Deep subsurface hot brines in North West Poland, extracted through the boreholes reaching 1.6 and 2.6 km below the ground surface, were microbiologically investigated using culture-independent and culture-dependent methods. The high-throughput sequencing of 16S rRNA gene amplicons showed a very low diversity of bacterial communities, that were dominated by phyla Proteobacteria and Firmicutes. Bacterial genera potentially involved in the sulfur oxidation and the nitrate reduction (Halothiobacillus and Methylobacterium) prevailed in both waters over the sulfate reducers ("Candidatus Desulforudis" and Desulfotomaculum). Only one archaeal taxon, affiliated to the order Thermoplasmatales, was detected in analyzed samples. Bacterial isolates obtained from these deep hot brines were closely related to Bacillus paralicheniformis based on the 16S rRNA sequence similarity. However, genomic and physiological analyses made for one of the isolates, Bacillus paralicheniformis strain TS6, revealed the existence of more diverse metabolic pathways compared to its moderate temperature counterpart. These specific traits may be associated with the ecological adaptations to the extreme habitat, which suggest that some lineages of B. paralicheniformis are halothermophilic.

IMPORTANCE

Deep subsurface aquifers, buried thousands of meters down the Earth's crust, belong to the most underexplored microbial habitats. Although few studies revealed the existence of microbial life at the depths, the knowledge about the microbial life in the deep hydrosphere is still scarce due to the limited access to such environments. Studying the subsurface microbiome provide unique information on microbial diversity, community structure and geomicrobiological processes occurring under extreme conditions of the deep subsurface. Our study shows that low-diversity microbial assemblages in subsurface hot brines were dominated by the bacteria involved in biogeochemical cycles of sulfur and nitrogen. Based on the genomic and physiological analyses we found that Bacillus paralicheniformis isolate obtained from the brine under study, differed from the mesophilic species in the presence of specific adaptations to harsh environmental conditions. We indicate that some lineages of B. paralicheniformis are halothermophilic, which was not previously reported.

通过不依赖于培养物和依赖于培养物的方法，通过微生物学研究了波兰西北部深地下热盐水，这些盐水是通过钻孔提取的，地下深度低于地面1.6和2.6 km。16S rRNA基因扩增子的高通量测序显示细菌群落的多样性非常低，这些细菌群落以门菌，变形杆菌和Firmicutes为主。可能涉及硫氧化和硝酸盐还原的细菌属（嗜盐杆菌和甲基细菌）在两种水域中均胜过硫酸盐还原剂（“ Candidatus Desulforudis”和Desulfotomaculum）。）。在分析的样品中仅检测到一个与Thermoplasmatales隶属的古细菌类群。基于16S rRNA序列相似性，从这些深热盐水中获得的细菌分离物与副粘芽孢杆菌密切相关。然而，对分离株之一的副芽孢杆菌TS6菌株进行的基因组和生理学分析显示，与其中等温度的菌株相比，存在更多种代谢途径。这些特定的特征可以与生态适应到极致的栖息地，这表明，一些谱系相关B. paralicheniformis是halothermophilic。

重要性

埋在地壳下数千米的深层地下蓄水层是开发程度最差的微生物栖息地。尽管很少有研究揭示深处存在微生物生活，但由于进入此类环境的机会有限，因此对深水圈微生物生活的了解仍然很少。对地下微生物组的研究提供了在深层地下极端条件下发生的微生物多样性，群落结构和地球微生物过程的独特信息。我们的研究表明，地下热盐水中的低多样性微生物群落主要由参与硫和氮生物地球化学循环的细菌主导。根据基因组和生理分析，我们发现副粘芽孢杆菌从研究中的盐水中分离得到的分离物与嗜温菌种有所不同，因为它们对恶劣的环境条件具有特定的适应性。我们表明，某些副粘芽孢杆菌谱系是嗜盐嗜热菌，以前没有报道。