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The bioflocculant producing bacterial strain - UKD24 was isolated from the domestic sewage treatment plant. The isolated strain was identified as

The bioflocculant producing bacterial strain – UKD24 was isolated from the domestic sewage treatment plant. The isolated strain was identified as Klebsiella pneumoniae by using 16S rRNA gene sequencing. The K. pneumoniae UKD24 showed remarkable flocculation rates when grown with the carbon sources namely glucose, sucrose and lactose, and many commercial nitrogen sources. Furthermore, the fish waste extract (FE) was used to enhance the productivity of the bioflocculant as a nitrogen supplement and it showed a significant level of flocculation rate similar to the commercial nitrogen sources. The Box–Behnken experiments were designed to predict the optimal conditions for bioflocculant production and it suggested that glucose – 3.247 g L−1, FE – 0.5 g L−1 and inoculum size – 1% are the suitable levels for bioflocculant production. The FTIR analysis of the bioflocculant showed the functional groups related to the polysaccharides and the EEM analysis showed the fluorescence components related to the proteins and humic acids. The biochemical composition of the bioflocculant was identified as polysaccharides (24.36 ± 1.5%) and protein (12.15 ± 0.2%). The tested optimum conditions of the bioflocculant to induce flocculation were tested in the kaolin wastewater and it showed that the optimum dosage of the flocculant was 5 mg L−1 and the pH range was broad as 5–10. The cation dependency tests revealed that the monovalent and divalent cations are highly suitable for flocculation while the trivalent cations showed moderate flocculation. The Cr(VI) removal efficiency of the bioflocculant showed that ∼35% of heavy metal is trapped into flocks during the flocculation.

Nearly 1.3 billion tonnes of food is lost or wasted across the food supply chain. Of this, nearly 46% are generated during the processing, distribution, and consumer levels and are often designated as food waste. Because of the difficulty in identifying virgin finite natural resources, food waste is considered to be an alternative source and has been the focus of intensive research over the last two decades. The efficient utilization of food waste in different treatment technologies such as composting and anaerobic digestion is highly influenced by the physicochemical properties of the waste. The high moisture, rapid degradable nature of food waste initiates a cascade of events, for example, during composting, ultimately affecting the rate of degradation and/or stabilization. To overcome these limitations, an understanding of the properties of food waste is key. This chapter analyses the properties of food waste reported in the literature and their implications to different treatment technologies are highlighted.

The increasing quantity of food waste generation and the disposal of food waste are major issues in cities and urban areas. Disposal of food waste poses a serious environmental problem worldwide. The landfill of food waste is common practice for its disposal and a large quantity of food waste ends up in landfill. However, food wastes can be used as valuable resources and recycled into new added-value products like compost, biogas through anaerobic digestion, and animal feed. Animal feed production from food waste has caught the attention of many countries. This chapter provides comprehensive information on the sources, types, and methods of preparation of different types of animal feed from food waste.

Laccases are cuproproteins belonging to the oxidoreductase family that catalyse the oxidation of various aromatic and non-aromatic compounds. With wide occurrence in bacteria, fungi, higher plants and insects, laccases have been majorly exploited due to their pivotal role in bioremediation and industrial uses. Low productivity and high cost limit the use of native laccases. Besides these drawbacks, native sources yield a mixture of isozymes, which is not desirable for commercial scopes. Thus, in conjunction with this, recombinant laccases have gained importance for sustainable processing due to their improved catalysis, stabilities, and solvent and anionic tolerance. Henceforth, this review mainly focuses to accentuate the recombinant laccases from fungal, mushroom, bacterial and actinobacterial sources, laccase engineering and their proficient industrial applications. The characteristic traits of the recombinant forms of laccase from distinct sources emphasise the requirement to study them more for their upcoming, hidden environmental and biotechnological applications.

In present study, the efficiency of three oleaginous yeasts i.e., Yarrowia lipolytica, Rhodotorula glutinis and Cryptococcus curvatus were compared for their lipid assimilation capacities using three different FW-leachates as a medium. The FW-leachates were collected from dry anaerobic digesters and diluted to achieve carbohydrate content of 25gL-1 prior to yeast inoculations. Around 5% of yeast cultures were individually mixed in three different FW-leachate mediums and incubated under 30°C and 150rpm agitation for 6days. The Y. lipolytica produced high biomass with lipid contents of 49.0±2% on dry weight basis. Whereas, the acetic acid concentration of >6gL-1 inhibited the growth of R. glutinis. The study observed that the selection of appropriate FW-leachate composition is highly important for biolipid accumulation by oleaginous yeasts.

The aqueous extract of various plants like Coriandrum sativum (AECS), Alternanthera tenella colla (AEAT), Spermacoce hispida (AESH) and Mollugo verticillata (AEMV) was studied for its hexavalent chromium (CrVI) reduction property. Even though antioxidant activity was present, AEAT, AESH and AEMV did not reduce CrVI. AECS showed rapid and dose-dependent CrVI reduction. The efficient reduction of 50 mg/L of CrVI using AECS was attained in the presence of 250 µg/mL of starting plant material, incubating the reaction mixture at pH 2, 30°C and agitation at 190 rpm. Under such conditions, about 40 mg/L of CrVI was reduced at 3 h of incubation. FT-IR analysis revealed the involvement of phenols, alcohols, alpha-hydroxy acid and flavonoids present in the AECS for the CrVI reduction. These results indicate that not all the plant extracts with rich antioxidants are capable of reducing CrVI. Using the conditions standardized in the present study, AECS reduced about 80% of CrVI present in the tannery effluent...

The main concern of extensive production of biobutanol has been associated with the high cost of the substrate and the relatively low tolerance of Clostridia to biobutanol production. In this study, the use of fermentable cassava waste residue (CWR) as substrate for biobutanol production was investigated using solvent-tolerant Clostridium sp. Four of obligatory, solvent-producing bacteria were isolated from sago industry waste sites. The NSW, PNAS1, SB5 and SBI4 strains showed identical profiles of 16S rRNA gene sequence similarity of Bacillus coagulans, Clostridium bifermentans and Clostridium sp. (97% similarity) and a wide range of carbohydrate substrate; however, the CWR was found to be suitable for the production of biobutanol considerably. Batch culture study was carried out using parameters such as time and temperature and carbon sources have been studied and optimized. Using pre-optimized CWR medium, significant amount of solvent production was observed in NSW, PNAS1, SB5 and SBI4 with 1.53, 3.36, 1.56 and 2.5 g L

Biogenic flocculant produced by Acidithiobacillus ferrooxidans was used for sludge conditioning to improve the dewaterability of anaerobically-digested sludge, and its efficiency was compared with commercial cationic polyacrylamide (PAM). Biogenic flocculant rapidly reduced the pH and increased the oxidation-reduction potential of sludge. Capillary suction time (CST) and specific resistant to filtration (SRF) of sludge was decreased by 74% and 89%, respectively, compared with control; and the reductions were 58% CST and 67% SRF higher when compared with commercial polymer. Biogenic treatment improved the sludge calorific value by 13%, and also reduced the unpleasant odor. The small-scale mechanical filter press study showed that the biogenic flocculant can reduce the moisture content of sludge to 70%, and improve the clarity of the filtrate in terms of removal of total suspended solids and total dissolved solids when compared with synthetic polymer treatment.

This study investigated the improvement in dewaterability of activated sludge (ACS) and anaerobically digested sludge (ADS) through bioacidification approach using iron-oxidizing bacterium, Acidithiobacillus ferrooxidans. ACS and ADS were treated with A. ferrooxidans culture with addition of different concentrations of energy substrate, in terms of Fe(2+):sludge solids ratio (0:1, 0.01:1, 0.05:1 and 0.1:1), and the dewaterability was assessed by determining the capillary suction time (CST), time to filter (TTF) and specific resistance to filtration (SRF) of the sludge. The results revealed that the levels of Fe(2+) significantly influenced the sludge acidification (pH⩽3). The CST, TTF and SRF values rapidly decreased in treated sludge, indicating that dewaterability of the sludge was significantly (p

In this study, the flocculation efficiency (FE) of avian egg-white was investigated as a protein rich natural bioflocculant to flocculate kaolin dispersion. The FE was optimized under various conditions. Its cation dependent interaction with kaolin basal planes was also investigated through FT-IR, EEM, Zeta Potential and SEM-EDX techniques. The maximum flocculation rate (91 %) was observed at the CaCl2 dosage of 100 ppm and at pH 6.0 due to the electrostatic interaction of Ca2+ ions with the gibbsite basal planes of kaolin at this condition. Among several monovalent, divalent and trivalent cations, Ca2+ alone showed higher FE than other cations. It showed the unique interaction of Ca2+ ions with Avian Egg-white Flocculant (AVGF) functional groups. EEM study was used to reveal the involvement of such functional groups. The results revealed that the carboxylate groups instead of aromatic amino acid side chains are involving in such interaction. This hypothesis was further confirmed in wastewater flocculation experiments in which the Ca2+ and AVGF complex showed weak interaction with suspended particles of domestic wastewater.

In this work, djembe like ZnO microstructures was successfully synthesized by surfactant-assisted hydrothermal method and its composite with g-C3N4 was prepared by an ethanolic reflux method for the first time. Moreover, the structural, morphological, electrical, optical properties and its photocatalytic activities were studied. The result revealed that the formation heterojunction between djembe like ZnO and g-C3N4, decreased the optical band gap energy thereby the light absorption was shifted towards visible region. The photocatalytic performance was studied by dye degradation experiment under visible light irradiation. The degradation efficiency of the ZnO/g-C3N4 composite for MB and RhB degradation was found to be ~95% and ~97% respectively, which is higher than that of the same for pure ZnO and g-C3N4. The scavenger studies indicated the active role of hydroxyl radicals in the degradation process. Furthermore, djembe like ZnO/g-C3N4 composite was successfully reused for five cycles of photodegradation without any drastic change in its activity and crystalline properties.

Bioleaching using an iron-oxidizing bacterium, Acidithiobacillus ferrooxidans, and its biogenic flocculants was evaluated to improve the dewaterability of chemically enhanced primary treatment (CEPT) sewage sludge. CEPT sludge in flasks was inoculated with A. ferrooxidans culture, medium-free cells and the cell-free culture filtrate with and without the energy substance Fe2+, and periodically the sludge samples were analysed for the dewaterability. This investigation proves that bioleaching effectively improved the sludge dewaterability as evidenced from drastic reduction in capillary suction time (≤20 seconds) and specific resistance to filtration (≥90%); however, it requires an adaptability period of 1–2 days. On the other hand, the biogenic flocculant produced by A. ferrooxidans greatly decreased the time-to-filtration and facilitated the dewaterability within 4 h. Results indicate that rapid dewatering of CEPT sludge by biogenic flocculants provides an opportunity to replace the synthetic organic polymer for dewatering.

Laccase is industrially important but a major challenge is the production of an ideal laccase with suitable physicochemical properties to tolerate temperature, surfactants, metal ions and solvents towards its potential application in bioremediation.A laccase with a molecular mass of 43 kDa was purified from Pleurotus sp. MAK-II. It was optimally active at pH 4.5 and 60 °C using ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) as substrate. The laccase was susceptible to NaN3 and NaCN. Activity was strongly enhanced by Cu(2+), Mg(2+) and Ca(2+). The purified laccase showed stability towards various surfactants and solvents and decolorized, in the presence of violuric acid as redox mediator, the diazo dye Congo Red and the anthraquinone dye Remazol Brilliant Blue R to the extent of 96 and 72 %, respectively.The ideal physicochemical properties of Pleurotus sp. MAK-II-derived laccase suggest that it could be effectively used in the textile dye industry.

Pretreatment of activated sludge with sulfuric acid and bioleaching using Acidithiobacillus ferrooxidans along with addition of Fe 2+ on sludge dewaterability was investigated. The sludge dewatering efficiency in terms of capillary suction time (CST) and specific resistant to filtration (SRF) was increased with a decrease in sludge pH. A pH of 2.67 was found to be optimum for dewatering, at which 81% and 63% reduction of CST and SRF were achieved, respectively. The dewaterability of sludge was enhanced after the addition of Fe 2+ and A. ferrooxidans . Ideal concentration of Fe 2+ was 2 g/L for sludge dewaterability, which showed 96% and 88% reduction in CST and SRF, respectively. In the control sludge, maximum part of the biopolymeric macromolecules was contributing by the tightly bound extracellular polymeric substances (TB-EPS). At optimum Fe 2+ concentration, total EPS was reduced by 73%, enhancing sludge dewaterability. Bioleaching conducted by A. ferrooxidans could solubilized 88% Cu and 99% Zn within 120 h.

This study investigated the preparation of a reusable adsorbent from the phyto-waste Terminalia catappa fruit shells by acid-thermal modification and utilization for the removal of diclofenac from aqueous systems. The structural characteristic features of the modified T. catappa fruit shells (MTCFS) were analysed using Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy and Brunauer–Emmett–Teller analysis. Batch experiments proved that temperature and pH mainly influenced the adsorption process. The Langmuir and Freundlich isotherms were obeyed for the diclofenac adsorption. The Temkin isotherm model revealed that increasing temperature affected the adsorption of diclofenac. The Dubinin–Radushkevich isotherm indicated that the present adsorption system was achieved through physical interactions. A pseudo-second-order kinetic model was well fitted for the diclofenac adsorption. Intraparticle diffusion results indicated increases in the rate of adsorption and in the boundary layer thickness. The thermodynamic results revealed that increasing the temperature inversely affected the diclofenac adsorption. Recycling experiments confirmed that the MTCFS were found to be quite stable and retained their adsorption efficiency for up to eight cycles of diclofenac removal.

Dewatering of sludge at wastewater treatment plants is an essential and costly step in the subsequent sludge processing. Prior to dewatering, sludge is conditioned by addition of expensive organic and inorganic conditioners. The present study aimed at developing an effective biological process for sludge dewatering in comparison with commercial polyacrylamide polymers. A complex ferric biogenic flocculant produced by Acidithiobacillus ferrooxidans was used for dewatering of sludge generated after the Chemically Enhanced Primary Treatment process from municipal sewage. Within 1 h of treatment, the ferric biogenic flocculant reduced the capillary suction time (CST) and specific resistant to filtration (SRF) of sludge by 92 and 91%, respectively, as compared to the 89 and 72% respectively achieved by using polymer. The acidification of the sludge after the addition of ferric biogenic flocculant caused charge neutralization of sludge particles and led to enhanced dewaterability. It also enhanced the floc structure of sludge with much bigger sized flocs as compared to the control, which facilitate its dewatering capacity. Ferric biogenic flocculant treatment improved the calorific value of the sludge by 27% due to improved settlement of organic matter into the sludge pellet. The small scale mechanical filter press study confirmed that the ferric biogenic flocculant is effective in reducing sludge moisture content to 69% as well as improving the effluent quality in terms of total suspended solids and total dissolved solids removal compared with polymer treatment.

Sewage treatment plants generate a large volume of waste sludge as a by-product with water content over 95%, which requires further treatment, volume reduction, dewatering, stabilization, and safe disposal. Sludge dewatering is a major issue in sewage treatment as dewatering consumes a large quantity of expensive synthetic chemical flocculants. Moreover, the commercial chemical flocculants create several environmental issues including generation of odor and release of toxic compounds. As an alternative to chemical flocculant-based dewatering, a sustainable and eco-friendly process is necessary. A number of studies have been reported on this aspect using flocculants produced by heterotrophic bacteria, chemolithoautotrophic bacteria, and fungi. A composite flocculant from iron-oxidizing bacteria has been found to be a promising flocculating agent. This chapter presents a comprehensive review of developments in biotechnological approaches to sludge flocculation and dewatering, which includes background on sewage treatment, sludge flocculation, and dewatering methods using microbial flocculants.

Role of Acidithiobacillus ferrooxidans culture in bioacidification and dewaterability of anaerobically digested sewage sludge (ADS) was investigated. A. ferrooxidans culture grown in 9K medium along with Fe(2+) produced iron flocculant containing, secondary iron minerals and biopolymeric substances as confirmed by FT-IR, XRD, and SEM-EDX. Bioacidification of ADS was performed using 10% (v/v) A. ferrooxidans culture, isolated cells and cell-free culture filtrate; and dewaterability was assessed using the capillary suction time (CST) and specific resistance to filtration (SRF). Isolated bacterial cells significantly (P0.05) reduced the sludge dewaterability when supplemented with Fe(2+) while the whole culture and cell-free filtrate rapidly acidified the sludge without Fe(2+) and showed significant reduction of CST (71.3-73.5%) and SRF (84-88%). Results clearly indicated that the culture and filtrate of the A. ferrooxidans facilitated rapid sludge dewaterability while the cells supplemented with Fe(2+) also enhanced dewaterability but required 2-4 days.

In this study, filamentous fungal strains isolated from sewage sludge bioleached with iron-oxidizing bacteria were evaluated their effectiveness in improving the flocculation and dewaterability of chemically enhanced primary treatment (CEPT) sludge. Augmentation of the pre-grown mycelial biomass in the CEPT sludge had no significant changes in sludge pH but, improved sludge dewaterability, as evidenced from the decrease in capillary suction time. Improvement on sludge flocculation and dewaterability depended on the fungal strains, and a pellet forming Penicillium sp. was more effective than the fungal isolates producing filamentous form of mycelial biomass due to entrapment of sludge solids onto mycelial pellets. Fungal treatment also reduced the chemical oxygen demand of the CEPT sludge by 35–76%. Supplementation metal cations (Ca 2+ , Mg 2+ , and Fe 3+ ) to fungal pre-augmented sludge rapidly improved the sludge dewaterability. This study indicates that augmentation of selective fungal biomass can be a potential method for CEPT sludge flocculation and dewaterability.

Aims To demonstrate the biodegradation of dibenzofuran (DF) and its structural analogs by a newly isolated Agrobacterium sp. PH-08. Methods and Results To assess the biodegradation potential of newly isolated Agrobacterium sp. PH-08, various substrates were evaluated as sole carbon sources in growth and biotransformation experiments. ESI LC-MS/MS analysis revealed the presence of angular degrading by-products as well as lateral dioxygenation metabolites in the upper pathway. The metabolites in the lower pathway also were detected. In addition, the cometabolically degraded daughter compounds of DF-related compounds such as BP and dibenzothiophene (DBT) in dual substrate degradation were observed. Strain PH-08 exhibited the evidence of meta-cleavage pathway as confirmed by the activity and gene expression of catechol-2,3-dioxygenase. Conclusions Newly isolated bacterial strain, Agrobacterium sp. PH-08, grew well with and degraded DF via both angular and lateral dioxygenation as demonstrated by metabolites identified through ESI LC-MS/MS and GC-MS analyses. The other heterocyclic pollutants were also cometabolically degraded. Significance and Impact of the Study Few reports have described the complete degradation of DF by a cometabolic lateral pathway. Our study demonstrates the novel results that the newly isolated strain utilized the DF as a sole carbon source and mineralized it via multiple dioxygenation.

The reactivity of FeS-coated iron nanoparticles (nFe/FeS) toward trichloroethylene (TCE) reduction was examined in both synthetic and real groundwater matrices to evaluate the potential performance of nFe/FeS in field treatment. The rate of TCE reduction increased with increasing pH, which is consistent with the pH effect reported previously for iron sulfide systems, but opposite that has been observed for (nonsulfidic) Fe0 systems. The rates of TCE reduction were unaffected by ionic strength over the range of 0.1–10 mM NaCl, increased with Ca2+ or Mg2+ concentrations, and inhibited by the presence of humic acid. The inhibitory effect of humic acid on the reactivity of nFe/FeS was largely alleviated when humic acid was combined with Ca2+/Mg2+, presumably due to decreased adsorption of humic acid onto nFe/FeS surface by the formation of humic acid–Ca2+/Mg2+ complexes.

The continuous release of toxic persistent organic pollutants (POPs) into the environment has raised a need for effective cleanup methods. The tremendous natural diversity of microbial catabolic mechanisms suggests that catabolic routes may be applied to the remediation of POP-contaminated fields. A large number of the recalcitrant xenobiotics have been shown to be removable via the natural catabolic mechanisms of microbes, and detailed biochemical studies of the catabolic methods, together with the development of sophisticated genetic engineering, have led to the use of synthetic microbes for the bioremediation of POPs. However, the steric effects of substituted halogen moieties, microbe toxicity, and the low bioavailability of POPs still deteriorate the efficiency of removal strategies based on natural and synthetic catabolic mechanisms. Recently, abiotic redox processes that induce rapid reductive dehalogenation, hydroxyl radical-based oxidation, or electron shuttling have been reasonably coupled with microbial catabolic actions, thereby compensating for the drawbacks of biotic processes in POP removal. In this review, we first compare the pros and cons of individual methodologies (i.e., the natural and synthetic catabolism of microbes and the abiotic processes involving zero-valent irons, advanced oxidation processes, and small organic stimulants) for POP removal. We then highlight recent trends in coupling the biotic–abiotic methodologies and discuss how the processes are both feasible and superior to individual methodologies for POP cleanup. Cost-effective and environmentally sustainable abiotic redox actions could enhance the microbial bioremediation potential for POPs.

The dioxin isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) has been reported as the deadliest compound known to science. Due to its highly recalcitrant nature and low bioavailability, it is stubborn toward bioremediation and chemical treatment. Efforts to degrade it using one single technique have not accomplished the desired results. In this study, we have tried to develop an integrated 2,3,7,8-TeCDD removal process using palladized iron nanoparticles (Pd/nFe) for initial reductive dechlorination under anoxic conditions and subsequent oxidative biomineralization. Using laboratory synthesized Pd/nFe, 2,3,7,8-TeCDD was completely dechlorinated to form the end product dibenzo-p-dioxin (DD). Oxidative degradation of DD was successfully achieved by growing active cells of a dioxin-degrading microorganism Sphingomonas wittichii RW1 (DSM 6014) under aerobic culture conditions. Metabolite identification was done by high performance liquid chromatography (HPLC) and whole cell protein was measured as the indicator for cell growth. To the best of our knowledge, this is the first report on integrated hybrid degradation method for 2,3,7,8-TeCDD.

This study investigated the fate of extracellular polymeric substances (EPS) of anaerobically digested saline sewage sludge during its preconditioning. Sludge was conditioned with Acidithiobacillus ferrooxidans (AF) culture for 24h in the presence and absence of Fe(2+) as an energy substrate. pH decreased from 7.24 to 3.12 during sludge conditioning process. The capillary suction time (CST) of conditioned sludge significantly decreased to10s, and specific resistance to filtration (SRF) was reduced by94% as compared with control within 4h of conditioning with or without Fe(2+), indicating a significant (P0.001) improvement in sludge dewaterability. A noticeable decrease in extractable EPS was observed in conditioned sludge. The EPS contents showed a significant negative correlation with dewaterability of sludge (P0.05). The results suggest that bioacidification treatment using A. ferrooxidans effectively improved sludge dewaterability through modification of sludge EPS.

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) are emerging persistent organic pollutants. Degradation of PBDEs is a significant challenge owing to their extreme persistence and recalcitrance nature. The objective of this study was to evaluate the effect of a sequential nano-bio treatment using nanoscale zero-valent iron (nZVI) and diphenyl ether degrading bacteria Sphingomonas sp. PH-07 for degradation of PBDEs. RESULTS: In the bacterial tolerance test for determining the maximum endurable concentration of nZVI, the PH-07 strain was able to grow in the presence of nZVI up to 5 g L−1 in minimal salt medium by using non-brominated diphenyl ether as growth substrate. Reductive debromination of decabrominated diphenyl ether (deca-BDE; 1 mg) with nZVI (100 mg per vial) resulted in a 67% reduction of deca-BDE and produced various intermediates ranging from nona-BDEs to tri-BDEs during a 20 day period. Additional experiments with 2,4,4′-tri-BDE and 2,4,6-tri-BDE as initial substrates revealed that both tri-BDEs were further debrominated to mono-BDEs. Following the reductive debromination process, reaction mixtures were aerobically treated with DE-grown Sphingomonas sp. PH-07 strain to mineralize the low brominated-DEs (tri-BDEs—mono-BDEs) for additional 4 days. During bacterial treatment, the low brominated-DEs were biologically degraded to bromophenols and other prospective metabolites. CONCLUSIONS: The nZVI-biological sequential treatment method was found to be effective for degradation of PBDEs through reductive debromination followed by biological oxidation. This hybrid treatment method may lead to the development of a remediation strategy for highly halogenated environmental pollutants in contaminated sites. Copyright © 2011 Society of Chemical Industry

Laccases are oxidases that contain several copper atoms, and catalyse single-electron oxidations of phenolic compounds with concomitant reduction of oxygen to water. The enzymes are particularly widespread in ligninolytic basidiomycetes, but also occur in certain prokaryotes, insects and plants. Depending on the species, laccases are involved in various biosynthetic processes contributing to carbon recycling in land ecosystems and the morphogenesis of biomatrices, wherein low-molecular-weight naturally occurring phenols serve as key enzyme substrates. Studies of these in vivo synthetic pathways have afforded new insights into fungal laccase applicability in green synthetic chemistry. Thus, we here review fungal laccase-catalysed oxidations of naturally occurring phenols that are particularly relevant to the synthesis of fine organic chemicals, and we discuss how the discovered synthetic strategies mimic laccase-involved in vivo pathways, thus enhancing the green nature of such reactions. Laccase-catalysed in vivo processes yield several types of biopolymers, including those of cuticles, lignin, polyflavonoids, humus and the melanin pigments, using natural mono- or poly-phenols as building blocks. The in vivo synthetic pathways involve either phenoxyl radical-mediated coupling or cross-linking reactions, and can be adapted to the design of in vitro oxidative processes involving fungal laccases in organic synthesis; the laccase substrates and the synthetic mechanisms reflect in vivo processes. Notably, such in vitro synthetic pathways can also reproduce physicochemical properties (e.g. those of chromophores, and radical-scavenging, hydration and antimicrobial activities) found in natural biomaterials. Careful study of laccase-associated in vivo metabolic pathways has been rewarded by the discovery of novel green applications for fungal laccases. This review comprehensively summarizes the available data on laccase-catalysed biosynthetic pathways and associated applications in fine chemical syntheses.

The well-known bacterium Sphingomonas wittichii RW1 catabolically degrades dibenzo-p-dioxin and dibenzofuran, as well as their chlorinated derivatives. The catabolic degradation of dioxin is initiated by a ring-hydroxylating dioxygenase. The biotransformation of carbazole by S. wittichii RW1 was determined in the present study. Dioxin dioxygenase from the dibenzofuran induced RW1 strain was thought to be unable to attack carbazole, which includes a heterocyclic aromatic dibenzopyrrole system. However, our results showed that carbazole was transformed to anthranilic acid and catechol. The color of the culture suspension changed upon addition of carbazole due to formation of a nitrogen-containing metabolite. Relevant metabolic intermediates were identified by gas chromatographic mass spectrometry and electrospray ionization time-of-flight mass spectrometry with comparison to the corresponding authentic compounds. The dioxygenase of the dibenzofuran induced RW1 attacked at the angular position adjacent to the nitrogen atom to give a dihydroxylated metabolic intermediate. Contrary to predictions made in previous reports, S. wittichii RW1 displayed positive catabolic activity toward carbazole.

In this study, we have evaluated the effect of palladium–iron bimetallic nanoparticles ( n Fe–Pd) on diphenyl ether (DE) degrading bacterial strain Sphingomonas sp. PH-07 as well as a sequential nano-bio hybrid process with n Fe–Pd as catalytic reductant and PH-07 as biocatalyst for degradation of triclosan. Strain PH-07 grew well in the presence of n Fe–Pd up to 0.1 g/L in minimal salts medium with DE as carbon source. In aqueous system, TCS (17.3 μM) was completely dechlorinated within 2 h by n Fe–Pd (0.1 g/L) with concomitant release of 2-phenoxyphenol (16.8 μM) and chloride ions (46 μM). All possible dichloro- and monochloro-2-phenoxyphenol intermediates were identified by HPLC and GC–MS analyses, and the dechlorination pathway was proposed. Addition of PH-07 cells into the reactor effectively degraded the 2-phenoxyphenol. Our results reveal that strain PH-07 survives well in the presence of n Fe–Pd and n Fe–Pd/PH-07 hybrid treatment could be a potential strategy for degradation of TCS.

The antimicrobial agent triclosan is an emerging and persistent environmental pollutant. This study evaluated the susceptibility and biodegradation potential of triclosan by three bacterial strains (Sphingomonas wittichii RW1, Burkholderia xenovorans LB400 and Sphingomonas sp. PH-07) that are able to degrade aromatic pollutants (dibenzofuran, biphenyl and diphenyl ether, respectively) with structural similarities to triclosan. These strains showed less susceptibility to triclosan when grown in complex and mineral salts media. Biodegradation experiments revealed that only strain PH-07 was able to catabolize triclosan to intermediates that included hydroxylated compounds (monohydroxy-triclosan, and dihydroxy-triclosan) and the ether bond cleavage products (4-chlorophenol and 2,4-dichlorophenol), indicating that the initial dihydroxylation occurred on both aromatic rings of triclosan. Additional growth inhibition tests demonstrated that the main intermediate, 2,4-dichlorophenol, was less toxic to strain PH-07 than was triclosan. Our results indicate that ether bond cleavage might be the primary mechanism of avoiding triclosan toxicity by this strain.

The aerobic metabolism of monofluorophenols (mono-FPs) by the actinomycete, Pseudonocardia benzenivorans, was studied. This strain was able to grow on 4-fluorophenol (4-FP) and readily transform 2- and 3-fluorophenol to the corresponding metabolites. The detailed mechanism of mono-FPs degradation by P. benzenivorans was elucidated from enzymatic assays and the identification of reaction intermediates by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry. Two types of fluorocatechols (i.e., 3- and 4-fluorocatechol) were identified as the key transformation products. During 4-FP degradation, only 4-fluorocatechol was detected, and a stoichiometric level of fluoride was released. Both fluorocatechols were observed together in cultures containing 3-fluorophenol (3-FP), while only 3-fluorocatechol was found to accumulate in 2-fluorophenol (2-FP)-containing cultures. Whole-cell extracts of P. benzenivorans expressed catechol 1,2-dioxygenase activity, indicating that the transformation of the three tested mono-FPs proceeded via ortho-cleavage pathway. The results presented in this paper provide comprehensive information regarding the metabolism of mono-FPs by a single bacterium.

In this study, we investigated the efficacy of phenolic extract of wheat bran and lignin-related phenolic compounds as natural redox mediators on laccase-mediated transformation of malachite green (MG) using purified laccase from the white-rot fungus Ganoderma lucidum. G. lucidum laccase was able to decolorize 40.7% MG dye (at 25 mg l−1) after 24 h of incubation. Whereas, the addition of phenolic extract of wheat bran enhanced the decolorization significantly (p

A new bacterial strain PH-06 was isolated using enrichment culture technique from river sediment contaminated with 1,4-dioxane, and identified as belonging to the genus Mycobacterium based on 16S rRNA sequencing (Accession No. EU239889). The isolated strain effectively utilized 1,4-dioxane as a sole carbon and energy source and was able to degrade 900 mg/l 1,4-dioxane in minimal salts medium within 15 days. The key degradation products identified were 1,4-dioxane-2-ol and ethylene glycol, produced by monooxygenation. Degradation of 1,4-dioxane and concomitant formation of metabolites were demonstrated by GC/MS analysis using deuterium labeled 1,4-dioxane (1,4-dioxane-d8). In addition to 1,4-dioxane, this bacterium could also transform structural analogues such as 1,3-dioxane, cyclohexane and tetrahydrofuran when pre-grown with 1,4-dioxane as the sole growth substrate. Our results suggest that PH-06 can maintain sustained growth on 1,4-dioxane without any other carbon sources.

Dye decolorizing potential of the white rot fungus Ganoderma lucidum KMK2 was demonstrated for recalcitrant textile dyes. G. lucidum produced laccase as the dominant lignolytic enzyme during solid state fermentation (SSF) of wheat bran (WB), a natural lignocellulosic substrate. Crude enzyme shows excellent decolorization activity to anthraquinone dye Remazol Brilliant Blue R (RBBR) without redox mediator whereas diazo dye Remazol Black-5 (RB-5) requires a redox mediator. Polyacrylamide gel electrophoresis (PAGE) of crude enzyme confirms that the laccase enzyme was the major enzyme involved in decolorization of either dyes. Native and SDS-PAGE indicates that the presence of single laccase with molecular weight of 43 kDa. N-Hydroxybenzotriazole (HBT) at a concentration of 1 mM was found as the best redox mediator. RB-5 (50 mg l−l) was decolorized by 62% and 77.4% within 1 and 2 h, respectively by the crude laccase (25 U ml−1). RBBR (50 mg l−l) was decolorized by 90% within 20 h, however, it was more efficient in presence of HBT showing 92% decolorization within 2 h. Crude laccase showed high thermostability and maximum decolorization activity at 60 °C and pH 4.0. The decolorization was completely inhibited by the laccase inhibitor sodium azide (0.5 mM). Enzyme inactivation method is a good method which averts the undesirable color formation in the reaction mixture after decolorization. High thermostability and efficient decolorization suggest that this crude enzyme could be effectively used to decolorize the synthetic dyes from effluents.

Response surface methodology (RSM) was applied for the decolourization of the azo dye reactive black 5 (RB-5) using purified laccase from a white rot fungus Pleurotus sajor-caju. We observed that the presence of 1-hydroxybenzotriazole (HBT) is essential for decolourization of RB-5 by purified laccase from P. sajor-caju. Box–Behnken design using RSM with four variables namely dye (25–100 mg l−1), enzyme (0.5–2.5 U ml−1), redox mediator (0.5–1.5 mM) concentrations and incubation time (24–48 h) was employed in this study to optimize significant correlation between the effects of these variables on the decolourization of RB-5. The optimum concentrations of dye, enzyme, HBT, and time were found to be 62.5 mg l−1, 2.5 U ml−1, 1.5 mM and 36 h, respectively, for maximum decolourization of RB-5 (84.4%). A quadratic model was obtained for dye decolourization through this design. The experimental values were in good agreement with predicted values and the model was highly significant, the correlation coefficient being 0.999. Increased decolourization was observed with increase in enzyme concentration at lower dye concentration. Interaction between HBT and dye concentrations was negligible. The optimization of HBT is independent of dye concentration.

Several aerobic bacteria possess unique catabolic pathways enabling them to degrade persistent organic pollutants (POPs), including polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), polybrominated diphenylethers (PBDEs), and polychlorinated biphenyls (PCBs). The catabolic activity of aerobic bacteria employed for removal of POPs in the environment may be modulated by several biotic (i.e. fungi, plants, algae, earthworms, and other bacteria) and abiotic (i.e. zero-valent iron, advanced oxidation, and electricity) agents. This review describes the basic biochemistry of the aerobic bacterial catabolism of selected POPs and discusses how biotic and abiotic agents enhance or inhibit the process. Solutions allowing biotic and abiotic agents to exert physical and chemical assistance to aerobic bacterial catabolism of POPs are also discussed.

Pseudomonas veronii strain PH-03 has been shown to convert benzene to cyclohexanone through phenol. Mass spectrometry results revealed that unusual isotopic effects have been occurred in the transformation product, cyclohexanone. The isotopic composition was strongly depends on the compound specific hydrogen or oxygen source. The exchange of labile deuterium atoms has been investigated through electrospray ionization liquid chromatography mass spectrometry. The mass spectrometric analysis of biotransformation products enabled the proposal of a corresponding bioconversion pathway.

An extracellular laccase was isolated and purified from Pleurotus sajor-caju grown in submerged culture in a bioreactor, and used to investigate its ability to decolorize three azo dyes. The extracellular laccase production was enhanced up to 2.5-fold in the medium amended with xylidine (1 mM). Purification was carried out using ammonium sulfate (70% w/v), DEAE-cellulose, and Sephadex G-100 column chromatography. The enzyme was purified up to 10.3-fold from the initial protein preparation with an overall yield of 53%. The purified laccase was monomeric with an apparent molecular mass of 61.0 kDa. The purified enzyme exerted its optimal activity with 2,2-azino-bis(3-ethylbenzo-thiazoline-6-sulfonate (ABTS) and oxidized various lignin-related phenols. The catalytic efficiencies kcat/Km determined for ABTS and syringaldazine were 9.2x10(5) and 8.7x10(5), respectively. The optimum pH and temperature for the purified enzyme was 5.0 and 40 degrees C, respectively. Sodium azide completely inhibited the laccase activity. The absorption spectrum revealed type 1 and type 3 copper signals. The purified enzyme decolorized azo dyes such as acid red 18, acid Black 1, and direct blue 71 up to 90, 87, and 72%, respectively. Decolorization ability of P. sajor-caju laccase suggests that this enzyme could be used for decolorization of industrial effluents.

The dioxin-degrading strain Pseudomonas veronii PH-03 was isolated from contaminated soil by selective enrichment techniques. Strain PH-03 grew on dibenzo-p-dioxin and dibenzofuran as a sole carbon source. Further, 1-chlorodibenzo-p-dioxin, 2-chlorodibenzo-p-dioxin and other dioxin metabolites, salicylic acid, and catechol were also metabolized well. Resting cells of strain PH-03 transformed dibenzo-p-dioxin, dibenzofuran, 2,2',3-trihydroxybiphenyl, and some chlorodioxins to their corresponding metabolic intermediates such as catechol, salicylic acid, 2-hydroxy-(2-hydroxyphenoxy)-6-oxo-2,4-hexadienoic acid, and chlorocatechols. The formation of these metabolites was confirmed by comparison of gas chromatography-mass spectrometry (GC-MS) data with those of authentic compounds. Although we did observe the production of 3,4,5,6-tetrachlorocatechol (3,4,5,6-TECC) from 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) with resting cell suspensions of PH-03, growth of strain PH-03 in the presence of 1,2,3,4-TCDD was poor. This result suggests that strain PH-03 is unable to utilize 3,4,5,6-TECC, even at very low concentration (0.01 mM) due to its toxicity. In cell-free extracts of DF-grown cells, 2,2',3-trihydroxybiphenyl dioxygenase, 2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid hydrolase, and catechol-2,3-dioxygense activities were detected. Moreover, the activities of meta-pyrocatechase and 2,2',3-trihydroxybiphenyl dioxygenase from the crude cell-free extracts were inhibited by 3-chlorocatechol. However, no inhibition was observed in intact cells when 3-chlorocatechol was formed as intermediate.

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This study investigated the cytotoxicity, genotoxicity, and growth inhibition effects of four different inorganic nanoparticles (NPs) such as aluminum (nAl), iron (nFe), nickel (nNi), and zinc (nZn) on a dibenzofuran (DF) degrading bacterium Agrobacterium sp. PH-08. NP (0–1,000 mg L−1) -treated bacterial cells were assessed for cytotoxicity, genotoxicity, growth and biodegradation activities at biochemical and molecular levels. In an aqueous system, the bacterial cells treated with nAl, nZn and nNi at 500 mg L−1 showed significant reduction in cell viability (30–93.6 %, p

Laccase was produced from Pleurotus florida under solid-state fermentation, and the production was optimized by response surface methodology. The predicted maximum laccase production of 8.81 U g(-1) was obtained by the optimum concentration of malt extract, banana peel, wheat bran and CuSO4, which was found to be 0.69 g, 10.61 g, 10.68 g and 77.15 ppm, respectively. The validation results suggested that the laccase production was 7.96 U g(-1) in the optimized medium, which was close to the predicted value. Decolorization efficiency of P. florida laccase was evaluated against malachite green (MG). Rapid decolorization of MG dye was observed, and a dark-coloured precipitate was formed in the reaction mixture. HPLC analysis indicated that the laccase enzyme degraded MG by the demethylation process. The toxicity of MG was reduced to 67% after the treatment with laccase, which was confirmed by a phytotoxicity study.

Pleurotus florida NCIM 1243 produced laccase as the dominant lignolytic enzyme during the dye decolorization. Banana peel was the best substrate for extracellular laccase production under solid state fermentation when compared to mandarin peel and cantaloupe peel. The maximum activity of laccase (5.4 U/g) was detected on the 10 day. The ratio of banana peel: mandarin peel: cantaloupe peel (5:2:3) showed increased production of laccase (6.8 U/g). P. florida produced two extracellular laccase isoenzymes (L1 and L2). The half life of laccase at 60 degrees C was 2 h and at 4 h it retained 25% residual activity. P. florida laccase showed high thermostability and an interesting difference was noticed in the behavior of laccase isoenzymes at different temperature. The L1 isoenzyme of laccase showed remarked thermostability at 60 degrees C in the native PAGE when compared to L2 isoenzyme. The optimum pH, temperature and enzyme concentration for maximum decolorization was found to be 4.5, 60 degrees C and 1.2 U/ml, respectively. Partially purified laccase enzyme showed excellent decolorization activity to Reactive blue 198. The maximum decolorization (96%) was observed at lower dye concentrations (50-100 ppm) which decreased markedly when the dye concentration was increased beyond 150 ppm. The thermostable laccase of P. florida could be effectively used to decolorize the synthetic dyes in the textile effluent and other biotechnological applications.

In this study, a sequential reduction-oxidation method was developed for complete degradation of triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether, TCS) in aqueous solution. Rapid reductive dechlorination of TCS was achieved with palladized zero-valent iron nanoparticles (Pd/nFe), under anaerobic conditions, with generation of 2-phenoxyphenol as the sole dechlorination product. Sequentially, 2-phenoxyphenol was transformed into a non-toxic polymer using laccase (EC:1.10.3.2) derived from Trametes versicolor in the presence of natural redox mediator syringaldehyde (SYD). High performance liquid chromatography combined with electrospray ionization mass spectroscopy (HPLC-ESI-MS) revealed the formation of dimer and trimer products during the laccase-mediated transformation process. The efficiency of the integrated method is critically dependent on the Fe(2+) concentration, which was effectively controlled by optimizing the solution pH. To the best of our knowledge, this is the first report of a redox two-step hybrid system for the complete transformation of TCS into non-toxic products.