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.

Diverse thermophilic microorganisms with the potential to withstand extreme physiological conditions have long been investigated and explored for human commercial benefit. Thermozymes with distinct functional and structural properties isolated from these thermophiles are known to have high thermostability without significant loss of specific enzyme activity. Thermophiles isolated and characterised from the thermophilic ecological niche of India are well documented. There is a plethora of work in the literature emphasising its industrial significance. However, in-depth knowledge of the thermophilic oxidoreductase group of enzymes (Oxizymes) is restricted. Sulfur Oxygenase Reductases or Sulfur Oxygen-Reductases (SORs) are a group of thermophilic oxizymes reported predominantly from thermophilic and mesophilic archaea and bacteria, which catalyse oxygen-dependent disproportionation reactions of elemental sulfur, producing sulfite, thiosulfate, and sulphide. There have been few reports on isolated and characterised SORs from the Indian geothermal niche. The review article will highlight the SORs reported till date with a concise overview of different archaeal and bacterial species producing the enzymes. Based on the literature available till date, characteristics including physico-chemical properties, amino acid sequence homology, conserved motifs and their 3D structure comparison have been discussed. In-silico sequence and structure level preliminary comparative analysis of various SORs has also been discussed. However, a few SORs whose structural information is not reported in the protein data bank have been modelled to enrich our analysis.

The genus Geobacillus is one of the most important genera which mainly comprises gram-positive thermophilic bacterial strains including obligate aerobes, denitrifiers and facultative anaerobes having capability of endospore formation as well. The genus Geobacillus is widely distributed in nature and mostly abundant in extreme locations such as cool soils, hot springs, hydrothermal vents, marine trenches, hay composts and dairy plants. Due to plasticity towards environmental adaptation, the Geobacillus sp. shows remarkable genome diversification and acquired many beneficial properties, which facilitates their exploitation for many biotechnological applications. Many thermophiles are of biotechnological importance and having considerable interest in commercial applications for the production of industrially important products. Recently, due to catabolic versatility especially in the degradation of hemicellulose and starch containing agricultural waste and rapid growth rates, these microorganisms show potential for the production of biofuels, thermostable enzymes and bioremediation. This review mainly summarizes the status of Geobacillus sp. including its notable properties, biotechnological studies and its potential application in the production of industrially important products.

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.

Every year, new organisms that survive and colonize adverse environments are discovered and isolated. Those organisms, called extremophiles, are distributed throughout the world, both in aquatic and terrestrial environments, such as sulfurous marsh waters, hydrothermal springs, deep waters, volcanos, terrestrial hot springs, marine saltern, salt lakes, among others. According to the ecosystem inhabiting, extremophiles are categorized as thermophiles, psychrophiles, halophiles, acidophiles, alkalophilic, piezophiles, saccharophiles, metallophiles and polyextremophiles. They have developed chemical adaptation strategies that allow them to maintain their cellular integrity, altering physiology or improving repair capabilities; one of them is the biosynthesis of extracellular polysaccharides (EPS), which constitute a slime and hydrated matrix that keep the cells embedded, protecting from environmental stress (desiccation, salinity, temperature, radiation). EPS have gained interest; they are explored by their unique properties such as structural complexity, biodegradability, biological activities, and biocompatibility. Here, we present a review concerning the biosynthesis, characterization, and potential EPS applications produced by extremophile microorganisms, namely, thermophiles, halophiles, and psychrophiles. A bibliometric analysis was conducted, considering research articles published within the last two decades. Besides, an overview of the culture conditions used for extremophiles, the main properties and multiple potential applications of their EPS is also presented.

The genus Geobacillus, belonging to the phylum Firmicutes, is one of the most important genera and comprises thermophilic bacteria. The genus Geobacillus was erected with the taxonomic reclassification of various Bacillus species. Taxonomic studies of Geobacillus remain in progress. However, there is no comprehensive review of the characteristic features, taxonomic status and study of various applications of this interesting genus. The main aim of this review is to give a comprehensive account of the genus Geobacillus. At present the genus acomprises 25 taxa, 14 validly published (with correct name), nine validly published (with synonyms) and two not validly published species. We describe only validly published species of the genera Geobacillus and Parageobacillus. Vegetative cells of Geobacillus species are Gram-strain-positive or -variable, rod-shaped, motile, endospore-forming, aerobic or facultatively anaerobic, obligately thermophilic and chemo-organotrophic. Growth occurs in the pH range 6.08.5 and a temperature of 37-75 °C. The major cellular fatty acids are iso-C15:o, iso-C16:0 and iso-C17:o. The main menaquinone type is MK-7. The G-+C content of the DNA ranges between 48.2 and 58 mol%. The genus Geobacillus is widely distributed in nature, being mostly found in many extreme locations such as hot springs, hydrothermal vents, marine trenches, hay composts, etc. Geobacillus species have been widely exploited in various industrial and biotechnological applications, and thus are promising candidates for further studies in the future.

Extremophiles, notably archaea and bacteria, offer a good platform for treating industrial waste streams that were previously perceived as hostile to the model organisms in microbial electrochemical systems (MESs). Here we present a critical overview of the fundamental and applied biology aspects of halophiles and thermophiles in MESs. The current study suggests that extremophiles enable the MES operations under a seemingly harsh conditions imposed by the physical (pressure, radiation, and temperature) and geochemical extremes (oxygen levels, pH, and salinity). We highlight a need to identify the underpinning mechanisms that define the exceptional electrocatalytic performance of extremophiles in MESs.

Most of the potential bioprospecting is currently related to the study of the extremophiles and their potential use in industrial processes. Recently microbial cellulases find applications in various industries and constitute a major group of industrial enzymes. Considerable amount of work has been done on microbial cellulases, especially with resurgence of interest in biomass ethanol production employing cellulases and use of cellulases in textile and paper industry. Most efficient method of lignocellulosic biomass hydrolysis is through enzymatic saccharification using cellulases. Significant information has also been gained about the physiology of thermophilic cellulases producers and process development for enzyme production and biomass saccharification. The review discusses the current knowledge on cellulase producing thermophilic microorganisms, their physiological adaptations and control of cellulase gene expression. It discusses the industrial applications of thermophilic cellulases, their cost of production and challenges in cellulase research especially in the area of improving process economics of enzyme production.