Abstract
Biodegradation of lobster shells by chitinolytic microorganisms are an environment safe approach to utilize lobster processing wastes for chitin derivation. In this study, we report degradation activities of two microbes, “S223” and “S224” isolated from soil samples that had the highest rate of deproteinization, demineralization and chitinolysis among ten microorganisms screened. Isolates S223 and S224 had 27.3 and 103.8 protease units mg-1 protein and 12.3 and 11.2 μg ml-1 of calcium in their samples, respectively, after 1 week of incubation with raw lobster shells. Further, S223 contained 23.8 μg ml-1 of N-Acetylglucosamine on day 3, while S224 had 27.3 μg ml-1 on day 7 of incubation with chitin. Morphological observations and 16S rDNA sequencing suggested both the isolates were Streptomyces. The culture conditions were optimized for efficient degradation of lobster shells and chitinase (∼30 kDa) was purified from crude extract by affinity chromatography. The digested lobster shell extracts induced disease resistance in Arabidopsis by induction of defense related genes (PR1 > 500-fold, PDF1.2 > 40-fold) upon Pseudomonas syringae and Botrytis cinerea infection. The study suggests that soil microbes aid in sustainable bioconversion of lobster shells and extraction of chitin derivatives that could be applied in plant protection.
Highlights
American lobster (Homarus americanus) is Canada’s most valuable fishery resource and exported around the world
All the microorganisms were grown in M9 buffer with 0.5% (w/v) lobster shell powder (LSP) at 25◦C for 48 h by inoculating a loop of scrapped colonies or mycelium grown on agar plates and this propagation method was followed to obtain the starter inoculum for all the other experiments. 1 mL of starter culture was incubated with 1% (w/v) LSP in M9 buffer at 25◦C, 150 rpm and samples were collected by centrifugation (6,000 × g, 20 min) for assaying degradation activity
The isolated microbes and B. subtilis, P. fluorescens, L. acidophilus, T. harzianum were tested for their ability to grow on chitin, raw and cooked lobster shells and colony diameter was measured on 7th day of incubation
Summary
American lobster (Homarus americanus) is Canada’s most valuable fishery resource and exported around the world. Annual lobster landings in the waters of Atlantic Canada show an upward trend over recent decades and remain at one of the highest levels recorded in 100 years and 82,741 tons of lobster valued at $2 billion CAD were exported from this region in 2015 (Fisheries and Oceans Canada, 2016). Lobsters are processed into product forms (cooked or raw meat) except for a small faction being sold live. The processing begins with removal of the hard shell (exoskeleton) and huge volumes of it are generated during commercial scale processing. The present waste management practices pose a serious environmental challenge to lobster and other crustacean processing plants. The exoskeleton of American lobster is composed of chitin, proteins, calcium, carotenoids and traces
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