Summary auto-generated
This study describes the discovery and characterization of two novel halophilic archaeal strains, DX253T and GY252, isolated from Zodletone Spring in Oklahoma. These strains represent a new genus and species, Haladaptatus paucihalophilus, within the family Halobacteriaceae. Unlike most halophilic archaea that require hypersaline conditions (>20% salt), these organisms grow across a wide salinity range (0.8–5.1 M NaCl) with optimal growth at 2.6–3.1 M, and remarkably remain viable in distilled water for extended periods. The cells are Gram-negative cocci or coccobacilli that require magnesium for stability and grow at pH 5–7.5 and temperatures of 25–45°C. Phylogenetic analysis based on 16S rRNA genes shows only 89.5–90.8% similarity to the nearest recognized species, supporting their classification as a novel genus. Both strains contain characteristic lipids including phosphatidylglycerol sulfate and possess multiple divergent 16S rRNA gene sequences, features that may facilitate survival in fluctuating salt environments. These findings expand understanding of halophilic archaeal diversity in low-salinity systems and demonstrate that members of this group are physiologically adapted to variable salt conditions rather than extreme salinity.
Key findings
- Two novel halophilic archaeal strains (DX253T and GY252) form a new genus and species, Haladaptatus paucihalophilus, with only 89.5–90.8% 16S rRNA gene similarity to nearest relatives, justifying novel taxonomic classification
- These archaea grow across unusually wide salt concentrations (0.8–5.1 M NaCl) and survive exposure to distilled water for up to 2 weeks, adaptations suited to the fluctuating salinity of their sulfide-rich spring source
- Each strain possesses two divergent 16S rRNA gene sequences differing by ~4.2%, a feature potentially characteristic of the novel genus and possibly related to environmental stress tolerance
- Lipid composition includes the diagnostic marker phosphatidylglycerol sulfate (PGS) plus two unidentified glycolipids, distinguishing these organisms from other neutrophilic halophilic genera
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Abstract
Two novel strains of halophilic archaea, DX253T and GY252, were isolated from Zodletone Spring, a low-salt, sulfide- and sulfur-rich spring in south-western Oklahoma, USA. The cells were cocci or coccobacilli and occurred singly or in pairs. The two strains grew in a wide range of salt concentrations (0.85.1 M) and required at least 5 mM Mg2+ for growth. The pH range for growth was 57.5 and the temperature range was 2545 °C. In addition to having the capacity to grow at relatively low salt concentrations, cells remained viable in distilled water after prolonged incubation. The two diether phospholipids that are typical of members of the order Halobacteriales, phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester, were present. Phosphatidylglycerol sulfate and two unidentified glycolipids were also detected. Each strain had two distinct 16S rRNA gene sequences that were only 89.590.8 % similar to sequences from the most closely related cultured and recognized species within the order Halobacteriales. The DNA G+C content of the type strain was found to be 60.5 mol%. The closest relatives were clones and uncharacterized isolates obtained from coastal salt-marsh sediments with salinities equivalent to that of seawater. The physiological, biochemical and phylogenetic differences between strains DX253T and GY252 and other previously described genera of extremely halophilic archaea suggest that these novel strains represent a novel species and genus within the family Halobacteriaceae, for which the name Haladaptatus paucihalophilus gen. nov., sp. nov. is proposed. The type strain is DX253T (=JCM 13897T=DSM 18195T=ATCC BAA-1313T=KCTC 4006T).