Halophilic archaea are a group of microorganisms that require high-salt conditions for optimal growth and most of them are classified within the class Halobacteria of the domain Archaea (Oren, 2008). These extremophiles are predominantly found in hypersaline environments, including salt lakes, solar salterns, and salt mines (Cui and Dyall-Smith, 2021). Notably, saline environments such as seawater, saline lakes, and saline rocks serve as primary sources for commercial salt production. During salt production, halophilic archaea are encapsulated within the salt crystals while maintaining viability. In recent years, an increasing number of novel halophilic archaea, such as Halobacterium yunchengense (Cui et al., 2024), Halovalidus salilacus (Dong et al., 2024), Halobaculum halobium (Tan et al., 2024), Halorussus caseinilyticus (Hu et al., 2024), Salinirarus marinus (Zhang et al., 2024), Halobellus ordinarius (Zhu et al., 2025), Halopiger thermotolerans (Minegishi et al., 2016), Halorubrum aethiopicum (Gibtan et al., 2018), and Haloparvum alkalitolerans (Kondo et al., 2016), have been isolated and identified from saline lakes, salt mines, and commercial salt using culture-dependent methods.

China possesses a vast and diverse distribution of saline environments, providing not only abundant resources for halophilic archaea but also substantial reserves for salt production, including the numerous saline lakes in the northwestern region and the Qinghai-Xizang Plateau (Yang et al., 2020; Dong et al., 2006), as well as the coastal tidal flats and marine salt marshes along the eastern coastal region. In the previous investigations of halophilic archaeal diversity from these hypersaline environments and salt products, seven novel strains DYHT-AS-1T, SHR40T, TS25T, SYNS179T, GDY60T, XH63T, and ZY30T were isolated from the coastal tidal flat of Dongying in Shandong province, Dabancheng Salt Lake, Tuosu Lake, Sheyang marine solar saltern, and three coarse sea salt samples, respectively. These strains were found to be closely related to the genera Halosimplex and Halovenus.

The genus Halosimplex (family Haloarculaceae) was established in 2002 (Vreeland et al., 2002) and contains seven species with valid published names up to now (https://lpsn.dsmz.de/genus/halosimplex). Members of this genus are characterized by rod-shaped or pleomorphic cells, forming pink or red colonies on agar media. All known species are neutrophilic halophilic archaea, with optimal growth typically occurring at temperatures of 37–42 °C, NaCl concentrations of 2.6–4.3 M, and MgCl₂ concentrations of 0.05–0.8 M. Notably, the type species Halosimplex carlsbadense differs from others of the genus in that growth was restricted to pyruvate, pyruvate-glycerol, or glycerol-acetate as sole carbon sources. The presence of sulfated mannosyl glucosyl diether (S-DGD-1), mannosylglucosyl diethyl ether sulfate (S2-DGD), and two unidentified glycolipids (UGs) has been detected in both the type species and other representative species. The genome size of the existing species in the genus Halosimplex ranges from 4.16 Mbp to 5.16 Mbp, with the GC content 66.5–70.0 %.

The genus Halovenus (family Haloarculaceae) was established in 2012 (Makhdoumi-Kakhki et al., 2012). To date, four species within this genus have been described. The type species Halovenus aranensis EB27T was isolated from the Aran-Bidgol salt lake in Iran (Makhdoumi-Kakhki et al., 2012) while Halovenus carboxidivorans WSH3T (Myers and King, 2020), Halovenus rubra R28T (Han et al., 2015), and Halovenus salina ASP54T (Infante-Domínguez et al., 2015) from the Bonneville Salt Flats in Utah, USA, the brown alga Laminaria in China, and a water sample of the Isla Bacuta saltern in Huelva (Spain), respectively. The cells of the existing species of the genus are rod-shaped or polymorphic, forming red colonies on agar media. The current species are neutrophilic halophilic archaea and the optimal growth conditions include temperatures of 37–50 °C, NaCl of 3.9–4.3 M, and MgCl₂ of 0.01–0.5 M. The genome size of current species of the genus Halovenus ranges from 3.25 Mbp to 3.77 Mbp, with the GC content 55.2–64.0 %.

This study investigated the diversity of halophilic archaea from Dongying tidal flats, Dabancheng Salt Lake, Tuosu Lake, Sheyang marine solar saltern, and three types of coarse sea salt through metagenomic sequencing and amplicon sequencing. Based on phylogenetic analysis, phenotypic characteristics, genomic taxonomy, and comparative genomics, the taxonomic status of the novel strains DYHT-AS-1T, GDY60T, TS25T, XH63T, SHR40T, SYNS179T, and ZY30T isolated from the above samples was systematically evaluated. The results indicated that these seven strains represent four novel species of the genus Halosimplex and three novel species of the genus Halovenus. Furthermore, the environmental occurrence patterns of these species were assessed.