Diversity and Activity of Sulfate-Reducing Prokaryotes in Kamchatka Hot Springs

Microbial communities of the Kamchatka Peninsula terrestrial hot springs were studied using radioisotopic and cultural approaches, as well as by the amplification and sequencing of dsrB and 16S rRNA genes fragments. Radioisotopic experiments with 35S-labeled sulfate showed that microbial communities of the Kamchatka hot springs are actively reducing sulfate. Both the cultivation experiments and the results of dsrB and 16S rRNA genes fragments analyses indicated the presence of microorganisms participating in the reductive part of the sulfur cycle. It was found that sulfate-reducing prokaryotes (SRP) belonging to Desulfobacterota, Nitrospirota and Firmicutes phyla inhabited neutral and slightly acidic hot springs, while bacteria of phylum Thermodesulofobiota preferred moderately acidic hot springs. In high-temperature acidic springs sulfate reduction was mediated by archaea of the phylum Crenarchaeota, chemoorganoheterotrophic representatives of genus Vulcanisaeta being the most probable candidates. The 16S rRNA taxonomic profiling showed that in most of the studied communities SRP was present only as a minor component. Only in one microbial community, the representatives of genus Vulcanisaeta comprised a significant group. Thus, in spite of comparatively low sulfate concentrations in terrestrial hot springs of the Kamchatka, phylogenetically and metabolically diverse groups of sulfate-reducing prokaryotes are operating there coupling carbon and sulfur cycles in these habitats.

Diversity and Distribution of Culturable Thermus Species in Terrestrial Hot Springs of Southwestern Yunnan Province in China

The Yunnan geothermal area has many neutral and alkalescent thermal springs. Members of the genus Thermus have been found in thermal environments. In this study, we attempted to cultivate numerically abundant Thermus species using a variety of different strategies. A total of 223 strains of Thermus-like bacteria were isolated from seventeen hot spring samples of four geothermal regions (Baoshan, Dali, Lincang and Dehong). These strains were classified into two genera, Thermus and Meiothermus, based on 16S rDNA. The optimal isolation temperature of the Thermus genus was 63–70 °C. The highest Thermus diversity was found at 63 °C. Thermus brockianus was a universal culturable bacterium in the four geothermal regions. The principal component analysis (PCA) showed that T. oshimai preferred to inhabit the hot springs of the Baoshan (Bs) geothermal region, and T. amyloliquefaciens dominated the Dali (Dl) geothermal region, whereas T. tengchongensis accumulated in the Lincang (Lc) and Dehong (Dh) geothermal regions. The results suggested that Thermus species had habitat-preferable characteristics among the four geothermal regions. The findings may help identify the niche from which Thermus strains can likely be isolated.

Bacteriophages of Thermophilic ‘Bacillus Group’ Bacteria—A Review

Bacteriophages of thermophiles are of increasing interest owing to their important roles in many biogeochemical, ecological processes and in biotechnology applications, including emerging bionanotechnology. However, due to lack of in-depth investigation, they are underrepresented in the known prokaryotic virosphere. Therefore, there is a considerable potential for the discovery of novel bacteriophage-host systems in various environments: marine and terrestrial hot springs, compost piles, soil, industrial hot waters, among others. This review aims at providing a reference compendium of thermophages characterized thus far, which infect the species of thermophilic ‘Bacillus group’ bacteria, mostly from Geobacillus sp. We have listed 56 thermophages, out of which the majority belong to the Siphoviridae family, others belong to the Myoviridae and Podoviridae families and, apparently, a few belong to the Sphaerolipoviridae, Tectiviridae or Corticoviridae families. All of their genomes are composed of dsDNA, either linear, circular or circularly permuted. Fourteen genomes have been sequenced; their sizes vary greatly from 35,055 bp to an exceptionally large genome of 160,590 bp. We have also included our unpublished data on TP-84, which infects Geobacillus stearothermophilus (G. stearothermophilus). Since the TP-84 genome sequence shows essentially no similarity to any previously characterized bacteriophage, we have defined TP-84 as a new species in the newly proposed genus Tp84virus within the Siphoviridae family. The information summary presented here may be helpful in comparative deciphering of the molecular basis of the thermophages’ biology, biotechnology and in analyzing the environmental aspects of the thermophages’ effect on the thermophile community.

Microbial Diversity of Terrestrial Geothermal Springs in Armenia and Nagorno-Karabakh: A Review

The microbial diversity of high-altitude geothermal springs has been recently assessed to explore their biotechnological potential. However, little is known regarding the microbiota of similar ecosystems located on the Armenian Highland. This review summarizes the known information on the microbiota of nine high-altitude mineralized geothermal springs (temperature range 25.8–70 °C and pH range 6.0–7.5) in Armenia and Nagorno-Karabakh. All these geothermal springs are at altitudes ranging from 960–2090 m above sea level and are located on the Alpide (Alpine–Himalayan) orogenic belt, a seismically active region. A mixed-cation mixed-anion composition, with total mineralization of 0.5 mg/L, has been identified for these thermal springs. The taxonomic diversity of hot spring microbiomes has been examined using culture-independent approaches, including denaturing gradient gel electrophoresis (DGGE), 16S rRNA gene library construction, 454 pyrosequencing, and Illumina HiSeq. The bacterial phyla Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes are the predominant life forms in the studied springs. Archaea mainly include the phyla Euryarchaeota, Crenarchaeota, and Thaumarchaeota, and comprise less than 1% of the prokaryotic community. Comparison of microbial diversity in springs from Karvachar with that described for other terrestrial hot springs revealed that Proteobacteria, Bacteroidetes, Actinobacteria, and Deinococcus–Thermus are the common bacterial groups in terrestrial hot springs. Contemporaneously, specific bacterial and archaeal taxa were observed in different springs. Evaluation of the carbon, sulfur, and nitrogen metabolism in these hot spring communities has revealed diversity in terms of metabolic activity. Temperature seems to be an important factor in shaping the microbial communities of these springs. Overall, the diversity and richness of the microbiota are negatively affected by increasing temperature. Other abiotic factors, including pH, mineralization, and geological history, also impact the structure and function of the microbial community. More than 130 bacterial and archaeal strains (Bacillus, Geobacillus, Parageobacillus, Anoxybacillus, Paenibacillus, Brevibacillus Aeribacillus, Ureibacillus, Thermoactinomyces, Sporosarcina, Thermus, Rhodobacter, Thiospirillum, Thiocapsa, Rhodopseudomonas, Methylocaldum, Desulfomicrobium, Desulfovibrio, Treponema, Arcobacter, Nitropspira, and Methanoculleus) have been reported, some of which may be representative of novel species (sharing 91–97% sequence identity with their closest matches in GenBank) and producers of thermozymes and biomolecules with potential biotechnological applications. Whole-genome shotgun sequencing of T. scotoductus K1, as well as of the potentially new Treponema sp. J25 and Anoxybacillus sp. K1, were performed. Most of the phyla identified by 16S rRNA were also identified using metagenomic approaches. Detailed characterization of thermophilic isolates indicate the potential of the studied springs as a source of biotechnologically valuable microbes and biomolecules.

Photoreduction of inorganic carbon(+IV) by elemental sulfur: Implications for prebiotic synthesis in terrestrial hot springs

Terrestrial hydrothermal systems have been proposed as alternative birthplaces for early life but lacked reasonable scenarios for the supply of biomolecules. Here, we show that elemental sulfur (S0), as the dominant mineral in terrestrial hot springs, can reduce carbon dioxide (CO2) into formic acid (HCOOH) under ultraviolet (UV) light below 280 nm. The semiconducting S0 is indicated to have a direct bandgap of 4.4 eV. The UV-excited S0 produces photoelectrons with a highly negative potential of −2.34 V (versus NHE, pH 7), which could reduce CO2 after accepting electrons from electron donors such as reducing sulfur species. Simultaneously, UV light breaks sulfur bonds, benefiting the adsorption of charged carbonates onto S0 and assisting their photoreduction. Assuming that terrestrial hot springs covered 1% of primitive Earth’s surface, S0 at 10 μM could have produced maximal 109 kg/year HCOOH within 10-cm-thick photic zones, underlying its remarkable contributions to the accumulation of prebiotic biomolecules.

Spatial Metagenomics of Three Geothermal Sites in Pisciarelli Hot Spring Focusing on the Biochemical Resources of the Microbial Consortia

Terrestrial hot springs are of great interest to the general public and to scientists alike due to their unique and extreme conditions. These have been sought out by geochemists, astrobiologists, and microbiologists around the globe who are interested in their chemical properties, which provide a strong selective pressure on local microorganisms. Drivers of microbial community composition in these springs include temperature, pH, in-situ chemistry, and biogeography. Microbes in these communities have evolved strategies to thrive in these conditions by converting hot spring chemicals and organic matter into cellular energy. Following our previous metagenomic analysis of Pisciarelli hot springs (Naples, Italy), we report here the comparative metagenomic study of three novel sites, formed in Pisciarelli as result of recent geothermal activity. This study adds comprehensive information about phylogenetic diversity within Pisciarelli hot springs by peeking into possible mechanisms of adaptation to biogeochemical cycles, and high applicative potential of the entire set of genes involved in the carbohydrate metabolism in this environment (CAZome). This site is an excellent model for the study of biodiversity on Earth and biosignature identification, and for the study of the origin and limits of life.

Silica Precipitation in a Wet–Dry Cycling Hot Spring Simulation Chamber

Terrestrial hot springs have emerged as strong contenders for sites that could have facilitated the origin of life. Cycling between wet and dry conditions is a key feature of these systems, which can produce both structural and chemical complexity within protocellular material. Silica precipitation is a common phenomenon in terrestrial hot springs and is closely associated with life in modern systems. Not only does silica preserve evidence of hot spring life, it also can help it survive during life through UV protection, a factor which would be especially relevant on the early Earth. Determining which physical and chemical components of hot springs are the result of life vs. non-life in modern hot spring systems is a difficult task, however, since life is so prevalent in these environments. Using a model hot spring simulation chamber, we demonstrate a simple yet effective way to precipitate silica with or without the presence of life. This system may be valuable in further investigating the plausible role of silica precipitation in ancient terrestrial hot spring environments even before life arose, as well as its potential role in providing protection from the high surface UV conditions which may have been present on early Earth.