Direct evidence for the role of light‐mediated gas vesicle collapse in the buoyancy regulation of Anabaena flos‐aquae (cyanobacteria)1

Abstract

Quantitative measurements were made of the changes in gas vacuole volume and the major components of cell mass (protein and carbohydrate) on cultures of Anabaenaflos-aquae which lost buoyancy as they were shifted from low to high light intensity. Assuming densities of 1,300 kg. rn-' for protein and 1,600 for carbohydrate, we calculated the change in ballast brought about by changes in these components and compared them with ballast changes resulting from gas vacuole collapse. We also compared the calculated excess density of filaments with direct measurements of filament density in gradients of Percoll. The results clearly demonstrated that increased density resulted from the loss of gas vacuoles. Small variations in density could be attributed to changes in protein and carbohydrate but these would not have caused a loss of buoyancy in the absence of a decrease in gas vacuole content. Analyses of the type described can be used to determine the cause of buoyancy change in other microorganisms and can be performed onOphytoplankton collected from lakes.

Numerical simulation of the vertical migration of Microcystis (cyanobacteria) colonies based on turbulence drag

“…Microcystis colonies achieved vertical migration with the help of buoyancy regulating system of gas vesicles and ballast (e.g., carbohydrate) (Oliver and Walsby, 1984;Kromkamp et al, 1984). These mechanisms were well described by Walsby (1994) that Microcystis colonies always rise during night due to synthesis of gas vesicles and carbohydrate utilization.…”

The effect of variations in irradiance on buoyancy regulation in Microcystis aeruginosa

“…Measurements-Cells were pressurized (1.5 MPa) to collapse the gas vesicles, and their density was measured using Percoll density gradients (Oliver et al 1981). The Percoll gradients were osmotically adjusted to the density of the lake water (Kromkamp and Mur 1984).…”

“…The existence of cyanobacteria that can regulate their buoyancy has been well documented (Walsby 1969a(Walsby , 1970Oliver and Walsby 1984;Utkilen et al 1985; Thomas and Walsby 1986;Kromkamp et al 1986; Humphries and Lyne 1988;Zohary and Robarts 1989;Kromkamp and Walsby 1990;Ibelings et al 1991;Walsby et al 1991). This characteristic is considered to be important in contributing to the success of cyanobacteria in a wide range of aquatic ecosystems (Reynolds and Walsby 1975;Reynolds , 1987Reynolds et al 1987) because it provides the advantage of being able to alter position in the water column through physiological changes.…”

Cyanobacterial dominance: The role of buoyancy regulation in dynamic lake environments

“…There is now abundant evidence (Oliver & Walsby 1984;Utkilen, Oliver & Walsby 1985) to show that overall unit density is sufficiently sensitive to short-term fluctuation in the ballast content and gas-filled space to bring about rapid (in the order of 0.5-5 hours) reversals in density, from p' > p to p' < p. The presence of a mucilaginous sheath damps the impact of changes in individual cell density but its volume contributes to an enhanced value of r (Walsby & Reynolds 1980). In this way, a small change in cell density may be translated into a considerable change in buoyancy (positive or negative w s ).…”

“…1. and, in Microcystis, to extracellular mucilage (stipple), and of the "negative ballast" contributed by gas vesicle space (open figures) in selected cyanobacteria, as grown under "low" light (15 umol m" 2 s" 1 ) intensity and 7-24 hours after transfer to "high" light (>50 umol m~2 s~')-Original data from Oliver & Walsby (1984), Utkilen et al (1985a), and ; redrawn from Reynolds (1987b: fig. 3 and 6).…”