A novel application for Neurospora crassa: Progress from batch culture to a membrane bioreactor for the bioremediation of phenols

Decisional tool development and application for techno-economic analysis of fungal laccase production

Textile and medical effluents causing bioaccumulation and biomagnification have been successfully biodegraded by fungal laccases. Here, a decision-making tool was developed and applied to evaluate 45 different laccase production strategies which determined the best potential source from a techno-economical perspective. Laccase production cost was calculated with a fixed output of 109 enzymatic units per batch (USD$per109U) and a sensitivity analysis was performed. Results indicate that optimization of enzymatic kinetics for each organism is essential to avoid exceeding the fermentation time point at which production titer reaches its peak and, therefore, higher production costs. Overall, the most cost-effective laccase-producing strategy was obtained when using Pseudolagarobasidium acaciicola with base production cost of USD $42.46 per 109 U. This works serves as platform for decision-making to find the optimal laccase production strategy based on techno-economic parameters.

Wastewater Treatment Using Membrane Bioreactor Technologies: Removal of Phenolic Contaminants from Oil and Coal Refineries and Pharmaceutical Industries

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols' biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively.

Biological depolymerization of lignin using laccase harvested from the autochthonous fungus Schizophyllum commune employing various production methods and its efficacy in augmenting in vitro digestibility in ruminants

A laccase-producing hyper performer, Schizophyllum commune, a white-rot fungus, was evaluated for its ability to selectively degrade lignin of diverse crop residues in vitro. Relative analysis of crop residue treatment using laccase obtained from immobilized cells demonstrated degradation of 30–40% in finger millet straw and sorghum stover, 27–32% in paddy straw, 21% in wheat straw, and 26% in maize straw, while 20% lignin degradation was observed when purified and recombinant laccase was used. Further investigations into in vitro dry matter digestibility studies gave promising results recording digestibility of 54–59% in finger millet straw 33–36% in paddy straw and wheat straw, 16% in maize straw for laccase obtained from cell immobilization method, whereas 14% digestibility was observed when purified and recombinant laccase was used. Sorghum stover recorded digestibility of 13–15% across all straws treated with laccase. The results obtained elucidated the positive influence of laccase treatment on lignin degradation and in vitro dry matter digestibility. The present research gave encouraging figures confirming the production of laccase using the cell immobilization method to be an efficient production method commensurate with purified and recombinant laccase under conditions of submerged cultivation, proclaiming a cost-effective, environmentally safe green technology for effectual lignin depolymerization.

Myco-remediation: A mechanistic understanding of contaminants alleviation from natural environment and future prospect

Industrialization and modernization of agricultural systems contaminated lithosphere, hydrosphere, and biosphere of the Earth. Sustainable remediation of contamination is essential for environmental sustainability. Myco-remediation is proposed to be a green, economical, and efficient technology over conventional remediation technologies to combat escalating pollution problems at a global scale. Fungi can perform remediation of pollutants through several mechanisms like biosorption, precipitation, biotransformation, and sequestration. Myco-remediation significantly removes or degrades metal metals, persistent organic pollutants, and other emerging pollutants. The current review highlights the species-specific remediation potential, influencing factors, genetic and molecular control mechanism, applicability merits to enhance the bioremediation efficiency. Structure and composition of fungal cell wall is crucial for immobilization of toxic pollutants and a subtle change on fungal cell wall structure may significantly affect the immobilization efficiency. The utilization protocol and applicability of enzyme engineering and myco-nanotechnology to enhance the bioremediation efficiency of any potential fungus was proposed. It is advocated that the association of hyper-accumulator plants with plant growth-promoting fungi could help in an effective cleanup strategy for the alleviation of persistent soil pollutants. The functions, activity, and regulation of fungal enzymes in myco-remediation practices required further research to enhance the myco-remediation potential. Study of the biotransformation mechanisms and risk assessment of the products formed are required to minimize environmental pollution. Recent advancements in molecular "Omic techniques"and biotechnological tools can further upgrade myco-remediation efficiency in polluted soils and water.

Simultaneous Biological Pretreatment and Saccharification of Rice Straw by Ligninolytic Enzymes from Panus neostrigosus I9 and Commercial Cellulase

The utilization of rice straw for biofuel production is limited by its composition. The pretreatment process is required to improve the enzymatic accessibility of polysaccharides in the biomass prior to enzymatic saccharification. In this study, simultaneous biological pretreatment and saccharification (SPS) of rice straw starting from laccase production by Panus neostrigosus I9 was operated in a 2-L fermenter. It was found that fungal physiology was strongly influenced by the agitation, and that the highest laccase production was obtained at an agitation speed of 750 rpm (209.96 ± 0.34 U/L). The dilution rate of 0.05 h-1 was set in continuous fermentation which resulted in laccase activity of 678.49 ± 20.39 U/L, approximately three times higher than that in batch culture. Response surface methodology (RSM) was applied to achieve the condition for maximum percentage of delignification. The maximum percentage of delignification of 45.55% was accomplished after pretreatment of rice straw with laccase enzyme 39.40 U/g rice straw at 43.70 °C for 11.19 h. Reducing sugar of 3.85 ± 0.15 g/L was obtained from the digested rice straw in a SPS reactor, while non-pretreated rice straw gave only 1.13 ± 0.10 g/L within 12 h of incubation. The results indicated that simultaneous biological pretreatment and saccharification (SPS) of rice straw by laccase helped to improve the accessibility of cellulose by cellulolytic enzymes.

The role of cosubstrate and mixing on fungal biofilm efficiency in the removal of tannins

Tannins are polyphenolic compounds produced by plants and they are used in industrial vegetable tanning of leather. Tannins represent one of the low biodegradability substances in tannery wastewaters with high recalcitrant soluble chemical oxygen demand, furthermore high concentration of tannins can inhibit biological treatment. In the present study, four novel rotating submerged packed bed reactors were inoculated with a selected fungal strain to reach a biological degradation of tannins in non-sterile conditions. The selected fungal strain, Aspergillus tubingensis MUT 990, was immobilised in polyurethane foam cubes carriers and inserted inside a submerged rotating cage reactors. The reactors were feed with a solution composed of four tannins: Quebracho (Schinopsis spp.), Wattle (Mimosa spp.), Chestnut (Castanea spp.) and Tara (Caesalpinia spp.). Four reactors with a volume of 4 L each were used, the co-substrate was pure malt extract, the hydraulic retention time was 24 h and the pH setpoint was 5.5. The reactors configuration was chosen to allow the study of the effect of rotation and the co-substrate addition on tannins removal. The experiment lasted two months and it was achieved 80% of chemical oxygen demand and up to 90% dissolved organic carbon removal, furthermore it was detected an important tannase activity.

Enhanced aniline degradation by Desulfatiglans anilini in a synthetic microbial community with the phototrophic purple sulfur bacterium Thiocapsa roseopersicina

Desulfatiglans anilini is a sulfate-reducing bacterium (SRB) capable of oxidizing aniline, although growth and aniline turnover rates are slow, making it difficult to analyze the metabolism of the strain. Therefore, this study was designed to investigate the effect of sulfide on growth of D. anilini cultures, in order to improve its growth and aniline turnover rates, and study the biochemical mechanisms of sulfide inhibition. Hydrogen sulfide was found to inhibit growth of D. anilini, regardless of whether the strain was grown with aniline or phenol, and complete inhibition was observed at 20mM hydrogen sulfide. For improving the growth of D. anilini with aniline, the sulfide-consuming phototrophic bacterium Thiocapsa roseopersicina was co-cultured in a synthetic microbial community with D. anilini using a co-cultivation device that continuously removed hydrogen sulfide from the culture. The doubling time of D. anilini with aniline was 15 days in the co-cultivation device, compared to 26 days in the absence of a sulfide-oxidizing partner. Moreover, the aniline degradation rate was significantly increased by a factor of 2.66 during co-cultivation of D. anilini with T. roseopersicina. The initial carboxylation reaction during aniline degradation was measured in cell-free extracts of D. anilini with carbon dioxide (CO₂) as a co-substrate in the presence of aniline and ATP. The effects of hydrogen sulfide on this aniline carboxylating system and on phenylphosphate synthase activity for phenol activation were studied, and it was concluded that hydrogen sulfide severely inhibited these enzyme activities.

Lignocellulose degradation: An overview of fungi and fungal enzymes involved in lignocellulose degradation

This review aims to present current knowledge of the fungi involved in lignocellulose degradation with an overview of the various classes of lignocellulose-acting enzymes engaged in the pretreatment and saccharification step. Fungi have numerous applications and biotechnological potential for various industries including chemicals, fuel, pulp, and paper. The capability of fungi to degrade lignocellulose containing raw materials is due to their highly effective enzymatic system. Along with the hydrolytic enzymes consisting of cellulases and hemicellulases, responsible for polysaccharide degradation, they have a unique nonenzymatic oxidative system which together with ligninolytic enzymes is responsible for lignin modification and degradation. An overview of the enzymes classification is given by the Carbohydrate-Active enZymes (CAZy) database as the major database for the identification of the lignocellulolytic enzymes by their amino acid sequence similarity. Finally, the recently discovered novel class of recalcitrant polysaccharide degraders-lytic polysaccharide monooxygenases (LPMOs) are presented, because of these enzymes importance in the cellulose degradation process.

An Innovative Porous Nanocomposite Material for the Removal of Phenolic Compounds from Aqueous Solutions

Energy efficient, low-cost, user-friendly, and green methods for the removal of toxic phenolic compounds from aqueous solution are necessary for waste treatment in industrial applications. Herein we present an interesting approach for the utilization of oxidized carbon nanotubes (CNTs) in the removal of phenolic compounds from aqueous solution. Dried pristine CNTs were stably incorporated in a solid porous support of polydimethylsiloxane (PDMS) facilitating the handling during both oxidation process of the nanomaterial and uptake of phenolic compounds, and enabling their safe disposal, avoiding expensive post-treatment processes. The adsorption studies indicated that the materials can efficiently remove phenolic compounds from water with different affinities towards different phenolic compounds. Furthermore, the adsorption kinetics and isotherms were studied in detail. The experimental data of adsorption fitted well with Langmuir and Freundlich isotherms, and pseudo-second-order kinetics, and the results indicated that the adsorption process was controlled by a two-step intraparticle diffusion model. The incorporation of CNTs in polymeric matrices did not affect their functionality in phenol uptake. The material was also successfully used for the removal of phenolic compounds from agricultural waste, suggesting its possible application in the treatment of wastewater. Moreover, the surface of the material could be regenerated, decreasing treatment costs.

Antifungal Activity against Filamentous Fungi of Ts1, a Multifunctional Toxin from Tityus serrulatus Scorpion Venom

Antimicrobial peptides (AMPs) are ubiquitous and multipotent components of the innate immune defense arsenal used by both prokaryotic and eukaryotic organisms. The search for new AMPs has increased in recent years, due to the growing development of microbial resistance to therapeutical drugs. In this work, we evaluate the effects of Tityus serrulatus venom (Tsv), its fractions and its major toxin Ts1, a beta-neurotoxin, on fungi growth. The fractions were obtained by ion-exchange chromatography of Tsv. The growth inhibition of 11 pathogenic and non-pathogenic filamentous fungi (Aspergillus fumigatus, A. nidulans, A. niger, A. terreus, Neurospora crassa, Penicillium corylophilum, P. ochrochloron, P. verrucosum, P. viridicatum, P. waksmanii, and Talaromyces flavus) was evaluated by quantitative microplate reader assay. Tsv (100 and 500 μg/well, which correspond to 1 and 5 mg/mL, respectively, of total soluble protein) was active in inhibiting growth of A. nidulans, A. terreus, P. corylophilum, and P. verrucosum, especially in the higher concentration used and at the first 30 h. After this period, fungi might have used Tsv components as alternative sources of nutrients, and therefore, increased their growth tax. Only fractions IX, X, XI, XIIA, XIIB (3 and 7.5 μg/well, which correspond to 30 and 75 μg/mL, respectively, of total soluble protein) and Ts1 (1.5, 3, and 6 μg/well, which correspond to 2.18, 4.36, and 8.72 μM, respectively) showed antifungal activity. Ts1 showed to be a non-morphogenic toxin with dose-dependent activity against A. nidulans, inhibiting 100% of fungal growth from 3 μg/well (4.36 μM). The inhibitory effect of Ts1 against A. nidulans growth was accompanied by fungistatic effects and was not amended by 1 mM CaCl₂ or tetrodotoxin (46.98 and 93.96 μM). The structural differences between Ts1 and drosomycin, a potent cysteine-rich antifungal peptide, are discussed here. Our results highlight the antifungal potential of the first cysteine-containing scorpion toxin. Since Ts1 is a multifunctional toxin, we suggest that it could be used as a template in the design of engineered scorpion AMPs and in the search for new mechanisms of action of antifungal drugs.

A comparison of the response of twoBurkholderia fungorumstrains grown as planktonic cells versus biofilm to dibenzothiophene and select polycyclic aromatic hydrocarbons

In natural environments, bacteria often exist in close association with surfaces and interfaces by establishing biofilms. Here, we report on the ability of Burkholderia fungorum strains DBT1 and 95 to survive in high concentrations of hydrocarbons, and we compare their growth as a biofilm vs. planktonic cells. The 2 compounds tested were dibenzothiophene (DBT) and a mixture of naphthalene, phenanthrene, and pyrene (5:2:1) as representative compounds of thiophenes and polycyclic aromatic hydrocarbons (PAHs), respectively. The results showed that both strains were able to degrade DBT and to survive in the presence of up to a 2000 mg·L−1concentration of this compound both as a biofilm and as free-living cells. Moreover, B. fungorum DBT1 showed reduced tolerance towards the mixed PAHs (2000 mg·L−1naphthalene, 800 mg·L−1phenanthrene, and 400 mg·L−1pyrene) both as a biofilm and as free-living cells. Conversely, biofilms of B. fungorum 95 enhanced resistance against these toxic compounds compared with planktonic cells (P < 0.05). Visual observation through confocal laser scanning microscopy showed that exposure of biofilms to DBT and PAHs altered their structure: high concentrations of DBT triggered an aggregation of biofilm cells. These findings provide new perspectives on the effectiveness of using DBT-degrading bacterial strains in bioremediation of hydrocarbon-contaminated sites.

Bioremediation of Food Industry Effluents: Recent Applications of Free and Immobilised Polyphenoloxidases

Enzymes are specific biological catalysts able to react under mild conditions of temperature and pH and their use in food industry for bioremediation is well known. Research in recent years has been intense, much of it elicited by the great number of different exploitable enzymes. Employment of enzymes in many bioremediation processes is made in order to protect the environment from damage caused by industrial polluting effluents. In particular, the food industry is one of the most important sectors among the manufacturing industries as far as production values are concerned; indeed, food industry processes involve large amounts of water and contribute to pollution loads discharged into water resources. In particular the presence of phenols in agroindustrial effluents has attracted interest for laccases and tyrosinases use in wastewater treatment and bioremediation. The presence of phenolic compounds in drinking and irrigation water or in cultivated land represents a significant health and/or environmental hazard and, therefore, the development of methods for their removal and transformation have received increased attention in recent years. The main purpose of this paper was to present the most recent results dealing with the fundamental and applied aspects of free and immobilised polyphenoloxidases for food industry wastewater processing.

Production of cellobionate from cellulose using an engineered Neurospora crassa strain with laccase and redox mediator addition

We report a novel production process for cellobionic acid from cellulose using an engineered fungal strain with the exogenous addition of laccase and a redox mediator. A previously engineered strain of Neurospora crassa (F5∆ace-1∆cre-1∆ndvB) was shown to produce cellobionate directly from cellulose without the addition of exogenous cellulases. Specifically, N. crassa produces cellulases, which hydrolyze cellulose to cellobiose, and cellobiose dehydrogenase (CDH), which oxidizes cellobiose to cellobionate. However, the conversion of cellobiose to cellobionate is limited by the slow re-oxidation of CDH by molecular oxygen. By adding low concentrations of laccase and a redox mediator to the fermentation, CDH can be efficiently oxidized by the redox mediator, with in-situ re-oxidation of the redox mediator by laccase. The conversion of cellulose to cellobionate was optimized by evaluating pH, buffer, and laccase and redox mediator addition time on the yield of cellobionate. Mass and material balances were performed, and the use of the native N. crassa laccase in such a conversion system was evaluated against the exogenous Pleurotus ostreatus laccase. This paper describes a working concept of cellobionate production from cellulose using the CDH-ATBS-laccase system in a fermentation system.

Biotransformation of 14-deoxy-14-methylenetriptolide into a novel hydroxylation product by Neurospora crassa

The biotransformation of 14-deoxy-14-methylenetriptolide by Neurospora crassa CGMCC AS 3.1604 to produce a new hydroxylation derivative was studied. The structure of this novel compound was determined using spectral data. This biotransformation using whole cells conditioned for 4 days transformed approximately 65% (mol ratio) of the substrate into the compound (5R)-5-hydroxy-14-deoxy-14-methylenetriptolide.

Quorus bioreactor: a new perfusion-based technology for microbial cultivation

: This chapter briefly reviews perfusion-based cultivation solutions used in biomanufacturing. It further introduces the innovative single-use Quorus Bioreactor, which was designed for the efficient cultivation of nontraditional production cell types. The Quorus Bioreactor design, process control, and productivity are described. Case studies are presented using Aspergillus niger and Lactococcus lactis as model organisms to demonstrate process flexibility, efficiency, and scalability.

A novel biochemical route for fuels and chemicals production from cellulosic biomass

The conventional biochemical platform featuring enzymatic hydrolysis involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as reactive intermediates for subsequent fermentation to fuels and chemicals. Herein, an alternative biochemical route is proposed. Pretreatment, enzymatic hydrolysis and cellulase production is consolidated into one single step, referred to as consolidated aerobic processing, and sugar aldonates are produced as the reactive intermediates for biofuels production by fermentation. In this study, we demonstrate the viability of consolidation of the enzymatic hydrolysis and cellulase production steps in the new route using Neurospora crassa as the model microorganism and the conversion of cellulose to ethanol as the model system. We intended to prove the two hypotheses: 1) cellulose can be directed to produce cellobionate by reducing β-glucosidase production and by enhancing cellobiose dehydrogenase production; and 2) both of the two hydrolysis products of cellobionate—glucose and gluconate—can be used as carbon sources for ethanol and other chemical production. Our results showed that knocking out multiple copies of β-glucosidase genes led to cellobionate production from cellulose, without jeopardizing the cellulose hydrolysis rate. Simulating cellobiose dehydrogenase over-expression by addition of exogenous cellobiose dehydrogenase led to more cellobionate production. Both of the two hydrolysis products of cellobionate: glucose and gluconate can be used by Escherichia coli KO 11 for efficient ethanol production. They were utilized simultaneously in glucose and gluconate co-fermentation. Gluconate was used even faster than glucose. The results support the viability of the two hypotheses that lay the foundation for the proposed new route.

Laccase: microbial sources, production, purification, and potential biotechnological applications

Laccase belongs to the blue multicopper oxidases and participates in cross-linking of monomers, degradation of polymers, and ring cleavage of aromatic compounds. It is widely distributed in higher plants and fungi. It is present in Ascomycetes, Deuteromycetes and Basidiomycetes and abundant in lignin-degrading white-rot fungi. It is also used in the synthesis of organic substance, where typical substrates are amines and phenols, the reaction products are dimers and oligomers derived from the coupling of reactive radical intermediates. In the recent years, these enzymes have gained application in the field of textile, pulp and paper, and food industry. Recently, it is also used in the design of biosensors, biofuel cells, as a medical diagnostics tool and bioremediation agent to clean up herbicides, pesticides and certain explosives in soil. Laccases have received attention of researchers in the last few decades due to their ability to oxidize both phenolic and nonphenolic lignin-related compounds as well as highly recalcitrant environmental pollutants. It has been identified as the principal enzyme associated with cuticular hardening in insects. Two main forms have been found: laccase-1 and laccase-2. This paper reviews the occurrence, mode of action, general properties, production, applications, and immobilization of laccases within different industrial fields.

Fungal laccases: production, function, and applications in food processing

Laccases are increasingly being used in food industry for production of cost-effective and healthy foods. To sustain this trend widespread availability of laccase and efficient production systems have to be developed. The present paper delineate the recent developments that have taken place in understanding the role of laccase action, efforts in overexpression of laccase in heterologous systems, and various cultivation techniques that have been developed to efficiently produce laccase at the industrial scale. The role of laccase in different food industries, particularly the recent developments in laccase application for food processing, is discussed.

Innate and induced resistance mechanisms of bacterial biofilms

Bacterial biofilms are highly recalcitrant to antibiotic treatment, which holds serious consequences for therapy of infections that involve biofilms. The genetic mechanisms of this biofilm antibiotic resistance appear to fall into two general classes: innate resistance factors and induced resistance factors. Innate mechanisms are activated as part of the biofilm developmental pathway, the factors being integral parts of biofilm structure and physiology. Innate pathways include decreased diffusion of antibiotics through the biofilm matrix, decreased oxygen and nutrient availability accompanied by altered metabolic activity, formation of persisters, and other specific molecules not fitting into the above groups. Induced resistance factors include those resulting from induction by the antimicrobial agent itself. Biofilm antibiotic resistance is likely manifested as an intricate mixture of innate and induced mechanisms. Many researchers are currently trying to overcome this extreme biofilm antibiotic resistance by developing novel therapies aimed at disrupting biofilms and killing the constituent bacteria. These studies have led to the identification of several molecules that effectively disturb biofilm physiology, often by interrupting bacterial quorum sensing. In this manner, manipulation of innate and induced resistance pathways holds much promise for treatment of biofilm infections.

Metabolism of androst-4-en-3,17-dione by the filamentous fungus Neurospora crassa

Microbial transformation of androst-4-en-3,17-dione (AD; I) using Neurospora crassa afforded six metabolites; 6beta,14alpha-dihydroxyandrost-4-en-3,17-dione (II), 6beta,9alpha-dihydroxyandrost-4-en-3,17-dione (III), 7alpha-hydroxyandrost-4-en-3,17-dione (IV), 9alpha-hydroxyandrost-4-en-3,17-dione (V), 14alpha-hydroxyandrost-4-en-3,17-dione (VI), and androst-4,6-dien-3,17-dione (VII). The steroid products were assigned by interpretation of their spectral data such as (1)H NMR, (13)C NMR, FTIR, and mass spectroscopy. The characteristic transformations observed were C-6beta, C-7alpha, C-9alpha, C-14alpha hydroxylations, and C6-C7 dehydrogenation. The best fermentation condition was found to be 6-day incubation at 25 degrees C and pH value of 5.0-6.5 according to TLC profiles. Time course study showed the accumulation of V and VI from the third day and IV from the fourth day of the fermentation. Optimum concentration of the substrate, which gave maximum bioconversion efficiency, was 3.5mM in one batch. Biotransformation was completely inhibited in a concentration above 7.0mM.

Laccase production at reactor scale by filamentous fungi

Laccases have received much attention from researchers during the past decades due to their broad substrate specificity and to the fact that they use molecular oxygen as the final electron acceptor instead of hydrogen peroxide as used by peroxidases. This makes laccases highly interesting for a wide variety of processes, such as textile dye decolouration, pulp bleaching, effluent detoxification, biosensors and bioremediation. The successful application of laccases to the above-mentioned processes requires the production of large quantities of enzyme at low cost. Filamentous fungi are able to produce laccases in high amounts, however, an efficient production system at bioreactor scale is still lacking. This is mainly due to the fact that laccase production by wild-type strains of filamentous fungi is linked to secondary metabolism, which implies that the following drawbacks must be overcome: uncontrolled fungal growth, the formation of polysaccharides around mycelia and the secretion of certain compounds (i.e. proteases) that inactivate laccases. This review summarizes the current status of laccase production by wild-type strains of filamentous fungi at the bioreactor scale.

Potential applications of the oxidoreductive enzymes in the decolorization and detoxification of textile and other synthetic dyes from polluted water: a review

Recently, the enzymatic approach has attracted much interest in the decolorization/degradation of textile and other industrially important dyes from wastewater as an alternative strategy to conventional chemical, physical and biological treatments, which pose serious limitations. Enzymatic treatment is very useful due to the action of enzymes on pollutants even when they are present in very dilute solutions and recalcitrant to the action of various microbes participating in the degradation of dyes. The potential of the enzymes (peroxidases, manganese peroxidases, lignin peroxidases, laccases, microperoxidase-11, polyphenol oxidases, and azoreductases) has been exploited in the decolorization and degradation of dyes. Some of the recalcitrant dyes were not degraded/decolorized in the presence of such enzymes. The addition of certain redox mediators enhanced the range of substrates and efficiency of degradation of the recalcitrant compounds. Several redox mediators have been reported in the literature, but very few of them are frequently used (e.g., 1-hydroxybenzotriazole, veratryl alcohol, violuric acid, 2-methoxy-phenothiazone). Soluble enzymes cannot be exploited at the large scale due to limitations such as stability and reusability. Therefore, the use of immobilized enzymes has significant advantages over soluble enzymes. In the near future, technology based on the enzymatic treatment of dyes present in the industrial effluents/wastewater will play a vital role. Treatment of wastewater on a large scale will also be possible by using reactors containing immobilized enzymes.

Laccase activity from the fungus Trametes hirsuta using an air-lift bioreactor

AIM

To produce high laccase activities from the white-rot fungus Trametes hirsuta in an in-house air-lift bioreactor (ALB).

METHODS AND RESULTS

Trametes hirsuta was grown in a 6-l ALB. A fed-batch strategy with glycerol as an addition resulted in maximum laccase activity of 19,400 U l(-1), which was the highest reported from the fungus.

CONCLUSION

The ALB configuration with additional glycerol resulted in high laccase activities.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides useful information on how to produce high concentrations of laccase.

Enhanced benzaldehyde tolerance in Zymomonas mobilis biofilms and the potential of biofilm applications in fine-chemical production

Biotransformation plays an increasingly important role in the industrial production of fine chemicals due to its high product specificity and low energy requirement. One challenge in biotransformation is the toxicity of substrates and/or products to biocatalytic microorganisms and enzymes. Biofilms are known for their enhanced tolerance of hostile environments compared to planktonic free-living cells. Zymomonas mobilis was used in this study as a model organism to examine the potential of surface-associated biofilms for biotransformation of chemicals into value-added products. Z. mobilis formed a biofilm with a complex three-dimensional architecture comprised of microcolonies with an average thickness of 20 microm, interspersed with water channels. Microscopic analysis and metabolic activity studies revealed that Z. mobilis biofilm cells were more tolerant to the toxic substrate benzaldehyde than planktonic cells were. When exposed to 50 mM benzaldehyde for 1 h, biofilm cells exhibited an average of 45% residual metabolic activity, while planktonic cells were completely inactivated. Three hours of exposure to 30 mM benzaldehyde resulted in sixfold-higher residual metabolic activity in biofilm cells than in planktonic cells. Cells inactivated by benzaldehyde were evenly distributed throughout the biofilm, indicating that the resistance mechanism was different from mass transfer limitation. We also found that enhanced tolerance to benzaldehyde was not due to the conversion of benzaldehyde into less toxic compounds. In the presence of glucose, Z. mobilis biofilms in continuous cultures transformed 10 mM benzaldehyde into benzyl alcohol at a steady rate of 8.11 g (g dry weight)(-1) day(-1) with a 90% molar yield over a 45-h production period.

Immobilized viable microbial cells: from the process to the proteome… or the cart before the horse

Biotechnological processes based on immobilized viable cells have developed rapidly over the last 30 years. For a long time, basic studies of the physiological behaviour of immobilized cells (IC) have remained in the shadow of the applications. Natural IC structures, i.e. biofilms, are being increasingly investigated at the cellular level owing to their definite importance for human health and in various areas of industrial and environmental relevance. This review illustrates this paradoxical development of research on ICs, starting from the initial rationale for IC emergence and main application fields of the technology--with particular emphasis on those that exploit the extraordinary resistance of ICs to antimicrobial compounds--to recent advances in the proteomic approach of IC physiology.

Study of dye decolorization in an immobilized laccase enzyme-reactor using online spectroscopy

Decolorization of textile dyes by a laccase from Trametes modesta immobilized on gamma-aluminum oxide pellets was studied. An enzyme reactor was equipped with various UV/Vis spectroscopic sensors allowing the continuous online monitoring of the decolorization reactions. Decolorization of the dye solutions was followed via an immersion transmission probe. Adsorption processes were observed using diffuse reflectance measurements of the solid carrier material. Generally, immobilization of the laccase does not seem to sterically affect dye decolorization. A range of commercial textile dyes was screened for decolorization and it was found that the application of this enzymatic remediation system is not limited to a certain structural group of dyes. Anthrachinonic dyes (Lanaset Blue 2R, Terasil Pink 2GLA), some azo dyes, Indigo Carmine, and the triphenylmethane dye Crystal Violet were efficiently decolorized. However, the laccase displayed pronounced substrate specificities when a range of structurally related model azodyes was subjected to the biotransformation. Azodyes containing hydroxy groups in ortho or para position relative to the azo bond were preferentially oxidized. The reactor performance was studied more closely using Indigo Carmine.