Degradation of keratinous materials by the plant pathogenic fungus Myrothecium verrucaria

Microbial Keratinases: Enzymes with Promising Biotechnological Applications

Keratin is a complex and structurally stable protein found in human and animal hard tissues, such as feathers, wool, hair, hoof and nails. Some of these, like feathers and wool, represent one of the main sources of protein-rich waste with significant potential to be transformed into value-added products such as feed, fertilizers or bioenergy. A major limitation impeding valorization of keratinous substrates is their recalcitrant structure and resistance to hydrolysis by common proteases. However, specialized keratinolytic enzymes produced by some microorganisms can efficiently degrade these substrates. Keratinases have already found a purpose in pharmaceutical, textile and leather industries. However, their wider implementation in other processes, such as cost-effective (pre)treatment of poultry waste, still requires optimization of production and performance of the available enzymes. Here we present a comprehensive review covering molecular properties and characteristics of keratinases, their classification, traditional and novel approaches in discovery of novel enzymes, production, characterization, improvement and biotechnological applications.

Newly isolated Bacillus sp. G51 from Patagonian wool produces an enzyme combination suitable for felt-resist treatments of organic wool

Bacteria from Patagonian Merino wool were isolated to assess their wool-keratinolytic activity and potential for felt-resist treatments. Strains from Bacillus, Exiguobacterium, Deinococcus, and Micrococcus produced wool-degrading enzymes. Bacillus sp. G51 showed the highest wool-keratinolytic activity. LC-MS/MS analysis revealed that G51 secreted two serine proteases belonging to the peptidase family S8 (MEROPS) and a metalloprotease associated with Bacillolysin, along with other enzymes (γ-glutamyltranspeptidase and dihydrolipoyl dehydrogenases) that could be involved in reduction of keratin disulfide bonds. Optimum pH and temperature of G51 proteolytic activity were 9 and 60 °C, respectively. More than 80% of activity was retained in H₂O₂, Triton X-100, Tween 20, Lipocol OXO650, Teridol B, and β-mercaptoethanol. Treatment of wool top with G51 enzyme extract caused a decrease in wool felting tendency without significant weight loss (<1.5%). Sparse work has so far been performed to investigate suitable keratinases for the organic wool sector. This eco-friendly treatment based on a new enzyme combination produced by a wild bacterium has potential for meeting the demands of organic wool processing which bans the use of hazardous chemicals and genetic engineering.

Innovative pretreatment strategies for biogas production

Biogas or biomethane is traditionally produced via anaerobic digestion, or recently by thermochemical or a combination of thermochemical and biological processes via syngas (CO and H₂) fermentation. However, many of the feedstocks have recalcitrant structure and are difficult to digest (e.g., lignocelluloses or keratins), or they have toxic compounds (such as fruit flavors or high ammonia content), or not digestible at all (e.g., plastics). To overcome these challenges, innovative strategies for enhanced and economically favorable biogas production were proposed in this review. The strategies considered are commonly known physical pretreatment, rapid decompression, autohydrolysis, acid- or alkali pretreatments, solvents (e.g. for lignin or cellulose) pretreatments or leaching, supercritical, oxidative or biological pretreatments, as well as combined gasification and fermentation, integrated biogas production and pretreatment, innovative biogas digester design, co-digestion, and bio-augmentation.

Purification and characterization of an efficient poultry feather degrading-protease from Myrothecium verrucaria

The purpose of this work was to characterize an alkaline protease from the filamentous fungus Myrothecium verrucaria and to explore its capability to degrade native poultry feathers. The enzyme was purified to homogeneity using a single chromatographic step. Recovery was high, 62%, with a specific activity of 12,851.8 U/mg protein. The enzyme is a small monomeric protein with a molecular mass of 22 +/- 1.5 kDa. It presented pH optimum of 8.3 and was stable over a broad pH range (5.0-12.0). The temperature optimum was 37 degrees C, with thermal stability at temperatures up to 45 degrees C. The enzyme presented an efficiency of 80.3% in the degradation of poultry feather meal, releasing amino acids and soluble peptides. It was able to hydrolyze beta-keratin without necessity of chemical or enzymatic reduction of the disulphide bonds. Considering that, everyday, poultry-processing plants produce feathers as a waste products, this protease can be useful in biotechnological processes aiming to improve the transformation of poultry feathers through solubilization of beta-keratin into usable peptides. Furthermore, it can also be useful in processes aiming to reduce the environmental pollution caused by the accumulation of feathers.