Extremozymes--biocatalysts with unique properties from extremophilic microorganisms

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.

Microbial diversity of extreme habitats in human homes

High-throughput sequencing techniques have opened up the world of microbial diversity to scientists, and a flurry of studies in the most remote and extreme habitats on earth have begun to elucidate the key roles of microbes in ecosystems with extreme conditions. These same environmental extremes can also be found closer to humans, even in our homes. Here, we used high-throughput sequencing techniques to assess bacterial and archaeal diversity in the extreme environments inside human homes (e.g., dishwashers, hot water heaters, washing machine bleach reservoirs, etc.). We focused on habitats in the home with extreme temperature, pH, and chemical environmental conditions. We found a lower diversity of microbes in these extreme home environments compared to less extreme habitats in the home. However, we were nonetheless able to detect sequences from a relatively diverse array of bacteria and archaea. Habitats with extreme temperatures alone appeared to be able to support a greater diversity of microbes than habitats with extreme pH or extreme chemical environments alone. Microbial diversity was lowest when habitats had both extreme temperature and one of these other extremes. In habitats with both extreme temperatures and extreme pH, taxa with known associations with extreme conditions dominated. Our findings highlight the importance of examining interactive effects of multiple environmental extremes on microbial communities. Inasmuch as taxa from extreme environments can be both beneficial and harmful to humans, our findings also suggest future work to understand both the threats and opportunities posed by the life in these habitats.

Discovery, Molecular Mechanisms, and Industrial Applications of Cold-Active Enzymes

Cold-active enzymes constitute an attractive resource for biotechnological applications. Their high catalytic activity at temperatures below 25°C makes them excellent biocatalysts that eliminate the need of heating processes hampering the quality, sustainability, and cost-effectiveness of industrial production. Here we provide a review of the isolation and characterization of novel cold-active enzymes from microorganisms inhabiting different environments, including a revision of the latest techniques that have been used for accomplishing these paramount tasks. We address the progress made in the overexpression and purification of cold-adapted enzymes, the evolutionary and molecular basis of their high activity at low temperatures and the experimental and computational techniques used for their identification, along with protein engineering endeavors based on these observations to improve some of the properties of cold-adapted enzymes to better suit specific applications. We finally focus on examples of the evaluation of their potential use as biocatalysts under conditions that reproduce the challenges imposed by the use of solvents and additives in industrial processes and of the successful use of cold-adapted enzymes in biotechnological and industrial applications.

Biofuels 2020: Biorefineries based on lignocellulosic materials

The production of liquid biofuels to blend with gasoline is of worldwide importance to secure the energy supply while reducing the use of fossil fuels, supporting the development of rural technology with knowledge‐based jobs and mitigating greenhouse gas emissions. Today, engineering for plant construction is accessible and new processes using agricultural residues and municipal solid wastes have reached a good degree of maturity and high conversion yields (almost 90% of polysaccharides are converted into monosaccharides ready for fermentation). For the complete success of the 2G technology, it is still necessary to overcome a number of limitations that prevent a first‐of‐a‐kind plant from operating at nominal capacity. We also claim that the triumph of 2G technology requires the development of favourable logistics to guarantee biomass supply and make all actors (farmers, investors, industrial entrepreneurs, government, others) aware that success relies on agreement advances. The growth of ethanol production for 2020 seems to be secured with a number of 2G plants, but public/private investments are still necessary to enable 2G technology to move on ahead from its very early stages to a more mature consolidated technology.

Construction of an Immobilized Thermophilic Esterase on Epoxy Support for Poly(ε-caprolactone) Synthesis

Developing an efficient immobilized enzyme is of great significance for improving the operational stability of enzymes in poly(ε-caprolactone) synthesis. In this paper, a thermophilic esterase AFEST from the archaeon Archaeoglobus fulgidus was successfully immobilized on the epoxy support Sepabeads EC-EP via covalent attachment, and the immobilized enzyme was then employed as a biocatalyst for poly(ε-caprolactone) synthesis. The enzyme loading and recovered activity of immobilized enzyme was measured to be 72 mg/g and 10.4 U/mg using p-nitrophenyl caprylate as the substrate at 80 °C, respectively. Through the optimization of reaction conditions (enzyme concentration, temperature, reaction time and medium), poly(ε-caprolactone) was obtained with 100% monomer conversion and low number-average molecular weight (M_n < 1300 g/mol). Further, the immobilized enzyme exhibited excellent reusability, with monomer conversion values exceeding 75% during 15 batch reactions. Finally, poly(ε-caprolactone) was enzymatically synthesized with an isolated yield of 75% and M_n value of 3005 g/mol in a gram-scale reaction.

Co-utilization of glucose and xylose by evolved Thermus thermophilus LC113 strain elucidated by (13)C metabolic flux analysis and whole genome sequencing

We evolved Thermus thermophilus to efficiently co-utilize glucose and xylose, the two most abundant sugars in lignocellulosic biomass, at high temperatures without carbon catabolite repression. To generate the strain, T. thermophilus HB8 was first evolved on glucose to improve its growth characteristics, followed by evolution on xylose. The resulting strain, T. thermophilus LC113, was characterized in growth studies, by whole genome sequencing, and (13)C-metabolic flux analysis ((13)C-MFA) with [1,6-(13)C]glucose, [5-(13)C]xylose, and [1,6-(13)C]glucose+[5-(13)C]xylose as isotopic tracers. Compared to the starting strain, the evolved strain had an increased growth rate (~2-fold), increased biomass yield, increased tolerance to high temperatures up to 90°C, and gained the ability to grow on xylose in minimal medium. At the optimal growth temperature of 81°C, the maximum growth rate on glucose and xylose was 0.44 and 0.46h(-1), respectively. In medium containing glucose and xylose the strain efficiently co-utilized the two sugars. (13)C-MFA results provided insights into the metabolism of T. thermophilus LC113 that allows efficient co-utilization of glucose and xylose. Specifically, (13)C-MFA revealed that metabolic fluxes in the upper part of metabolism adjust flexibly to sugar availability, while fluxes in the lower part of metabolism remain relatively constant. Whole genome sequence analysis revealed two large structural changes that can help explain the physiology of the evolved strain: a duplication of a chromosome region that contains many sugar transporters, and a 5x multiplication of a region on the pVV8 plasmid that contains xylose isomerase and xylulokinase genes, the first two enzymes of xylose catabolism. Taken together, (13)C-MFA and genome sequence analysis provided complementary insights into the physiology of the evolved strain.

Extremophiles and biotechnology: current uses and prospects

Biotechnology has almost unlimited potential to change our lives in very exciting ways. Many of the chemical reactions that produce these products can be fully optimized by performing them at extremes of temperature, pressure, salinity, and pH for efficient and cost-effective outcomes. Fortunately, there are many organisms (extremophiles) that thrive in extreme environments found in nature and offer an excellent source of replacement enzymes in lieu of mesophilic ones currently used in these processes. In this review, I discuss the current uses and some potential new applications of extremophiles and their products, including enzymes, in biotechnology.

Truncation of the unique N-terminal domain improved the thermos-stability and specific activity of alkaline α-amylase Amy703

High pH condition is of special interest for the potential applications of alkaline α-amylase in textile and detergent industries. Thus, there is a continuous demand to improve the amylase's properties to meet the requirements set by specific applications. Here we reported the systematic study of modular domain engineering to improve the specific activity and stability of the alkaline α-amylase from Bacillus pseudofirmus 703. The specific activity of the N-terminal domain truncated mutant (N-Amy) increased by ~35-fold with a significantly improved thermo-stability. Kinetic analysis demonstrated that the Kcat and Kcat/Kmof N-Amy were enhanced by 1300-fold and 425.7-fold, respectively, representing the largest catalytic activity improvement of the engineered α-amylases through the methods of domain deletion, fusion or swapping. In addition, different from the wild-type Amy703, no exogenous Ca(2+) were required for N-Amy to maintain its full catalytic activity, implying its superior potential for many industrial processes. Circular dichroism analysis and structure modeling revealed that the increased compactness and α-helical content were the main contributors for the improved thermo-stability of N-Amy, while the improved catalytic efficiency was mainly attributed by the increased conformational flexibility around the active center.

Expression and characterization of a new esterase with GCSAG motif from a permafrost metagenomic library

As a result of construction and screening of a metagenomic library prepared from a permafrost-derived microcosm, we have isolated a novel gene coding for a putative lipolytic enzyme that belongs to the hormone-sensitive lipase family. It encodes a polypeptide of 343 amino acid residues whose amino acid sequence displays maximum likelihood with uncharacterized proteins from Sphingomonas species. A putative catalytic serine residue of PMGL2 resides in a new variant of a recently discovered GTSAG sequence in which a Thr residue is replaced by a Cys residue (GCSAG). The recombinant PMGL2 was produced in Escherichia coli cells and purified by Ni-affinity chromatography. The resulting protein preferably utilizes short-chain p-nitrophenyl esters (C4 and C8) and therefore is an esterase. It possesses maximum activity at 45°C in slightly alkaline conditions and has limited thermostability at higher temperatures. Activity of PMGL2 is stimulated in the presence of 0.25-1.5 M NaCl indicating the good salt tolerance of the new enzyme. Mass spectrometric analysis demonstrated that N-terminal methionine in PMGL2 is processed and cysteine residues do not form a disulfide bond. The results of the study demonstrate the significance of the permafrost environment as a unique genetic reservoir and its potential for metagenomic exploration.

Functional metagenomics of extreme environments

The bioprospecting of enzymes that operate under extreme conditions is of particular interest for many biotechnological and industrial processes. Nevertheless, there is a considerable limitation to retrieve novel enzymes as only a small fraction of microorganisms derived from extreme environments can be cultured under standard laboratory conditions. Functional metagenomics has the advantage of not requiring the cultivation of microorganisms or previous sequence information to known genes, thus representing a valuable approach for mining enzymes with new features. In this review, we summarize studies showing how functional metagenomics was employed to retrieve genes encoding for proteins involved not only in molecular adaptation and resistance to extreme environmental conditions but also in other enzymatic activities of biotechnological interest.

Production of Thermoalkaliphilic Lipase from Geobacillus thermoleovorans DA2 and Application in Leather Industry

Thermophilic and alkaliphilic lipases are meeting a growing global attention as their increased importance in several industrial fields. Over 23 bacterial strains, novel strain with high lipolytic activity was isolated from Southern Sinai, Egypt, and it was identified as Geobacillus thermoleovorans DA2 using 16S rRNA as well as morphological and biochemical features. The lipase was produced in presence of fatty restaurant wastes as an inducing substrate. The optimized conditions for lipase production were recorded to be temperature 60°C, pH 10, and incubation time for 48 hrs. Enzymatic production increased when the organism was grown in a medium containing galactose as carbon source and ammonium phosphate as nitrogen source at concentrations of 1 and 0.5% (w/v), respectively. Moreover, the optimum conditions for lipase production such as substrate concentration, inoculum size, and agitation rate were found to be 10% (w/v), 4% (v/v), and 120 rpm, respectively. The TA lipase with Triton X-100 had the best degreasing agent by lowering the total lipid content to 2.6% as compared to kerosene (7.5%) or the sole crude enzyme (8.9%). It can be concluded that the chemical leather process can be substituted with TA lipase for boosting the quality of leather and reducing the environmental hazards.

Pretreatment and conversion of lignocellulose biomass into valuable chemicals

Lignocellulose biomass can be utilized in many sectors of industry such as energy, chemical, and transportation. However, pretreatment is needed to break down the intricate bonding before converting it into wanted product.

Asymmetric reductive amination by a wild-type amine dehydrogenase from the thermophilic bacteria Petrotoga mobilis

Biocatalytic potential of a new wild-type amine dehydrogenase used in an enzyme-catalyzed synthesis of an enantiomerically pure primary amine.

Fast and reliable production, purification and characterization of heat-stable, bifunctional enzyme chimeras

Degradation of complex plant biomass demands a fine-regulated portfolio of glycoside hydrolases. The LE (LguI/Eco81I)-cloning approach was used to produce two enzyme chimeras CB and BC composed of an endoglucanase Cel5A (C) from the extreme thermophilic bacterium Fervidobacterium gondwanense and an archaeal β-glucosidase Bgl1 (B) derived from a hydrothermal spring metagenome. Recombinant chimeras and parental enzymes were produced in Escherichia coli and purified using a two-step affinity chromatography approach. Enzymatic properties revealed that both chimeras closely resemble the parental enzymes and physical mixtures, but Cel5A displayed lower temperature tolerance at 100°C when fused to Bgl1 independent of the conformational order. Moreover, the determination of enzymatic performances resulted in the detection of additive effects in case of BC fusion chimera. Kinetic measurements in combination with HPLC-mediated product analyses and site-directed mutation constructs indicated that Cel5A was strongly impaired when fused at the N-terminus, while activity was reduced to a slighter extend as C-terminal fusion partner. In contrast to these results, catalytic activity of Bgl1 at the N-terminus was improved 1.2-fold, effectively counteracting the slightly reduced activity of Cel5A by converting cellobiose into glucose. In addition, cellobiose exhibited inhibitory effects on Cel5A, resulting in a higher yield of cellobiose and glucose by application of an enzyme mixture (53.1%) compared to cellobiose produced from endoglucanase alone (10.9%). However, the overall release of cellobiose and glucose was even increased by catalytic action of BC (59.2%). These results indicate possible advantages of easily produced bifunctional fusion enzymes for the improved conversion of complex polysaccharide plant materials.

Genome Assembly of Chryseobacterium polytrichastri ERMR1:04, a Psychrotolerant Bacterium with Cold Active Proteases, Isolated from East Rathong Glacier in India

We report here the genome assembly of a psychrotolerant bacterium, Chryseobacterium polytrichastri ERMR1:04, which secretes cold-active proteases. The bacterium was isolated from a pristine location, the East Rathong Glacier in the Sikkim Himalaya. The 5.53-Mb genome provides insight into the cold-active industrial enzyme and adaptation in the cold environment.

Production of halophilic proteins using Haloferax volcanii H1895 in a stirred-tank bioreactor

The success of biotechnological processes is based on the availability of efficient and highly specific biocatalysts, which can satisfy industrial demands. Extreme and remote environments like the deep brine pools of the Red Sea represent highly interesting habitats for the discovery of novel halophilic and thermophilic enzymes. Haloferax volcanii constitutes a suitable expression system for halophilic enzymes obtained from such brine pools. We developed a batch process for the cultivation of H. volcanii H1895 in controlled stirred-tank bioreactors utilising knockouts of components of the flagella assembly system. The standard medium Hv-YPC was supplemented to reach a higher cell density. Without protein expression, cell dry weight reaches 10 g L(-1). Two halophilic alcohol dehydrogenases were expressed under the control of the tryptophanase promoter p.tna with 16.8 and 3.2 mg gCDW (-1), respectively, at a maximum cell dry weight of 6.5 g L(-1). Protein expression was induced by the addition of L-tryptophan. Investigation of various expression strategies leads to an optimised two-step induction protocol introducing 6 mM L-tryptophan at an OD650 of 0.4 followed by incubation for 16 h and a second induction step with 3 mM L-tryptophan followed by a final incubation time of 4 h. Compared with the uncontrolled shaker-flask cultivations used until date, dry cell mass concentrations were improved by a factor of more than 5 and cell-specific enzyme activities showed an up to 28-fold increased yield of the heterologous proteins.

Complete genome sequence, metabolic model construction and phenotypic characterization of Geobacillus LC300, an extremely thermophilic, fast growing, xylose-utilizing bacterium

We have isolated a new extremely thermophilic fast-growing Geobacillus strain that can efficiently utilize xylose, glucose, mannose and galactose for cell growth. When grown aerobically at 72 °C, Geobacillus LC300 has a growth rate of 2.15 h(-1) on glucose and 1.52 h(-1) on xylose (doubling time less than 30 min). The corresponding specific glucose and xylose utilization rates are 5.55 g/g/h and 5.24 g/g/h, respectively. As such, Geobacillus LC300 grows 3-times faster than E. coli on glucose and xylose, and has a specific xylose utilization rate that is 3-times higher than the best metabolically engineered organism to date. To gain more insight into the metabolism of Geobacillus LC300 its genome was sequenced using PacBio's RS II single-molecule real-time (SMRT) sequencing platform and annotated using the RAST server. Based on the genome annotation and the measured biomass composition a core metabolic network model was constructed. To further demonstrate the biotechnological potential of this organism, Geobacillus LC300 was grown to high cell-densities in a fed-batch culture, where cells maintained a high xylose utilization rate under low dissolved oxygen concentrations. All of these characteristics make Geobacillus LC300 an attractive host for future metabolic engineering and biotechnology applications.

Biotechnological applications of extremophiles, extremozymes and extremolytes

In the last decade, attention to extreme environments has increased because of interests to isolate previously unknown extremophilic microorganisms in pure culture and to profile their metabolites. Microorganisms that live in extreme environments produce extremozymes and extremolytes that have the potential to be valuable resources for the development of a bio-based economy through their application to white, red, and grey biotechnologies. Here, we provide an overview of extremophile ecology, and we review the most recent applications of microbial extremophiles and the extremozymes and extremolytes they produce to biotechnology.

Diversity of hydrolases from hydrothermal vent sediments of the Levante Bay, Vulcano Island (Aeolian archipelago) identified by activity-based metagenomics and biochemical characterization of new esterases and an arabinopyranosidase

A metagenomic fosmid expression library established from environmental DNA (eDNA) from the shallow hot vent sediment sample collected from the Levante Bay, Vulcano Island (Aeolian archipelago) was established in Escherichia coli. Using activity-based screening assays, we have assessed 9600 fosmid clones corresponding to approximately 350 Mbp of the cloned eDNA, for the lipases/esterases/lactamases, haloalkane and haloacid dehalogenases, and glycoside hydrolases. Thirty-four positive fosmid clones were selected from the total of 120 positive hits and sequenced to yield ca. 1360 kbp of high-quality assemblies. Fosmid inserts were attributed to the members of ten bacterial phyla, including Proteobacteria, Bacteroidetes, Acidobateria, Firmicutes, Verrucomicrobia, Chloroflexi, Spirochaetes, Thermotogae, Armatimonadetes, and Planctomycetes. Of ca. 200 proteins with high biotechnological potential identified therein, we have characterized in detail three distinct α/β-hydrolases (LIPESV12_9, LIPESV12_24, LIPESV12_26) and one new α-arabinopyranosidase (GLV12_5). All LIPESV12 enzymes revealed distinct substrate specificities tested against 43 structurally diverse esters and 4 p-nitrophenol carboxyl esters. Of 16 different glycosides tested, the GLV12_5 hydrolysed only p-nitrophenol-α-(l)-arabinopyranose with a high specific activity of about 2.7 kU/mg protein. Most of the α/β-hydrolases were thermophilic and revealed a high tolerance to, and high activities in the presence of, numerous heavy metal ions. Among them, the LIPESV12_24 was the best temperature-adapted, retaining its activity after 40 min of incubation at 90 °C. Furthermore, enzymes were active in organic solvents (e.g., >30 % methanol). Both LIPESV12_24 and LIPESV12_26 had the GXSXG pentapeptides and the catalytic triads Ser-Asp-His typical to the representatives of carboxylesterases of EC 3.1.1.1.

Extracellular peptidases from Deinococcus radiodurans

The extremophile Deinococcus radiodurans wild type R1 produces peptidases (metallo- and serine-) in TGY medium and in the media supplemented with human hair (HMY) and chicken feathers (FMY). Enzymatic screening on agar plates revealed peptidase activity. In TGY medium metallopeptidases were detected corresponding to a molecular mass range of 300-85 kDa (gelatinases); 280-130 (caseinases) and a 300 and a 170 kDa (keratinases); and a gelatinolytic serine peptidase (75 kDa). In HMY medium after 144 h, D. radiodurans produced keratinase (290 U/ml), gelatinase (619 U/ml) and sulfite (26 µg/ml). TGY medium produced higher proteolytic activity: 950 U/ml of gelatinolytic (24 h); 470 U/ml of keratinolytic (24 h) and 110 U/ml of caseinolytic (72 h). In the FMY medium, we found gelatinolytic (317 U/ml), keratinolytic (43 U/ml) and caseinolytic (85 U/ml) activities. The sulfite had a maximum release at 48 h (8.1 µg/ml). Enzymography analysis revealed that the keratinases degraded keratin after 24 h of reaction. The addition of sodium sulfite (1.0 %) improved the keratin degradation. Environmental Scanning Electron microscopy revealed alterations such as damage and holes in the hair fiber cuticle after D. radiodurans growth. This work presents for the first time D. radiodurans as a new keratinolytic microorganism.

Discovery a novel organic solvent tolerant esterase from Salinispora arenicola CNP193 through genome mining

An esterase gene, encoding a 325-amino-acid protein (SAestA), was mined form obligate marine actinomycete strain Salinispora arenicola CNP193 genome sequence. Phylogenetic analysis of the deduced amino acid sequence showed that the enzyme belonged to the family IV of lipolytic enzymes. The gene was cloned, expressed in Escherichia coli as a His-tagged protein, purified and characterized. The molecular weight of His-tagged SAestA is ∼38 kDa. SAestA-His6 was active in a temperature (5-40 °C) and pH range (7.0-11.0), and maximal activity was determined at pH 9.0 and 30 °C. The activity was severely inhibited by Hg(2+), Cu(2+), and Zn(2+). In particular, this enzyme showed remarkable stability in presence of organic solvents (25%, v/v) with log P>2.0 even after incubation for 7 days. All these characteristics suggested that SAestA may be a potential candidate for application in industrial processes in aqueous/organic media.

Exploration of extremophiles for high temperature biotechnological processes

Industrial processes often take place under harsh conditions that are hostile to microorganisms and their biocatalysts. Microorganisms surviving at temperatures above 60°C represent a chest of biotechnological treasures for high-temperature bioprocesses by producing a large portfolio of biocatalysts (thermozymes). Due to the unique requirements to cultivate thermophilic (60-80°C) and hyperthermophilic (80-110°C) Bacteria and Archaea, less than 5% are cultivable in the laboratory. Therefore, other approaches including sequence-based screenings and metagenomics have been successful in providing novel thermozymes. In particular, polysaccharide-degrading enzymes (amylolytic enzymes, hemicellulases, cellulases, pectinases and chitinases), lipolytic enzymes and proteases from thermophiles have attracted interest due to their potential for versatile applications in pharmaceutical, chemical, food, textile, paper, leather and feed industries as well as in biorefineries.

Calcium alginate matrix increases the stability and recycling capability of immobilized endo-β-1,4-xylanase from Geobacillus stearothermophilus KIBGE-IB29

Exploration of microbial pool from extremely diversified ecosystem is significantly important for various industrial applications. Bacterial communities from extreme habitats including volcanic vents, hot springs, and industrial sectors are eagerly explored for the isolation of thermophiles. Geobacillus stearothermophilus KIBGE-IB29, isolated from blast furnace site of a steel processing industry, is capable of producing thermostable endo-β-1,4-xylanase. In the current study, this enzyme was immobilized within calcium alginate beads using entrapment technique. Amalgamation of sodium alginate (40.0 gL(-1)) and calcium chloride (0.4 M) was used for the formation of immobilized beads. It was observed that temperature (50 °C) and pH (7.0) optima of immobilized enzyme remained same, but enzyme-substrate reaction time increased from 5.0 to 30.0 min as compared to free enzyme. Diffusion limit of high molecular weight xylan (corncob) caused a decline in V max of immobilized enzyme from 4773 to 203.7 U min(-1), whereas K m value increased from 0.5074 to 0.5722 mg ml(-1) with reference to free enzyme. Immobilized endo-β-1,4-xylanase showed its stability even at high temperatures as compared to free enzyme and retained 18 and 9 % residual activity at 70 and 80 °C, respectively. Immobilized enzyme also exhibited sufficient recycling efficiency up to five reaction cycles which indicated that this enzyme can be a plausible candidate in paper and pulp industry.

Thermophiles in the genomic era: Biodiversity, science, and applications

Thermophiles and hyperthermophiles are present in various regions of the Earth, including volcanic environments, hot springs, mud pots, fumaroles, geysers, coastal thermal springs, and even deep-sea hydrothermal vents. They are also found in man-made environments, such as heated compost facilities, reactors, and spray dryers. Thermophiles, hyperthermophiles, and their bioproducts facilitate various industrial, agricultural, and medicinal applications and offer potential solutions to environmental damages and the demand for biofuels. Intensified efforts to sequence the entire genome of hyperthermophiles and thermophiles are increasing rapidly, as evidenced by the fact that over 120 complete genome sequences of the hyperthermophiles Aquificae, Thermotogae, Crenarchaeota, and Euryarchaeota are now available. In this review, we summarise the major current applications of thermophiles and thermozymes. In addition, emphasis is placed on recent progress in understanding the biodiversity, genomes, transcriptomes, metagenomes, and single-cell sequencing of thermophiles in the genomic era.

Life in extreme environments: single molecule force spectroscopy as a tool to explore proteins from extremophilic organisms

Extremophiles are organisms which survive and thrive in extreme environments. The proteins from extremophilic single-celled organisms have received considerable attention as they are structurally stable and functionally active under extreme physical and chemical conditions. In this short article, we provide an introduction to extremophiles, the structural adaptations of proteins from extremophilic organisms and the exploitation of these proteins in industrial applications. We provide a review of recent developments which have utilized single molecule force spectroscopy to mechanically manipulate proteins from extremophilic organisms and the information which has been gained about their stability, flexibility and underlying energy landscapes.

Nocardiopsis species: Incidence, ecological roles and adaptations

Members of the genus Nocardiopsis are ecologically versatile and biotechnologically important. They produce a variety of bioactive compounds such as antimicrobial agents, anticancer substances, tumor inducers, toxins and immunomodulators. They also secrete novel extracellular enzymes such as amylases, chitinases, cellulases, β-glucanases, inulinases, xylanases and proteases. Nocardiopsis species are aerobic, Gram-positive, non-acid-fast, catalase-positive actinomycetes with nocardioform substrate mycelia and their aerial mycelia bear long chains of spores. Their DNA possesses high contents of guanine and cytosine. There is a marked variation in properties of the isolates obtained from different ecological niches and their products. An important feature of several species is their halophilic or halotolerant nature. They are associated with a variety of marine and terrestrial biological forms wherein they produce antibiotics and toxins that help their hosts in evading pathogens and predators. Two Nocardiopsis species, namely, N. dassonvillei and N. synnemataformans (among the thirty nine reported ones) are opportunistic human pathogens and cause mycetoma, suppurative infections and abscesses. Nocardiopsis species are present in some plants (as endophytes or surface microflora) and their rhizospheres. Here, they are reported to produce enzymes such as α-amylases and antifungal agents that are effective in warding-off plant pathogens. They are prevalent as free-living entities in terrestrial locales, indoor locations, marine ecosystems and hypersaline habitats on account of their salt-, alkali- and desiccation-resistant behavior. In such natural locations, Nocardiopsis species mainly help in recycling organic compounds. Survival under these diverse conditions is mediated by the production of extracellular enzymes, antibiotics, surfactants, and the accumulation of compatible solutes. The accommodative genomic features of Nocardiopsis species support their existence under the diverse conditions where they prevail.

Nocardiopsis species as potential sources of diverse and novel extracellular enzymes

Members of the genus Nocardiopsis are generally encountered in locations that are inherently extreme. They are present in frozen soils, desert sand, compost, saline or hypersaline habitats (marine systems, salterns and soils) and alkaline places (slag dumps, lake soils and sediments). In order to survive under these severe conditions, they produce novel and diverse enzymes that allow them to utilize the available nutrients and to thrive. The members of this genus are multifaceted and release an assortment of extracellular hydrolytic enzymes. They produce enzymes that are cold-adapted (α-amylases), thermotolerant (α-amylases and xylanases), thermoalkalotolerant (cellulases, β-1,3-glucanases), alkali-tolerant thermostable (inulinases), acid-stable (keratinase) and alkalophilic (serine proteases). Some of the enzymes derived from Nocardiopsis species act on insoluble polymers such as glucans (pachyman and curdlan), keratin (feathers and prion proteins) and polyhydroxyalkanoates. Extreme tolerance exhibited by proteases has been attributed to the presence of some amino acids (Asn and Pro) in loop structures, relocation of multiple salt bridges to outer regions of the protein or the presence of a distinct polyproline II helix. The range of novel enzymes is projected to increase in the forthcoming years, as new isolates are being continually reported, and the development of processes involving such enzymes is envisaged in the future.

Generating bifunctional fusion enzymes composed of heat-active endoglucanase (Cel5A) and endoxylanase (XylT)

Bifunctional enzyme constructs were generated comprising two genes encoding heat-active endoglucanase (cel5A) and endoxylanase (xylT). The fused proteins Cel5A-XylT and XylT-Cel5A were active on both β-glucan and beechwood xylan. An improvement in endoglucanase and endoxylanase catalytic activities was observed. The specific activity of the fusion towards xylan was significantly raised when compared to XylT. The fusion constructs were active from 40 to 100 °C for endoglucanase and from 40 to 90 °C for endoxylanase, but the temperature optima were lowered from 90 to 80 °C for the endoglucanase and from 80 to 70 °C for the endoxylanase. XylT in the construct XylT-Cel5A was less stable at higher temperatures compared to Cel5A-XylT. Due to the enzymatic performance, these fusion enzymes are attractive candidates for applications in biorefineries based on plant waste.