not increase in concentration with the increase in light (Wiedner et al 2003). High light intensities may also stimulate passive release of microcystin from lysed cells, and its active export from living Microcystis cells (Schatz .…”