Hypersaline environments harbor halophiles capable of producing extracellular polysaccharides (EPSs). This study reports EPS production, chemical composition and genomic insights by the halophilic archaeon Haloarcula japonica strain SST1, isolated from a subterranean salt deposit in Avan, Armenia. The highest extracellular product (EP) yield (628.4 mg L−1) was achieved at 120 h cultivation in sucrose-supplemented medium. Sucrose-derived EP had high carbohydrate content (48.5%), while molasses yielded 275.2 mg L−1 with 20.8% carbohydrate. Gel filtration revealed a heterogeneous molecular mass (10–100 kDa). GC–MS, HPAE-PAD, and NMR identified a heteropolymer of mannose, galactose, and glucose. Genome sequence data confirmed genes for monosaccharide activation, polymerization, and secretion. Use of molasses as substrate highlights SST1’s potential as a cost-effective EPS producer for circular bioeconomy. Binding of raw EPS to human C-type lectins suggests possible biomedical applications in innate immunity modulation.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-18462-4.

Lycopene β-cyclase (LCYb) serves as a pivotal gatekeeper enzyme in carotenoid biosynthesis, catalyzing an enzymatic conversion of lycopene to β-carotene. While phylogenetically widespread across life domains, structural and functional characterization of archaeal LCYbs remains conspicuously understudied. Here, we report biochemical validation and mechanistic dissection of a putative LCYb from the hypersaline-adapted archaeon Haloarcula marismortui (Hma-LCYb). Heterologous expression of Hma-LCYb in the lycopene-accumulating Escherichia coli strain resulted in the efficient β-carotene biosynthesis (0.91 ± 0.01 mg/g DCW, dried cell weight), demonstrating cross-domain functionality. Remarkably, introducing the Hma-LCYb gene into the LCYb-deficient haloarchaeon Haloferax volcanii not only enabled β-carotene production but achieved the titers (0.21 ± 0.002 mg/g DCW) surpassing the endogenous bacterioruberin levels (0.06 ± 0.003 mg/g DCW), establishing the first archaeal platform for halo-adapted carotenoid engineering. Mutational analyses revealed that a combination of residues D55, W64, E82, Y140, R168, and E214 of Hma-LCYb is critical for catalyzing lycopene-to-β-carotene conversion. These findings resolve long-standing questions regarding archaeal carotenoid cyclization mechanisms and highlight biotechnological potential of extremophilic enzymes in industrial carotenoid production.

The genus Haloarcula is one of the most extensively studied genera within the class Halobacteria. In this study, analyses of average nucleotide identity (ANI), average amino acid identity (AAI), digital DNA-DNA hybridization (dDDH) values, and phylogenomic data indicated that "Haloarcula californiae" ATCC 33799 and "Haloarcula sinaiiensis" ATCC 33800 served as reference strains for Haloarcula marismortui. Furthermore, a halophilic archaeal strain, GH36T, isolated from the inland Gahai Salt Lake in China, was subjected to comprehensive polyphasic taxonomic characterization. The ANI, AAI, and dDDH comparisons between strain GH36T and other Haloarcula species were below the established thresholds for species demarcation. Strain GH36T was assigned to a novel species within the genus Haloarcula based on phylogenetic, phylogenomic, and comparative genomic analyses. Moreover, distinct phenotypic differences were observed in strain GH36T. In strain GH36T, the primary phospholipids detected were phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), and phosphatidylglycerol sulfate (PGS), whereas the principal glycolipids were sulfated mannosyl glucosyl diether (S-DGD-1) and mannosyl glucosyl diether (DGD-1). Accordingly, the novel species Haloarcula montana sp. nov. is proposed to accommodate strain GH36T (=CGMCC 1.62631T = MCCC 4K00122T).

Tat-fimbriae ("tafi"): An unusual type of haloarchaeal surface structure depending on the twin-arginine translocation pathway.

The novel esterase gene lipP1, which encodes HjEstP1, was discovered in the genome of the extremely halophilic archaeon Haloarcula japonica. A homology search and sequence alignment revealed that HjEstP1 is a member of family IV esterases with conserved GXSXG and HGGG motifs. lipP1 was expressed in its parental strain, and recombinant HjEstP1 was purified and characterized. Optimal pH and temperature of HjEstP1 were 6.0 and > 60 °C, respectively. HjEstP1 showed higher activity with increasing NaCl concentration, and optimal NaCl concentration was > 4.5 M. Furthermore, HjEstP1 preferentially hydrolyzed pNP and glycerol esters with short chain fatty acids. To our knowledge, this is the first report of an esterase from an extremely halophilic archaeon obtained via homologous expression.

The halophilic archaeon Haloarcula hispanica utilizes the sugar alcohols mannitol and sorbitol as carbon and energy sources. Genes, enzymes, and transcriptional regulators involved in uptake and degradation of these sugar alcohols were identified by growth experiments with deletion mutants and enzyme characterization. It is shown that both mannitol and sorbitol are taken up via a single ABC transporter of the CUT1 transporter family. Then, mannitol and sorbitol are oxidized to fructose by two distinct dehydrogenases. Fructose is further phosphorylated to fructose-1-phosphate by a haloarchaeal ketohexokinase, providing the first evidence for a physiological function of ketohexokinase in prokaryotes. Finally, fructose-1-phosphate is phosphorylated via fructose-1-phosphate kinase to fructose-1,6-bisphosphate, which is cleaved to triosephosphates by a Class I fructose-1,6-bisphosphate aldolase. Two distinct transcriptional regulators, acting as activators, have been identified: an IclR-like regulator involved in activating genes for sugar alcohol uptake and oxidation to fructose, and a GfcR-like regulator that likely activates genes involved in the degradation of fructose to pyruvate. This is the first comprehensive analysis of a sugar alcohol degradation pathway in Archaea.

Currently, the main α-amylase family GH13 has been divided into 47 subfamilies in CAZy, with new subfamilies regularly emerging. The present in silico study was performed to highlight the groups, represented by the maltogenic amylase from Thermotoga neapolitana and the α-amylase from Haloarcula japonica, which are worth of creating their own new GH13 subfamilies. This enlarges functional annotation and thus allows more precise prediction of the function of putative proteins. Interestingly, those two share certain sequence features, e.g. the highly conserved cysteine in the second conserved sequence region (CSR-II) directly preceding the catalytic nucleophile, or the well-preserved GQ character of the end of CSR-VII. On the other hand, the two groups bear also specific and highly conserved positions that distinguish them not only from each other but also from representatives of remaining GH13 subfamilies established so far. For the T. neapolitana maltogenic amylase group, it is the stretch of residues at the end of CSR-V highly conserved as L-[DN]. The H. japonica α-amylase group can be characterized by a highly conserved [WY]-[GA] sequence at the end of CSR-II. Other specific sequence features include an almost fully conserved aspartic acid located directly preceding the general acid/base in CSR-III or well-preserved glutamic acid in CSR-IV. The assumption that these two groups represent two mutually related, but simultaneously independent GH13 subfamilies has been supported by phylogenetic analysis as well as by comparison of tertiary structures. The main α-amylase family GH13 has thus been expanded by two novel subfamilies GH13_48 and GH13_49.Key points• In silico analysis of two groups of family GH13 members with characterized representatives• Identification of certain common, but also some specific sequence features in seven CSRs• Creation of two novel subfamilies—GH13_48 and GH13_49 within the CAZy database

Marine and extreme environments harbor a huge diversity of microorganisms able to produce new bioactive metabolites with beneficial health effects. In this study, ethanol, aqueous, methanol, and acetone extracts and protein hydrolysates were obtained from five different microalgae species and two haloarchaea. An in vitro study of cytotoxicity, migration, angiogenic effect, antioxidant capacity, and modulation of detoxifying enzyme expression was carried out using resistant (HCT-15) and non-resistant (T84) colon cancer tumor lines. Our results showed that the aqueous extract of the microalga Chlorella sorokiniana induced the greatest cytotoxic effect in both cell lines, while the ethanolic extracts of the archaea Haloarcula hispanica and Halobacterium salinarum caused the greatest inhibition on the migratory capacity. Meanwhile, the protein hydrolyzate and the aqueous extract of the microalga Chlorella sorokiniana significantly protected cells against hydrogen peroxide damage. Moreover, the aqueous extracts of Haloarcula hispanica and Halobacterium salinarum resulted in inducing the greatest increase in the activity of the detoxifying enzymes enzyme quinone oxidoreductase and glutathione S-transferase. These preliminary results suggest that aqueous extracts of some microalgae and haloarchaea may be promising candidates for an adjuvant therapy against colorectal cancer. However, additional research is required to identify the active principles and elucidate the mechanisms of action involved.

Marine microbiota is garnering increasing interest as a potential source of novel foods with enhanced nutritional and functional properties. In this study, the proximate composition and antioxidant capacity of five haloarchaea and microalgae species from the Andalusian Atlantic shoreline (Halobacterium salinarum, Haloarcula hispanica, Dunaliella salina, C5 and C13, and Picochlorum spp) were compared to two freshwater species (Chlamydomonas reinhardtii and Chlorella sorokiniana). All the species studied exhibited high protein content and antioxidant activity, with noticeable variations in total mineral content and fatty acid profile. Among the four extraction methodologies tested to prepare functional extracts, forced aqueous extraction followed by protein hydrolysis resulted in significantly greater yields and antioxidant activity, while microalgae demonstrated higher activity compared to haloarchaea tested in the present study. In conclusion, the diverse species examined displayed high nutritional and functional value, showing great potential to be part of the human diet as rich sources of readily available protein and antioxidant compounds.

The extremophile Halobacterium salinarum is an aerobic archaeon that has adapted to thrive in high-salt environments such as salted fish, hypersaline lakes, and salterns. Halophiles have garnered significant interest due to their unique interactions with bacteriophages known as haloarchaeophages. Studies have identified and characterized prophages in halophilic archaea, such as Haloferax volcanii, Haloquadratum walsbyi, and Haloarcula marismortui. Still, an investigation has yet to be conducted into the presence of prophage elements on Halobacterium salinarum ATCC 33170. This is of particular interest to us as we are using this strain as a source of archaeol, as one of the components of our sulfated lactosyl archaeol (SLA) archaeosome adjuvant. Genomic contigs of strain 33170 were bioinformatically assessed for prophage-like features using BLAST, PHASTER, InterProScan, and PHYRE2. A 7 kb region encoding six genes was identified as an incomplete prophage, and the proteins were further analyzed, revealing high homology to proteins encoded by bacteria, archaea, and an IS200 transposon. Restricting the BLASTp database to viruses resulted in hits to both myo- and siphoviral proteins, which would be unusual for an intact prophage. Additionally, no known phage structural proteins were identified in the search, suggesting a low chance that H. salinarum ATCC 33170 harbors a latent prophage.

Timely regulation of carbon metabolic pathways is essential for cellular processes and to prevent futile cycling of intracellular metabolites. In Halobacterium salinarum, a hypersaline adapted archaeon, a sugar-sensing TrmB family protein controls gluconeogenesis and other biosynthetic pathways. Notably, Hbt. salinarum does not utilize carbohydrates for energy, uncommon among Haloarchaea. We characterized a TrmB-family transcriptional regulator in a saccharolytic generalist, Haloarcula hispanica, to investigate whether the targets and function of TrmB, or its regulon, is conserved in related species with distinct metabolic capabilities. In Har. hispanica, TrmB binds to 15 sites in the genome and induces the expression of genes primarily involved in gluconeogenesis and tryptophan biosynthesis. An important regulatory control point in Hbt. salinarum, activation of ppsA and repression of pykA, is absent in Har. hispanica. Contrary to its role in Hbt. salinarum and saccharolytic hyperthermophiles, TrmB does not act as a global regulator: it does not directly repress the expression of glycolytic enzymes, peripheral pathways such as cofactor biosynthesis, or catabolism of other carbon sources in Har. hispanica. Cumulatively, these findings suggest rewiring of the TrmB regulon alongside metabolic network evolution in Haloarchaea.

The extremely halophilic archaeon Haloarcula japonica accumulates the C50 carotenoid, bacterioruberin (BR). To reveal the BR biosynthetic pathway, unidentified phytoene desaturase candidates were functionally characterized in the present study. Two genes encoding the potential phytoene desaturases, c0507 and d1086, were found from the Ha. japonica genome sequence by a homology search using the Basic Local Align Search Tool. Disruption mutants of c0507 and d1086 and their complemented strains transformed with expression plasmids for c0507 and d1086 were subsequently constructed. High-performance liquid chromatography (HPLC) ana­lyses of carotenoids produced by these strains revealed that C0507 and D1086 were both bifunctional enzymes with the same activities as both phytoene desaturase (CrtI) and 3,4-desaturase (CrtD). C0507 and D1086 complemented each other during BR biosynthesis in Ha. japonica. This is the first study to identify two distinct enzymes with both CrtI and CrtD activities in an extremely halophilic archaeon.

First antibiotic in the oxazolidinone class, linezolid fights gram-positive multiresistant bacteria by inhibiting protein synthesis through its interaction with the 50S subunit of the functional bacterial ribosome. For its antimicrobial action, it is necessary that its chiral carbon located in the oxazolidinone ring is in the S-conformation. Computational calculation at time-dependent density functional theory methodology, ultraviolet-visible (UV-Vis), and electronic circular dichroism spectra was obtained for noncomplexed and complexed forms of linezolid to verify the possible chirality of nitrogen atom in the acetamide group of the molecule. The molecular system has two chiral centers. So, there are now four possible configurations: RR, RS, SR, and SS. For a better understanding of the system, the electronic spectra at the PBE0/6-311++G(3df,2p) level of theory were obtained. The complexed form was obtained from the crystallographic data of the ribosome, containing the S-linezolid molecular system. The computational results obtained for the electronic properties are in good agreement with the experimental crystallographic data and available theoretical results.

Microorganisms that can survive in saline environments, known as halotolerant or halophilic organisms, have a wide range of current and potential uses in biotechnology. In this study, it was aimed to determine the carotenoids of halophilic archaea strains isolated from the brine samples taken from different points of Salt Lake (Turkey) and determine the antioxidant activities of their carotenoids. To identify the halophilic archaea strains, they were cultivated in MAM JCM 168 medium and subjected to antibiotic susceptibility, fatty acid, two-dimensional and three-dimensional imaging by scanning electron microscopy and atomic force microscopy, biochemical and phylogenetic assays. The findings show that five different halophilic archaea strains have been identified as Halorubrum lipolyticum, Halorubrum sodomense, Haloarcula salaria, Halorubrum chaoviator, and Haloarcula japonica with 98% and above similarity ratio. The main fatty acids of all haloarchaeal strains were octadecanoic acid (C18:0) and palmitic acid (C16:0). The major carotenoid of the species was determined as all-trans bacterioruberin, and different carotenoid types such as lycopene, β-carotene, and 2-isopentenyl-3,4-dehydrorodopin were found as well as bacterioruberin isomers. The antioxidant activities of carotenoids extracted from the species were analyzed by the 2,2-diphenyl-1-picrylhydrazyl radical scavenging method and the extracts showed antioxidant activity statistically significantly higher than ascorbic acid and butylated hydroxytoluene as reference products (p < 0.05).

Ribosome-targeting antibiotics comprise over half of antibiotics used in medicine, but our fundamental knowledge of their binding sites is derived primarily from ribosome structures of non-pathogenic species. These include Thermus thermophilus, Deinococcus radiodurans and the archaean Haloarcula marismortui, as well as the commensal and sometimes pathogenic organism, Escherichia coli. Advancements in electron cryomicroscopy have allowed for the determination of more ribosome structures from pathogenic bacteria, with each study highlighting species-specific differences that had not been observed in the non-pathogenic structures. These observed differences suggest that more novel ribosome structures, particularly from pathogens, are required for a more accurate understanding of the level of diversity of the entire bacterial ribosome, with the potential of leading to innovative advancements in antibiotic research. In this study, high accuracy covariance and hidden Markov models were used to annotate ribosomal RNA and protein sequences respectively from genomic sequence, allowing us to determine the underlying ribosomal sequence diversity using phylogenetic methods. This analysis provided evidence that the current non-pathogenic ribosome structures are not sufficient representatives of some pathogenic bacteria, such as Campylobacter pylori, or of whole phyla such as Bacteroidota (Bacteroidetes).

Oxygen and chlorine isotope fractionation during microbial perchlorate reduction in static and flow through systems

The attachment of a sugar to a hydrophobic lipid carrier is the first step in the biosynthesis of many glycoconjugates. In the halophilic archaeon Haloarcula hispanica, HAH_1206, renamed AepG, is a predicted glycosyltransferase belonging to the CAZy Group 2 family that shares a conserved amino acid sequence with dolichol phosphate mannose synthases. In this study, the function of AepG was investigated by genetic and biochemical approaches. We found that aepG deletion led to the disappearance of dolichol phosphate-glucuronic acid. Our biochemical assays revealed that recombinant cellulose-binding, domain-tagged AepG could catalyze the formation of dolichol phosphate-glucuronic acid in time- and dose-dependent manners. Based on the invivo and invitro analyses, AepG was confirmed to be a dolichol phosphate glucuronosyltransferase involved in the synthesis of the acidic exopolysaccharide produced by H.hispanica. Furthermore, lack of aepG resulted in hindered growth and cell aggregation in high salt medium, indicating that AepG is vital for the adaptation of H.hispanica to a high salt environment. In conclusion, AepG is the first dolichol phosphate glucuronosyltransferase identified in any of the three domains of life and, moreover, offers a starting point for further investigation into the diverse pathways used for extracellular polysaccharide biosynthesis in archaea.

Halophilic Archaea are a unique group of microorganisms living in saline environments. They constitute a complex group whose biodiversity has not been thoroughly studied. Here, we report three draft genomes of halophilic Archaea isolated from brines, representing the genera of Halorubrum, Halopenitus, and Haloarcula. Two of these strains, Boch-26 and POP-27, were identified as members of the genera Halorubrum and Halopenitus, respectively. However, they could not be assigned to any known species because of the excessive difference in genome sequences between these strains and any other described genomes. In contrast, the third strain, Boch-26, was identified as Haloarcula hispanica. Genome lengths of these isolates ranged from 2.7 Mbp to 3.0 Mbp, and GC content was in the 63.77%-68.77% range. Moreover, functional analysis revealed biosynthetic gene clusters (BGCs) related to terpenes production in all analysed genomes and one BGC for RRE (RiPP recognition element)-dependent RiPP (post-translationally modified peptides) biosynthesis. Moreover, the obtained results enhanced the knowledge about the salt mines microbiota biodiversity as a poorly explored environment so far.

We study the escape process of nascent proteins at the ribosomal exit tunnel of bacterial Escherichia coli by using molecular dynamics simulations with coarse-grained and atomistic models. It is shown that the effects of hydrophobic and electrostatic interactions on the protein escape at the E. coli's tunnel are qualitatively similar to those obtained previously at the exit tunnel of archaeal Haloarcula marismortui, despite significant differences in the structures and interactions of the ribosome tunnels from the two organisms. Most proteins escape efficiently and their escape time distributions can be fitted to a simple diffusion model. Attractive interactions between nascent protein and the tunnel can significantly slow down the escape process, as shown for the CI2 protein. Interestingly, it is found that the median escape times of the considered proteins (excluding CI2) strongly correlate with the function \(N_h + 5.9 Q\) of the number of hydrophobic residues, \(N_h\), and the net charge, \(Q\), of a protein, with a correlation coefficient of 0.958 for the E. coli's tunnel. The latter result is in quantitative agreement with a previous result for the H. marismortui's tunnel.

The pandemic caused by SARS-CoV-2 is the most widely spread disease in the 21st century. Due to the continuous emergence of variants across the world, it is necessary to expand our understanding of host–virus interactions and explore new agents against SARS-CoV-2. In this study, it was found exopolysaccharides (EPSs) from halophilic archaeon Haloarcula hispanica ATCC33960 can bind to the spike protein of SARS-CoV-2 with the binding constant KD of 2.23 nM, block the binding of spike protein to Vero E6 and bronchial epithelial BEAS-2B cells, and inhibit pseudovirus infection. However, EPSs from the gene deletion mutant △HAH_1206 almost completely lost the antiviral activity against SARS-CoV-2. A significant reduction of glucuronic acid (GlcA) and the sulfation level in EPSs of △HAH_1206 was clearly observed. Our results indicated that sulfated GlcA in EPSs is possible for a main structural unit in their inhibition of binding of SARS-CoV-2 to host cells, which would provide a novel antiviral mechanism and a guide for designing new agents against SARS-CoV-2.