Disposal of waste sludges produced in large amounts in the pulp and paper industry imposes significant environmental and economical problems. One strategy to address these issues involves revalorization of paper mill sludges by their application as substrates for microbial production of biotechnologically relevant enzymes. The application of lignocellulolytic enzymes in paper, textile and bioenergy industries is encouraged in order to decrease chemicals and energy consumptions. In the following work, deinking sludge was assessed as a substrate for production of lignocellulases. Based on the results of growth and activity screenings, Pleurotus ostreatus PLAB was chosen as the most promising candidate among 30 tested strains and its secretome was further studied by quantitative enzyme assays and mass spectrometry. While endoglucanase and xylanase activities detected in P. ostreatus secretome produced on deinking sludge were similar to activities of cultures grown on other lignocellulosic substrates, average laccase activity was significantly higher (46?000 U/kg DIS). Mass spectrometry identification of the most prominent proteins in the secretome of the target strain confirmed that significant amounts of different lignin-modifying oxidases were produced on this substrate despite its low lignin content, indicating the presence of other inducible compounds. The findings of this study suggest deinking sludge may represent a good substrate for fungal production of the aforementioned enzymes with broad biotechnological applications, including bioremediation, paper and bioenergy industries.
Bioethanol and biobutanol hold great promise as alternative biofuels, especially for transport sector, because they can be produced from lignocellulosic agro-industrial residues. From techno-economic point of view, the bioprocess for biofuels production should involve minimal processing steps. Consolidated bioprocessing (CBP), which combines various processing steps such as pretreatment, hydrolysis and fermentation in a single bioreactor, could be of great relevance for the production of bioethanol and biobutanol or solvents (acetone, butanol, ethanol), employing clostridia. For CBP, Clostridium holds best promise because it possesses multi-enzyme system involving cellulosome and xylanosome, which comprise several enzymes such as cellulases and xylanases. The aim of this article was to review the recent developments on enzyme systems of clostridia, especially xylanase and cellulase with an effort to analyse the information available on molecular approaches for the improvement of strains with ultimate aim to improve the efficiencies of hydrolysis and fermentation.
Aspergillus niger NII-08121/MTCC 7956 exhibited differences in expression of ?-glucosidase (BGL) in response to carbon sources provided in the medium. Activity staining with methyl umbelliferyl ?-d-glucopyranoside (MUG) indicated that four different isoforms of BGL were expressed when A. niger was grown under submerged fermentation with either lactose or cellulose, whereas only two were expressed when wheat bran or rice straw was used as the carbon source. Among the four isoforms of BGL expressed during lactose supplementation, two were found to retain 92% and 82% activity respectively in presence of 250 mM glucose in the MUG assay. The major ?-glucosidase (BGL1) was purified to homogeneity by electro elution from a Native PAGE gel. The purified 120 kDa protein was active at 50 °C and was stable for 48 h without any loss of activity. The optimum pH and temperature were 4.8 and 70 °C respectively.
Biomass feedstock having less competition with food crops are desirable for bio-ethanol production and such resources may not be localized geographically. A distributed production strategy is therefore more suitable for feedstock like water hyacinth with a decentralized availability. In this study, we have demonstrated the suitability of this feedstock for production of fermentable sugars using cellulases produced on site. Testing of acid and alkali pretreatment methods indicated that alkali pretreatment was more efficient in making the sample susceptible to enzyme hydrolysis. Cellulase and ?-glucosidase loading and the effect of surfactants were studied and optimized to improve saccharification. Redesigning of enzyme blends resulted in an improvement of saccharification from 57% to 71%. A crude trial on fermentation of the enzymatic hydrolysate using the common baker’s yeast Saccharomyces cerevisiae yielded an ethanol concentration of 4.4 g/L.