Spontaneous mutations in gas vesicle genes ofPlanktothrixspp. affect gas vesicle production and critical pressure

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Abstract
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, ΩC. Spontaneous non-buoyant mutants had lost some of the alternating gvpAC copies and their gvpC genes had a novel 3′-end sequence, ΨC; additional gvpC genes terminating in this sequence were also found in the wild-type and representatives of other GV genotypes. Alleles of gvpC terminating in ΨC occurred only at the downstream ends of the gvpAC clusters investigated; all other gvpC s terminated in ΩC. Mutants of strains with the GV3 genotype produced only 30–50% of the gas vesicles present in the wild-type; their gas vesicles had lower mean critical pressures (0.70–0.78 MPa) than those in the wild-type (1.05–1.10 MPa).