Archaea, Euryarchaeota, Halobacteria, Halobacteriales, Halobacteriaceae
Description and Significance
Salinarchaeum laminariae is a gram-negative halophilic archaea in the shape of pleomorphic rods. It is mesophilic, growing between 20 and 50°C with an optimum growth temperature of 37°C. S. laminariae will lyse in distilled water. A minimum sodium chloride concentration of 8 to 12 % is required to maintain cellular integrity. It will grow in a pH range of 5.5 to 9.5. Optimal growth is achieved with a pH range of 7 to 7.5. This is the model organism for the genus Salinarchaeum.
S. Laminariae was isolated from the brine of the commercially cultivated seaweed, Laminaria japonica. This seaweed is preserved by salting and storage at temperatures below freezing. When returned to room temperatures, the seaweed turns red and begins to rot. Halophiles from the family Halobacteriaceae are noted for forming red pigments. Viable cells from this family have been isolated from salt crystals and successfully cultured. It is suspected that S. Laminariae, along with other members of halobacteriaceae, is causing the spoilage of commercially packaged seaweed after introduction through the salt crystals used in the brining process.
Two strains of Salinarchaeum laminariae, R26T and R22, were reported. Their 16S rRNA sequences were 99.9% similar and their DNA-DNA hybridization value was 89%. Justification for the establishment of the genus Salinarchaeum was provided by analyzing the rpoβ’ gene, which codes for the β subunit of RNA polymerase. Both strains had a rpoβ’ gene length of 1830 base pairs and were 99.5% similar. The G+C content of the strains were 65.8 and 66.4 %mol, respectively.
The genome of S. laminariae is most similar to Natronoarchaeum mannanilyticum, a halophilic archaea isolated from commercial salt crystals made from Japanese seawater. A comparison of their 16S rRNA sequences reveals a 90.2 – 90.6% similarity. Phylogenetic analysis showed that these two organisms form a distinct clade.
Cell Structure, Metabolism and Life Cycle
The cell membrane of S. laminariae contains phosphatidylglycerol (PG) and phosphatidylglycerol phosphate methyl ester (PG-Me), which are common among members of the family Halobacteriaceae (Kamekara 1999). It also contains phosphatidylglycerol sulfate. The membrane has not been found to contain glycolipids. Lipid profiles are one of the key factors used to distinguish genera within halobacteriaceae.
S. laminariae is a heterotrophic obligate aerobe that obtains energy and carbon through the oxidation of sugars. It can also obtain energy, carbon, and nitrogen from the amino acid L-glutamate.
Members of the family Halobacteriaceae regulate osmotic pressure and prevent toxic accumulation of sodium through the use of selective inter-membrane ion pumps. Sodium ions are actively pumped out of cells and potassium and chloride ions are actively recruited into cells (Muller 2003, Oren 2002).
The red color associated with members of halobacteriaceae is a result of membrane bound pigments such a bacteriorhodopsin and carotenoids that are able to capture high energy photons that would otherwise be capable of causing photooxidative damage.
Ecology and Pathogenesis
Halophilic archaea are the dominant microbial population in saline bodies of water like the Dead Sea and the Great Salt Lake. They are also common in evaporative pools along oceanic coast line. The red color associated with these areas is a result of the pigments produced by halobacteriaceae. Food chains in these environments are typically short. For example, the only primary producer in the Dead Sea is an algae, Dunaliella sp. Halophilic archaea are able to utilize a wide range of carbon sources (Oren 1997). The survival strategy of halophilic archea like S. laminariae seems to be the occupation of environments that are otherwise uninhabitable to other organisms.
Heng-Lin C, et al. 2011. Salinarchaeum laminariae gen. nov., sp. nov.: a new member of the family Halobacteriaceae isolated from salted brown alga Laminaria. Extremophiles 15: 625-631.
Kamekara M, Kates M. 1999. Structural diversity of membrane lipids in members of Halobacteriaceae. Biosci. Biotechnol. Biochem. 63(6): 969-972.
Mancinelli R, et al. 2009. Halorubrum chaoviator sp. nov., a haloarchaeon isolated from sea salt in Baja, California, Mexico, Western Australia, and Naxos, Greece. International Journal of Systematic and Evolutionary Microbiology 59: 1908-1913.
Muller V and Oren A. 2003. Metabolism of chloride in halophilic archaea. Extremophiles 7: 261-266
Oren, A. 1994. The ecology of the extremely halophilic archaea. FEMS Microbiology Reviews 13: 415-440.
Oren A, et al. 1997. Proposed minimum standards for description of new taxa in the order Halobacteriales. International Journal of Systematic Bacteriology p.233-238.
Oren A. 2002. Diversity of halophilic organisms: environments, phylogeny, physiology, and applications. Journal of Industrial Microbiology and Biotechnology 28:56-63.
Oren A. 2012. Taxonomy of the family Halobacteriaceae: a paradigm for changing concepts in prokaryote systematics. International Journal of Systematic and Evolutionary Microbiology 62: 263-271.
Shimane Y, et al. 2010. Natronoarchaeum mannanilyticum gen. nov., sp. nov., an aerobic, extremely halophilic archaeon isolated from commercial salt. International Journal of Systematic and Evolutionary Microbiology 60: 2529-2534.
Page authored by Jason Matlock and Tracy Adkins at Michigan State University.