The relationship between critical pressure and width of gas vesicles in isolates of Planktothrix rubescens from Lake Zurich

The mean critical collapse pressure (p(c)) of gas vesicles in 81 strains of the cyanobacterium Planktothrix rubescens from Lake Zurich, Switzerland, w as bimodally distributed between a minimum of 0.86 MPa and a maximum of 1.1 7 MPa. Measurements were made of the cylinder diameter (d) of gas vesicles isolated from seven of the strains. The mean diameter, which varied from 48 to 61 nm, was inversely related to p(c), in keeping with the theory of str ength of thin-walled rigid cylinders. These measurements extended the range of p(c)-width relationship of gas vesicles, which can be described by the expression p(c) = 461(d/nm)(-1.53) MPa, p(c) was correlated with gas vesicl e genotype (see the accompanying paper by S. J. Beard, B. A. Handley, P. K. Hayes & A. E. Walsby, Microbiology 145, 2757-2768): of the 81 strains inve stigated, all those with the gas vesicle genotype GV2 produced gas vesicles with a mean p(c) of less than 1.0 MPa, whereas those of GV3 had a mean p(c ) of greater than 1.0 MPa. It is suggested that gas vesicles of the GV3 str ains, which are narrower and stronger than any previously recorded in fresh water cyanobacteria, have evolved to withstand the high hydrostatic pressur es during deep winter mixing in Lake Zurich.