Genus Halorubrum Research Articles

Halorubrum tebenquichense sp. nov., a novel halophilic archaeon isolated from the Atacama Saltern, Chile.

A novel extremely halophilic archaeon was isolated from Lake Tebenquiche, situated in the northern part of the Atacama Saltern, Chile. The cells of these micro-organisms were mostly irregularly disc-shaped. They grew in medium containing saturated concentrations of NaCl and did not require magnesium for optimal growth. The polar lipid composition revealed the presence of mannosyl-2-sulfate-(1-4)-glycosyl-archaeol, the main glycolipid of the genus Halorubrum, and two new glycolipids. The G+C content of the DNA was 63.2 mol%. Phylogenetic analysis of the 16S rRNA gene placed strain ALT6-92T within the Halorubrum cluster. The low DNA-DNA hybridization value justified classification in a new species for which the name Halorubrum tebenquichense sp. nov. is proposed. The type strain is ALT6-92T (= CECT 5317T = DSM 14210T).

Archaeal Biodiversity in Crystallizer Ponds from a Solar Saltern: Culture versus PCR.

The culturable haloarchaeal diversity in a crystallizer pond from a solar saltern has been analyzed and compared with the biodiversity directly retrieved by analysis of rRNA genes amplified from the environment. Two different sets of culture conditions have been assayed: solid medium with yeast extract as carbon source and liquid media with either yeast extract or a mixture of fishmeal, Spirulina sp., and Artemia salina. Seventeen colonies grown on plates with yeast extract incubated at 30 degrees C were analyzed by 16S rDNA partial sequencing. Sixteen were closely related to haloarchaea of the genus Halorubrum; 13 of them to Halorubrum coriense, a haloarchaeon isolated from a solar saltern pond in Australia, which had not been previously isolated from the pond analyzed in this study; and one to Haloarcula marismortui. Liquid cultures were analyzed by ribosomal internal spacer analysis (RISA) and partial sequencing of the 16SrRNA genes. A total of 18 sequences were analyzed, 15 corresponding to RISA bands obtained from cultures, and 3 from the environmental sample used as inoculum. Thirteen sequences obtained from cultures were related to several Halorubrum species, and 2 to Haloarcula. One of the clones obtained directly from the environmental sample was distantly related to a Natronobacterium, whereas two were related to SPhT, the phylotype most frequently retrieved from this environment by culture independent techniques. Our results show an extremely low diversity for the haloarchaea retrieved by cultivation even when modifications to the standard technique are introduced.

Diversity of alkaliphilic halobacteria: proposals for transfer of Natronobacterium vacuolatum, Natronobacterium magadii, and Natronobacterium pharaonis to Halorubrum, Natrialba, and Natronomonas gen. nov., respectively, as Halorubrum vacuolatum comb. nov., Natrialba magadii comb. nov., and Natronomonas pharaonis comb. nov., respectively.

The 16S rRNA genes of three species of the genus Natronobacterium (Natronobacterium gregoryi, Natronobacterium pharaonis, and Natronobacterium vacuolatum) were sequenced and compared to that of the previously sequenced species Natronobacterium magadii. The sequences revealed that Natronobacterium pharaonis was phylogenetically distinct from the other members of the genus and also from other recognized genera of the family Halobacteriaceae. However, Natronobacterium vacuolatum and Natronobacterium magadii were found to be most closely related to the genera Halorubrum and Natrialba, respectively. An unidentified haloalkaliphile, strain SSL1, was also closely related to Natronobacterium magadii and Natrialba asiatica. On the basis of phylogenetic tree reconstructions, signature bases specific for individual genera, and sequences of spacer regions between 16 and 23S rRNA genes, we propose the following changes: Natronobacterium pharaonis to be transferred to Natronomonas gen. nov. as Natronomonas pharaonis gen. nov., comb. nov.; Natronobacterium vacuolatum to be transferred to the genus Halorubrum as Halorubrum vacuolatum comb. nov.; and Natronobacterium magadii to be transferred to the genus Natrialba as Natrialba magadii.

A Proposal for the Transfer of Halorubrobacterium distributum and Halorubrobacterium coriense to the Genus Halorubrum as Halorubrum distributum comb. nov. and Halorubrum coriense comb. nov., Respectively

As the genus Halorubrum was validated before the genus Halorubrobacterium, we propose that the species Halorubrobacterium distributum and Halorubrobacterium coriense should be reclassified as Halorubrum distributum comb. nov. and Halorubrum coriense comb. nov., respectively.