Screening for chitin degrading bacteria in the environment of Saudi Arabia and characterization of the most potent chitinase from Streptomyces variabilis Am1

Forty-six promising chitinolytic isolates were recovered during a screening for chitinolytic bacteria in the environment of Saudi Arabia. The top three isolates belonged to the genus Streptomyces. Streptomyces variabilis Am1 was able to excrete the highest amount of chitinases, reaching the maximum at 84 h with 0.5% yeast extract and nitrogen source and 2% galactose as a carbon source. Purification of chitinase by DEAE-Cellulose and Sephadex G(75) improved the specific activity to 18.6-fold and the recovery to 23.8% and showed a mass at 56 kDa. The optimal catalysis of the purified chitinase was at 40 & DEG;C and pH 8 with high thermostability and pH stability as reflected by a midpoint temperature value of 66.6 & DEG;C and stability at pH 4-9. The protein reagents SDS, EDTA, and EGTA significantly inhibited the enzyme and the EDTA-chelated chitinase restored its activity after the addition of Fe2+ ions suggesting a metallo-chitinase type with ferric ions as cofactors. Chitinase exerted high antifungal activity against some phytopathogenic fungi. Interestingly, the tested Streptomyces were able to produce chitosan nanocubes along with chitosan from chitin degradation which may be an additional power in their antifungal activity in nature. This work also reveals the importance of unexplored environments as a pool of promising microorganisms with biotechnological applications.

Automated summary

Forty-six promising chitinolytic isolates were recovered in the environment of Saudi Arabia, with the top three isolates belonging to the genus Streptomyces. Streptomyces variabilis Am1 showed the highest chitinase activity at 84 hours, with 0.5% yeast extract and nitrogen source, and 2% galactose as carbon source. Purification of chitinase improved its specific activity and recovery, and revealed its metallo-chitinase type with ferric ions as cofactors. The chitinase demonstrated high antifungal activity against phytopathogenic fungi, and the tested Streptomyces were able to produce chitosan nanocubes, showing their additional power in antifungal activity. This work highlights the importance of unexplored environments for the discovery of promising microorganisms with biotechnological applications.