LccA, an archaeal laccase secreted as a highly stable glycoprotein into the extracellular medium by Haloferax volcanii

Harnessing the power of bacterial laccases for xenobiotic degradation in water: A 10-year overview

Industrialization and population growth are leading to the production of significant amounts of sewage containing hazardous xenobiotic compounds. These compounds pose a threat to human and animal health, as well as the overall ecosystem. To combat this issue, chemical, physical, and biological techniques have been used to remove these contaminants from water bodies affected by human activity. Biotechnological methods have proven effective in utilizing microorganisms and enzymes, particularly laccases, to address this problem. Laccases possess versatile enzymatic characteristics and have shown promise in degrading different xenobiotic compounds found in municipal, industrial, and medical wastewater. Both free enzymes and crude enzyme extracts have demonstrated success in the biotransformation of these compounds. Despite these advancements, the widespread use of laccases for bioremediation and wastewater treatment faces challenges due to the complex composition, high salt concentration, and extreme pH often present in contaminated media. These factors negatively impact protein stability, recovery, and recycling processes, hindering their large-scale application. These issues can be addressed by focusing on large-scale production, resolving operation problems, and utilizing cutting-edge genetic and protein engineering techniques. Additionally, finding novel sources of laccases, understanding their biochemical properties, enhancing their catalytic activity and thermostability, and improving their production processes are crucial steps towards overcoming these limitations. By doing so, enzyme-based biological degradation processes can be improved, resulting in more efficient removal of xenobiotics from water systems. This review summarizes the latest research on bacterial laccases over the past decade. It covers the advancements in identifying their structures, characterizing their biochemical properties, exploring their modes of action, and discovering their potential applications in the biotransformation and bioremediation of xenobiotic pollutants commonly present in water sources.

Extremozyme-Based Biosensors for Environmental Pollution Monitoring: Recent Developments

Extremozymes combine high specificity and sensitivity with the ability to withstand extreme operational conditions. This work presents an overview of extremozymes that show potential for environmental monitoring devices and outlines the latest advances in biosensors utilizing these unique molecules. The characteristics of various extremozymes described so far are presented, underlining their stability and operational conditions that make them attractive for biosensing. The biosensor design is discussed based on the detection of photosynthesis-inhibiting herbicides as a case study. Several biosensors for the detection of pesticides, heavy metals, and phenols are presented in more detail to highlight interesting substrate specificity, applications or immobilization methods. Compared to mesophilic enzymes, the integration of extremozymes in biosensors faces additional challenges related to lower availability and high production costs. The use of extremozymes in biosensing does not parallel their success in industrial applications. In recent years, the "collection" of recognition elements was enriched by extremozymes with interesting selectivity and by thermostable chimeras. The perspectives for biosensor development are exciting, considering also the progress in genetic editing for the oriented immobilization of enzymes, efficient folding, and better electron transport. Stability, production costs and immobilization at sensing interfaces must be improved to encourage wider applications of extremozymes in biosensors.

Optimization of laccase from Stenotrophomonas maltophilia E1 by submerge fermentation using coconut husk with its detoxification and biodecolorization ability of synthetic dyes

Enzymatic degradation of synthetic dyes holds an immense promise for addressing the environmental concerns associated with the textile and dye industries. This study aimed to isolate bacteria capable of producing laccase enzymes from an anthropogenic environment. Subsequently, viability of utilizing cost-effective agricultural residues as substrates for laccase production was assessed. Response Surface Methodology (RSM) and the One Variable at a Time (OVAT) approach was pursued for the optimization of laccase production, followed by pH and temperature stability, dye degradation and decolorization experiments, toxicological studies on the degraded dye metabolites. In results, laccase-producing bacterial strain was identified as Stenotrophomonas maltophilia strain E1 (S. maltophilia). Among variety of substrates, coconut husk exhibited optimal efficacy. In a statistical optimization study, it was found that S. maltophilia was capable of producing laccase 51.38 IU/mL, i.e., three times higher than the amount of laccase produced by unoptimized medium (16.7 IU/mL), and the enzyme activity was found to be steady at an acidic pH, and a mesophilic temperature range. The laccase obtained from S. maltophilia E1 demonstrated proficient dye decolorization capabilities, achieving a notable 92.1% reduction in Malachite green dye coloration at a concentration of 500 ppm. Gas chromatography-mass spectrometry (GC-MS) analysis of the decolorized derivatives of Malachite green revealed a conversion into a distinct compounds. Moreover, after undergoing laccase treatment, Malachite green exhibited decreased phytotoxic effects on Oryza sativa, pointing to enzymatic detoxification. Collectively, insights gained from the present study will contribute to the development of efficient enzymatic approaches for addressing the environmental pollution caused by synthetic dyes.

Secretory expression of recombinant small laccase genes in Gram-positive bacteria

BACKGROUND

Laccases are multicopper enzymes that oxidize a wide range of aromatic and non-aromatic compounds in the presence of oxygen. The majority of industrially relevant laccases are derived from fungi and are produced in eukaryotic expression systems such as Pichia pastoris and Saccharomyces cerevisiae. Bacterial laccases for research purposes are mostly produced intracellularly in Escherichia coli, but secretory expression systems are needed for future applications. Bacterial laccases from Streptomyces spp. are of interest for potential industrial applications because of their lignin degrading activities.

RESULTS

In this study, we expressed small laccases genes from Streptomyces coelicolor, Streptomyces viridosporus and Amycolatopsis 75iv2 with their native signal sequences in Gram-positive Bacillus subtilis and Streptomyces lividans host organisms. The extracellular activities of ScLac, SvLac and AmLac expressed in S. lividans reached 1950 ± 99 U/l, 812 ± 57 U/l and 12 ± 1 U/l in the presence of copper supplementation. The secretion of the small laccases was irrespective of the copper supplementation; however, activities upon reconstitution with copper after expression were significantly lower, indicating the importance of copper during laccase production. The production of small laccases in B. subtilis resulted in extracellular activity that was significantly lower than in S. lividans. Unexpectedly, AmLac and ScLac were secreted without their native signal sequences in B. subtilis, indicating that B. subtilis secretes some heterologous proteins via an unknown pathway.

CONCLUSIONS

Small laccases from S. coelicolor, S. viridosporus and Amycolatopsis 75iv2 were secreted in both Gram-positive expression hosts B. subtilis and S. lividans, but the extracellular activities were significantly higher in the latter.

Bioactive molecules from haloarchaea: Scope and prospects for industrial and therapeutic applications

Marine environments and salty inland ecosystems encompass various environmental conditions, such as extremes of temperature, salinity, pH, pressure, altitude, dry conditions, and nutrient scarcity. The extremely halophilic archaea (also called haloarchaea) are a group of microorganisms requiring high salt concentrations (2-6 M NaCl) for optimal growth. Haloarchaea have different metabolic adaptations to withstand these extreme conditions. Among the adaptations, several vesicles, granules, primary and secondary metabolites are produced that are highly significant in biotechnology, such as carotenoids, halocins, enzymes, and granules of polyhydroxyalkanoates (PHAs). Among halophilic enzymes, reductases play a significant role in the textile industry and the degradation of hydrocarbon compounds. Enzymes like dehydrogenases, glycosyl hydrolases, lipases, esterases, and proteases can also be used in several industrial procedures. More recently, several studies stated that carotenoids, gas vacuoles, and liposomes produced by haloarchaea have specific applications in medicine and pharmacy. Additionally, the production of biodegradable and biocompatible polymers by haloarchaea to store carbon makes them potent candidates to be used as cell factories in the industrial production of bioplastics. Furthermore, some haloarchaeal species can synthesize nanoparticles during heavy metal detoxification, thus shedding light on a new approach to producing nanoparticles on a large scale. Recent studies also highlight that exopolysaccharides from haloarchaea can bind the SARS-CoV-2 spike protein. This review explores the potential of haloarchaea in the industry and biotechnology as cellular factories to upscale the production of diverse bioactive compounds.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

Modifying Surface Charges of a Thermophilic Laccase Toward Improving Activity and Stability in Ionic Liquid

The multicopper oxidase enzyme laccase holds great potential to be used for biological lignin valorization alongside a biocompatible ionic liquid (IL). However, the IL concentrations required for biomass pretreatment severely inhibit laccase activity. Due to their ability to function in extreme conditions, many thermophilic enzymes have found use in industrial applications. The thermophilic fungal laccase from Myceliophthora thermophila was found to retain high levels of activity in the IL [C₂C₁Im][EtSO₄], making it a desirable biocatalyst to be used for lignin valorization. In contrast to [C₂C₁Im][EtSO₄], the biocompatibility of [C₂C₁Im][OAC] with the laccase was markedly lower. Severe inhibition of laccase activity was observed in 15% [C₂C₁Im][OAc]. In this study, the enzyme surface charges were modified via acetylation, succinylation, cationization, or neutralization. However, these modifications did not show significant improvement in laccase activity or stability in [C₂C₁Im][OAc]. Docking simulations show that the IL docks close to the T1 catalytic copper, likely interfering with substrate binding. Although additional docking locations for [OAc]^- are observed after making enzyme modifications, it does not appear that these locations play a role in the inhibition of enzyme activity. The results of this study could guide future enzyme engineering efforts by showing that the inhibition mechanism of [C₂C₁Im][OAc] toward M. thermophila laccase is likely not dependent upon the IL interacting with the enzyme surface.

Elimination and detoxification of phenanthrene assisted by a laccase from halophile Alkalibacillus almallahensis

Phenanthrene (Phe), a tricyclic Polycyclic Aromatic Hydrocarbon (PAH), is found in high concentrations as a pollutant in various environments. In this study, the removal or (oxidizing) ability of Phe by a laccase from Alkalibacillus almallahensis was investigated. The laccase (12 U mL-1) was able to remove 63% of Phe (50 mg L-1) under optimal conditions of 40 °C, pH 8, 1.5 M NaCl and in the presence of 1 mM HBT as a laccase mediator after a 72 h incubation period. The results for the effect of different solvents, ionic and non-ionic surfactants on the activity of the halophilic laccase towards Phe showed that the addition of these compounds increase removal efficiency and complete enzymatic removal of Phe will achieve in a solution of 5% (v/v) acetone and 1.5% tween 80. The kinetic parameters K m and V max of laccase-catalyzed removal of the substrate were determined as 0.544 mM and 0.882 µmol h-1 mg-1, respectively. A microtoxicity study with respect to the inhibition of algal growth showed a decrease in toxicity of the laccase-treated Phe solution.

Assembly of wood-inhabiting archaeal, bacterial and fungal communities along a salinity gradient: common taxa are broadly distributed but locally abundant in preferred habitats

Wood decomposition in water is a key ecosystem process driven by diverse microbial taxa that likely differ in their affinities for freshwater, estuarine, and marine habitats. How these decomposer communities assemble in situ or potentially colonize from other habitats remains poorly understood. At three watersheds on Coiba Island, Panama, we placed replicate sections of branch wood of a single tree species on land, and in freshwater, estuarine and marine habitats that constitute a downstream salinity gradient. We sequenced archaea, bacteria and fungi from wood samples collected after 3, 9, and 15 months to examine microbial community composition, and to examine habitat specificity and abundance patterns. We found these microbial communities were broadly structured by similar factors, with a strong effect of salinity, but little effect of watershed identity on compositional variation. Moreover, common aquatic taxa were also present in wood incubated on land. Our results suggest that taxa either dispersed to both terrestrial and aquatic habitats, or that microbes with broad habitat ranges were initially present in the wood as endophytes. Nonetheless, these habitat generalists varied greatly in abundance across habitats suggesting an important role for habitat filtering in maintaining distinct aquatic communities in freshwater, estuarine and marine habitats.

Phenoloxidases in Plants-How Structural Diversity Enables Functional Specificity

The metabolism of polyphenolic polymers is essential to the development and response to environmental changes of organisms from all kingdoms of life, but shows particular diversity in plants. In contrast to other biopolymers, whose polymerisation is catalysed by homologous gene families, polyphenolic metabolism depends on phenoloxidases, a group of heterogeneous oxidases that share little beyond the eponymous common substrate. In this review, we provide an overview of the differences and similarities between phenoloxidases in their protein structure, reaction mechanism, substrate specificity, and functional roles. Using the example of laccases (LACs), we also performed a meta-analysis of enzyme kinetics, a comprehensive phylogenetic analysis and machine-learning based protein structure modelling to link functions, evolution, and structures in this group of phenoloxidases. With these approaches, we generated a framework to explain the reported functional differences between paralogs, while also hinting at the likely diversity of yet undescribed LAC functions. Altogether, this review provides a basis to better understand the functional overlaps and specificities between and within the three major families of phenoloxidases, their evolutionary trajectories, and their importance for plant primary and secondary metabolism.

Extremophilic Oxidoreductases for the Industry: Five Successful Examples With Promising Projections

In a global context where the development of more environmentally conscious technologies is an urgent need, the demand for enzymes for industrial processes is on the rise. Compared to conventional chemical catalysts, the implementation of biocatalysis presents important benefits including higher selectivity, increased sustainability, reduction in operating costs and low toxicity, which translate into cleaner production processes, lower environmental impact as well as increasing the safety of the operating staff. Most of the currently available commercial enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of conditions, which limits their actual application under industrial settings. For this reason, enzymes from extremophilic microorganisms stand out for their specific characteristics, showing higher stability, activity and robustness than their mesophilic counterparts. Their unique structural adaptations allow them to resist denaturation at high temperatures and salinity, remain active at low temperatures, function at extremely acidic or alkaline pHs and high pressure, and participate in reactions in organic solvents and unconventional media. Because of the increased interest to replace chemical catalysts, the global enzymes market is continuously growing, with hydrolases being the most prominent type of enzymes, holding approximately two-third share, followed by oxidoreductases. The latter enzymes catalyze electron transfer reactions and are one of the most abundant classes of enzymes within cells. They hold a significant industrial potential, especially those from extremophiles, as their applications are multifold. In this article we aim to review the properties and potential applications of five different types of extremophilic oxidoreductases: laccases, hydrogenases, glutamate dehydrogenases (GDHs), catalases and superoxide dismutases (SODs). This selection is based on the extensive experience of our research group working with these particular enzymes, from the discovery up to the development of commercial products available for the research market.

High-level synthesis and secretion of laccase, a metalloenzyme biocatalyst, by the halophilic archaeon Haloferax volcanii

Haloarchaea and their enzymes have extremophilic properties desirable for use as platform organisms and biocatalysts in the bioindustry. These GRAS (generally regarded as safe) designated microbes thrive in hypersaline environments and use a salt-in strategy to maintain osmotic homeostasis. This unusual strategy has resulted in the evolution of most of the intracellular and extracellular enzymes of haloarchaea to be active and stable not only in high salt (2-5M) but also in low salt (0.2M). This salt tolerance is correlated with a resilience to low water activity, thus, rendering the haloarchaeal enzymes active and stable in organic solvent and temperatures of 50-60°C used in the enzymatic biodelignification and saccharification of lignocellulosic materials. High-level secretion of haloarchaeal enzymes to the extracellular milieu is useful for many applications, including enzymes that deconstruct biomass to allow for lignin depolymerization and simultaneous fermentation of sugars released from hemicellulose and cellulose fractions of lignocellulosics. Here we detail strategies and methods useful for high-level secretion of a laccase, HvLccA, that mediates oxidation of various phenolics by engineering a recombinant strain of the haloarchaeon Haloferax volcanii.

Extremophiles, a Nifty Tool to Face Environmental Pollution: From Exploitation of Metabolism to Genome Engineering

Extremophiles are microorganisms that populate habitats considered inhospitable from an anthropocentric point of view and are able to tolerate harsh conditions such as high temperatures, extreme pHs, high concentrations of salts, toxic organic substances, and/or heavy metals. These microorganisms have been broadly studied in the last 30 years and represent precious sources of biomolecules and bioprocesses for many biotechnological applications; in this context, scientific efforts have been focused on the employment of extremophilic microbes and their metabolic pathways to develop biomonitoring and bioremediation strategies to face environmental pollution, as well as to improve biorefineries for the conversion of biomasses into various chemical compounds. This review gives an overview on the peculiar metabolic features of certain extremophilic microorganisms, with a main focus on thermophiles, which make them attractive for biotechnological applications in the field of environmental remediation; moreover, it sheds light on updated genetic systems (also those based on the CRISPR-Cas tool), which expand the potentialities of these microorganisms to be genetically manipulated for various biotechnological purposes.

Genome-based engineering of ligninolytic enzymes in fungi

Background

Many fungi grow as saprobic organisms and obtain nutrients from a wide range of dead organic materials. Among saprobes, fungal species that grow on wood or in polluted environments have evolved prolific mechanisms for the production of degrading compounds, such as ligninolytic enzymes. These enzymes include arrays of intense redox-potential oxidoreductase, such as laccase, catalase, and peroxidases. The ability to produce ligninolytic enzymes makes a variety of fungal species suitable for application in many industries, including the production of biofuels and antibiotics, bioremediation, and biomedical application as biosensors. However, fungal ligninolytic enzymes are produced naturally in small quantities that may not meet the industrial or market demands. Over the last decade, combined synthetic biology and computational designs have yielded significant results in enhancing the synthesis of natural compounds in fungi.

Main body of the abstract

In this review, we gave insights into different protein engineering methods, including rational, semi-rational, and directed evolution approaches that have been employed to enhance the production of some important ligninolytic enzymes in fungi. We described the role of metabolic pathway engineering to optimize the synthesis of chemical compounds of interest in various fields. We highlighted synthetic biology novel techniques for biosynthetic gene cluster (BGC) activation in fungo and heterologous reconstruction of BGC in microbial cells. We also discussed in detail some recombinant ligninolytic enzymes that have been successfully enhanced and expressed in different heterologous hosts. Finally, we described recent advance in CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas (CRISPR associated) protein systems as the most promising biotechnology for large-scale production of ligninolytic enzymes.

Short conclusion

Aggregation, expression, and regulation of ligninolytic enzymes in fungi require very complex procedures with many interfering factors. Synthetic and computational biology strategies, as explained in this review, are powerful tools that can be combined to solve these puzzles. These integrated strategies can lead to the production of enzymes with special abilities, such as wide substrate specifications, thermo-stability, tolerance to long time storage, and stability in different substrate conditions, such as pH and nutrients.

Halophilic archaea and their potential to generate renewable fuels and chemicals

Lignocellulosic biofuels and chemicals have great potential to reduce our dependence on fossil fuels and mitigate air pollution by cutting down on greenhouse gas emissions. Chemical, thermal, and enzymatic processes are used to release the sugars from the lignocellulosic biomass for conversion to biofuels. These processes often operate at extreme pH conditions, high salt concentrations, and/or high temperature. These harsh treatments add to the cost of the biofuels, as most known biocatalysts do not operate under these conditions. To increase the economic feasibility of biofuel production, microorganisms that thrive in extreme conditions are considered as ideal resources to generate biofuels and value-added products. Halophilic archaea (haloarchaea) are isolated from hypersaline ecosystems with high salt concentrations approaching saturation (1.5-5 M salt concentration) including environments with extremes in pH and/or temperature. The unique traits of haloarchaea and their enzymes that enable them to sustain catalytic activity in these environments make them attractive resources for use in bioconversion processes that must occur across a wide range of industrial conditions. Biocatalysts (enzymes) derived from haloarchaea occupy a unique niche in organic solvent, salt-based, and detergent industries. This review focuses on the use of haloarchaea and their enzymes to develop and improve biofuel production. The review also highlights how haloarchaea produce value-added products, such as antibiotics, carotenoids, and bioplastic precursors, and can do so using feedstocks considered "too salty" for most microbial processes including wastes from the olive-mill, shell fish, and biodiesel industries.

Lignin-oxidizing activity of bacterial laccases characterized using soluble substrates and polymeric lignin

Efficient biotransformation of lignin requires the activity of different oxidative enzymes. In this work, 19 bacterial multi-copper oxidases were screened for oxidase activity against 19 soluble substrates and revealed the highest activity in the laccase CotA_Bsu (BSU0630) from Bacillus subtilis. Structure-based site-directed mutagenesis of CotA_Bsu identified four conserved residues (His419, Cys492, His497, and Met502) as critical for activity against 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS). Greatly reduced oxidase activity was found in the CotA_Bsu mutant proteins E213A, N214A, C229A, N264A, E298A, T415A, R416A, Q468A, and T480A. We also designed a lignin-agarose plate screen for detecting oxidase activity of purified proteins against polymeric lignin, which confirmed the results obtained with ABTS and identified three mutant variants with increased activity toward kraft lignin (E213A, T415A, and T260A). X-ray photoelectron spectroscopy analysis of low sulfonate kraft lignin after incubation with CotA_Bsu revealed a reduction in the content of CC/CC bonds and increase in CO/CO bonds. Product analyses using mass spectrometry, liquid chromatography, and bright-field microscopy revealed an increased polymerization state of reaction products suggesting that formation of radical intermediates was followed by radical coupling. Our results provide further insights into the mechanisms of lignin oxidation by laccases.

Refolding, characterization, and dye decolorization ability of a highly thermostable laccase from Geobacillus sp. JS12

A putative laccase gene (lacG) from Geobacillus sp. JS12 was cloned and expressed as a fusion protein with six histidine residues in Escherichia coli BL21 (DE3) cells, and the protein was primarily found in inclusion bodies. The resulting insoluble proteins were solubilized with 6 M guanidine HCl and refolded using an on-column refolding procedure. Ni-chelation affinity chromatography found the laccase to be a 30 kDa monomeric protein. Spectrophotometry and electron paramagnetic resonance (EPR) analysis indicated LacG as a multi-copper oxidase, with the usual laccase copper sites, Type 1, 2, and 3 Cu(II). The optimum pH for enzymatic activity was 3.0, 6.0, and 6.5 with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), guaiacol and 2,6-dimethoxyphenol (2,6-DMP) as the substrate, respectively. The recombinant protein displayed high thermostability, with a heat inactivation half-life of approximately 2 h at 95 °C, and an optimum temperature of 80 °C with 2,6-DMP. Catalytic efficiency (k_cat/K_m) showed that guaiacol and 2,6-DMP were highly oxidized by the enzyme. The enzymatic reaction was significantly enhanced by Co²⁺ and Mn²⁺, while activity was strongly inhibited in the presence of Fe²⁺, Zn²⁺, and thiol compounds. LacG decolorized 43% of Congo red and 14% of Malachite green, and the addition of ABTS as a redox mediator dramatically increased the dye decolorization efficiency.

Laccase Properties, Physiological Functions, and Evolution

Discovered in 1883, laccase is one of the first enzymes ever described. Now, after almost 140 years of research, it seems that this copper-containing protein with a number of unique catalytic properties is widely distributed across all kingdoms of life. Laccase belongs to the superfamily of multicopper oxidases (MCOs)—a group of enzymes comprising many proteins with different substrate specificities and diverse biological functions. The presence of cupredoxin-like domains allows all MCOs to reduce oxygen to water without producing harmful byproducts. This review describes structural characteristics and plausible evolution of laccase in different taxonomic groups. The remarkable catalytic abilities and broad substrate specificity of laccases are described in relation to other copper-containing MCOs. Through an exhaustive analysis of laccase roles in different taxa, we find that this enzyme evolved to serve an important, common, and protective function in living systems.

Metal and organic pollutants bioremediation by extremophile microorganisms

Extremophiles comprise microorganisms that are able to grow and thrive in extreme environments, including in an acidic or alkaline pH, high or low temperatures, high concentrations of pollutants, and salts, among others. These organisms are promising for environmental biotechnology due to their unique physiological and enzymatic characteristics, which allow them to survive in harsh environments. Due to the stability and persistence of these microorganisms under adverse environmental conditions, they can be used for the bioremediation of environments contaminated with extremely recalcitrant pollutants. Here, we provide an overview of extremophiles and the role of "omics" in the field of bioremediation of environmental pollutants, including hydrocarbons, textile dyes and metals.

Haloferax volcanii for biotechnology applications: challenges, current state and perspectives

Haloferax volcanii is an obligate halophilic archaeon with its origin in the Dead Sea. Simple laboratory culture conditions and a wide range of genetic tools have made it a model organism for studying haloarchaeal cell biology. Halophilic enzymes of potential interest to biotechnology have opened up the application of this organism in biocatalysis, bioremediation, nanobiotechnology, bioplastics and the biofuel industry. Functionally active halophilic proteins can be easily expressed in a halophilic environment, and an extensive genetic toolkit with options for regulated protein overexpression has allowed the purification of biotechnologically important enzymes from different halophiles in H. volcanii. However, corrosion mediated damage caused to stainless-steel bioreactors by high salt concentrations and a tendency to form biofilms when cultured in high volume are some of the challenges of applying H. volcanii in biotechnology. The ability to employ expressed active proteins in immobilized cells within a porous biocompatible matrix offers new avenues for exploiting H. volcanii in biotechnology. This review critically evaluates the various application potentials, challenges and toolkits available for using this extreme halophilic organism in biotechnology.

Laccases: structure, function, and potential application in water bioremediation

The global rise in urbanization and industrial activity has led to the production and incorporation of foreign contaminant molecules into ecosystems, distorting them and impacting human and animal health. Physical, chemical, and biological strategies have been adopted to eliminate these contaminants from water bodies under anthropogenic stress. Biotechnological processes involving microorganisms and enzymes have been used for this purpose; specifically, laccases, which are broad spectrum biocatalysts, have been used to degrade several compounds, such as those that can be found in the effluents from industries and hospitals. Laccases have shown high potential in the biotransformation of diverse pollutants using crude enzyme extracts or free enzymes. However, their application in bioremediation and water treatment at a large scale is limited by the complex composition and high salt concentration and pH values of contaminated media that affect protein stability, recovery and recycling. These issues are also associated with operational problems and the necessity of large-scale production of laccase. Hence, more knowledge on the molecular characteristics of water bodies is required to identify and develop new laccases that can be used under complex conditions and to develop novel strategies and processes to achieve their efficient application in treating contaminated water. Recently, stability, efficiency, separation and reuse issues have been overcome by the immobilization of enzymes and development of novel biocatalytic materials. This review provides recent information on laccases from different sources, their structures and biochemical properties, mechanisms of action, and application in the bioremediation and biotransformation of contaminant molecules in water. Moreover, we discuss a series of improvements that have been attempted for better organic solvent tolerance, thermo-tolerance, and operational stability of laccases, as per process requirements.

Halophiles and Their Vast Potential in Biofuel Production

Global warming and the limitations of using fossil fuels are a main concern of all societies, and thus, the development of alternative fuel sources is crucial to improving the current global energy situation. Biofuels are known as the best alternatives of unrenewable fuels and justify increasing extensive research to develop new and less expensive methods for their production. The most frequent biofuels are bioethanol, biobutanol, biodiesel, and biogas. The production of these biofuels is the result of microbial activity on organic substrates like sugars, starch, oil crops, non-food biomasses, and agricultural and animal wastes. Several industrial production processes are carried out in the presence of high concentrations of NaCl and therefore, researchers have focused on halophiles for biofuel production. In this review, we focus on the role of halophilic microorganisms and their current utilization in the production of all types of biofuels. Also, the outstanding potential of them and their hydrolytic enzymes in the hydrolysis of different kind of biomasses and the production of biofuels are discussed.

Enhancement of laccase activity by pre-incubation with organic solvents

Laccases that are tolerant to organic solvents are powerful bio-catalysts with broad applications in biotechnology. Most of these uses must be accomplished at high concentration of organic solvents, during which proteins undergo unfolding, thereby losing enzyme activity. Here we show that organic-solvent pre-incubation provides effective and reversible 1.5- to 4.0-fold enhancement of enzyme activity of fungal laccases. Several organic solvents, including acetone, methanol, ethanol, DMSO, and DMF had an enhancement effect among all laccases studied. The enhancement was not substrate-specific and could be observed by using both phenolic and non-phenolic substrates. Laccase preincubated with organic solvents was sensitive to high temperature but remained stable at 25 °C, for an advantage for long-term storage. The acetone-pre-incubated 3-D structure of DLac, a high-efficiency fungal laccase, was determined and confirmed that the DLac protein structure remains intact and stable at a high concentration of organic solvent. Moreover, the turnover rates of fungal laccases were improved after organic-solvent pre-incubation, with DLac showing the highest enhancement among the fungal laccases examined. Our investigation sheds light on improving fungal laccase usage under extreme conditions and extends opportunities for bioremediation, decolorization, and organic synthesis.

Aptitude of Oxidative Enzymes for Treatment of Wastewater Pollutants: A Laccase Perspective

Natural water sources are very often contaminated by municipal wastewater discharges which contain either of xenobiotic pollutants and their sometimes more toxic degradation products, or both, which frustrates the universal millenium development goal of provision of the relatively scarce pristine freshwater to water-scarce and -stressed communities, in order to augment their socioeconomic well-being. Seeing that both regulatory measures, as regards the discharge limits of wastewater, and the query for efficient treatment methods remain unanswered, partially, the prospects of enzymatic treatment of wastewater is advisable. Therefore, a reconsideration was assigned to the possible capacity of oxidative enzymes and the respective challenges encountered during their applications in wastewater treatment, and ultimately, the prospects of laccase, a polyphenol oxidase that oxidizes aromatic and inorganic substrates with electron-donating groups in treatment aromatic contaminants of wastewater, in real wastewater situations, since it is assumed to be a vehicle for a greener community. Furthermore, the importance of laccase-driven catalysis toward maintaining mass-energy balance, hence minimizing environmental waste, was comprehensibly elucidated, as well the strategic positioning of laccase in a model wastewater treatment facility for effective treatment of wastewater contaminants.

Mapping the diversity of microbial lignin catabolism: experiences from the eLignin database

Lignin is a heterogeneous aromatic biopolymer and a major constituent of lignocellulosic biomass, such as wood and agricultural residues. Despite the high amount of aromatic carbon present, the severe recalcitrance of the lignin macromolecule makes it difficult to convert into value-added products. In nature, lignin and lignin-derived aromatic compounds are catabolized by a consortia of microbes specialized at breaking down the natural lignin and its constituents. In an attempt to bridge the gap between the fundamental knowledge on microbial lignin catabolism, and the recently emerging field of applied biotechnology for lignin biovalorization, we have developed the eLignin Microbial Database ( www.elignindatabase.com ), an openly available database that indexes data from the lignin bibliome, such as microorganisms, aromatic substrates, and metabolic pathways. In the present contribution, we introduce the eLignin database, use its dataset to map the reported ecological and biochemical diversity of the lignin microbial niches, and discuss the findings.

Molecular characterization of laccase genes from the basidiomycete Trametes hirsuta Bm-2 and analysis of the 5' untranslated region (5'UTR)

The aim of this study was to identify and characterize laccase genes produced by Trametes hirsuta Bm-2 in a liquid medium, both with and without induction. The amplification of 5'and 3'regions of laccase sequences was obtained by the RACE-PCR method, and these were assembled to obtain a cDNA of total length. Two new laccase genes were isolated from basal medium (lac-B) and lignocellulosic grapefruit substrate (lac-T), both encoding open reading frames of 2566 bp. Both laccase-predicted proteins consisted of 521 amino acids, four copper-binding regions, a signal peptide, and five potential glycosilation sites (Asn-Xaa-Ser/Tre). Moreover, the deduced amino acid sequences share about 76-85% identity with other laccases of WRF. Sequence comparison showed 47 synonymous point mutations between lac-B and lac-T. In addition, 5' untranslated regions (UTR) of laccase genes lac-B and lac-T showed differences in length and number of regulatory elements that may affect transcriptional or translational expression of these genes.

Production of highly thermo-tolerant laccase from novel thermophilic bacterium Bacillus sp. PC-3 and its application in functionalization of chitosan film

In this study, a novel thermophilic bacterial strain was isolated from Tattapani hot spring located in the Chhattisgarh state of India. The laccase was produced via submerged fermentation and purified by ammonium sulfate precipitation and anion exchange chromatography up to 13.7 fold. The 16S rRNA gene sequence and biochemical analysis revealed that the bacterial isolate is Bacillus sp. strain PC-3. The activity of extracellular crude laccase was determined to be 11.2 U/mL using 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as a substrate. The SDS-PAGE revealed that the enzyme consists of single subunit with molecular size of 36 kDa. The laccase exhibited the maximum enzyme activity at temperature of 60°C and pH 7. Moreover, the laccase retained 99.1% of its original activity for 180 min and exhibited half-life of 3.75 h at 60°C. Similarly, the laccase retained 95% activity at pH 7 for 240 min and displayed significant activity at wider pH range. In addition, the laccase was used for functionalization of chitosan film and characterized for antioxidant and antimicrobial activity. Interestingly, the functionalized chitosan film showed the improved antioxidant and antimicrobial activity.

Spore cells from BPA degrading bacteria Bacillus sp. GZB displaying high laccase activity and stability for BPA degradation

Laccase has been applied extensively as a biocatalyst to remove different organic pollutants. This study characterized a spore-laccase from the bisphenol A (BPA)-degrading strain Bacillus sp. GZB. The spore-laccase was encoded with 513 amino acids, containing spore coat protein A (CotA). It showed optimal activity at 70 °C and pH = 7.2 in presence of 2, 6-dimethoxyphenol. At 60 °C, optimal activity was also seen at pH = 3.0 and pH = 6.8 with 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate) and syringaldazine, respectively. The spore-laccase was stable at high temperature, at acidic to alkaline pH values, and in the presence of different organic solvents. Spore-laccase activity was increased by introducing Cu²⁺, Mg²⁺, and Na⁺, but was strongly inhibited by Fe²⁺, Ag⁺, l-cysteine, dithiothreitol, and NaN₃. The cotA gene was cloned and expressed in E. coli BL21 (DE3); the purified protein was estimated as having a molecular weight of ~63 kDa. Different synthetic dyes and BPA were effectively decolorized or degraded both by the spore laccase and recombinant laccase. When BPA oxidation was catalyzed using laccase, there was an initial formation of phenoxy radicals and further oxidation or CC bond cleavage of the radicals produced different organic acids. Detailed reaction pathways were developed based on nine identified intermediates. The acute toxicity decreased gradually during BPA degradation by laccase. This study is the first report about a genus of Bacillus that can produce a highly active and stable laccase to degrade BPA.

Characterization of the Microbial Population Inhabiting a Solar Saltern Pond of the Odiel Marshlands (SW Spain)

The solar salterns located in the Odiel marshlands, in southwest Spain, are an excellent example of a hypersaline environment inhabited by microbial populations specialized in thriving under conditions of high salinity, which remains poorly explored. Traditional culture-dependent taxonomic studies have usually under-estimated the biodiversity in saline environments due to the difficulties that many of these species have to grow at laboratory conditions. Here we compare two molecular methods to profile the microbial population present in the Odiel saltern hypersaline water ponds (33% salinity). On the one hand, the construction and characterization of two clone PCR amplified-16S rRNA libraries, and on the other, a high throughput 16S rRNA sequencing approach based on the Illumina MiSeq platform. The results reveal that both methods are comparable for the estimation of major genera, although massive sequencing provides more information about the less abundant ones. The obtained data indicate that Salinibacter ruber is the most abundant genus, followed by the archaea genera, Halorubrum and Haloquadratum. However, more than 100 additional species can be detected by Next Generation Sequencing (NGS). In addition, a preliminary study to test the biotechnological applications of this microbial population, based on its ability to produce and excrete haloenzymes, is shown.

Decolorization and detoxification of textile dyes using a versatile Streptomyces laccase-natural mediator system

Currently, there is increasing interest in assessing the potential of bacterial laccases for industrial and environmental applications especially in harsh conditions. The environmental impact of the textile industry requires novel and effective technologies to mitigate the presence of dyes in wastewaters before discharging into the environment. Dyes usually remain stable in the presence of a variety of chemicals, light and are recalcitrant to microbial degradation. Among available technologies the biological treatments offer environmentally friendly strategies for decolorizing and detoxifying these compounds. The recent discovery of versatile laccases in streptomycetes opens up new opportunities for their commercial application. The aim of this study is to assess the potential of a novel bacterial laccase SilA produced by Streptomyces ipomoeae CECT 3341 active over wide temperature and pH ranges for use as an eco-friendly, biological treatment for the degradation of textile dyes. Insights into the enhancement of the oxidative action of this enzyme through the use of natural redox mediators are presented together with an assessment of the potential toxicity of the degradation products. Our results confirm that the combination of the laccase and natural mediators such as acetosyringone and methyl syringate enhanced the decolorization and detoxification of a variety of textile dyes up to sixfold and 20-fold, respectively. Mediator concentration was found to have a significant effect (p < 0.05) on dye decolorization at 60 °C; thus, the decolorization of Acid Orange 63 increased from 6 to 70-fold when the mediator concentration was increased from 0.1 to 0.5 mM. Further, the toxicity of tartrazine decreased 36-fold when the SilA-MeS system was used to decolorize the dye. The thermal properties of the SilA coupled with the stability of SilA at high pH suggest a potential commercial application for use in the decolorization of textile wastewaters which generally are performed at high temperature (>55 °C) and salinity and neutral pH, conditions which are unfavourable for conventional fungal laccases.

Mechanism of salt-induced activity enhancement of a marine-derived laccase, Lac15

Laccase (benzenediol: oxygen oxidoreductases, EC1.10.3.2) is a multi-copper oxidase capable of oxidizing a variety of phenolic and other aromatic organic compounds. The catalytic power of laccase makes it an attractive candidate for potential applications in many areas of industry including biodegradation of organic pollutants and synthesis of novel drugs. Most laccases are vulnerable to high salt and have limited applications. However, some laccases are not only tolerant to but also activated by certain concentrations of salt and thus have great application potential. The mechanisms of salt-induced activity enhancement of laccases are unclear as yet. In this study, we used dynamic light scattering, size exclusion chromatography, analytical ultracentrifugation, intrinsic fluorescence emission, circular dichroism, ultraviolet-visible light absorption, and an enzymatic assay to investigate the potential correlation between the structure and activity of the marine-derived laccase, Lac15, whose activity is promoted by low concentrations of NaCl. The results showed that low concentrations of NaCl exert little influence on the protein structure, which was partially folded in the absence of the salt; moreover, the partially folded rather than the fully folded state seemed to be favorable for enzyme activity, and this partially folded state was distinctive from the so-called 'molten globule' occasionally observed in active enzymes. More data indicated that salt might promote laccase activity through mechanisms involving perturbation of specific local sites rather than a change in global structure. Potential binding sites for chloride ions and their roles in enzyme activity promotion are proposed.

Delignification and detoxification of peanut shell bio-waste using an extremely halophilic laccase from an Aquisalibacillus elongatus isolate

Lignocellulose bioconversion is a harsh process requiring the use of surfactants and organic solvents. Consequently, the incorporation of laccases in this bioconversion requires the bioprospecting of enzymes that can remain stable under extreme conditions. An extracellular, highly stable laccase was produced by the halophilic isolate Aquisalibacillus elongatus in submerged liquid culture fermentation. Statistical and non-statistical strategies gave the highest enzymatic activity (8.02 U mL^-1) following addition of glucose (1.7 g L^-1), copper sulfate (0.8 g L^-1), urea (15 g L^-1), and CaCl₂ (0.8 g L^-1). The enzyme, after purification using a synthetic affinity support, delignified a peanut shell substrate by 45%. A pH of 8.0 and a temperature of 35 °C were optimal for delignification of this bio-waste material. Addition of [Bmim][PF₆], 1,4-dioxane, acetone, and HBT promoted this bio-waste delignification. Bio-treatment in the presence of 50% [Bmim][PF₆] gave a maximal lignin removal of 87%. The surfactants tested had no significant effects on the delignification yield. The laccase also detoxified the toxic phenols found in peanut shell waste. The high catalytic efficiency of this enzyme against a lignocellulosic sample under extreme conditions suggests the suitability of this laccase for industrial applications.

Overexpression of a Laccase with Dye Decolorization Activity from sp. Induced in

Laccases from bacteria have been widely studied in the past 2 decades due to the higher growth rate of bacteria and their excellent thermal and alkaline pH stability. In this study, a novel laccase gene was cloned from<i> Bacillus</i> sp., analyzed, and functionally expressed in<i> Escherichia coli</i>. The laccase was highly induced in the <i>E. coli</i> expression system with a maximum intracellular activity of 16 U mg^-1 protein. The optimal temperature and pH of the purified laccase were 40°C and 4.6, respectively, when ABTS (2,2'-azino-bis[3-ethylbenzothiazoline-6-sulfonate]) was used as the substrate. The purified laccase showed high stability in the pH range of 3.0-9.0, and retained more than 70% of its activity after 24 h of incubation at 40°C with a pH value of 9.0. Furthermore, the enzyme exhibited extremely high temperature and ion metal tolerance. The half-life of the purified laccase at 70°C was 15.9 h. The purified laccase could efficiently decolorize 3 chemical dyes, especially in the presence of ABTS as a mediator. The high production of this laccase in<i> E. coli</i> and exceptional characteristics of the recombinant enzyme protein make it a promising candidate for industrial applications.

Systematics of haloarchaea and biotechnological potential of their hydrolytic enzymes

Halophilic archaea, also referred to as haloarchaea, dominate hypersaline environments. To survive under such extreme conditions, haloarchaea and their enzymes have evolved to function optimally in environments with high salt concentrations and, sometimes, with extreme pH and temperatures. These features make haloarchaea attractive sources of a wide variety of biotechnological products, such as hydrolytic enzymes, with numerous potential applications in biotechnology. The unique trait of haloarchaeal enzymes, haloenzymes, to sustain activity under hypersaline conditions has extended the range of already-available biocatalysts and industrial processes in which high salt concentrations inhibit the activity of regular enzymes. In addition to their halostable properties, haloenzymes can also withstand other conditions such as extreme pH and temperature. In spite of these benefits, the industrial potential of these natural catalysts remains largely unexplored, with only a few characterized extracellular hydrolases. Because of the applied impact of haloarchaea and their specific ability to live in the presence of high salt concentrations, studies on their systematics have intensified in recent years, identifying many new genera and species. This review summarizes the current status of the haloarchaeal genera and species, and discusses the properties of haloenzymes and their potential industrial applications.

Isolation, one-step affinity purification, and characterization of a polyextremotolerant laccase from the halophilic bacterium Aquisalibacillus elongatus and its application in the delignification of sugar beet pulp

The aim of the present work was to study the ability of a halophilic bacterial laccase to efficient delignification in extreme conditions. Here, a highly stable extracellular laccase showing ligninolytic activity from halophilic Aquisalibacillus elongatus is described. The laccase production was strongly influenced by NaCl and CuSO₄ and under optimal conditions reached 4.8UmL^-1. The monomeric enzyme of 75kDa was purified by a synthetic affinity column with 68.2% yield and 99.8-fold purification. The enzyme showed some valuable features viz. stability against a wide range of organic solvents, salts, metals, inhibitors, and surfactants and specificity to a wide spectrum of substrates diverse in structure and redox potential. It retained more than 50% of the original activity at 25-75°C and pH 5.0-10.0. Furthermore, the enzyme was found to be effective in the delignification of sugar beet pulp in an ionic liquid that makes it useful for industrial applications.

Yeast Hosts for the Production of Recombinant Laccases: A Review

Laccases are multi-copper oxidoreductases which catalyze the oxidation of a wide range of substrates during the simultaneous reduction of oxygen to water. These enzymes, originally found in fungi, plants, and other natural sources, have many industrial and biotechnological applications. They are used in the food, textile, pulp, and paper industries, as well as for bioremediation purposes. Although natural hosts can provide relatively high levels of active laccases after production optimization, heterologous expression can bring, moreover, engineered enzymes with desired properties, such as different substrate specificity or improved stability. Hence, diverse hosts suitable for laccase production are reviewed here, while the greatest emphasis is placed on yeasts which are commonly used for industrial production of various proteins. Different approaches to optimize the laccase expression and activity are also discussed in detail here.

Purification and characterization of laccase from Sinorhizobium meliloti and analysis of the lacc gene

The soil native bacterial strains were screened for laccase activity. Bacterial strain L3.8 with high laccase activity was identified as Sinorhizobium meliloti. The crude intracellular L3.8 enzyme extract was able to oxidize typical diagnostic substrates of plant and fungal laccases. Laccase L3.8 was purified 81-fold with a yield of 19.5%. The molecular mass of the purified bacterial laccase was found to be 70.0kDa and its pI was 4.77. UV-vis spectrum showed that L3.8 protein is a multicopper oxidase. The carbohydrate content of the purified enzyme was estimated at 3.2%. Moreover, the laccase active fraction was characterized in terms of kinetics, temperature, and pH optima as well as the effect of various chemical compounds on the laccase activity, and antioxidant properties, which indicated that the L3.8 laccase had unique properties that might be important in biotechnological applications. The lacc gene encoding S. meliloti laccase was cloned and characterized. The full-length sequence of 1950bp encoded a protein of 649 aa preceded by a signal peptide consisting of 26aa. Laccase L3.8 shared significant structural features characteristic of other laccases, including the conserved regions of four histidine-rich copper-binding sites. Potential biotechnological importance of a newly identified laccase is discussed.

High Level Secretion of Laccase (LccH) from a Newly Isolated White-Rot Basidiomycete, Hexagonia hirta MSF2

Newer and novel laccases attract considerable attention due to its promising and valuable multiple applications in biotech industry. This present investigation documents, for the first time, on high level extracellular secretion of laccase (LccH) in newly isolated wood-degrading basidiomycete Hexagonia hirta MSF2. LccH was optimally active at 40°C in citrate phosphate buffer with a pH of 3.4. Optimized Cu(2+) in glucose yeast extract (GY) medium enhanced the LccH production by H. hirta to 1944.44 U.ml(-1). A further increment in LccH activity of 5671.30 U.ml(-1) was achieved by the addition of a phenolic inducer, 2,5 Xylidine. Zymogram and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of LccH revealed that LccH is a monomer with a molecular mass of 66 kDa. MALDI-TOF-MS based peptide mass fingerprinting and comparative modeling of the amino acid sequence of LccH showed that it was closer to Trametes sp. AH28-2 (PDB: 3KW7) with 48% identity, 95% coverage, 0.011 alignment score and RMSD of 0.497Å. Crude LccH delignified lignocellulosic biomass such as wood and corncob, to a level of 28.6 and 16.5%, respectively. Such high level secretion, thermal and solvent stability of LccH make H. hirta a potential candidate not only for LccH production and biodelignification but also generation of lignin derived aromatic feed stock chemicals for industrial and environmental applications.

Archaeal Inorganic Pyrophosphatase Displays Robust Activity under High-Salt Conditions and in Organic Solvents

Soluble inorganic pyrophosphatases (PPAs) that hydrolyze inorganic pyrophosphate (PPi) to orthophosphate (Pi) are commonly used to accelerate and detect biosynthetic reactions that generate PPi as a by-product. Current PPAs are inactivated by high salt concentrations and organic solvents, which limits the extent of their use. Here we report a class A type PPA of the haloarchaeon Haloferax volcanii (HvPPA) that is thermostable and displays robust PPi-hydrolyzing activity under conditions of 25% (vol/vol) organic solvent and salt concentrations from 25 mM to 3 M. HvPPA was purified to homogeneity as a homohexamer by a rapid two-step method and was found to display non-Michaelis-Menten kinetics with a Vmax of 465 U · mg(-1) for PPi hydrolysis (optimal at 42°C and pH 8.5) and Hill coefficients that indicated cooperative binding to PPi and Mg(2+). Similarly to other class A type PPAs, HvPPA was inhibited by sodium fluoride; however, hierarchical clustering and three-dimensional (3D) homology modeling revealed HvPPA to be distinct in structure from characterized PPAs. In particular, HvPPA was highly negative in surface charge, which explained its extreme resistance to organic solvents. To demonstrate that HvPPA could drive thermodynamically unfavorable reactions to completion under conditions of reduced water activity, a novel coupled assay was developed; HvPPA hydrolyzed the PPi by-product generated in 2 M NaCl by UbaA (a "salt-loving" noncanonical E1 enzyme that adenylates ubiquitin-like proteins in the presence of ATP). Overall, we demonstrate HvPPA to be useful for hydrolyzing PPi under conditions of reduced water activity that are a hurdle to current PPA-based technologies.