Entomopathogenic efficacy of the chitinolytic bacteria: Aeromonas hydrophila isolated from Siwa Oasis, Egypt

Shereen M Korany,Hamdy H Aly,Abdel Naser A Kobisi,Amany N Mansour,Hoda H El-Hendawy

doi:10.1186/s41938-019-0116-x

Shereen M Korany, Hamdy H Aly + Show 3 more

Open Access

https://doi.org/10.1186/s41938-019-0116-x

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Abstract

Thirty-four bacterial isolates were isolated from soil samples collected from the North Western Coast and a water sample collected from brackish water at Siwa Oasis, Matrouh Governorate, Egypt. Only six isolates showed chitinase activity when screened on colloidal chitin agar medium. The highest chitinolytic activity was achieved by a bacterial isolate labeled as A.S. This isolate was identified as Aeromonas hydrophila based on analysis of 16S rRNA gene sequence and morphological, physiological, and biochemical characteristics. Optimization of the cultural conditions for maximum chitinase production by A. hydrophila revealed that the highest level of chitinase was recorded when the bacterium was grown in malt nitrogen-based medium containing 1% colloidal chitin at pH7 for 48 h incubation at 30 °C. Crude chitinase from isolate A. hydrophila was evaluated against first instar larvae of the greater wax moth; Galleria mellonella L. (Lepidoptera: Pyralidae) at different concentrations of 0, 185, 205, 235, 265, 295 U/mg protein. It increased larval and pupal mortality rates in a concentration-dependent manner. The tested crude chitinase significantly induced a decrease in adults’ emergence rate and their fecundity.

Highlights

Chitin, a β-1, 4-linked polymer of N-acetyl-D-glucosamine, is one of the most abundant polysaccharides in nature, next to cellulose (Elieh-Ali-Komi and Hamblin, 2016)
Isolation of chitinolytic bacteria Thirty-four bacterial isolates were isolated from the soil samples collected from different localities at North Western Coast, as well as one isolate from brackish water at Siwa Oasis, Matrouh Governorate, Egypt
These 35 bacterial isolates were screened for chitinase production on selective medium containing 1.5% colloidal chitin agar

Summary

Introduction

A β-1, 4-linked polymer of N-acetyl-D-glucosamine, is one of the most abundant polysaccharides in nature, next to cellulose (Elieh-Ali-Komi and Hamblin, 2016). It is widely distributed in nature as a structural component of crustaceans, fungi, and insects (Flach et al 1992). Chitin is present in the cuticle, gut lining, salivary glands, tracheal tubes, eggshells, and muscles (Kramer and Koga, 1986). It is a great target for controlling insect pests. Microorganisms produce chitinases in order to utilize chitin as an energy source whereas fungi and insect produce chitinases as they are involved in morphogenesis (Kitamura and Kamei, 2003)

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