Gas vesicle formation in halophilic Archaea
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© Springer-Verlag 1997
MINI-REVIEW
Felicitas Pfeifer · Kerstin Krüger · Richard Röder · Andrea Mayr · Sonia Ziesche · Sonja Offner
Gas vesicle formation in halophilic Archaea
Received: 13 November 1996 / Accepted: 17 January 1997
Abstract Gas vesicles are intracellular, microbial flotation devices that consist of mainly one protein, GvpA. The formation of halobacterial gas vesicles occurs along a complex pathway involving 14 different gvp genes that are clustered in a genomic region termed the “vac region”. Various vac regions found in Halobacterium salinarum (p-vac and c-vac), Haloferax mediterranei (mc-vac), and Natronobacterium vacuolatum (nv-vac) have been investigated. Except for the latter vac region, the arrangement of the gvp genes is identical. Single gvp genes have been mutated to study the effect on gas vesicle synthesis in transformants and to determine their possible function. Each vac region exhibits a characteristic transcription pattern, and regulatory steps have been observed at the DNA, RNA, and protein level, indicating a complex regulatory network acting during gas vesicle gene expression. Key words Halobacterium · Haloferax · Natronobacterium · gvp Gene regulation · Antisense RNA · Transcriptional activation · Archaeal promoter · Gas vesicle formation Abbreviations gvpX Gene encoding gas vesicle protein X · Vac Gas vesicle phenotype · GvpX Gas vesicle protein X
Introduction Many aquatic bacteria and archaea produce gas vesicles that provide buoyancy to the cell and promote flotation to the surface of the watery environment, where the presence of oxygen and light is favorable for the growth of these
F. Pfeifer (Y) · K. Krüger · R. Röder · A. Mayr · S. Ziesche · S. Offner Institut für Mikrobiologie und Genetik, Technische Hochschule Darmstadt, Schnittspahnstrasse 10, D-64287 Darmstadt, Germany Tel. +49-6151-162957; Fax +49-6151-162956 e-mail: [email protected]
cells. Cyanobacteria and Halobacterium salinarum (formerly H. salinarium or H. halobium; Ventosa and Oren 1996) use light as an energy source and also depend on the availability of oxygen for respiration. Another possible function of gas vesicles could be the reduction of the cytoplasmic volume leading to a higher surface-area-tovolume ratio. The resulting shorter diffusion times may be important for organisms growing at low temperatures, and the high number of gas-vesiculate bacteria found in the sea ice of Antarctica supports such a conclusion (Staley et al. 1989). Gas vesicles are easily detectable by phase-contrast microscopy as light refractile bodies inside the cell. Isolated gas vesicles usually have a cylindrical structure covered by two conical end caps; only in the case of H. salinarum wild-type is the majority of the gas vesicles spindle-shaped (Stoeckenius and Kunau 1968; Cohen-Bazire et al. 1969). In halobacteria, the size of the cylindershaped gas vesicles varies from 0.6 µm to 1.5 µm in length, and the diameter of their cylindrical section is approximately 200 nm. The diameter of cyanobacterial gas vesicl
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