Extremophiles最新文献

Haloarchaea thrive in extreme environments where hypersalinity, DNA damage, and nutrient scarcity pose significant stresses. Here, we provide insight into how defined phosphate levels, UV stress, and Orc1/Cdc6 homolog type influence growth and genome dynamics (ploidy) in the model haloarchaeon Haloferax volcanii. During phosphate limitation, cells exhibited reduced growth, heightened UV sensitivity and dynamic changes in chromosome ploidy, with an early log-phase increase followed by a reduction at later growth stages. To uncover underlying mechanisms, we examined the sixteen Orc1/Cdc6 homologs of H. volcanii using bioinformatics, AI-based structural predictions, genetics, site-directed mutagenesis, and biochemical assays. When constitutively expressed, Orc10 and Orc14 were found to increase ploidy, while Orc1 and Orc10 impaired growth in a manner exacerbated by low phosphate and UV stress. Substitutions at the lysine acetylation site within the Walker A motif (Orc1 K165) and conserved DNA-binding residues (R498 in Orc1 and R304 in Orc14) were found to affect Orc/Cdc6 homolog functions. Moreover, a ∆pat2 lysine acetyltransferase mutant was found to exhibit reduced ploidy and a striking phosphate-dependent flocking phenotype during transition to stationary phase. These results highlight the interplay between phosphate availability, chromosomal regulation, and stress adaptation. Together, this study provides insight into mechanisms that promote H. volcanii survival in conditions that induce DNA damage and phosphate limitation.

In this study, Sphingomonas sp. PAMC26617 and Sphingomonas sp. PAMC26621 isolated from rocks of an Arctic lichen, Umbillicaria sp. and Cetraria sp. respectively, were evaluated for their tolerance to abiotic stress of heavy metal(loid)s (HMMs), salt, and osmotic (drought-like) stress at two different temperatures. HMMs resistance protein (CzcC, CzcD, CopB, CopC, CopD, ArsH, and CorC), and osmoprotectant enzymes such as gamma-glutamyl phosphate reductase (ProA), glutamate 5-kinase (ProB), and pyrroline-5-carboxylate reductase (ProC) were identified in both strains during genome analysis. Heavy metal (HM) resistance protein (CorA) was only identified in Sphingomonas sp. PAMC26621. In addition, both strains showed tolerance to CuSO₄·5H₂O (0.1 mM at 15 °C and 0.25 mM at 25 °C), CoCl₂·6H₂O (0.25 mM at 15 °C and 0.1 mM at 25 °C), ZnSO₄·7H₂O (0.1 mM at 15 °C and 25 °C) and Na₂HAsO₄·7H₂O (10 mM at 15 °C and 25 °C), except for Cd(NO₃)₂·4H₂O. Sphingomonas sp. PAMC26617 showed 0.05 mM Cd(NO₃)₂·4H₂O at 15 °C and 0.01 mM at 25 °C and Sphingomonas sp. PAMC26621 showed 0.01 mM Cd(NO₃)₂·4H₂O at 15 °C and 25 °C, respectively. Furthermore, both strains showed tolerance up to 100 mM NaCl and 100 mM D-mannitol at both temperatures. This study is very informative and helpful in understanding the diversity and adaptability of lichen-associated bacteria in harsh environments.

The bacterial phylum Caldisericota has a wide geographical and environmental distribution, but cultivated representatives of this phylum have so far been limited to a single strain. We have isolated a novel anaerobic, thermophilic, fermentative bacterium, strain AR60^T from a thermal spring in Sakhalin Island, Russia. Cells of strain AR60^T were long rods and tended to form aggregates. Growth was observed between 50 and 70 °C (optimum at 60 °C) and between pH 6.0 and 7.5 (optimum pH 6.5). The isolate was capable for fermentative growth on yeast extract, tryptone and peptone. Thiosulfate, S⁰, DMSO stimulated growth. The strain contained iso-C_17:0 as the major fatty acid. Genome size of strain AR60^T was 1.58 Mb; G + C content of the genomic DNA was 34.47%. Phylogenetic analysis revealed that strain AR60^T belongs to the genus Caldisericum of the phylum Caldisericota and has 98.85% identity to C. exile. Based on physiological properties and phylogenetic analyses including an average nucleotide identity values and in silico DNA-DNA hybridization, strain AR60^T is considered as a new species of the genus Caldisericum. We propose to name strain AR60^T (= CGMCC 1.18100^T = VKM B-3836^T) Caldisericum insulae sp. nov. It is the second cultivated representative of the phylum Caldisericota.

Uncultured microorganisms represent a significant portion of the biodiversity of Earth and play crucial roles in ecosystem functioning, particularly in extreme environments. Among these, a novel archaeal lineage, the "OYS group," was recently identified via 16S rRNA gene sequencing from actively boiling hot springs in northeastern Japan. This lineage forms a deep-branching clade, an early-diverging group that is phylogenetically distinct from all the known archaeal phyla. However, no additional reports of the OYS group have emerged from other geothermal environments, raising questions about its ecological niche and geographic distribution. In this study, we conducted a comprehensive 16S rRNA gene-based survey of 17 hot spring sites in Central Kyushu, Japan, covering a broad range of temperatures (30-95 °C) and pH values (4.1-8.8), to assess the distribution and environmental preferences of the OYS group archaea. The OYS group was detected at five high-temperature sites with relative abundances of up to 16.9% and was particularly dominant in the Tsuetate hot spring. Phylogenetic analyses confirmed that these sequences formed a monophyletic clade, a single origin group with the previously reported OYS group sequences. Multivariate analyses revealed co-occurrence with other thermophilic taxa, indicating a possible preference for high-temperature niches. These findings expand the known habitat range of the OYS group and highlight their potential ecological significance in geothermal ecosystems.