Spontaneous mutations in gas vesicle genes of Planktothrix spp. affect gas vesicle production and critical pressure.

Wild-type strains of the cyanobacterium Planktothrix rubescens have a cluster of gas vesicle (gvp) genes with repeats of alternating gvpA and gvpC. The gvpC occurs in three length variants, all with the same 3'-sequence, OmegaC. Spontaneous non-buoyant mutants had lost some of the alternating gvpAC copies and their gvpC genes had a novel 3'-end sequence, PsiC; additional gvpC genes terminating in this sequence were also found in the wild-type and representatives of other GV genotypes.

The sequence of the major gas vesicle protein, GvpA, influences the width and strength of halobacterial gas vesicles.

Transformation experiments with Haloferax volcanii show that the amino acid sequence of the gas vesicle protein GvpA influences the morphology and strength of gas vesicles produced by halophilic archaea. A modified expression vector containing p-gvpA was used to complement a Vac(-) strain of Hfx. volcanii that harboured the entire p-vac region (from Halobacterium salinarum PHH1) except for p-gvpA.

Growth competition between strain PHH1 and mutants affected in gas vesicle synthesis.

To investigate the role of the buoyancy provided by gas vesicles in the facultative anaerobe PHH1, the growth of a gas-vacuolate (Gv) strain in competition with two gas-vesicle-defective (Gv) mutants was examined. The Gv strain synthesized gas vesicles throughout its growth cycle, and floated up to form a thick surface scum during the exponential growth phase in static culture. Mutant Gv produced significantly fewer gas vesicles than the Gv strain in corresponding stages of growth, although in late stationary phase a small proportion of cells floated up to the surface of static cultures.