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

The mean critical collapse pressure (p(c)) of gas vesicles in 81 strains of the cyanobacterium Planktothrix rubescens from Lake Zürich, Switzerland, was bimodally distributed between a minimum of 0.86 MPa and a maximum of 1.17 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 strength 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 vesicle 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 investigated, 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 strains, which are narrower and stronger than any previously recorded in freshwater cyanobacteria, have evolved to withstand the high hydrostatic pressures during deep winter mixing in Lake Zürich.