Summary Chitosan and its derivatives have numerous applications in wastewater treatment as bio‐coagulants, flocculants and bio‐adsorbents against both particulate and dissolved pollutants. Chitinolytic bacteria secrete an array of enzymes, which play crucial role in chitin to chitosan conversion. Consequently, there is a growing demand for identification and characterization of novel bacterial isolates with potential implications in chitosan production. We describe genomic features of the new isolate Streptomyces sp. UH6. Analysis of the 6.51 Mb genome revealed the GC content as 71.95% and presence of 6990 coding sequences of which 63% were functionally annotated. Further, we identified two possible chitin‐utilization pathways, which employ secreted enzymes like lytic polysaccharide monooxygenases and family‐18 glycoside hydrolases (GHs). More importantly, the genome has six family‐4 polysaccharide deacetylases with probable role in chitin to chitosan conversion, as well as two chitosanases belonging to GH46 and GH75 families. In addition, the gene clusters, dasABC and ngcEFG coding for transporters, which mediate the uptake of N,N′‐diacetylchitobiose and N‐acetyl‐d‐glucosamine were identified. Several genes responsible for hydrolysis of other polysaccharides and fermentation of sugars were also identified. Taken together, the phylogenetic and genomic analyses suggest that the isolate Streptomyces sp. UH6 secretes potential chitin‐active enzymes responsible for chitin to chitosan conversion.

Chitin, particularly α-chitin, is the most abundant and highly recalcitrant form, fortified by an intricate network of hydrogen bonds. Efficient valorization of α-chitin requires a mild pre-treatment and enzymatic hydrolysis. Streptomyces spp. secrete chitin-active CAZymes that can efficiently tackle the recalcitrant problem of chitin biomass. To better understand the potential of Streptomyces spp., a comparative analysis was performed between the novel isolate, Streptomyces sp. UH6 and the well-known chitin degraders, S. coelicolor and S. griseus. Growth studies and FE-SEM analysis revealed that all three Streptomyces spp. could utilize and degrade both α- and β-chitin. Zymogram analysis showed expression of 5-7 chitinases in the secretomes of Streptomyces strains. The chitin-active-secretomes produced by Streptomyces sp. UH6 and S. griseus were optimally active at acidic pH (pH 4.0 and 5.0) and 50°C. Time-course degradation of α- and β-chitin with the secretomes generated N-acetyl-D-glucosamine (GlcNAc) and N,N-diacetylchitobiose [(GlcNAc)2] as the predominant products. Further, the highly crystalline α-chitin was subjected to pre-treatment by ball-milling, which reduced the crystallinity from 88% to 56.6% and increased the BET surface area by 3-folds. Of note, the activity of all three Streptomyces secretomes was improved by a mild pre-treatment, while Streptomyces sp. UH6 secretome displayed improved GlcNAc and (GlcNAc)2 yields by 14.4 and 9.6-folds, respectively. Overall, our results suggest that the Streptomyces chitin-active-secretomes, particularly Streptomyces sp. UH6, can be deployed for efficient valorization of chitin biomass and to establish an economically feasible and eco-friendly process for valorizing highly recalcitrant α-chitin.

Chitin, particularly α-chitin, is the most abundant and highly recalcitrant form, fortified by an intricate network of hydrogen bonds. Efficient valorization of α-chitin requires mild pre-treatment and enzymatic hydrolysis. Streptomyces...