Extremophilic microorganisms play a key role in understanding how life on Earth originated and evolved over centuries. Their ability to thrive in harsh environments relies on a plethora of mechanisms developed to survive at extreme temperatures, pressures, salinity, and pH values. From a biotechnological point of view, thermophiles are considered a robust tool for synthetic biology as well as a reliable starting material for the development of sustainable bioprocesses. This review discusses the current progress in the biomanufacturing of high-added bioproducts from thermophilic microorganisms and their industrial applications.

Various environmental factors, including H2 availability, metabolic tradeoffs, optimal growth temperature, stochasticity, and hydrology, were examined to determine if they affect microbial competition between three autotrophic thermophiles. The thiosulfate reducer Desulfurobacterium thermolithotrophum (Topt72°C) was grown in mono- and coculture separately with the methanogens Methanocaldococcus jannaschii (Topt82°C) at 72°C and Methanothermococcus thermolithotrophicus (Topt65°C) at 65°C at high and low H2 concentrations. Both methanogens showed a metabolic tradeoff shifting from high growth rate-low cell yield at high H2 concentrations to low growth rate-high cell yield at low H2 concentrations and when grown in coculture with the thiosulfate reducer. In 1:1 initial ratios, D. thermolithotrophum outcompeted both methanogens at high and low H2, no H2S was detected on low H2, and it grew with only CO2 as the electron acceptor indicating a similar metabolic tradeoff with low H2. When the initial methanogen-to-thiosulfate reducer ratio varied from 1:1 to 104:1 with high H2, D. thermolithotrophum always outcompeted M. jannaschii at 72°C. However, M. thermolithotrophicus outcompeted D. thermolithotrophum at 65°C when the ratio was 103:1. A reactive transport model that mixed pure hydrothermal fluid with cold seawater showed that hyperthermophilic methanogens dominated in systems where the residence time of the mixed fluid above 72°C was sufficiently high. With shorter residence times, thermophilic thiosulfate reducers dominated. If residence times increased with decreasing fluid temperature along the flow path, then thermophilic methanogens could dominate. Thermophilic methanogen dominance spread to previously thiosulfate-reducer-dominated conditions if the initial ratio of thermophilic methanogen-to-thiosulfate reducer increased.
OBJECTIVE: The deep subsurface is the largest reservoir of microbial biomass on Earth and serves as an analog for life on the early Earth and extraterrestrial environments. Methanogenesis and sulfur reduction are among the more common chemolithoautotrophic metabolisms found in hot anoxic hydrothermal vent environments. Competition between H2-oxidizing sulfur reducers and methanogens is primarily driven by the thermodynamic favorability of redox reactions with the former outcompeting methanogens. This study demonstrated that competition between the hydrothermal vent chemolithoautotrophs Methanocaldococcus jannaschii, Methanothermococcus thermolithotrophicus, and Desulfurobacterium thermolithotrophum is also influenced by other overlapping factors such as staggered optimal growth temperatures, stochasticity, and hydrology. By modeling all aspects of microbial competition coupled with field data, a better understanding is gained on how methanogens can outcompete thiosulfate reducers in hot anoxic environments and how the deep subsurface contributes to biogeochemical cycling.

We isolated six Thermus thermophilus strains from Shirahama Hot Spring in Japan. Complete genome sequences, determined by combining Oxford Nanopore long-read and Illumina short-read sequence data, revealed that they showed >99.9% average nucleotide identities with each other and approximately 97% to the genome of the type strain HB8T.

Northeastern Algeria boasts numerous hot springs, yet these hydrothermal sites remain largely unexplored for their microbial ecology. The present study explores the bacterial abundance and diversity within two distinct Algerian hot springs (Hammam Saïda and Hammam Debagh) and investigates the link between the prevailing bacteria with geochemical parameters. High-throughput 16S rRNA gene sequencing of water and sediment samples revealed a bacterial dominance of 99.85-91.16% compared to Archaea (0.14-0.66%) in both springs. Interestingly, Saïda hot spring, characterized by higher temperatures and sodium content, harbored a community dominated by Pseudomonadota (51.13%), whereas Debagh, a Ca-Cl-SO4 type spring, was primarily populated by Bacillota with 55.33%. Bacteroidota displayed even distribution across both sites. Additional phyla, including Chloroflexota, Deinococcota, Cyanobacteriota, and Chlorobiota, were also present. Environmental factors, particularly temperature, sodium, potassium, and alkalinity, significantly influenced bacterial diversity and composition. These findings shed light on the interplay between distinct microbial communities and their associated geochemical properties, providing valuable insights for future research on biogeochemical processes in these unique ecosystems driven by distinct environmental conditions, including potential applications in bioremediation and enzyme discovery.

Two thermophilic spore-forming sulfate-reducing strains, 435T and 781, were isolated from oil and gas reservoirs in Western Siberia (Russia) about 50 years ago. Both strains were found to be neutrophilic, chemoorganotrophic, anaerobic bacteria, growing at 45-70 °C (optimum, 55-60 °C) and with 0-4.5% (w/v) NaCl (optimum, 0.5-1% NaCl). The major fatty acids were iso-C15:0, iso-C17:0, C16:0, and C18:0. In sulfate-reducing conditions, the strains utilized H2/CO2, formate, lactate, pyruvate, malate, fumarate, succinate, methanol, ethanol, propanol, butanol, butyrate, valerate, and palmitate. In 2005, based on phenotypic characteristics and a 16S rRNA gene sequence analysis, the strains were described as \'Desulfotomaculum salinum\' sp. nov. However, this species was not validly published because the type strain was not deposited in two culture collections. In this study, a genomic analysis of strain 435T was carried out to determine its taxonomic affiliation. The genome size of strain 435T was 2.886 Mb with a 55.1% genomic G + C content. The average nucleotide identity and digital DNA-DNA hybridization values were highest between strain 435T and members of the genus Desulfofundulus, 78.7-93.3% and 25.0-52.2%, respectively; these values were below the species delineation cut-offs (<95-96% and <70%). The cumulative phenotypic and phylogenetic data indicate that two strains represent a novel species within the genus Desulfofundulus, for which the name Desulfofundulus salinus sp. nov. is proposed. The type strain is 435T (=VKM B-1492T = DSM 23196T). A genome analysis of strain 435T revealed the genes for dissimilatory sulfate reduction, autotrophic carbon fixation via the Wood-Ljungdahl pathway, hydrogen utilization, methanol and organic acids metabolism, and sporulation, which were confirmed by cultivation studies.

Caldimonas thermodepolymerans, a Gram-negative, moderately thermophilic bacterium, exhibits a remarkable biotechnological potential. Given the presence of genes in its genome dedicated to the metabolization of ferulic acid (FA), this study aimed to explore the bacterium\'s capability for biotransforming FA into high-value metabolites. The results unequivocally demonstrate the bacterium\'s proficiency in the efficient and rapid conversion of FA into vanillyl alcohol (VOH) and vanillic acid (VA). By manipulating key cultivation parameters, such as adjusting initial FA doses and varying cultivation periods, the product profile can be tailored. Higher initial doses and shorter cultivation periods favor the production of VOH, while lower FA doses and extended cultivation periods lead to the predominant formation of VA. Furthermore, the process can be operated in a repeated-batch scenario. This underscores the potential of C. thermodepolymerans for industrial biotransformation of FA, presenting a promising avenue for leveraging its capabilities in practical applications.

Thermophilic Geobacillus kaustophilus HTA426 genome possesses a monoacylglycerol lipase (MAGL) gene. MAGLs can synthesize emulsifiers for use in the food and pharmaceutical industries from fatty acids and glycerol. They can also be used to analyze monoacylglycerol (MAG) levels in serum and food. The MAGL gene from strain HTA426 was artificially synthesized and heterologously expressed in Escherichia coli BL21(DE3). The recombinant His-tag fused MAGL (GkMAGL) was purified using a Ni2+-affinity column. The purified enzyme showed a temperature optimum at 65 °C and was stable up to 75 °C after 30 min incubation. In addition, the enzyme exhibited a pH optimum of 7.5 and was stable from pH 5.0 to 11.0. The enzyme hydrolyzed monoacylglycerols and showed the highest activity toward 1-monolauroylglycerol. The enzyme was stable in the presence of various organic solvents and detergents. The addition of Triton X-100 significantly increased GkMAGL activity. The thermal stability of the enzyme was higher than that of thermostable MAGL from Geobacillus sp. 12AMOR1 (12AMOR1_MAGL). Circular dichroism spectral analysis showed that the conformational stability of the GkMAGL was higher than that of 12AMOR1_MAGL at higher temperatures. These results indicate that the GkMAGL has useful features that can be used for various biotechnological applications.

Waste of any origin is one of the most serious global and man-made concerns of our day. It causes climate change, environmental degradation, and human health problems. Proper waste management practices, including waste reduction, safe handling, and appropriate treatment, are essential to mitigate these consequences. It is thus essential to implement effective waste management strategies that reduce waste at the source, promote recycling and reuse, and safely dispose of waste. Transitioning to a circular economy with policies involving governments, industries, and individuals is essential for sustainable growth and waste management. The review focuses on diverse kinds of environmental waste sources around the world, such as residential, industrial, commercial, municipal services, electronic wastes, wastewater sewerage, and agricultural wastes, and their challenges in efficiently valorizing them into useful products. It highlights the need for rational waste management, circularity, and sustainable growth, and the potential of a circular economy to address these challenges. The article has explored the role of thermophilic microbes in the bioremediation of waste. Thermophiles known for their thermostability and thermostable enzymes, have emerged to have diverse applications in biotechnology and various industrial processes. Several approaches have been explored to unlock the potential of thermophiles in achieving the objective of establishing a zero-carbon sustainable bio-economy and minimizing waste generation. Various thermophiles have demonstrated substantial potential in addressing different waste challenges. The review findings affirm that thermophilic microbes have emerged as pivotal and indispensable candidates for harnessing and valorizing a range of environmental wastes into valuable products, thereby fostering the bio-circular economy.

The taxonomic and metabolic diversity of prokaryotes and their adaptability to extreme environmental parameters have allowed extremophiles to find their optimal living conditions under extreme conditions for one or more environmental parameters. Natural habitats abundant in extremophilic microorganisms are relatively rare in Hungary. Nevertheless, alkaliphiles and halophiles can flourish in shallow alkaline lakes (soda pans) and saline (solonetz) soils, where extreme weather conditions favor the development of unique bacterial communities. In addition, the hot springs and thermal wells that supply spas and thermal baths and provide water for energy use are suitable colonization sites for thermophiles and hyperthermophiles. Polyextremophiles, adapted to multiple extreme circumstances, can be found in the aphotic, nutrient-poor and radioactive hypogenic caves of the Buda Thermal Karst, among others. The present article reviews the organization, taxonomic composition, and potential role of different extremophilic bacterial communities in local biogeochemical cycles, based on the most recent studies on extremophiles in Hungary.

Extremophiles and their products have been a major focus of research interest for over 40 years. Through this period, studies of these organisms have contributed hugely to many aspects of the fundamental and applied sciences, and to wider and more philosophical issues such as the origins of life and astrobiology. Our understanding of the cellular adaptations to extreme conditions (such as acid, temperature, pressure and more), of the mechanisms underpinning the stability of macromolecules, and of the subtleties, complexities and limits of fundamental biochemical processes has been informed by research on extremophiles. Extremophiles have also contributed numerous products and processes to the many fields of biotechnology, from diagnostics to bioremediation. Yet, after 40 years of dedicated research, there remains much to be discovered in this field. Fortunately, extremophiles remain an active and vibrant area of research. In the third decade of the twenty-first century, with decreasing global resources and a steadily increasing human population, the world\'s attention has turned with increasing urgency to issues of sustainability. These global concerns were encapsulated and formalized by the United Nations with the adoption of the 2030 Agenda for Sustainable Development and the presentation of the seventeen Sustainable Development Goals (SDGs) in 2015. In the run-up to 2030, we consider the contributions that extremophiles have made, and will in the future make, to the SDGs.