The Function of Gas Vesicles in Halophilic Archaea and Bacteria: Theories and Experimental Evidence

Abstract

A few extremely halophilic Archaea (Halobacterium salinarum, Haloquadratum walsbyi, Haloferax mediterranei, Halorubrum vacuolatum, Halogeometricum borinquense, Haloplanus spp.) possess gas vesicles that bestow buoyancy on the cells. Gas vesicles are also produced by the anaerobic endospore-forming halophilic Bacteria Sporohalobacter lortetii and Orenia sivashensis. We have extensive information on the properties of gas vesicles in Hbt. salinarum and Hfx. mediterranei and the regulation of their formation. Different functions were suggested for gas vesicle synthesis: buoying cells towards oxygen-rich surface layers in hypersaline water bodies to prevent oxygen limitation, reaching higher light intensities for the light-driven proton pump bacteriorhodopsin, positioning the cells optimally for light absorption, light shielding, reducing the cytoplasmic volume leading to a higher surface-area-to-volume ratio (for the Archaea) and dispersal of endospores (for the anaerobic spore-forming Bacteria). Except for Hqr. walsbyi which abounds in saltern crystallizer brines, gas-vacuolate halophiles are not among the dominant life forms in hypersaline environments. There only has been little research on gas vesicles in natural communities of halophilic microorganisms, and the few existing studies failed to provide clear evidence for their possible function. This paper summarizes the current status of the different theories why gas vesicles may provide a selective advantage to some halophilic microorganisms.

In vivo synthesis of selenium nanoparticles by Halococcus salifodinae BK18 and their anti‐proliferative properties against HeLa cell line

“…Halophilic Archaea (haloarchaea) are extremophilic salt loving organisms with a total of 36 genera and 129 species identified till date . These organisms have an absolute requirement of high concentrations of salt (35–40% NaCl).…”

“…Halophilic Archaea (haloarchaea) are extremophilic salt loving organisms with a total of 36 genera and 129 species identified till date. 20 These organisms have an absolute requirement of high concentrations of salt (35-40% NaCl). They maintain their osmolarity by intracellular accumulation of KCl (up to 5M) that counteracts the ionic strength of the extracellular environment.…”

Anaerobic Metabolism in Haloferax Genus

“…Related to this aspect, it is interesting to highlight that a few representative species of the Haloferax genus are able to float to the air-water interface thanks to the production of gas vesicles (Oren, 2002;Oren, 2012). Gas vesicles increase the buoyancy of cells and allow them to migrate vertically in the water body from low oxygen conditions to regions with optimal conditions to sustain microaerobic or aerobic growth (Pfeifer, 2015).…”

Therapeutic bacteria to combat cancer; current advances, challenges, and opportunities

“…They observed that this construct led to primary tumor regression (>60%) and reduced metastases (>90%) . Some bacteria ( Haloarchaea ) that produce gas vesicles (~width of 45‐250 nm and length of 100‐600 nm) have been examined as theranostic agents . Recently, Shapiro et al described a novel diagnostic strategy using gas vesicles (harvested from Anabaena flosaquae and Halobacterium NRC‐1) as ultrasound contrast agents for molecular imaging in mice.…”