Modular Engineering to Enhance Keratinase Production for Biotransformation of Discarded Feathers

Plant Growth Promotion and Plant Disease Suppression Induced by Bacillus amyloliquefaciens Strain GD4a

Botrytis cinerea, the causative agent of gray mold disease (GMD), invades plants to obtain nutrients and disseminates through airborne conidia in nature. Bacillus amyloliquefaciens strain GD4a, a beneficial bacterium isolated from switchgrass, shows great potential in managing GMD in plants. However, the precise mechanism by which GD4a confers benefits to plants remains elusive. In this study, an A. thaliana-B. cinerea-B. amyloliquefaciens multiple-scale interaction model was used to explore how beneficial bacteria play essential roles in plant growth promotion, plant pathogen suppression, and plant immunity boosting. Arabidopsis Col-0 wild-type plants served as the testing ground to assess GD4a's efficacy. Additionally, bacterial enzyme activity and targeted metabolite tests were conducted to validate GD4a's potential for enhancing plant growth and suppressing plant pathogens and diseases. GD4a was subjected to co-incubation with various bacterial, fungal, and oomycete pathogens to evaluate its antagonistic effectiveness in vitro. In vivo pathogen inoculation assays were also carried out to investigate GD4a's role in regulating host plant immunity. Bacterial extracellular exudate (BEE) was extracted, purified, and subjected to untargeted metabolomics analysis. Benzocaine (BEN) from the untargeted metabolomics analysis was selected for further study of its function and related mechanisms in enhancing plant immunity through plant mutant analysis and qRT-PCR analysis. Finally, a comprehensive model was formulated to summarize the potential benefits of applying GD4a in agricultural systems. Our study demonstrates the efficacy of GD4a, isolated from switchgrass, in enhancing plant growth, suppressing plant pathogens and diseases, and bolstering host plant immunity. Importantly, GD4a produces a functional bacterial extracellular exudate (BEE) that significantly disrupts the pathogenicity of B. cinerea by inhibiting fungal conidium germination and hypha formation. Additionally, our study identifies benzocaine (BEN) as a novel small molecule that triggers basal defense, ISR, and SAR responses in Arabidopsis plants. Bacillus amyloliquefaciens strain GD4a can effectively promote plant growth, suppress plant disease, and boost plant immunity through functional BEE production and diverse gene expression.

Sustainable valorizing high-protein feather waste utilization through solid-state fermentation by keratinase-enhanced Streptomyces sp. SCUT-3 using a novel promoter

Feather waste, a rich source of proteins, has traditionally been processed through high-temperature puffing and acid-base hydrolysis, contributing to generation of greenhouse gases and H2S. To address this issue, we employed circular economy techniques to recover the nutritional value of feather waste. Streptomyces sp. SCUT-3, an efficient proteolytic and chitinolytic bacterium, was isolated for feather degradation previously. This study aimed to valorize feather waste for feed purposes by enhancing its feather transformation ability through promoter optimization. Seven promoters were identified through omics analysis and compared to a common Streptomyces promoter ermE*p. The strongest promoter, p24880, effectively enhanced the expression of three candidate keratinases (Sep39, Sep40, and Sep53). The expression efficiency of double-, triple-p24880 and sandwich p24880-sep39-p24880 promoters were further verified. The co-overexpression strain SCUT-3-p24880-sep39-p24880-sep40 exhibited a 16.21-fold increase in keratinase activity compared to the wild-type. Using this strain, a solid-state fermentation process was established that increased the feather/water ratio (w/w) to 1:1.5, shortened the fermentation time to 2.5 days, and increased soluble peptide and free amino acid yields to 0.41 g/g and 0.14 g/g, respectively. The resulting has high protein content (90.49 %), with high in vitro digestibility (94.20 %). This method has the potential to revolutionize the feather waste processing industry.

Structure prediction, docking studies and molecular cloning of novel Pichia kudriavzevii YK46 metalloprotease (MetPr) for improvement of feather waste biodegradation

This study addresses the environmental risks associated with the accumulation of keratin waste from poultry, which is resistant to conventional protein degradation methods. To tackle this issue, microbial keratinases have emerged as promising tools for transforming resilient keratin materials into valuable products. We focus on the Metalloprotease (MetPr) gene isolated from novel Pichia kudriavzevii YK46, sequenced, and deposited in the NCBI GenBank database with the accession number OQ511281. The MetPr gene encodes a protein consisting of 557 amino acids and demonstrates a keratinase activity of 164.04 U/ml. The 3D structure of the protein was validated using Ramachandran's plot, revealing that 93% and 97.26% of the 557 residues were situated within the most favoured region for the MetPr proteins of template Pichia kudriavzevii strain 129 and Pichia kudriavzevii YK46, respectively. Computational analyses were employed to determine the binding affinities between the deduced protein and beta keratin. Molecular docking studies elucidated the optimal binding affinities between the metalloprotease (MetPr) and beta-keratin, yielding values of - 260.75 kcal/mol and - 257.02 kcal/mol for the template strains Pichia kudriavzevii strain 129 and Pichia kudriavzevii YK46, respectively. Subsequent molecular cloning and expression of the MetPr gene in E. coli DH5α led to a significantly higher keratinase activity of 281 ± 12.34 U/ml. These findings provide valuable insights into the potential of the MetPr gene and its encoded protein for keratin waste biotransformation, with implications for addressing environmental concerns related to keratinous waste accumulation.

Response surface methodology based optimization of keratinase from Bacillus velezensis strain ZBE1 and nanoparticle synthesis, biological and molecular characterization

The increasing demands of keratinases for biodegradation of recalcitrant keratinaceous waste like chicken feathers has lead to research on newer potential bacterial keratinases to produce high-value products with biological activities. The present study reports a novel keratinolytic bacterium Bacillus velezensis strain ZBE1 isolated from deep forest soil of Western Ghats of Karnataka, which possessed efficient feather keratin degradation capability and induced keratinase production. Production kinetics depicts maximum keratinase production (11.65 U/mL) on 4th day with protein concentration of 0.61 mg/mL. Effect of various physico-chemical factors such as, inoculum size, metal ions, carbon and nitrogen sources, pH and temperature influencing keratinase production were optimized and 3.74 folds enhancement was evidenced through response surface methodology. Silver (AgNP) and zinc oxide (ZnONP) nanoparticles with keratin hydrolysate produced from chicken feathers by the action of keratinase were synthesized and verified with UV-Visible spectroscopy that revealed biological activities like, antibacterial action against Bacillus cereus and Escherichia coli. AgNP and ZnONP also showed potential antioxidant activities through radical scavenging activities by ABTS and DPPH. AgNP and ZnONP revealed cytotoxic effect against MCF-7 breast cancer cell lines with IC50 of 5.47 µg/ml and 62.26 µg/ml respectively. Characterizations of nanoparticles were carried out by Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray, X-ray diffraction, thermogravimetric analysis and atomic force microscopy analysis to elucidate the thermostability, structure and surface attributes. The study suggests the prospective applications of keratinase to trigger the production of bioactive value-added products and significant application in nanotechnology in biomedicine.