Degradation of Oxo-Biodegradable Plastic by Pleurotus ostreatus

Growing concerns regarding the impact of the accumulation of plastic waste over several decades on the environmental have led to the development of biodegradable plastic. These plastics can be degraded by microorganisms and absorbed by the environment and are therefore gaining public support as a possible alternative to petroleum-derived plastics. Among the developed biodegradable plastics, oxo-biodegradable polymers have been used to produce plastic bags. Exposure of this waste plastic to ultraviolet light (UV) or heat can lead to breakage of the polymer chains in the plastic, and the resulting compounds are easily degraded by microorganisms. However, few studies have characterized the microbial degradation of oxo-biodegradable plastics. In this study, we tested the capability of Pleurotus ostreatus to degrade oxo-biodegradable (D₂W) plastic without prior physical treatment, such as exposure to UV or thermal heating. After 45 d of incubation in substrate-containing plastic bags, the oxo-biodegradable plastic, which is commonly used in supermarkets, developed cracks and small holes in the plastic surface as a result of the formation of hydroxyl groups and carbon-oxygen bonds. These alterations may be due to laccase activity. Furthermore, we observed the degradation of the dye found in these bags as well as mushroom formation. Thus, P. ostreatus degrades oxo-biodegradable plastics and produces mushrooms using this plastic as substrate.     

Degradation of Green Polyethylene by Pleurotus ostreatus

We studied the biodegradation of green polyethylene (GP) by Pleurotus ostreatus. The GP was developed from renewable raw materials to help to reduce the emissions of greenhouse gases. However, little information regarding the biodegradation of GP discarded in the environment is available. P. ostreatus is a lignocellulolytic fungus that has been used in bioremediation processes for agroindustrial residues, pollutants, and recalcitrant compounds. Recently, we showed the potential of this fungus to degrade oxo-biodegradable polyethylene. GP plastic bags were exposed to sunlight for up to 120 days to induce the initial photodegradation of the polymers. After this period, no cracks, pits, or new functional groups in the structure of GP were observed. Fragments of these bags were used as the substrate for the growth of P. ostreatus. After 30 d of incubation, physical and chemical alterations in the structure of GP were observed. We conclude that the exposure of GP to sunlight and its subsequent incubation in the presence of P. ostreatus can decrease the half-life of GP and facilitate the mineralization of these polymers.     

Lignocellulose Degradation during Solid-State Fermentation: Pleurotus ostreatus versus Phanerochaete chrysosporium

Lignocellulose degradation and activities related to lignin degradation were studied in the solid-state fermentation of cotton stalks by comparing two white rot fungi, Pleurotus ostreatus and Phanerochaete chrysosporium. P. chrysosporium grew vigorously, resulting in rapid, nonselective degradation of 55% of the organic components of the cotton stalks within 15 days. In contrast, P. ostreatus grew more slowly with obvious selectivity for lignin degradation and resulting in the degradation of only 20% of the organic matter after 30 days of incubation. The kinetics of ¹⁴C-lignin mineralization exhibited similar differences. In cultures of P. chrysosporium, mineralization ceased after 18 days, resulting in the release of 12% of the total radioactivity as ¹⁴CO₂. In P. ostreatus, on the other hand, 17% of the total radioactivity was released in a steady rate throughout a period of 60 days of incubation. Laccase activity was only detected in water extracts of the P. ostreatus fermentation. No lignin peroxidase activity was detected in either the water extract or liquid cultures of this fungus. 2-Keto-4-thiomethyl butyric acid cleavage to ethylene correlated to lignin degradation in both fungi. A study of fungal activity under solid-state conditions, in contrast to those done under defined liquid culture, may help to better understand the mechanisms involved in lignocellulose degradation.     

Biodegradation of aflatoxin B1 in contaminated rice straw by Pleurotus ostreatus MTCC 142 and Pleurotus ostreatus GHBBF10 in the presence of metal salts and surfactants

Aflatoxin B1 (AFB1) is a highly toxic fungal metabolite having carcinogenic, mutagenic and teratogenic effects on human and animal health. Accidental feeding of aflatoxin-contaminated rice straw may be detrimental for ruminant livestock and can lead to transmission of this toxin or its metabolites into the milk of dairy cattle. White-rot basidiomycetous fungus Pleurotus ostreatus produces ligninolytic enzymes like laccase and manganese peroxidase (MnP). These extracellular enzymes have been reported to degrade many environmentally hazardous compounds. The present study examines the ability of P. ostreatus strains to degrade AFB1 in rice straw in the presence of metal salts and surfactants. Laccase and MnP activities were determined spectrophotometrically. The efficiency of AFB1 degradation was evaluated by high performance liquid chromatography. Highest degradation was recorded for both P. ostreatus MTCC 142 (89.14 %) and P. ostreatus GHBBF10 (91.76 %) at 0.5 µg mL^?1 initial concentration of AFB1. Enhanced degradation was noted for P. ostreatus MTCC 142 in the presence of Cu²⁺ and Triton X-100, at toxin concentration of 5 µg mL^?1. P. ostreatus GHBBF10 showed highest degradation in the presence of Zn²⁺ and Tween 80. Liquid chromatography-mass spectrometric analysis revealed the formation of hydrated, decarbonylated and O-dealkylated products. The present findings suggested that supplementation of AFB1-contaminated rice straw by certain metal salts and surfactants can improve the enzymatic degradation of this mycotoxin by P. ostreatus strains.     

Can co-culturing of two white-rot fungi increase lignin degradation and the production of lignin-degrading enzymes?

The aim of this work was to investigate the poorly understood effects of co-culturing of two white rot fungi on the production of lignin-degrading enzyme activities. Four species, Ceriporiopsis subvermispora, Physisporinus rivulosus, Phanerochaete chrysosporium and Pleurotus ostreatus were cultured in pairs to study the degradation of aspen wood and the production of lignin-degrading enzymes. Potential of co-culturing for biopulping was evaluated. Chemical analysis of decayed aspen wood blocks showed that co-culturing of C. subvermispora with P. ostreatus could significantly stimulate wood decay, when compared to monocultures. Based on the fungi tested here, however, this effect is species-specific. Other combinations of fungi were slightly stimulating or not stimulatory. The pattern of lignin degradation was altered towards the acid insoluble part of lignin especially in co-cultures where P. ostreatus was included as a partner. The use of agar plates containing the polymeric dye Poly R-478 showed elevated dye decolourization at the confrontation zone between mycelia. Laccase was significantly stimulated only in the co-culture of P. ostreatus with C. subvermispora. Manganese peroxidase activity was stimulated in co-cultures of P. ostreatus with C. subvermispora or with P. rivulosus. Immunoblotting indicated changes in lignin-degrading enzymes and/or their isoform composition in response to co-culturing. This is the first report on the effects of co-culturing of potential biopulping fungi on wood degradation, and gives basic knowledge on fungal interactions during wood decay that can be utilized in practical applications.     

Enhancement of biodegradability of disposable polyethylene in controlled biological soil

Plastics as polyethylene are widely used in packaging and other agricultural applications. They accumulate in the environment at a rate of 25 million tons per year. Thus, the development and use of degradable plastics was proposed as a solution for plastic waste problem. Because of the ever-increasing use of plastic films, nowadays, biodegradability has become a useful characteristic for plastics. Conversely, the introduction of biodegradable plastics has generated a need for methods to evaluate the biodegradation of these polymers in landfills and solid waste treatment systems such as composting or anaerobic digestion treatment plants. The purpose of this study was to investigate the biodegradation of disposable low-density polyethylene bags containing starch (12%), autoxidizable fatty acid ester and catalytic agents in soil. Structurally this work intended to evaluate the capacity of Phanerochaete chrysosporium (ATCC 34541) to enhance polyethylene film biodegradation in soil microcosms. Soil samples inoculated with P. chrysosporium were mixed with LDPE/starch blend films and biological changes of the films and soil were monitored for 6 months. The biodegradation of polyethylene starch blend film has been determined by the physical, chemical and biological properties of the samples such as pH, biomass, CO₂ formation, percentage elongation, relative viscosity and FTIR spectrum.     

Valorization of solid olive mill wastes by cultivation of a local strain of edible mushrooms

Olive oil industry generates huge quantities of solid olive mill wastes (SOMW), causing environmental damage. Cultivation of edible mushrooms, such as Pleurotus ostreatus is a valuable approach for SOMW valorization. A local strain mycelium (Tizi-Ouzou, Algeria) of P. ostreatus (LPO) was isolated from castor oil plants. Oyster mushroom spawn, produced on barley grains, was used to inoculate wet SOMW, steamed in a traditional steamer during 45 min. The mycelium growth rate on SOMW was first estimated in Petri dish by measuring the surface colonized by the mycelium. The fruit body yields were estimated on culture bags containing 2 kg each of SOMW inoculated at 7% (w/w). The local strain potential was compared with that of a commercial one. Both strains produced high-quality mushrooms, but with low yields. The supplementation of the SOMW with wheat straw at the rate of 10% and 2% of CaCO₃ had significantly enhanced the productivity of the two strains, multiplying it by 3.2 for LPO and by 2.6 for CPO.     

Promising cellulolytic fungi isolates for rice straw degradation

The objective of this study was to evaluate the potential of eight fungal isolates obtained from soils in rice crops for straw degradation in situ. From the initial eight isolates, Pleurotus ostreatus T1.1 and Penicillium sp. HC1 were selected for further characterization based on qualitative cellulolytic enzyme production and capacity to use rice straw as a sole carbon source. Subsequently, cellulolytic, xylanolytic, and lignolytic (Pleurotus ostreatus) activity on carboxymethyl cellulose, oat xylan, and rice straw with different nitrogen sources was evaluated. From the results obtained it was concluded both isolates are capable to produce enzymes necessary for rice straw degradation. However, their production is dependent upon carbon and nitrogen source. Last, it was established that Pleurotus ostreatus T1.1 and Penicillium sp. HC1 capability to colonize and mineralize rice straw, in mono-and co-culture, without affecting nitrogen soil content.     

Degradation of fluorene,anthracene, phenanthrene,fluoranthene, and pyrene lacks connection to the production of extracellular enzymes by Pleurotus ostreatus and Bjerkandera adusta

The degradation of polycyclic aromatic hydrocarbons (PAH) was studied in liquid cultures of Bjerkandera adusta and Pleurotus ostreatus during 7 weeks of cultivation. During only 3 days of incubation, B. adusta removed 56% and 38% of fluorene and anthracene, while P. ostreatus degraded 43% and 60% of these compounds; other PAH were degraded to a lower extent. Except for anthracene in cultures of P. ostreatus, all PAH were removed uniformly during the cultivation time but fluorene and anthracene were degraded faster than other PAH. Supplementation of liquid cultures with milled wood decreased the concentration of PAH in the solution and diminished the degradation of PAH. The fungi produced valuable activity of manganese-dependent peroxidase; laccase was secreted only by P. ostreatus and was strongly induced by the addition of milled wood. The production of the oxidative enzymes did not correlate directly to the metabolisation of PAH.     

Exopolysaccharide-peptide complex from oyster mushroom (Pleurotus ostreatus) protects against hepatotoxicity in rats

Liver damage involves oxidative stress and a progression from chronic hepatitis to hepatocellular carcinoma (HCC). The increased incidence of liver disease in Egypt and other countries in the last decade, coupled with poor prognosis, justify the critical need to introduce alternative chemopreventive agents that may protect against liver damage. The aim of this study was to evaluate the efficacy of exopolysaccharide-peptide (PSP) complex extracted from Pleurotus ostreatus as a hepatoprotective agent against diethylnitrosamine (DEN)/carbon tetrachloride (CCL₄)-induced hepatocellular damage in rats. The levels of liver injury markers (ALT, AST and ALP) were substantially increased following DEN/CCl₄ treatment. DEN/CCl₄ - induced oxidative stress was confirmed by elevated levels of lipid peroxidation and decreased levels of superoxide dismutase, glutathione-S-transferase, and reduced glutathione. PSP reversed these alterations in the liver and serum, and provided protection evidenced by reversal of histopathological changes in the liver. The present study demonstrated that PSP extract from P. ostreatus exhibited hepatoprotective and antioxidant effects against DEN/CCl₄-induced hepatocellular damage in rats. Given the high prevalence of HCV-related liver damage in Egypt, our results suggest further clinical evaluation of P. ostreatus extracts and their potential hepatoprotective effects in patients with liver disease.     

Decontamination of aged creosote polluted soil: the influence of temperature,white rot fungus Pleurotus ostreatus,and pre-treatment

This study investigated the effect of inoculation of white rot fungus, Pleurotus ostreatus, temperature and two pre-treatment methods on PAH degradation in aged creosote contaminated soil. It is shown that Pleurotus ostreatus has an overall positive effect on PAH degradation, and that temperature and soil pre-treatment affect this degradation. In general, adding bark and incubating at 22°C before inoculation with white rot fungi has a better effect on PAH degradation than no pre-treatment, or pre-treatment with fertilizer. At low temperature (8°C) fungal inoculation had best effect when fertilizer was not added, and significant effect on degradation on different groups of PAH compounds, except for the more easily degradable compounds, 3-ring PAHs and heterocyclic compounds was obtained. Pre-treatment with fertilizer stimulated microbial activity at low temperature and enhanced PAH degradation even without addition of fungi.     

Yield,size, nutritional value,and antioxidant activity of oyster mushrooms grown on perilla stalks

Perilla is an edible medical plant with rapidly increasing acreage in China. In this study, we investigated the potential of perilla stalks (PSs) as an alternative substrate for the cultivation of oyster mushrooms (Pleurotus ostreatus). P. ostreatus was cultivated on cottonseed hulls (CSH) alone or mixed with PSs in different ratios. The production parameters, physical characteristics, nutritional values, and antioxidant activity of mushrooms cultivated on different substrate mixtures were determined. The addition of PSs to CSH significantly improved the growth rate, yield, biological efficiency, and proximate composition and shortened the cultivation cycle. Cultivation on PSs alone increased the amino acid content in P. ostreatus fruiting bodies and the antioxidant activity of mushroom extracts. The PS75 (25% CSH + 75% PS) substrate was deduced to be the most effective substrate on the basis of yield and biological efficiency obtained in a large area where perilla had been planted. The results demonstrate that mixtures of PS with CSHs could be used as novel, practical, and easily accessible alternative substrates for P. ostreatus cultivation.     

Cultivation of oyster mushrooms (<Emphasis Type="Italic">Pleurotus</Emphasis> spp.) on various lignocellulosic wastes

Cultivation of speciality mushrooms on lignocellulosic wastes represents one of the most economically and cost-effective organic recycling processes. Three species of Pleurotus, namely P. columbinus, P. sajor-caju and P. ostreatus were experimentally evaluated on untreated organic wastes including chopped office papers, cardboard, sawdust and plant fibres. Production studies were carried out in polyethylene bags of about 1 kg wet weight with 5% spawning rates of substrate fresh weight in a custom-made growth room especially designed for spawn run and cropping. The conversion percentage from dry substrate weight to fresh mushroom weight (biological efficiency) was determined. The highest biological efficiency was noted with P. columbinuson cardboard (134.5%) and paper (100.8%), whereas P. ostreatus produced maximum yield on cardboard (117.5%) followed by paper (112.4%). The overall yield of P. sajor-cajuwas comparatively low (range 47–78.4%). The average number of sporophore flushings ranged between 5 and 6 times. The findings that P. columbinus and P. ostreatus are superior to P. sajor-caju are consistent with previous reports elsewhere. Further evaluation of P. columbinus alone on different bagging systems containing partially pasteurized office papers as a growing substrate revealed that polyethylene bags resulted in 109.4% biological efficiency in contrast to pottery (86%), plastic trays (72%) or polyester net (56%). The above findings reveal an opportunity for commercial implication of oyster mushroom especially P. columbinus for utilization of different feasible and cheap recyclable residues.     

Unicellular Microcystis aeruginosa cannot revert back to colonial form after short-term exposure to natural conditions

Colonial Microcystis aeruginosa isolates tend to lose their typical colonial morph after some generations under laboratory conditions, one interesting but yet important question is whether unicellular M. aeruginosa, originally isolated from the field, can revert back to colonial morphology when growing back in natural waters. Based on this idea, we employed dialysis bags and plastic bottles to conduct an in situ experiment. Each of the dialysis bags and plastic bottles was filled with unicellular M. aeruginosa with high concentrations and then submerged to two natural lakes (Lake Caiyue and Lake Taihu) for 40 and 28 days, respectively. Results showed M. aeruginosa grew well in dialysis bags but not in plastic bottles; no colonies were observed in M. aeruginosa incubated in either dialysis bags or plastic bottles exposed in both lakes. This suggests laboratory maintained unicellular M. aeruginosa cannot revert back to colonial form after short-term exposure in natural conditions.     

Effect of different carbon and nitrogen sources on laccase and peroxidases production by selected Pleurotus species

Pleurotus eryngii, P. ostreatus and P. pulmonarius produced laccase (Lac) both under conditions of submerged fermentation (SF) and solid-state fermentation (SSF) with all of the investigated carbon and nitrogen sources. The highest levels of Lac activity were found in P. eryngii, under SF conditions of dry ground mandarine peels and in P. ostreatus, strain No. 493, under SSF conditions of grapevine sawdust.High levels of peroxidases activities were occurred in P. ostreatus, strain No. 494, and P. pulmonarius, under SSF conditions of grapevine sawdust, whereas in SF, these activities were either very low or absent.After purification of extracellular crude enzyme mixture of investigated species and strain which were grown in the medium with the best carbon sources, the Lac activity measurements revealed two peaks in P. eryngii, three peaks in both P. ostreatus strains and three in P. pulmonarius. Results obtained after purification also showed that the levels of phenol red oxidation in absence of external Mn²⁺ were higher than phenol red oxidation levels in presence of external Mn²⁺.In the medium with the best carbon sources (mandarine peels and grapevine sawdust, respectively), both P. eryngii and P. ostreatus, strain No. 493, showed the highest Lac activity with (NH₄)₂SO₄, as a nitrogen source, with a nitrogen concentration of 20 and 30 mM, respectively.In P. ostreatus, strain No. 494, and P. pulmonarius, the best nitrogen sources for peroxidases production were peptone in a concentration of 0.5% and NH₄NO₃ with a nitrogen concentration of 30 mM, respectively.     

Decolorization of synthetic dyes by white rot fungi,involving laccase enzyme in the process

In this study, decolorization of Remazol Brillant Blue Royal (RBBR) and Drimaren Blue CL-BR (DB) was investigated using three white rot fungi named as Pleurotus ostreatus (P. ostreatus), Coriolus versicolor (C. versicolor) and Funalia trogii (F. trogii). Decolorization studies were continued for 48 h under static conditions at 30 °C and pH 5.0. The degree of pH, dry mycelium weight (DMW), dye concentration, laccase activity and protein content were analyzed; the enzyme responsible for decolorization was detected for both dyes. Maximum and minimum decolorizations were obtained by F. trogii and P. ostreatus, respectively. Both dyes at all concentrations were found to be toxic for P. ostreatus growth, whereas only DB above 60 mg/L was found to be toxic for C. versicolor growth. Maximum and minimum laccase activities were detected in decolorization media of F. trogii and P. ostreatus, respectively. Results of activity staining following SDS-PAGE showed that laccase is the only enzyme that is responsible for decolorization of DB and RBBR.     

Kinetics of wheat straw solid-state fermentation with Trametes versicolor and Pleurotus ostreatus — lignin and polysaccharide alteration and production of related enzymatic activities

Summary The kinetics of straw solid-state fermentation (SSF) with Trametes versicolor and Pleurotus ostreatus was investigated to characterize the delignification processes by these white-rot fungi. Two successive phases could be defined during straw transformation, characterized by changes in respiratory activity, changes in lignin and polysaccharide content and composition, increase in in-vitro digestibility, and enzymatic activities produced by the fungi. Lignin composition was analysed after CuO alkaline degradation, and decreases in syringyl/guaiacyl and syringyl/p-hydroxyphenyl ratios and cinnamic acid content were observed during the fungal treatment. An increase in the phenolic acid yield, revealing fungal degradation of side-chains in lignin, was produced by P. ostreatus. The highest xylanase level was produced by P. ostreatus, and exocellulase activity was nearly absent from straw treated with this fungus. Lactase activity was found in straw treated with both fungi, but lignin peroxidase was only detected during the initial phase of straw transformation with T. versicolor. High levels of H₂O₂-producing aryl-alcohol oxidase occurred throughout the straw SSF with P. ostreatus. Offprint requests to: A. T. Martínez     

No difference in colony formation of Scenedesmus obliquus exposed to lakes with different nutrient levels

The algal genus Scenedesmus is famous for its highly phenotypic plasticity in response to various environmental factors. In laboratory, axenic cultures of Scenedesmus often fail to form colonies and remain in unicellular morph. To examine whether unicellular Scenedesmus can form colonies after exposure to natural lakes, dialysis bags and plastic bottles which contained the precultured Scenedesmus obliquus were exposed in two lakes with different nutrient levels for four weeks. Results showed S. obliquus grew well in dialysis bags but not in plastic bottles; S. obliquus can form colonies when incubated in dialysis bags which allow exchange with the aquatic environment of the substances, regardless of the nutrient levels of the two lakes. However, no colonies were observed in S. obliquus incubated in plastic bottles exposed in both lakes. This suggested that active growth and zooplankton infochemicals contributed together to the colony formation of S. obliquus exposed in situ environment.     

Liposome-mediated mycelial transformation of filamentous fungi

Liposome-mediated transformation is common for cells with no cell wall, but has very limited usage in cells with walls, such as bacteria, fungi, and plants. In this study, we developed a procedure to introduce DNA into mycelium of filamentous fungi, Rhizopus nigricans LH 21 and Pleurotus ostreatus TD 300, by liposome-mediation but with no protoplast preparation. The DNA was transformed into R. nigricans via plasmid pEGFP-C1 and into P. ostreatus via 7.2 kb linear DNA. The mycelia were ground in 0.6 M mannitol without any grinding aids or glass powder for 15 min to make mycelial fragments suspension; the suspension was mixed with a mixture of the DNA and Lipofectamine 2000, and placed on ice for 30 min; 100 μL of the transformation solution was plated on potato dextrose agar (PDA) plate and cultivated at 28 °C for transformant screening. The plasmid and the linear DNA were confirmed to be integrated into the host chromosome, proving the success of transformation. The transformation efficiencies were similar to those of electroporation-mediated protoplast transformation (EMPT) of R. nigricans or PEG/CaCl₂-mediated protoplast transformation (PMT) of P. ostreatus, respectively. The results showed that our procedure was effective, fast, and simple transformation method for filamentous fungi.     

The feeding value for ruminants of straw and wholecrop barley and oats treated with anhydrous or aqueous ammonia or urea

Ammonia-treated or untreated barley straw supplemented with urea was given as the only feed to two groups of Friesian heifers weighing approximately 550 kg. The digestibility of dry matter (DM) was 58.8 and 49.9%, daily feed intake was 5.88 and 3.87 kg and daily liveweight change was +324 and -447 g for the ammonia-treated and control barley straw diets, respectively.Anhydrous or aqueous ammonia (NH₃) was injected into large round straw bales covered with plastic. The rates of degradation of barley straw in nylon bags and digestibility in vivo were the same for both ammonia treatments. The distribution of N in the bales was also similar and uniform with both treatments. No differences were recorded in the rate of degradation in nylon bags if the plastic was removed 2 or 8 weeks after treatment.Anhydrous or aqueous ammonia or isonitrogenous amounts of urea were injected into large round bags containing whole-crop barley or oats collected with a forage harvester. The digestibility of starch by steers was about 92% for ammonia-treated samples and 78% for the urea-treated samples. Urea and ammonia efficiently preserved the whole-crop materials but untreated control samples and samples treated with NaOH deteriorated during storage.