Production of feather oligopeptides by a newly isolated bacterium Pseudomonas otitis H11

Harnessing the potential of microbial keratinases for bioconversion of keratin waste

The increasing global consumption of poultry meat has led to the generation of a vast quantity of feather keratin waste daily, posing significant environmental challenges due to improper disposal methods. A growing focus is on utilizing keratinous polymeric waste, amounting to millions of tons annually. Keratins are biochemically rigid, fibrous, recalcitrant, physiologically insoluble, and resistant to most common proteolytic enzymes. Microbial biodegradation of feather keratin provides a viable solution for augmenting feather waste's nutritional value while mitigating environmental contamination. This approach offers an alternative to traditional physical and chemical treatments. This review focuses on the recent findings and work trends in the field of keratin degradation by microorganisms (bacteria, actinomycetes, and fungi) via keratinolytic and proteolytic enzymes, as well as the limitations and challenges encountered due to the low thermal stability of keratinase, and degradation in the complex environmental conditions. Therefore, recent biotechnological interventions such as designing novel keratinase with high keratinolytic activity, thermostability, and binding affinity have been elaborated here. Enhancing protein structural rigidity through critical engineering approaches, such as rational design, has shown promise in improving the thermal stability of proteins. Concurrently, metagenomic annotation offers insights into the genetic foundations of keratin breakdown, primarily predicting metabolic potential and identifying probable keratinases. This may extend the understanding of microbial keratinolytic mechanisms in a complex community, recognizing the significance of synergistic interactions, which could be further utilized in optimizing industrial keratin degradation processes.

Genome-wide analysis of Keratinibaculum paraultunense strain KD-1 T and its key genes and metabolic pathways involved in the anaerobic degradation of feather keratin

Keratinibaculum paraultunense strain KD-1 ^T (= JCM 18769 ^T = DSM 26752 ^T) is a strictly anaerobic rod-shaped bacterium. Under optimal conditions, feather keratin can be completely degraded by strain KD-1 within 24 h. Genomic sequencing showed that the genome was a single circular chromosome consisting of 2,307,997 base pairs (bp), with an average G + C content of 29.8% and no plasmids. A total of 2308 genes were annotated, accounting for 88.87% of the genomic sequence, and 1495 genes were functionally annotated. Among these, genes Kpa0144, Kpa0540, and Kpa0541 encoding the thioredoxin family members were identified, and may encode the potential disulfide reductases, with redox activity for protein disulfide bonds. Two potential keratinase-encoding genes, Kpa1675 and Kpa2139, were also identified, and corresponded to the ability of strain KD-1 to hydrolyze keratin. Strain KD-1 encoded genes involved in the heterotrophic metabolic pathways of 14 amino acids and various carbohydrates. The metabolic pathways for amino acid and carbohydrate metabolism were mapped in strain KD-1 based on KEGG annotations. The complete genome of strain KD-1 provided fundamental data for the further investigation of its physiology and genetics.

Chicken Feather Waste Hydrolysate as a Superior Biofertilizer in Agroindustry

Billions of tons of keratinous waste in the form of feathers, antlers, bristles, claws, hair, hoofs, horns, and wool are generated by different industries and their demolition causes environmental deterioration. Chicken feathers have 92% keratin that can be a good source of peptides, amino acids, and minerals. Traditional methods of feather hydrolysis require large energy inputs, and also reduce the content of amino acids and net protein utilization values. Biological treatment of feathers with keratinolytic microbes is a feasible and environmental favorable preference for the formulation of hydrolysate that can be used as bioactive peptides, protein supplement, livestock feed, biofertilizer, etc. The presence of amino acids, soluble proteins, and peptides in hydrolysate facilitates the growth of microbes in rhizosphere that promotes the uptake and utilization of nutrients from soil. Application of hydrolysate enhances water holding capacity, C/N ratio, and mineral content of soil. The plant growth promoting activities of hydrolysate potentiates its possible use in organic farming, and improves soil ecosystem and microbiota. This paper reviews the current scenario on the methods available for management of keratinous waste, nutritional quality of hydrolysate generated using keratinolytic microbes, and its possible application as plant growth promoter in agroindustry.

Production and characterization of keratinase by Ochrobactrum intermedium for feather keratin utilization

A newly isolated bacterium producing 55.5 U/mL keratinase on feather meal minimal medium was identified as Ochrobactrum intermedium. Optimization of process parameters by one-variable-at-a-time (OVAT) approach (substrate concentration 0.5% w/v, inoculum size 5% w/v, pH 7.0, 200 rpm for 96 h at 40 °C) resulted in 2.1-fold increase in keratinase secretion (117 U/mL). Keratinase was optimally active at pH 9.0 and 40 °C and was stable at pH 9.0 and 60 °C for 120 min. Calcium ions enhanced keratinase activity (158%) significantly, while it was strongly inhibited by both PMSF and EDTA, indicating it to be a metallo-serine protease. Keratinase degraded native chicken feathers efficiently resulting in 97.9% weight loss along with release of 745.5 μg/mL soluble proteins and 4196.69 μg/mL amino acids. Feather hydrolysate generated by NKIS 1 exhibited significant anti-oxidant and free-radical scavenging activity (90.46%). The present study revealed that O. intermedium NKIS 1 has potential applications in the biodegradation of chicken feathers and the value-addition of poultry waste.

The feather degradation mechanisms of a new Streptomyces sp. isolate SCUT-3

Feather waste is the highest protein-containing resource in nature and is poorly reused. Bioconversion is widely accepted as a low-cost and environmentally benign process, but limited by the availability of safe and highly efficient feather degrading bacteria (FDB) for its industrial-scale fermentation. Excessive focuses on keratinase and limited knowledge of other factors have hindered complete understanding of the mechanisms employed by FDB to utilize feathers and feather cycling in the biosphere. Streptomyces sp. SCUT-3 can efficiently degrade feather to products with high amino acid content, useful as a nutrition source for animals, plants and microorganisms. Using multiple omics and other techniques, we reveal how SCUT-3 turns on its feather utilization machinery, including its colonization, reducing agent and protease secretion, peptide/amino acid importation and metabolism, oxygen consumption and iron uptake, spore formation and resuscitation, and so on. This study would shed light on the feather utilization mechanisms of FDBs.

Li et a. report a new Streptromyces isolate, SCUT-3 which can efficiently degrade feather into products with high amino acid content, useful as feed for plants, animals and microbes. Using multiple omics and other techniques, they report how SCUT-3 turns on its feather utilization machinery and suggest a number of expressed genes most likely implicated in feather degradation.

Beyond plucking: Feathers bioprocessing into valuable protein hydrolysates

The livestock production and subsequent processing of meat results in huge quantities of solid waste such as viscera, bones, skin and keratin-rich materials, including feathers, hair, wool, claws and hooves. In particular, the continuous growth of poultry industry generates massive amounts of feathers as major waste material. The conversion of such by-products into materials with increased value has been studied. Hydrothermal, chemical or biological approaches have been investigated to achive effective conversion of highly recalcitrant proteins that are abundant in animal waste, but increasing interest is devoted to the development of biotechnological methods. The processing of feathers and other by-products into protein hydrolysates may have industrial and commercial significance. Therefore, this review comprehensively addresses the postulated applications of hydrolysates obtained from keratinous biomasses. Examples on the utilization of feather hydrolysates as organic soil fertilizers, feed ingredients, cosmetic formulations and biofuel production are described in the literature. Microbial feather hydrolysis can generate bioactive peptides as well. The use of protein-rich waste from meat industry to produce hydrolysates with biological activities constitutes a point of utmost interest for development of functional ingredients with elevated value.