Salinibacter, the Red Bacterial Extreme Halophile

Abstract

The genus Salinibacter (family Salinibacteraceae, order Rhodothermales, class Rhodothermia, phylum Rhodothermaeota) consist of extremely halophilic, red‐orange pigmented aerobic bacteria. Currently (July 2019), the genus consists of two species. Existence of extremely halophilic members of the Bacteria was first documented in 1999 based on cultivation‐independent studies of saltern crystallizer brines. Salinibacter shares many features with the Archaea (class Halobacteria) that live in the same habitat: it uses KCl for osmotic adaptation, has a very acidic proteome, and possesses different retinal pigments including a light‐driven proton pump (xanthorhodopsin) and a putative chloride pump. Its carotenoid pigment named salinixanthin acts as a light antenna and transfers energy to the retinal group of xanthorhodopsin. An unusual type of sulfonolipid is present in the cell membrane. Salinibacter is an excellent model organism for the study of biogeography, ecology, and evolution of bacteria adapted to life at high salt concentrations.

Key Concepts

  • Salinibacter is a genus of bacteria found worldwide in hypersaline environments such as salt lakes and solar salterns.
  • Salinibacter is one of the most halophilic microorganisms known.
  • Salinibacter coexists in its natural environment with halophilic Archaea of the class Halobacteria.
  • Salinibacter is pigmented red‐orange by the carotenoid salinixanthin and the retinal protein xanthorhodopsin.
  • Salinixanthin acts as an antenna pigment for xanthorhodopsin which serves as a light‐driven proton pump.
  • Salinibacter contains unique sulfonolipids that resemble capnine lipids found in a few other members of the Bacteroidetes phylum and also in diatoms.
  • Comparative biogeographic studies including cultivation‐dependent approaches, metagenomics and metabolomics have shown that Salinibacter populations worldwide show considerable variation.

Keywords: Salinibacter; Bacteroidetes; halophiles; salterns; hypersaline environments; xanthorhodopsin; sulfonolipids; salinixanthin

Figure 1. Phase‐contrast micrograph of Salinibacter ruber strain M31T. Bar, 5 μm. Antón et al. . Reproduced with permission of Microbiology Society.
Figure 2. Scanning electron micrograph of Salinibacter ruber strain M31T. Bar, 2.5 μm. Antón et al. . Reproduced with permission of Microbiology Society.
Figure 3. The structure of salinixanthin, the C40‐carotenoid acyl glycoside pigment of Salinibacter ruber. Oren . Reproduced with permission of Oxford University Press.
Figure 4. The structure of the unusual membrane sulfonolipid ('halocapnine') of Salinibacter ruber. Oren . Reproduced with permission of Oxford University Press.
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Further Reading

Antón J, Peña A, Valens M, et al. (2005) Salinibacter ruber: genomics and biogeography. In: Gunde‐Cimerman N, Oren A and Plemenitaš A (eds) Adaptation to Life at High Salt Concentrations in Archaea, Bacteria, and Eukarya, pp 257–266. Kluwer Academic Publishers: Dordrecht, The Netherlands.

Antón J, Peña A, Santos F, et al. (2008) Distribution, abundance and diversity of the extremely halophilic bacterium Salinibacter ruber. Saline Systems 4: 15.

Antón J, Amann R and Rosselló‐Mora R (2011) Salinibacter Antón, Oren, Benlloch, Rodríguez‐Valera, Amann and Rosselló‐Mora 2002, 490VP. In: Whitman WB (ed.) Bergey's Manual of Systematics of Archaea and Bacteria. John Wiley & Sons, Inc., in association with Bergey's Manual Trust.

Lanyi JK and Balashov SP (2011) Xanthorhodopsin. In: Ventosa A, Oren A and Ma Y (eds) Halophiles and Hypersaline Environments, pp 319–340. Berlin: Springer‐Verlag.

Oren A, Rodríguez‐Valera F, Antón J, et al. (2004) Red, extremely halophilic, but not archaeal: the physiology and ecology of Salinibacter ruber, a bacterium isolated from saltern crystallizer ponds. In: Ventosa A (ed.) Halophilic Microorganisms, pp 63–76. Springer‐Verlag: Berlin.

Oren A (2006) The genera Rhodothermus, Thermonema, Hymenobacter and Salinibacter. In: Dworkin M, Falkow S, Rosenberg E, et al. (eds) The Prokaryotes. A Handbook on the Biology of Bacteria: Ecophysiology and Biochemistry, vol. 7, pp 712–740. Springer: New York.

Peña A, Teeling H, Huerta‐Cepas J, et al. (2011) From genomics to microevolution and ecology: the case of Salinibacter ruber. In: Ventosa A, Oren A and Ma Y (eds) Halophiles and Hypersaline Environments, pp 109–122. Springer‐Verlag: Berlin.

Peña A, Gomariz M, Lucio M, et al. (2014) Salinibacter ruber: the never ending microdiversity? In: Papke RT and Oren A (eds) Halophiles: Genetics and Genomics, pp 37–56. Caister Academic Press: Norfolk, UK.

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Oren, Aharon(Nov 2019) Salinibacter, the Red Bacterial Extreme Halophile. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0028925]