Gas Vacuole Genes in Halobacteria

Abstract

As previously shown by us there are two, highly homologous genes in Halobacterium halobium encoding gas vacuole proteins (GVP). These genes are located on the plasmid pHH1 (gene for GVP-A) and on the chromosome (gene for GVP-B). Recently we found that copies of both genes are also located on “minor circular DNA” (MCD), a heterogeneous collection of extrachromosomal DNA molecules which occur in very low concentrations in H. halobium. The origin of MCD is discussed using the gvp genes as markers.

In cyanobacteria there is an additional protein (GVP-c) involved in the formation of gas vesicles. Using a 25mer oligonucleotide deduced from a conserved region of the cyanobacterial gvpC gene, we could show hybridization to chromosomal DNA from H. halobium. Other halobacterial strains, natural isolates, rod shaped and purple membrane forming but not closely related to H. halobium also synthesize gas vacuoles. Examination of the strain Halobacterium sp. GRA revealed the presence of the H. halobium gvpB type gene and the gvpC gene in the chromosomal DNA and in the 160 kbp MCD. These genes were cloned from the plasmid DNA and sequenced. gvpB from GRA was shown to be almost identical to gvpB in H. halohium. For the gvpC gene our sequence data from both strains indicate that this gene is located at the same distance downstream from gvpB, the sequence between the two genes being identical.