PubMed · 15416710
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L E R PICKEN, W LOTMAR. 1950-04-15. Oriented protein in chitinous structures.. https://doi.org/10.1038/165599a0
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The Chytridiomycota (chytrids) are early diverging fungi, many of which function in ecosystems as saprotrophs; however, associated adaptive traits are poorly understood. We focused on chitin degradation, a common ecosystem function of aquatic chytrids, using the model chitinophilic Rhizoclosmatium globosum and comparison of other chytrid genomes. Zoospores are chemotactic to the chitin monomer N-acetylglucosamine and accelerate development when grown with chitin. The R. globosum secretome is dominated by different glycoside hydrolase (GH) family GH18 chitinases, with abundance matching reciprocal transcriptome mRNA sequences. Models of the secreted chitinases indicate a range of sizes and domain configurations. Along with R. globosum, the genomes of other chitinophilic chytrids also have expanded inventories of GH-encoding genes responsible for chitin processing. Several R. globosum GH18 chitinases have bacteria-like chitin-binding module domains, also present in the genomes of other chitinophilic chytrids yet absent in non-chitinophilic chytrids. Chemotaxis, increased abundance and diversity of secreted chitinases, complemented with the acquisition of novel chitin-binding capability, are probably adaptive traits that facilitate chitin saprotrophy. Our study reveals the underpinning mechanisms that have supported the niche expansion of some chytrids to utilize lucrative chitin-rich particles in aquatic ecosystems and is a demonstration of the adaptive ability of this successful fungal group.
The optimization of nutrient levels for chitinase production by Enterobacter sp. NRG4 in solid-state fermentation conditions (SSF) was carried out using response surface methodology (RSM) based on central composite design (CCD). The design was employed by selecting wheat bran-to-flake chitin ratio, moisture level, inoculum size, and incubation time as model factors. The results of first-order factorial design experiments showed that all four independent variables have significant effects on chitinase production. The optimum concentrations for chitinase production were wheat bran-to-flake chitin ratio, 1; moisture level, 80%; inoculum size, 2.6 mL; and incubation time, 168 h. Using this statistical optimization method, chitinase production was found to increase from 616 U . g(-1) dry weight of solid substrate to 1475 U . g(-1) dry weight of solid substrate.
Beta-chitin microfibrils were treated with ChiA and ChiB (chitinases A and B respectively) from Serratia marcescens 2170. The beta-chitin microfibrils were shortened, and the tips appeared narrowed and sharpened at both ends, after either consecutive or simultaneous degradation by ChiA and ChiB. Increased production of reducing sugars by simultaneous degradation (by ChiA and ChiB) of beta-chitin, but not of glycol chitin, suggests synergistic interactions between the two enzymes. A combined analysis using the tilt microdiffraction method to determine the crystallographic axes, together with the biotin-streptavidin-gold-labelling method specific to the reducing ends, was used to investigate the polarity of the degraded beta-chitin microcrystals. The digestion of the beta-chitin fibrils by ChiA occurred from the reducing end to the nonreducing end, whereas digestion by ChiB occurred from the non-reducing end to the reducing end. The results are in agreement with the previously determined three-dimensional structures of these enzymes.