Halobacterium noricense is a halophilic, rod-shaped microorganism that thrives in environments with salt levels near saturation. Despite the implication of the name, Halobacterium is actually a genus of archaea, not bacteria. H. noricense can be isolated from environments with high salinity such as the Dead Sea and the Great Salt Lake in Utah. Members of the Halobacterium genus are excellent model organisms for DNA replication and transcription due to the stability of their proteins and polymerases when exposed to high temperatures. To be classified in the genus Halobacterium, a microorganism must exhibit a membrane composition consisting of ether-linked phosphoglycerides and glycolipids.
Scientific classification This organism is a member of the genus Halobacterium and its taxonomic classification is as follows: Archaea, Euryarchaeota, Euryarchaeota, Halobacteria, Halobacteriales, Halobacteriaceae, Halobacterium, Halobacterium noricense. There are currently 19 known halophilic archaeal genera and 57 known species within the genus Halobacterium.
Relatives Three reported strains Halobacterium salinarium NRC-1, Halobacterium sp. DL1, and Halobacterium salinarium R1 were compared to Halobacterium noricense strain CBA1132. The phylogenetic trees based on Multi-Locus Sequence Typing (MLST) and Average Nucleotide Identity (ANI) indicated that strain CBA1132 and strain DL1 are closely related while strains NRC-1 and R1 are closely related. Multi-Locus Sequence Typing is a technique that uses genomic information to establish evolutionary relationships between bacterial taxa. Average Nucleotide Identity is a genetic method used to compare the similarity between nucleotides of two strains based on the coding regions of their genomes, which has allowed scientists to veer away from traditional methods of classifying prokaryotes based on phenotypic similarities. The defining characteristic between strains CBA1132 and DL1 is that they both contain high GC content in their chromosomes, providing stability in a harsh environment. Other close relatives of H. noricense within the genus Halobacterium include Halobacterium denitrificans, Halobacterium halobium, and Halobacterium volcanii.
Morphology Halobacterium noricense is known to be free living, and it typically appears as red or pink colonies due to the presence of carotenoids and bacterioruberin in their membranes. The carotenoids have the ability to absorb light between the wavelengths of 330-600 nm, as determined by light spectroscopy. Typical colony morphology is round with a diameter of 0.4 mm. Under the microscope, they can typically be measured at around 5 μm and appear gram-negative and rod-shaped. H. noricense does not contain the gas vesicles that are present in their close relative, Halobacterium salinarium, which often appear as floating cultures. Halobacterium noricense may occasionally appear as coccus-shaped when grown in liquid broth rather than on solid media.
Discovery
Etymology Halobacterium noricense is named after Noricum, Austria, which is the location of the salt deposit in which the organism was isolated. The archaeon was discovered in 2004 by a group of scientists led by Claudia Gruber. The group isolated two strains of H. noricense, along with other Halobacterium species including H. salinarium.
Sources The first two strains (A1 and A2) of Halobacterium noricense were isolated from samples taken out of a salt deposit in Austria. The salt deposit was approximately 400 meters below the surface and is believed to have been formed during the Permian period. To obtain the samples, the researchers used a pre-existing mine to travel below the Earth's surface. They used a core drill to remove cylindrical sections of the salt deposit, which were then taken for sequencing. The deposit retained high salt levels over approximately 250 million years due to the surrounding clay and limestone. These conditions do not allow the salt to escape, which formed an ideal environment for halophilic archaea.
Media Halobacterium noricense was isolated on ATCC 2185 medium with 250.0 grams of NaCl, 20.0 grams of MgSO4 7H2O, 2.0 grams of KCl, 3.0 grams of yeast extract, 5.0 grams of tryptone, and other compounds required for the isolate's growth. After an incubation period of approximately 2 weeks, red circular colonies appeared. This is the characteristic colony morphology of H. noricense.
Growth Conditions Halobacterium noricense is known to be a mesophile, where optimum growth temperature is approximately 37 °C with an incubation period of 18 days. It thrives in acidic conditions at pH 5.2-7.0. NaCl concentration between 15-17% has resulted in the highest growth rates in previous studies. It has been found that Halobacterium can survive in high metal concentrations because they are extremely halophilic. This can be achieved through metal resistance, which indicates that the H. noricense strain CBA1132 might also be able to survive in these high metal ion concentrations.
Genome H. noricense strains A1 and A2 from Gruber et al. had 97.1% similarity to genus Halobacterium through their 16S rDNA sequences. H. noricense genome, strain CBA1132, composed of four contigs containing 3,012,807 base pairs, approximately 3,084 gene coding sequences, and 2,536 genes. It has a GC content of approximately 65.95%, and 687 of the genes in the H. noricense genome have unknown functions. Metabolism and amino acid transport-related genes make up the largest group of known genes. This group contains 213 known genes. The genus Halobacterium is currently known as monophyletic because their 16S rRNA have less than 80% similarity with their closest relatives, the methanogens.
Sequencing According to Joint Genome Institute, another complete genome analysis of Halobacterium (strain DL1) species was sequenced using 454 GS FLX, Illumina GAIIx. Halobacterium noricense (strain CBA1132) was recently isolated from solar salt and a complete genomic analysis was performed by researchers from Korea in 2016. The researchers extracted the DNA using a QuickGene DNA tissue kit, which uses a membrane with extremely fine pores to collect DNA and nucleic acids. They purified the DNA using the MG Genomic DNA purification kit. Once extracted and purified, the strategy for sequencing the genome was Whole Genome Sequencing by the method of a PacBio RS II system. Lastly, the genome was analyzed and performed by the Rapid Annotation using Subsystem Technology (RAST) server.
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