Bacteriorhodopsin and the purple membrane of halobacteria

A fellow of my acquaintance, on seeing a colleague drink undiluted water (55.5 molal), has been known to comment in disapproval that water at such a concentration should not be used for that purpose and that its main function is for putting around the outside of boats. He conceded that dilution with a little salt is acceptable for boats but for no other purpose. The proponent of this philosophy is not a biologist and it is unlikely that many biologists would accept his generalization without some qualification. Nevertheless, it is a point of view. Another point of view with which all biologists might not agree, at least initially, is one which I wish to advance in this review. It is that, notwithstanding the indispensability of water in living systems and the unique properties of solvent water, quantitative variations in the amount of water available are of less direct microbiological significance than is generally conceded.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1991&context=smhpapers

Microbial water stress.

The genome of the halophilic archaeon Halobacterium sp. NRC-1 and predicted proteome have been analyzed by computational methods and reveal characteristics relevant to life in an extreme environment distinguished by hypersalinity and high solar radiation: (1) The proteome is highly acidic, with a median pI of 4.9 and mostly lacking basic proteins. This characteristic correlates with high surface negative charge, determined through homology modeling, as the major adaptive mechanism of halophilic proteins to function in nearly saturating salinity. (2) Codon usage displays the expected GC bias in the wobble position and is consistent with a highly acidic proteome. (3) Distinct genomic domains of NRC-1 with bacterial character are apparent by whole proteome BLAST analysis, including two gene clusters coding for a bacterial-type aerobic respiratory chain. This result indicates that the capacity of halophiles for aerobic respiration may have been acquired through lateral gene transfer. (4) Two regions of the large chromosome were found with relatively lower GC composition and overrepresentation of IS elements, similar to the minichromosomes. These IS-element-rich regions of the genome may serve to exchange DNA between the three replicons and promote genome evolution. (5) GC-skew analysis showed evidence for the existence of two replication origins in the large chromosome. This finding and the occurrence of multiple chromosomes indicate a dynamic genome organization with eukaryotic character.

/pdf/understanding-the-adaptation-of-halobacterium-species-nrc-1-55nja906b2.pdf

Understanding the Adaptation of Halobacterium Species NRC-1 to Its Extreme Environment through Computational Analysis of Its Genome Sequence

Despite the obvious ubiquity, ecological importance and limnological interest of temporary waters, most limnological texts have little to say about them. Dussart (1966), Schwoerbel (1974), Golterman (1975), Moss (1980), Goldman & Horne (1983), and Wetzel (1983), to mention just a few recent and otherwise comprehensive texts of North American or European provenance, make scant if any reference. Cole’s (1983) text does better, but only those authors who live in or have lived in tropical or arid countries make extensive reference (e.g. Bayly & Williams, 1973; Beadle, 1981). Temporary waters are especially widespread in arid and semi-arid regions. Even the most cursory glance at maps of world climate will indicate the vast extent of these regions in Africa, Australia, the Middle East and Central Asia, parts of South America, and in W. North America. The paucity of permanent waters in arid and semi-arid regions means, of course, that temporary waters have an ecological significance much greater there than in more temperate regions. For example, throughout most of continental Australia, waterfowl are closely dependent for survival on the occurrence of temporary water-bodies (Frith, 1967). The limnological interest of temporary waters relates above all to the nature of the ecological stresses that assail their biota, and the nature of corresponding adaptation.

Biotic adaptations in temporary lentic waters, with special reference to those in semi-arid and arid regions

Halobacterium salinarium, a member of the extremely halophilic archaebacteria, contains a C50-carotenoid namely bacterioruberin. We have previously reported the high resistance of this organism against the lethal actions of DNA-damaging agents including ionizing radiation and ultraviolet light (UV). In this study, we have examined whether bacterioruberin and the highly concentrated salts in this bacterium play protective roles against the lethal actions of ionizing radiation, UV, hydrogen peroxide, and mitomycin-C (MMC). The colourless mutant of H. salinarium deficient in bacterioruberin was more sensitive than the red-pigmented wild-type to all tested DNA-damaging agents except MMC. Circular dichroism (CD) spectra of H. salinarium chromosomal DNA at various concentrations of KCl (0-3.5 M) were similar to that of B-DNA, indicating that no conformational changes occurred as a result of high salt concentrations. However, DNA strand-breaks induced by ionizing radiation were significantly reduced by the presence of either bacterioruberin or concentrated KCl, presumably due to scavenging of free radicals. These results suggest that bacterioruberin and intracellular KCl of H. salinarium protect this organism against the lethal effects of oxidative DNA-damaging agents.

Protective Roles of Bacterioruberin and Intracellular KCl in the Resistance of Halobacterium salinarium against DNA-damaging Agents

Extremely halophilic bacteria are able to survive in a natural environment exposed to high doses of ultraviolet irradiation. One such organism, Halobacterium cutirubrum, has been characterized to p...

M. A. Hescox

Papers

Photoreactivation in Halobacterium cutirubrum