Halomicroarcula amylolytica sp. nov., a novel halophilic archaeon isolated from a salt mine.

A halophilic archaeon named strain LR21T was isolated from a salt mine in Yunnan Province, PR China. Cells were spherical, Gram-stain-negative and motile. Strain LR21T grew at 20-50 °C (optimum, 42 °C), with 8-30 % (w/v) NaCl (optimum, 23 %) and at pH 5.5-9.5 (optimum, pH 7.5-8.5). Mg2+ was not required for growth. The major polar lipid profile comprised phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and phosphatidylglycerol sulfate. Strain LR21T had two dissimilar 16S rRNA genes (rrnA and rrnB) and they were closely related to Halomicroarcula limicola YGHS32T, Hma. pellucida BNERC31T and Hma. salina YGHS18T with sequence similarities of 95.3-99.0, 93.0-96.2 and 93.2-95.9 %, respectively, and much lower values to other members. The rpoB' gene sequence similarities between strain LR21T and Hma. limicola YGHS32T, Hma. pellucida BNERC31T and Hma. salina YGHS18T were 95.2, 91.2 and 91.2 % respectively. The values of average nucleotide identity (ANI) and average amino-acid identity (AAI) between strain LR21T and Hma. limicola YGHS32T, were 89.0 and 90.1 %, respectively. DNA relatedness between strains LR21T and Hma. limicola YGHS32T determined by in silico DNA-DNA hybridization was 36.8 %. Values of ANI and AAI between strain LR21T and other members in the genus Halomicroarcula were far below 95 % and the DNA-DNA relatedness values between strain LR21T and its close relatives were much lower than 70 %, which is far below the boundary for delineation of a new species prokaryote. The DNA G+C content of strain LR21T was 62.0 mol% (genome). The results suggested that strain LR21T represents a novel species of the genus Halomicroarcula, for which the name Halomicroarcula amylolytica sp. nov. is proposed. The type strain is LR21T (=CGMCC 1.13611T=NBRC 113588T).

Reclassification of the genus Natronolimnobius: proposal of two new genera, Natronolimnohabitans gen. nov. to accommodate Natronolimnobius innermongolicus and Natrarchaeobaculum gen. nov. to accommodate Natronolimnobius aegyptiacus and Natronolimnobius sulfurireducens.

The genus Natronolimnobius, currently including four species, is a member of the order Natrialbales, class Halobacteria, and consists of obligately alkaliphilic and extremely halophilic members found exclusively in highly alkaline hypersaline soda lakes. The species were classified into this genus mostly based on phylogenetic analysis of the 16S rRNA gene. However, a more advanced phylogenomic reconstruction based on 122 conserved single-copy archaeal protein markers clearly indicates a polyphyletic origin of the species included into this genus, thus warranting its reclassification into three separate genera. We therefore propose to transfer Nlb. innermongolicus (type strain N-1311) to a new genus Natronolimnohabitans as Nlh. innermongolicus comb. nov. and to transfer Nlb. aegyptiacus (type strain JW/NM-HA 15) and Nlb. sulfurireducens (type strain AArc1) to a new genus Natrarchaeobaculum as Nbl. aegyptiacum comb. nov. and Nbl. sulfurireducens comb. nov. The phylogenomic differentiation of these four species is also supported by the ANI/AAI distances and unique phenotypes. The most important physiological differences includes a previously unreported ability for cellulose and xylan utilization in Nlb. baerhuensis, thermophily in Nbl. aegyptiacus and anaerobic sulfur respiration in Nbl. sulfurireducens. We further present an emended description of Natronolimnobius baerhuensis.

A phylogenomic reappraisal of family-level divisions within the class Halobacteria: proposal to divide the order Halobacteriales into the families Halobacteriaceae, Haloarculaceae fam. nov., and Halococcaceae fam. nov., and the order Haloferacales into the families, Haloferacaceae and Halorubraceae fam nov.

The evolutionary interrelationships between the archaeal organisms which comprise the class Halobacteria have proven difficult to elucidate using traditional phylogenetic tools. The class currently contains three orders. However, little is known about the family level relationships within these orders. In this work, we have completed a comprehensive comparative analysis of 129 sequenced genomes from members of the class Halobacteria in order to identify shared molecular characteristics, in the forms of conserved signature insertions/deletions (CSIs) and conserved signature proteins (CSPs), which can provide reliable evidence, independent of phylogenetic trees, that the species from the groups in which they are found are specifically related to each other due to common ancestry. Here we present 20 CSIs and 31 CSPs which are unique characteristics of infra-order level groups of genera within the class Halobacteria. We also present 40 CSIs and 234 CSPs which are characteristic of Haloarcula, Halococcus, Haloferax, or Halorubrum. Importantly, the CSIs and CSPs identified here provide evidence that the order Haloferacales contains two main groups, one consisting of Haloferax and related genera supported by four CSIs and five CSPs and the other consisting of Halorubrum and related genera supported by four CSPs. We have also identified molecular characteristics that suggest that the polyphyletic order Halobacteriales contains at least two large monophyletic clusters of organisms in addition to the polyphyletic members of the order, one cluster consisting of Haloarcula and related genera supported by ten CSIs and nineteen CSPs and the other group consisting of the members of the genus Halococcus supported by nine CSIs and 23 CSPs. We have also produced a highly robust phylogenetic tree based on the concatenated sequences of 766 proteins which provide additional support for the relationships identified by the CSIs and CSPs. On the basis of the phylogenetic analyses and the identified conserved molecular characteristics presented here, we propose a division of the order Haloferacales into two families, an emended family Haloferacaceae and Halorubraceae fam. nov. and a division of the order Halobacteriales into three families, an emended family Halobacteriaceae, Haloarculaceae fam. nov., and Halococcaceae fam. nov.

Trehalose/2-sulfotrehalose biosynthesis and glycine-betaine uptake are widely spread mechanisms for osmoadaptation in the Halobacteriales.

We investigated the mechanisms of osmoadaptation in the order Halobacteriales, with special emphasis on Haladaptatus paucihalophilus, known for its ability to survive in low salinities. H. paucihalophilus genome contained genes for trehalose synthesis (trehalose-6-phosphate synthase/trehalose-6-phosphatase (OtsAB pathway) and trehalose glycosyl-transferring synthase pathway), as well as for glycine betaine uptake (BCCT family of secondary transporters and QAT family of ABC transporters). H. paucihalophilus cells synthesized and accumulated ∼1.97-3.72 µmol per mg protein of trehalose in a defined medium, with its levels decreasing with increasing salinities. When exogenously supplied, glycine betaine accumulated intracellularly with its levels increasing at higher salinities. RT-PCR analysis strongly suggested that H. paucihalophilus utilizes the OtsAB pathway for trehalose synthesis. Out of 83 Halobacteriales genomes publicly available, genes encoding the OtsAB pathway and glycine betaine BCCT family transporters were identified in 38 and 60 genomes, respectively. Trehalose (or its sulfonated derivative) production and glycine betaine uptake, or lack thereof, were experimentally verified in 17 different Halobacteriales species. Phylogenetic analysis suggested that trehalose synthesis is an ancestral trait within the Halobacteriales, with its absence in specific lineages reflecting the occurrence of gene loss events during Halobacteriales evolution. Analysis of multiple culture-independent survey data sets demonstrated the preference of trehalose-producing genera to saline and low salinity habitats, and the dominance of genera lacking trehalose production capabilities in permanently hypersaline habitats. This study demonstrates that, contrary to current assumptions, compatible solutes production and uptake represent a common mechanism of osmoadaptation within the Halobacteriales.

Microbial life in the Lake Medee, the largest deep-sea salt-saturated formation.

Deep-sea hypersaline anoxic lakes (DHALs) of the Eastern Mediterranean represent some of the most hostile environments on our planet. We investigated microbial life in the recently discovered Lake Medee, the largest DHAL found to-date. Medee has two unique features: a complex geobiochemical stratification and an absence of chemolithoautotrophic Epsilonproteobacteria, which usually play the primary role in dark bicarbonate assimilation in DHALs interfaces. Presumably because of these features, Medee is less productive and exhibits reduced diversity of autochthonous prokaryotes in its interior. Indeed, the brine community almost exclusively consists of the members of euryarchaeal MSBL1 and bacterial KB1 candidate divisions. Our experiments utilizing cultivation and [(14)C]-assimilation, showed that these organisms at least partially rely on reductive cleavage of osmoprotectant glycine betaine and are engaged in trophic cooperation. These findings provide novel insights into how prokaryotic communities can adapt to salt-saturated conditions and sustain active metabolism at the thermodynamic edge of life.

A multilocus sequence analysis approach to the phylogeny and taxonomy of the Halobacteriales.

Members of the order Halobacteriales are obligate extreme halophiles that belong to the domain Archaea. The classification of the Halobacteriales currently relies on a polyphasic approach, which integrates phenotypic, genotypic and chemotaxonomic characterization. However, the most utilized genetic marker for phylogeny, the 16S rRNA gene, has multiple drawbacks for use with the Halobacteriales: the species of many genera exhibit large intragenic differences between multiple ribosomal RNA operons, the gene is too conserved to discriminate reliably at the species level and it appears to be the most frequently recombined gene between closely related species. Moreover, the Halobacteriales is a rapidly expanding group due to recent successes at cultivating novel strains from a diverse set of hypersaline environments; a fast, reliable, inexpensive, portable molecular method for discriminating species is required for their investigation. Recently, multilocus sequence analysis (MLSA) has been shown to be an effective tool for strain identification and taxonomic designation, even for those taxa that experience frequent lateral gene transfer and homologous recombination. In this study, MLSA was utilized for evolutionary and taxonomic investigation of the Halobacteriales. Efficacy of the MLSA approach was tested across a hierarchical gradient using 52 halobacterial strains, representing 33 species (including names without standing in nomenclature) and 14 genera. A subset of 21 strains from the genus Haloarcula was analysed separately to test the sensitivity and relevance of the MLSA approach among closely related strains and species. The results demonstrated that MLSA differentiated individual strains, reliably grouped strains into species and species into genera and identified potential novel species and also family-like relationships. This study demonstrates that MLSA is a rapid and informative molecular method that will probably accommodate strain analysis at any taxonomic level within the Halobacteriales.

Haloterrigena saccharevitans sp. nov., an extremely halophilic archaeon from Xin-Jiang, China.

A novel extremely halophilic strain, isolated from Aibi salt lake, Xin-Jiang, China, was subjected to polyphasic taxonomic characterization. This strain, designated AB14T, is neutrophilic, motile and requires at least 10 % (w/v) NaCl for growth. Strain AB14T grows at 24-58 degrees C, with optimal growth at 42-45 degrees C. Mg2+ is not required, but growth is observed in MgCl2 concentrations as high as 1.0 M. Strain AB14T possesses the diphytanyl (C20C20) and phytanyl-sesterterpanyl diether (C20C25) derivatives of phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and mannose-2,6 disulfate 1-->2 glucose-glycerol diether. The genomic DNA G+C content is 66.6 mol%. The 16S rRNA gene sequence similarity values of strain AB14T with its nearest phylogenetic neighbours (Haloterrigena thermotolerans and Haloterrigena turkmenica) are 98.6 and 96.0 %, respectively. DNA-DNA hybridization revealed 54 % relatedness between strain AB14T and Haloterrigena thermotolerans JCM 11050T and 21 % between strain AB14T and Haloterrigena turkmenica JCM 9101T. It is therefore proposed that strain AB14T represents a novel species, for which the name Haloterrigena saccharevitans sp. nov. is proposed. The type strain is AB14T (=AS 1.3730T=JCM 12889T).