Eight of fourteen gyp genes are sufficient for formation of gas vesicles in halophilic archaea

Abstract

The minimal number of genes required for the formation of gas vesicles in halophilic archaea has been determined. Single genes of the 14 gyp genes present in the p-vac region on plasmid pHH1 of Halobacterium salinarum (p-gvpACNO and p-gvpDEFGHIJKLM) were deleted, and the remaining genes were tested for the formation of gas vesicles in Haloferax volcanii transformants. The deletion of six gyp genes (p-gvpCN, p-gvpDE, and p-gvpHI) still enabled the production of gas vesicles in H. volcanii. The gas vesicles formed in some of these gyp gene deletion transformants were altered in shape (ΔI, ΔC) or strength (ΔH) but still functioned as flotation devices. A minimal p-vac region (minvac) containing the eight remaining genes (gvpFGJKLM-gvpAO) was constructed and tested for gas vesicle formation in H. volcanii. The minvac transformants did not form gas vesicles; however, minvac/gvpJKLM double transformants contained gas vesicles seen as light refractile bodies by phase-contrast microscopy. Transcript analyses demonstrated that minvac transformants synthesized regular amounts of gvpA mRNA, but the transcripts derived from gvpFGJKLM were mainly short and encompassed only gvpFG(J), suggesting that the gvpJKLM genes were not sufficiently expressed. Since gvpAO and gvpFGJKLM are the only gyp genes present in minvac/JKLM transformants containing gas vesicles, these gvp genes represent the minimal set required for gas vesicle formation in halophilic archaea. Homologs of six of these gyp genes are found inAnabaenaflos-aquae, and homologs of all eight minimal halobacterial gyp genes are present in Bacillus megaterium and in the genome of Streptomyces coelicolor.