Buoyancy Regulation in a Strain of Microcystis

Abstract

A strain of the gas-vacuolate cyanobacterium Microcystis was found to float in cultures grown at low light intensities and to sink in those grown at high intensities. The loss of buoyancy that occurred within 1 to 5 h on increasing the photon flux density from 10 to 100 pmol m-2 s-' was investigated by centrifuging the cell suspensions in a horizontally placed capillary with a rectangular cross-section, and then separately counting the floating cells under the upper tube surface and sinking cells on the lower surface. Buoyancy loss was not accompanied by loss of gas vesicles, as occurs in some other planktonic cyanobacteria, but was caused by a relative increase in dry matter, principally carbohydrate, without a corresponding increase in gas vesicles. The increase in light intensity gave an increase in cell turgor pressure but this was insufficient to collapse the strong gas vesicles present in this strain, which had a median critical pressure of 0.75 MPa (7.5 bar).

Artificial mixing to control cyanobacterial blooms: a review

“…According to the carbohydrate ballast mechanism, the concentration of carbohydrates in the cells depends on the temporal integration of carbon storage during the day by photosynthesis and by reductions in carbon storage during the night by respiration. This mechanism has been demonstrated in Oscillatoria (Utkilen et al 1985), Microcystis (Kromkamp and Mur 1984; Thomas and Walsby 1985), Aphanizomenon (Konopka et al 1987) and Anabaena . Gas vesicles synthesis is stimulated by low irradiance and allows cyanobacteria a faster return towards illuminated surface layers when water column stability permits this (Deacon and Walsby 1990).…”

“…A large number of papers describe how cyanobacteria genera change their buoyancy in response to light changes in laboratory experiments (Thomas and Walsby 1985;Kromkamp et al 1988) or through the diel cycle of light and dark in field experiments Wallace and Hamilton 1999). All studies consistently report an increase in buoyancy under low light and a decrease under high light.…”

Differences in Responses to Darkness betweenMicrocystis aeruginosaandChlorella pyrenoidosa

“…The strategies of withstanding a dark condition can determine the survival and competitive success of species in an environment frequently exhibiting such conditions (Jochem et al 1999). Since cyanobacteria can competitively exclude eukaryotic phytoplankton and become the dominant species in eutrophic lakes (Reynolds and Walsby 1975, Grilli Caiola and Pellegrini 1984, Thomas and Walsby 1985, Pellegrini et al 1988, Bucka and Wilk-Woznika 1999, an understanding of cyanobacteria and eukaryotic phytoplankton species survival strategies in dark conditions may be valuable.…”

Gas vesicle formation and buoyancy regulation in Pelodictyon phaeoclathratiforme (Green sulfur bacteria)

“…The storage polysaccharides formed during photosynthesis are metabolized again during the stationary phase thus leading to a decrease in cell density. This very closely resembles the situation in cyanobacteria where this mechanism is especially important in those species which, similarly to Pelodictyon phaeoclathratiforme, possess gas vesicles too strong to be collapsed by turgot pressure (e. g. Microcystis aeruginosa, and a redcolored Oscillatoria agardhii strain) (Kromkamp and Mur 1984;Thomas and Walsby 1985;Utkilen et al 1985).…”