The biodegradation of recalcitrant effluents from an olive mill by a white-rot fungus

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA)

Coastal wetlands are highly efficient 'blue carbon' sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO₂ and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments.

GRAPHICAL ABSTRACT

Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-022-01008-5.

Dephenolization of palm oil mill effluent by oil palm fiber-immobilized Trametes hirsuta AK04 in temporary immersion bioreactor for the enhancement of biogas production

The dephenolization of palm oil mill effluent (POME) with oil palm fiber-immobilized Trametes hirsuta AK 04 was conducted in a temporary immersion bioreactor to reduce the inhibitory effects of phenolics in anaerobic digestion. Longer immersion times provided greater removal of phenolics due to a higher release of manganese peroxidase. The most effective dephenolization was observed at 6 h immersed and 2 h non-immersed time (immersion ratio 6/8) with maximum removal of 85% from 1277 mg L^-1 of phenolics in 4 days. The immobilized fungus maintained its high activity during multiple repeated batch treatments. The pretreated POME of 2 h showed higher methane yields compared with the untreated POME substrate. The methane yields increased with increasing pretreatment time and dephenolization levels. The results suggested that an increased abundance of methanogens was associated with the detoxification of phenolics. The fungal biomass contained crude protein, amino acids, and essential phenolics, which can be used as animal feed supplements.

Impact of olive mill wastewaters on the physiological behavior of a wild-type new Ganoderma resinaceum isolate

A new wild-type Ganoderma resinaceum isolate was cultivated on glucose-enriched liquid cultures with olive mill wastewaters (OMWs) in initial phenolic compounds concentrations 0.0 (control), 0.5, 0.8, and 1.5 g/l. The effect of the fungus on the reduction of phenolics and color was assessed, whereas biomass production, glucose consumption, intra-cellular (IPS) and extra-cellular (EPS) polysaccharides biosynthesis, antioxidant activity of the biomass, and laccase synthesis were monitored. Results showed that significant phenolic reduction (94.5%) and decolorization (76.5%) occurred, 14.6 g/l of biomass was produced, glucose was almost totally consumed, EPS were produced in sufficient amounts (0.79 g/l), whereas the presence of OMWs enhanced the synthesis of IPS (maximum absolute values 4.0-5.2 g/l corresponding to 35-42% w/w). Kinetic analysis demonstrated that EPS and IPS values fluctuated with time, regardless of the available amount of glucose in the media, showing a maximum in the 17th day of culture. Laccase was highly synthesized in the middle of the fermentation, reaching the maximum value of 14 U/ml. Little growth was however observed at 1.5 g/l phenolics. Strong correlation between total phenolic content and free radical scavenging activity has been noticed in the methanolic extracts of the mycelium. Results strongly suggest the potentiality of G. resinaceum utilization in the OMW waste treatment.

Phytoremediation of samples extracted from wastewater treatment plant and their socioeconomic impact

The physico-chemical and bacteriological quality was evaluated in wastewater samples before and after treatment by microalgae enrichment. Three types of wastewater samples - raw water, inlet water and outlet water - were taken directly from the wastewater treatment plant and subjected to microalgae enrichment culture during two months. The main objective of this work was to apply a phytoremediation process based on the use of compulsory microalgae treatment of wastewater from treatment plants compared to other secondary treatments. The biomass of microalgae was extracted to determine the concentrations of phenolic compounds, sugars and especially lipids, which can be subsequently transformed into biodiesel. As a result, the pH showed a significant increase after microalgae proliferation, with values ranging from 9.94 to 10.36. Bacterial community analysis before and after microalgae culture showed a clear shift in biomass content. The total coliform (TC) and the fecal coliform (FC) contents decreased after microalgae enrichment. In addition, the fecal streptococci (FS) and Pseudomonas present in the different wastewater samples completely disappeared after treatment. The applied phytoremediation process showed a drop until the disappearance of the contagious microbes - which present a very serious health risk - due to the release of the quinic acid. The quinic acid observed in the treated waters exceeded the content of 464.328 mg/L. This phenolic compound naturally produced during the process demonstrated a very effective antimicrobial power. However, a significant increment of 100% of phenol compound removal was observed after microalgae enrichment. The lipid content in the various studied samples appeared after microalgae culture. In addition, the heavy metals, namely cadmium and chromium, were completely eliminated after the treatment. Several socioeconomic advantages can be achieved by the use of this process, notably the environmental advantages of bioenergetics and economic and social benefits of the non-expensive valorization of wastewaters for irrigation.

Fungal bioremediation of olive mill wastewater: using a multi-step approach to model inhibition or stimulation

BACKGROUND

Olive mill wastewaters (OMWWs) possess a strong environmental impact; the use of fungi as tools for bioremediation could be a promising method.

RESULTS

Twenty-nine fungi were grown on minimal media supplemented with five different kinds of OMWWs (5-15%). Radial growth was assessed for 21 days and the data were modelled through the Dantigny-logistic like function to estimate τ, i.e. the time to attain half of the maximum diameter. Growth on potato dextrose agar and water agar (WA, minimal medium without supplementation) was used as reference. The differences in τ between PDA/WA and minimal media with OMWWs were modelled through a multi-factorial ANOVA, using the concentration of OMWW, the kind of wastes and fungi as categorical predictors. Finally, a principal component analysis was run to group and divide resistant and sensitive fungi. Some fungi experienced a positive Δτ, thus suggesting an inhibition by OMWW, whereas other isolates were enhanced.

CONCLUSIONS

Some isolates (for example Aspergillus ochraceus) showed a promising trend and could be possible candidates for a validation on a real scale. © 2016 Society of Chemical Industry.

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.

Olive mill wastewater biodegradation potential of white-rot fungi--Mode of action of fungal culture extracts and effects of ligninolytic enzymes

Forty-nine white-rot strains belonging to 38 species of Basidiomycota were evaluated for olive-mill wastewater (OMW) degradation. Almost all fungi caused high total phenolics (>60%) and color (⩽ 70%) reduction, while COD and phytotoxicity decreased to a lesser extent. Culture extracts from selected Agrocybe cylindracea, Inonotus andersonii, Pleurotus ostreatus and Trametes versicolor strains showed non-altered physicochemical and enzymatic activity profiles when applied to raw OMW in the presence or absence of commercial catalase, indicating no interaction of the latter with fungal enzymes and no competition for H2O2. Hydrogen peroxide's addition resulted in drastic OMW's decolorization, with no effect on phenolic content, suggesting that oxidation affects colored components, but not necessarily phenolics. When fungal extracts were heat-treated, no phenolics decrease was observed demonstrating thus their enzymatic rather than physicochemical oxidation. Laccases added to OMW were reversibly inhibited by the effluent's high phenolic load, while peroxidases were stable and active during the entire process.

Parameters and kinetics of olive mill wastewater dephenolization by immobilized Rhodotorula glutinis cells

Olive mill wastewater (OMW) with total phenol (TP) concentration range of 300-1200 mg/L was treated with alginate-immobilized Rhodotorula glutinis cells in batch system. The effects of pellet properties (diameter, alginate concentration and cell loading (CL)) and operational parameters (initial TP concentration, agitation rate and reusability of pellets) on dephenolization of OMW were studied. Up to 87% dephenolization was obtained after 120 h biodegradations. The utilization number of pellets increased with the addition of calcium ions into the biodegradation medium. The overall effectiveness factors calculated for different conditions showed that diffusional limitations arising from pellet size and pellet composition could be neglected. Mass transfer limitations appeared to be more effective at high substrate concentrations and low agitation rates. The parameters of logistic model for growth kinetics of R. glutinis in OMW were estimated at different initial phenol concentrations of OMW by curve-fitting of experimental data with the model.

Comparative examination of the olive mill wastewater biodegradation process by various wood-rot macrofungi

Olive mill wastewater (OMW) constitutes a major cause of environmental pollution in olive-oil producing regions. Sixty wood-rot macrofungi assigned in 43 species were evaluated for their efficacy to colonize solidified OMW media at initially established optimal growth temperatures. Subsequently eight strains of the following species were qualified: Abortiporus biennis, Ganoderma carnosum, Hapalopilus croceus, Hericium erinaceus, Irpex lacteus, Phanerochaete chrysosporium, Pleurotus djamor, and P. pulmonarius. Fungal growth in OMW (25%v/v in water) resulted in marked reduction of total phenolic content, which was significantly correlated with the effluent's decolorization. A. biennis was the best performing strain (it decreased phenolics by 92% and color by 64%) followed by P. djamor and I. lacteus. Increase of plant seeds germination was less pronounced evidencing that phenolics are only partly responsible for OMW's phytotoxicity. Laccase production was highly correlated with all three biodegradation parameters for H. croceus, Ph. chrysosporium, and Pleurotus spp., and so were manganese-independent and manganese dependent peroxidases for A. biennis and I. lacteus. Monitoring of enzymes with respect to biomass production indicated that Pleurotus spp., H. croceus, and Ph. chrysosporium shared common patterns for all three activities. Moreover, generation of enzymes at the early biodegradation stages enhanced the efficiency of OMW treatment.

Sequential treatment of olive oil mill wastewater with adsorption and biological and photo-Fenton oxidation

Olive oil mill wastewater (OMWW), a recalcitrant pollutant, has features including high phenolic content and dark color; thereby, several chemical or physical treatments or biological processes were not able to remediate it. In this study, the treatment efficiencies of three treatments, including adsorption, biological application, and photo-Fenton oxidation were sequentially evaluated for OMWW. Adsorption, biological treatment, and photo-Fenton caused decreasing phenolic contents of 48.69 %, 59.40 %, and 95 %, respectively. However, after three sequential treatments were performed, higher reduction percentages in phenolic (total 99 %) and organic contents (90 %) were observed. Although the studied fungus has not induced significant color reduction, photo-Fenton oxidation was considered to be an attractive solution, especially for color reduction. Besides, toxicity of OMWW treatment was significantly reduced.

Separation of Polyphenols from Jordanian Olive Oil Mill Wastewater

This research aims at separation of polyphenols from Jordanian olive mill wastewater which have possible applications in pharmaceutical industry. The phenolic compounds were isolated using silica column chromatography based on using different solvents after extracting the acidified solution with n-hexane and ethyl acetate. The structural elucidation of the separated compounds was achieved using 1H-NMR, 13C-NMR and mass spectrometry. The concentrations of these compounds were determined by GC-MS after derivatization with N, O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). The concentrations of the main isolated phenolic compounds in the Jordanian olive mill wastewater were ferulic acid (93.6 mg/L), trans-cinnamic acid (105.3 mg/L), p-coumaric acid (117.0 mg/L), vanillic acid (128.7 mg/L), caffeic acid (140.4 mg/L), tyrosol (210.6 mg/L), and hydroxytyrosol (315.9 mg/L).

New secoiridoid from olive mill wastewater

A new secoiridoid, olenoside A (1a) and its known epimer olenoside B (1b), were isolated from olive mill wastewater as a mixture of two isomers. Their structures, 1-methyl-7-oxo-6,6a,8,8a-tetrahydro-1H,3H-pyrano[3,4-c]pyran-4-carboxylic acid methyl ester, were determined by spectroscopic methods including 2-D NMR. The structure of major compound 1a was confirmed by X-ray diffraction.

Selection of non-conventional yeasts and their use in immobilized form for the bioremediation of olive oil mill wastewaters

The yeast population dynamics in olive wastewaters (OMW), sampled in five mills from Salento (Apulia, Southern Italy), were investigated. Three hundred yeasts were isolated in five industrial mills and identified by molecular analysis. Strains belonging to Geotrichum, Saccharomyces, Pichia, Rhodotorula and Candida were detected. Five G. candidum strains were able to grow in OMW as the sole carbon source and to reduce phenolics, chemical oxygen demand (COD) and antimicrobial compounds. One G. candidum isolate was selected for whole-cell immobilization in calcium alginate gel. The COD and phenolic reduction obtained with immobilized cells showed a 2.2- and 2-fold increase compared to the removal obtained with free cells, respectively. The immobilization system enhanced yeast oxidative activity by avoiding the presence of microbial protease in treated OMW. To our knowledge, this is the first report on G. candidum whole-cell immobilization for OMW bioremediation.

Enhanced laccase production in white-rot fungus Rigidoporus lignosus by the addition of selected phenolic and aromatic compounds

The white rot fungus Rigidoporus lignosus produces substantial amounts of extracellular laccase, a multicopper blue oxidase which is capable of oxidizing a wide range of organic substrates. Laccase production can be greatly enhanced in liquid cultures supplemented with various aromatic and phenolic compounds. The maximum enzyme activity was reached at the 21st or 24th day of fungal cultivation after the addition of inducers. The zymograms of extracellular fluid of culture preparation in the presence of inducers, at maximum activity day, revealed two bands with enzymatic activity, called Lac1 and Lac2, having different intensities. Lac2 band shows the higher intensity which changed with the different inducers. Laccase induction can be also obtained by adding to the culture medium olive mill wastewaters, which shows a high content of phenolic compounds.

Elemental and spectroscopic characterization of humic-acid-like compounds during composting of olive mill by-products

Humic acids (HAs) were isolated at different stages of composting from two piles of solid olive mill residues (SOR) treated for the first 30 days with tap water (pile C1) or olive mill wastewater (pile C2), for a total composting period of 9 months. The HA fractions were characterized by elemental analysis, UV-visible, Fourier transform infrared and fluorescence spectroscopy in order to monitor humification process and the maturity of the composts. As composting proceeded, the elemental composition of the humic acids showed a decrease in C and H content, and in the C/N ratio, and an increase in N and O contents and in the C/H and O/C ratios. These changes could be attributed to a loss of aliphatic groups and to an increase of aromatic character, polycondensation and degree of oxidation of the HAs. Spectroscopic data agree and support these results, suggesting that the chemical and structural features of the HAs of both composts tend to reach those typical of native soil HAs, that is compounds with a high degree of humification and a high molecular weight and complexity. Therefore, both composting processes seem suitable to produce well-humified organic matter, with important benefits for their use in soil amendment. No differences appeared between the two treatments concerning the humic character of the two final composts.

Bioremediation and biovalorisation of olive-mill wastes

Olive-mill wastes are produced by the industry of olive oil production, which is a very important economic activity, particularly for Spain, Italy and Greece, leading to a large environmental problem of current concern in the Mediterranean basin. There is as yet no accepted treatment method for all the wastes generated during olive oil production, mainly due to technical and economical limitations but also the scattered nature of olive mills across the Mediterranean basin. The production of virgin olive oil is expanding worldwide, which will lead to even larger amounts of olive-mill waste, unless new treatment and valorisation technologies are devised. These are encouraged by the trend of current environmental policies, which favour protocols that include valorisation of the waste. This makes biological treatments of particular interest. Thus, research into different biodegradation options for olive-mill wastes and the development of new bioremediation technologies and/or strategies, as well as the valorisation of microbial biotechnology, are all currently needed. This review, whilst presenting a general overview, focus critically on the most significant recent advances in the various types of biological treatments, the bioremediation technology most commonly applied and the valorisation options, which together will form the pillar for future developments within this field.

Detoxification of olive mill wastewaters by Moroccan yeast isolates

A total of 105 yeast strains were isolated from Moroccan olive oil production plants and evaluated for their ability to grow in olive oil mill wastewaters (OMW). The 9 isolates that grew best on OMW were selected for further study to evaluate their effect on removal of organic pollutants and OMW phytotoxicity (barley seed germination test). The results showed that at least four yeast isolates effectively lowered the toxicity of this effluent in addition to providing very useful materials in terms of both yeast biomass (6 g/l DW) and an irrigation fluid. This group of yeast isolates significantly reduced the concentration of total phenols (44% removal) and Chemical Oxygen Demand, COD (63% removal). The best germination rate of 80% for undiluted OMW was obtained for strain Candida holstii that also increased the pH from 4.76 to 6.75. Principal component analysis of the results obtained for the best yeast strains confirmed the importance of COD and total phenol reduction along with increase of organic nitrogen and final pH for the improvement of germination rates and phytotoxic reduction. This study has highlighted the potential of indigenous yeasts in detoxification of olive mill wastewaters.

Clostridium tunisiense sp. nov., a new proteolytic, sulfur-reducing bacterium isolated from an olive mill wastewater contaminated by phosphogypse

A new sporulated fermentative bacterium designated strain E1(T) (T=type strain), was isolated from an anaerobic mud of an olive mill wastewater basin contaminated by phosphogypse produced by a Tunisian factory. Strain E1(T) was a motile Gram-positive slightly curved rod with spherical terminal spore swelling the cell. It grew between 18 degrees C and 43 degrees C with an optimum at 37 degrees C and pH 7.8 (range 5.5-8.7), without NaCl (range 0-3%). Strain E1(T) was a chemoorganotrophic anaerobic bacterium fermenting only proteins and amino acids. Yeast extract was required for growth. Elemental sulfur was used as terminal electron acceptor. The G+C content of the DNA was 32.6 mol%. The closest phylogenetical relatives of strain E1(T) were Clostridium thiosulfatireducens and C. subterminale (97.3% similarity for partial rRNA gene sequences). DNA-DNA hybridization values between strain E1(T) and both species were 17% and 20.8%, respectively. On the basis of differences in genotypic and phenotypic characteristics, strain E1(T) (DSM 15206(T), CIP 107666(T)) is proposed as the type strain of a new species, C. tunisiense sp. nov. GenBank accession number for the 16S rRNA gene sequence of strain E1(T) is AY187622.

Effect of bioaugmentation of activated sludge with white-rot fungi on olive mill wastewater detoxification

AIMS

To test the potential use of Phanerochaete chrysosporium and other white-rot fungi to detoxify olive mill wastewaters (OMW) in the presence of a complex activated sludge. To combine the aerobic with anaerobic treatment to optimize the conversion of OMW in biogas.

METHODS AND RESULTS

A 25-l air lift reactor was used to pretreat OMW by white-rot fungi. Detoxification of the OMW was monitored by size exclusion HPLC analysis, chemical oxygen demand (COD)/biological oxygen demand (BOD(5)) ratio evolution, and bioluminescence toxicity test. Anaerobic treatment of OMW was performed in a 12-l anaerobic filter reactor. Efficiency of the treatment was evaluated by organic matter removal, and biogas production. By comparison with the pretreatment by activated sludge only, the bioaugmentation with Phanerochaete chrysosporium or Trametes versicolor led to high removal of organic matter, decreased the COD/BOD(5) ratio and the toxicity. The subsequent anaerobic digestion of the OMW pretreated with activated sludge-white-rot fungi showed higher biomethanization yields than that pretreated with activated sludge only. Higher loading rates (7 g COD l(-1) day(-1)) were reached without any acidification or inhibition of biomethanization.

CONCLUSIONS

The use of white-rot fungi, even in the presence of complex biological consortia to detoxify OMW, proved to be possible and made the anaerobic digestion of OMW for methane production feasible.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of fungi for OMW reuse and energy production could be adapted to industrial applications.

Treatment of olive mill effluents Part I. Organic matter degradation by chemical and biological processes--an overview

Olive mill effluents constitute a serious environmental problem in the Mediterranean Sea region due to the unique features associated with this type of agro-waste (i.e. seasonal and localized production, high and diverse organic load, low flow rates). Therefore, it is not surprising that research efforts have been directed towards the development of efficient treatment technologies including various physico-chemical and biological processes. This work reviews recent advances regarding olive mill effluent treatment with emphasis given on biological and chemical degradation processes.

Panus tigrinus efficiently removes phenols, color and organic load from olive-mill wastewater

This study was aimed at assessing the potential of the white-rot fungus Panus tigrinus CBS 577.79 in removing organic load, color and toxic phenols from agro-industrial effluent olive-mill wastewater (OMW). The influence of wastewater composition on P. tigrinus degradative capability was investigated in shaken cultures using two different OMWs. The initial soluble COD of 85,000 mg l(-1) led to a delay in removal of color, organic load and phenol by the fungus. This was associated with delayed onset of laccase and Mn-dependent peroxidase. On the other hand, P. tigrinus, when grown on OMW with an initial soluble COD content of 43,000 mg l(-1), promptly and efficiently removed the aforementioned components. Chromatographic analyses showed that 4-hydroxy-substituted simple phenols were predominantly removed. The polymeric aromatic fraction underwent simultaneous polymerization and depolymerization. This study is a contribution to the understanding of the degradative specificity of P. tigrinus on OMW aromatic components and provides good indications for possible future applications of the fungus.

Activity and elution profile of laccase during biological decolorization and dephenolization of olive mill wastewater

The performance and enzymatic strategy exhibited by basidiomycete Euc-1, a laccase producing strain, was investigated during the biodegradation of olive mill wastewater (OMW). This strain yielded better decolorization of solidified OMW than Phanerochaete chrysosporium and removed 90% of phenols (initial concentration=800 mg l(-1)), 73% of color (initial A465=4.4), and 45% of chemical oxygen demand in batch cultures containing OMW. Since partial phenol removal occurred before the detection of enzymatic activity, no plausible correlation could be established between them. In contrast, decolorization occurred only after the detection of laccase activity and coincided with its production over time. Two laccase fractions (Lac1 and Lac2) were separated by chromatography. OMW strongly induced Lac2 that was almost absent in defined liquid medium. Furthermore, Lac2 was the main laccase fraction in the presence of OMW. This study pointed out that basidiomycete Euc-1 and its ligninolytic system could be a useful tool for the bioremediation of wastewater generated in the process of olive oil extraction.

Lentinula edodes removes phenols from olive-mill wastewater: impact on durum wheat (Triticum durum Desf.) germinability

Olive-mill wastewater (OMW) exhibits highly phytotoxic properties, mainly due to phenols. A valuable option for OMW disposal is its agricultural use provided that phytotoxic effects are removed. The present investigation was aimed at evaluating the efficacy of the lignin-degrading fungus Lentinula edodes in achieving OMW detoxification. Germinability experiments on durum wheat showed that OMW phytotoxicity was significantly reduced by L. edodes cultures. Germinability on undiluted and twofold diluted OMW from fungal cultures was 34+/-5% and 57+/-6%, respectively, while on related incubation controls it was almost completely suppressed. These results suggest that fungal cultures of L. edodes would decrease the phytotoxicity of this waste.

Combined sequence and structure analysis of the fungal laccase family

Plant and fungal laccases belong to the family of multi-copper oxidases and show much broader substrate specificity than other members of the family. Laccases have consequently been of interest for potential industrial applications. We have analyzed the essential sequence features of fungal laccases based on multiple sequence alignments of more than 100 laccases. This has resulted in identification of a set of four ungapped sequence regions, L1-L4, as the overall signature sequences that can be used to identify the laccases, distinguishing them within the broader class of multi-copper oxidases. The 12 amino acid residues in the enzymes serving as the copper ligands are housed within these four identified conserved regions, of which L2 and L4 conform to the earlier reported copper signature sequences of multi-copper oxidases while L1 and L3 are distinctive to the laccases. The mapping of regions L1-L4 on to the three-dimensional structure of the Coprinus cinerius laccase indicates that many of the non-copper-ligating residues of the conserved regions could be critical in maintaining a specific, more or less C-2 symmetric, protein conformational motif characterizing the active site apparatus of the enzymes. The observed intraprotein homologies between L1 and L3 and between L2 and L4 at both the structure and the sequence levels suggest that the quasi C-2 symmetric active site conformational motif may have arisen from a structural duplication event that neither the sequence homology analysis nor the structure homology analysis alone would have unraveled. Although the sequence and structure homology is not detectable in the rest of the protein, the relative orientation of region L1 with L2 is similar to that of L3 with L4. The structure duplication of first-shell and second-shell residues has become cryptic because the intraprotein sequence homology noticeable for a given laccase becomes significant only after comparing the conservation pattern in several fungal laccases. The identified motifs, L1-L4, can be useful in searching the newly sequenced genomes for putative laccase enzymes.

The contribution of melanin to microbial pathogenesis

Melanins are enigmatic pigments that are produced by a wide variety of microorganisms including several species of pathogenic bacteria, fungi and helminths. The study of melanin is difficult because these pigments defy complete biochemical and structural analysis. Nevertheless, the availability of new reagents in the form of monoclonal antibodies and melanin-binding peptides, combined with the application of various physical techniques, has provided insights into the process of melanization. Melanization is important in microbial pathogenesis because it has been associated with virulence in many microorganisms. Melanin appears to contribute to virulence by reducing the susceptibility of melanized microbes to host defence mechanisms. However, the interaction of melanized microbes and the host is complex and includes immune responses to melanin-related antigens. Production of melanin has also been linked to protection against environmental insults. Interference with melanization is a potential strategy for antimicrobial drug and pesticide development. The process of melanization poses fascinating problems in cell biology and provides a type of pathogenic strategy that is common to highly diverse pathogens.

Reduction of the phenolic components in olive-mill wastewater by an enzymatic treatment and its impact on durum wheat (Triticum durum Desf.) germinability

Olive-mill wastewater (OMW), an effluent of olive oil extraction process, is annually produced in huge amounts in olive growing areas. An interesting option for its disposal is the spreading on agricultural land, provided that phytotoxic effects are neutralized. The objective of the present investigation was to evaluate the potential of an enzyme-based treatment in removing OMW phytotoxicity. To this aim, germinability experiments on durum wheat (Triticum durum Desf. cv. Duilio) were conducted in the presence of different dilutions of raw or enzyme-treated OMW. OMW treatment with laccase resulted in a 65% and 86% reduction in total phenols and ortho-diphenols respectively, due their polymerization as revealed by size-exclusion chromatography. Raw OMW exerted a significant concentration-dependent inhibition on the germinability of durum wheat seeds which was evident up to a dilution rate of 1:8. When the effluent was treated with a fungal laccase, germinability was increased by 57% at a 1:8 dilution and by 94% at a 1:2 dilution, as compared to the same dilutions using untreated OMW. The treatment with laccase also decreased the mean germination time by about 1 day as compared to untreated controls. These results show that germinability inhibition due to OMW can be reduced effectively using fungal laccase, suggesting that phenols are the main determinants of its phytotoxicity.

Lignin degrading system of white-rot fungi and its exploitation for dye decolorization

With global attention and research now focused on looking for the abatement of pollution, white-rot fungi is one of the hopes of the future. The lignin-degrading ability of these fungi have been the focus of attention for many years and have been exploited for a wide array of human benefits. This review highlights the various enzymes produced by white-rot fungi for lignin degradation, namely laccases, peroxidases, aryl alcohol oxidase, glyoxal oxidase, and pyranose oxidase. Also discussed are the various radicals and low molecular weight compounds that are being produced by white-rot fungi and its role in lignin degradation. A brief summary on the developments in research of decolorization of dyes using white-rot fungi has been made.