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.

As a potential renewable and nitrogen-rich feedstock, tons of shrimp shell waste is generated from the increasing consumption of seafood. However, its traditional processing is costly and creates pollution. The bioconversion of shell waste into valuable nitrogen-containing chemicals via enzymatic hydrolysis is a promising technology. However, intact shells are poorly hydrolyzed by chitinases unless pre-demineralization and deproteinization with chemicals or proteases are performed. In this study, three carbohydrate-binding modules (CBMs) were fused to the C-terminal of a chitinase Chit46 to enhance its hydrolysis of shrimp shell waste. The addition of CBMs significantly improved the chitinase activity and substrate-binding activity of Chit46. Chimeric chitinases could directly hydrolyze shrimp shells without pretreatment and their hydrolysis efficiency was much higher than that of previously reported chitinases. With the modified chitinase (‘Chit46-CBM3’), we developed a one-step shrimp shell processing method. The method could convert 46.5% of chitin in shrimp shells to chitin oligomers by hydrolysis in 12 h. Partial protein release accompanied chitin hydrolysis. Consisting of 8.8 g l⁻¹ chitin oligomers and 11.3 g l⁻¹ protein, the hydrolysate could support robust microbial growth and the residue was more digestible by mammals than conventional shrimp shell powder. This process is superior to previously reported methods in cost, conversion efficiency and labour. The one-step process also exhibited a much lower ecological footprint than conventional processing and can be applied to other types of chitinous waste in addition to shrimp shells.

The ongoing development of new production methods may lead to the commercialization of N-acetyl chitooligosaccharides (NACOS), such as chitosan oligosaccharides (COS). The bioactivity of NACOS, although not well detailed, differs from that of COS, as they have more acetyl groups than COS. We used two enzymatically produced NACOS with different molecular compositions and six NACOS (NACOS1–6) with a single degree of polymerization to verify their immunomodulatory effects on the RAW264.7 macrophage cell line. We aimed to identify any differences between COS and various NACOS with a single degree of polymerization. The results showed that NACOS had similar immune enhancement effects on RAW264.7 cells as COS, including the generation of reactive oxygen species (ROS), phagocytotic activity, and the production of pro-inflammation cytokines (IL-1β, IL-6, and TNF-α). However, unlike COS and lipopolysaccharide (LPS), NACOS1 and NACOS6 significantly inhibited nitric oxide (NO) production. Besides their immune enhancement effects, NACOS also significantly inhibited the LPS-induced RAW264.7 inflammatory response with some differences between various polymerization degrees. We confirmed that the NF-κB pathway is associated with the immunomodulatory effects of NACOS on RAW264.7 cells. This study could inform the application of NACOS with varying different degrees of polymerization in human health.