Enhanced Production of Ligninolytic Enzymes by a Mushroom Stereum ostrea

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.

Iron-reducing bacteria decompose lignin by electron transfer from soil organic matter

Iron-reducing bacteria (IRB) are crucial for electron transfer in anaerobic soil microsites. The utilization of the energy gathered by this mechanism by decomposers of organic matter is a challenging and fascinating issue. We hypothesized that bacteria reducing Fe(III) (oxyhydr)oxides to soluble Fe(II) obtain electrons from reduced soil organic matter (SOM_r) involving lignin oxidation. Iron-reducing bacteria were isolated from topsoils of various climates (humid temperate, cold temperate, subpolar), vegetation types (mostly grasslands and forests), and derived from various parent materials treatments assigned as Granitic, Volcanic-allophanic, Fluvio-glacial, Basaltic-Antarctic and Metamorphic. After the screening of IRB by phospholipid fatty acid (PLFA) analysis and PCR identification (full-length 16S rDNA), the IRB were inoculated to 20 samples (five soils and 4 replicates) and a broad range of parallel processes were traced. Geobacter metallireducens and Geobacter lovleyi were the main Geobacteraceae-strains present in all soils and strongly increased the activity of ligninolytic enzymes: lignin peroxidase and manganese peroxidase. Carbon dioxide (CO₂) released from IRB-inoculated soils was 140% higher than that produced by Fenton reactions (induced by H₂O₂ and Fe(II) addition) but 40% lower than in non-sterile soils. CO₂ release was closely correlated with the produced Fe (II) and H₂O₂ consumption. The highest CO₂ was released from Basaltic-Antarctic soils with the highest Fe content and was closely correlated with lignin depolymerization (detection by fluorescence images). All IRB oxidized the lignin contained in the SOM within a wide pH range and in soils from all parent materials. We present a conceptual model showing electron shuttling from SOM containing lignin (as a C and energy source) to IRB to produce energy and promote Fe(III) (oxyhydr)oxides reduction was proposed and discussed.

Synergy effect of peroxidase enzymes and Fenton reactions greatly increase the anaerobic oxidation of soil organic matter

In temperate rainforest soils of southern Chile (38 °S), there are high rates of soil organic carbon (SOC) mineralization under oxygen (O₂) limitation. We study the combined effects of Fenton reactions and the activity of two enzymes manganese peroxidase (MnP) and lignin peroxidase (LiP), which was hypothesised potentiate SOC mineralization under anoxic conditions leading to carbon dioxide (CO₂) release. Both mechanisms produce free radicals when competing for SOC oxidation in the absence of microorganisms. We quantify the CO₂ release by induced Fenton reactions in combination with MnP and LiP under aerobic and anaerobic conditions (20 °C, 36 h) in temperate rainforest soils. CO₂ levels released by Fenton reactions and enzyme activity were eight times higher than those released by Fenton reaction and peroxidase enzymes in individual treatment. Approximately 31% of the CO₂ released under aerobic soil incubation was found to be abiotic (sterilized), while 69% was biotic (non-sterilized soils), and respective values of 17% and 83% were recorded under anaerobic conditions. The relative fluorescence intensity clearly shows ·OH radicals production from Fenton reactions. In conclusion, levels of MnP and LiP coupled with Fenton reactions strongly increase SOC mineralization under long periods of O₂ limitation in temperate rainforest soils.

Cultivation of Mushrooms and Their Lignocellulolytic Enzyme Production Through the Utilization of Agro-Industrial Waste

A large amount of agro-industrial waste is produced worldwide in various agricultural sectors and by different food industries. The disposal and burning of this waste have created major global environmental problems. Agro-industrial waste mainly consists of cellulose, hemicellulose and lignin, all of which are collectively defined as lignocellulosic materials. This waste can serve as a suitable substrate in the solid-state fermentation process involving mushrooms. Mushrooms degrade lignocellulosic substrates through lignocellulosic enzyme production and utilize the degraded products to produce their fruiting bodies. Therefore, mushroom cultivation can be considered a prominent biotechnological process for the reduction and valorization of agro-industrial waste. Such waste is generated as a result of the eco-friendly conversion of low-value by-products into new resources that can be used to produce value-added products. Here, we have produced a brief review of the current findings through an overview of recently published literature. This overview has focused on the use of agro-industrial waste as a growth substrate for mushroom cultivation and lignocellulolytic enzyme production.

Ligninolytic behavior of the white-rot fungus Stereum ostrea under influence of culture conditions, inducers and chlorpyrifos

The production of three ligninolytic enzymes, laccase (LAC), manganese peroxidase (MnP) and lignin peroxidase (LiP) by the white-rot fungus, Stereum ostrea, was significantly more in Koroljova liquid medium in the presence of chlorpyrifos under shaking conditions than under stationary conditions. These enzymes were secreted into the broth to the extent of 214.37, 82.75 and 8.05 U/ml under influence of chlorpyrifos on 10th day of incubation in comparison with 138.06, 51.85 and 6.44 U/ml, respectively, under similar conditions in control. Maximum production of LAC, MnP and LiP on liquid medium with/without chlorpyrifos under stationary conditions did not exceed 80-85, 33-40, 0.6-0.7 U/ml, respectively. Among lignosulfonic acid, veratryl alcohol (VA), gallic acid (GA) and tannic acid tested, GA induced maximum production of LAC (300.53 U/ml) and MnP (181.66 U/ml) after 10 days of growth in the presence of chlorpyriphos, while maximum LiP (1.134 U/ml) was produced when grown with the inducer VA during this period. Our data suggest that chlorpyrifos and inducers interacted positively in producing higher amounts of the ligninolytic enzymes in S. ostrea.

Elevated levels of laccase synthesis by Pleurotus pulmonarius BPSM10 and its potential as a dye decolorizing agent

Laccases (EC 1.10.3.2) are a class of multi-copper oxidases that have industrial value. In the present study, forty-five isolates of wild mushrooms were screened for laccase production. Eight of the isolates exhibited exploitable levels of substrate oxidation capacity. Isolate BPSM10 exhibited the highest laccase activity of 103.50 U/ml. Internal Transcribed Spacer (ITS) rRNA gene sequencing was used to identify BPSM10 as Pleurotus pulmonarius. The response of BPSM10 to two nutritional media supplemented with various inducers was characterized and the results indicated that Malt Extract Broth (MEB) supplemented with Xylidine increased laccase production by 2.8× (349.5 U/ml) relative to the control (122 U/ml), while Potato Dextrose Broth (PDB) supplemented with xylidine increased laccase production by 1.9× (286 U/ml). BPSM10 has the ability to decolorize seven synthetic dyes in a liquid medium. Maximum decolorization was observed of malachite green (MG); exhibiting 68.6% decolorization at 100 mg/L. Fourier-transform infrared spectroscopy (FTIR) was employed to confirm the decolorization capacity. The present study indicates that P. pulmonarius BPSM10 has the potential to be used as a potent alternative biosorbent for the removal of synthetic dyes from aqueous solutions, especially in the detoxification of polluted water.

Potential of ligninolytic enzymatic complex produced by white-rot fungi from genus Trametes isolated from Bulgarian forest soil

Because of the crucial role of ligninolytic enzymes in a variety of industrial processes, the demand for a new effective producer has been constantly increasing. Furthermore, information on enzyme synthesis by autochthonous fungal strains is very seldom found. Two fungal strains producing ligninolytic enzymes were isolated from Bulgarian forest soil. They were identified as being Trametes trogii and T. hirsuta. These two strains were assessed for their enzyme activities, laccase (Lac), lignin peroxidase (LiP) and Mn-dependent peroxidase (MnP) in culture filtrate depending on the temperature and the type of nutrient medium. T. trogii was selected as the better producer of ligninolytic enzymes. The production process was further improved by optimizing a number of parameters such as incubation time, type of cultivation, volume ratio of medium/air, inoculum size and the addition of inducers. The maximum activities of enzymes synthesized by T. trogii was detected as 11100 U/L for Lac, 2.5 U/L for LiP and 4.5 U/L for MnP after 14 days of incubation at 25°C under static conditions, volume ratio of medium/air 1:6, and 3 plugs as inoculum. Among the supplements tested, 5% glycerol increased Lac activity to a significant extent. The addition of 1% veratryl alcohol had a positive effect on MnP.

Production, characterization and Congo red dye decolourizing efficiency of a laccase from Pleurotus ostreatus MTCC 142 cultivated on co-substrates of paddy straw and corn husk

A laccase produced by Pleurotus ostreatus MTCC 142 under solid-state fermentation using co-substrates of paddy straw and corn husk (1.5:1.5, g w/w) showed an activity of 2.54 U gds-1. Laccase activity was determined spectrophotometrically using 0.5 mM 2,2'- azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS). Supplementation with fructose and potassium nitrate resulted in maximum enzyme production at initial pH 5.8 ± 0.2 and initial moisture content of 70%. A carbon: nitrogen ratio of 0.5:0.1 yielded highest laccase activity in the presence of surfactant Tween 20 (0.05%, w/v). Incorporation of vanillin (5 mM) and copper sulphate (10 mM) facilitated enhanced synthesis of laccase. A 4.8-fold increase in enzyme activity was recorded after optimization of nutritional parameters. The apparent molecular mass of this enzyme was revealed as 43 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The laccase showed optimal activity at pH 3 and 35 °C with 82.8% residual activity after 1 h of incubation. The K m and V max values on ABTS were found to be 0.52 mM and 9.33 U gds-1, respectively. The enzyme activity was enhanced by Cu2+ and remained unaffected with Ba2+, Mn2+, Pb2+, Mg2+, Ca2+ and Fe3+. However, pre-incubation of the enzyme with reagents like sodium azide, sodium lauryl sulphate and 2-mercaptoethanol demonstrated an inhibition of its activity. Addition of crude laccase to Congo red dye solution resulted in 36.84% decolourization after 20 h of incubation at 35 ± 2 °C. This study discusses the production and characterization of a laccase from P. ostreatus strain with potential for azo dye decolourization.