Background Haloarchaea, belonging to the class Halobacteria, currently include more than 400 validly published species. The isolation of novel halophilic archaea is important for understanding their evolutionary, ecological, and taxonomic diversity. Within the family Haloferacaceae, the genus Halorarum comprises two species reclassified from Halobaculum and one newly described species. In this study, we propose a new genus, Halonovum, to accommodate two novel species that are phylogenetically related to the genera Halobaculum and Halorarum. Results Two novel halophilic archaeal strains, MBLA0143T and MBLA0147T, were isolated from a solar saltern in Republic of Korea. Strain MBLA0143T and MBLA0147T showed the highest 16 S rRNA gene similarity (94.5% and 94.3%) to Halorarum salinum NJ-3-1T, and these two isolates were confirmed to represent different species, with 93.7% 16 S rRNA gene similarity between them. Their growth occurred at 25–55 °C (optimum, 40 °C), 2.5–5.1 M NaCl (optimum, 4.2 M), 0.1–1.0 M MgCl2 (optimum, 0.1 M), and pH 5.0–9.0 (optimum, 6.0–7.0). The predominant polar lipids detected in these two strains included phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester. The genome size and G + C content of strain MBLA0143T were 3.58 Mbp and 68.3%, while those of strain MBLA0147T was 4.29 Mbp and 67.6%. The OrthoANI (74.6–76.1% for MBLA0143ᵀ and 73.8–75.3% for MBLA0147ᵀ), AAI (66.9–71.7% for MBLA0143ᵀ and 66.9–67.8% for MBLA0147ᵀ), and isDDH (20.8–21.5% for MBLA0143ᵀ and 20.0–20.7% for MBLA0147ᵀ) values between these two species and currently recognized Halobaculum and Halorarum species support their placement in different genera within the family Haloferacaceae, based on the genus delimitation thresholds. In addition, phylogenomic analyses confirmed that the two novel species are distinct from species of other genera. Conclusions These results combined with polyphasic taxonomic analyses support that strains MBLA0143T and MBLA0147T represent a novel genus related to the genera Halobaculum and Halorarum. Two novel species are proposed to be classified into a novel genus and species, named Halonovum salinarum gen. nov., sp. nov. and Halonovum rutilum sp. nov. The type strains are MBLA0143T (= KCTC 4317T = JCM 36640T) and MBLA0147T (= KCTC 4319T = JCM 36641T).

Genome-based classification of Halonovum salinarum gen. nov., sp. nov., and Halonovum rutilum sp. nov., two novel halophilic archaea isolated from a solar saltern

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2025年11月29日

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Chi Young Hwang,
Eui-Sang Cho,
Ki-Eun Lee,
Eun-Young Lee,
Myung-Ji Seo

摘要

Background

Haloarchaea, belonging to the class Halobacteria, currently include more than 400 validly published species. The isolation of novel halophilic archaea is important for understanding their evolutionary, ecological, and taxonomic diversity. Within the family Haloferacaceae, the genus Halorarum comprises two species reclassified from Halobaculum and one newly described species. In this study, we propose a new genus, Halonovum, to accommodate two novel species that are phylogenetically related to the genera Halobaculum and Halorarum.

Results

Two novel halophilic archaeal strains, MBLA0143^T and MBLA0147^T, were isolated from a solar saltern in Republic of Korea. Strain MBLA0143^T and MBLA0147^T showed the highest 16 S rRNA gene similarity (94.5% and 94.3%) to Halorarum salinum NJ-3-1^T, and these two isolates were confirmed to represent different species, with 93.7% 16 S rRNA gene similarity between them. Their growth occurred at 25–55 °C (optimum, 40 °C), 2.5–5.1 M NaCl (optimum, 4.2 M), 0.1–1.0 M MgCl₂ (optimum, 0.1 M), and pH 5.0–9.0 (optimum, 6.0–7.0). The predominant polar lipids detected in these two strains included phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester. The genome size and G + C content of strain MBLA0143^T were 3.58 Mbp and 68.3%, while those of strain MBLA0147^T was 4.29 Mbp and 67.6%. The OrthoANI (74.6–76.1% for MBLA0143ᵀ and 73.8–75.3% for MBLA0147ᵀ), AAI (66.9–71.7% for MBLA0143ᵀ and 66.9–67.8% for MBLA0147ᵀ), and isDDH (20.8–21.5% for MBLA0143ᵀ and 20.0–20.7% for MBLA0147ᵀ) values between these two species and currently recognized Halobaculum and Halorarum species support their placement in different genera within the family Haloferacaceae, based on the genus delimitation thresholds. In addition, phylogenomic analyses confirmed that the two novel species are distinct from species of other genera.

Conclusions

These results combined with polyphasic taxonomic analyses support that strains MBLA0143^T and MBLA0147^T represent a novel genus related to the genera Halobaculum and Halorarum. Two novel species are proposed to be classified into a novel genus and species, named Halonovum salinarum gen. nov., sp. nov. and Halonovum rutilum sp. nov. The type strains are MBLA0143^T (= KCTC 4317^T = JCM 36640^T) and MBLA0147^T (= KCTC 4319^T = JCM 36641^T).