Screening and enzyme activity determination of cellulase-producing strains from the gut bacteria of Dolycoris baccarum L.

Abstract:

[Background] Dolycoris baccarum L. is a herbivorous pest that harms sorghum, maize, soybean and other crops and fruit plants. Studying its gut bacteria is essential for the control of D. baccarum L. and the exploration of functional bacterial resources from the gut. [Objective] This study aims to gain insights into the culturable bacteria in the gut of D. baccarum L. and screen out cellulase-producing strains. The cellulase activities of the strains screened out were determined. The enzyme production conditions of several strains were explored. [Methods] The gut bacteria of D. baccarum L. were isolated by the culture method and identified by morphological observation and 16S rRNA gene sequencing. The inhibition zone method was employed to screen out the strains capable of producing cellulase. The cellulase activities of the strains were determined by the 3,5-dinitrosalicylic acid (DNS) method. [Results] A total of 35 strains were isolated from the gut of D. baccarum L., they are 10 species of bacteria belonging to 5 genera, including 3 species of Enterococcus, 4 species of Bacillus, and 1 species of Lactococcus, Serratia, and Pantoea, respectively. A total of 13 strains capable of producing cellulase were screened out. Strains B8, B22, B23, and B25 had strong cellulase-producing capacity, among which B22 had the most prominent cellulase-producing ability (D/d=7.01). The cellulase-producing capacity was the strongest in the medium with pH 5.0, culture with B8, B23, and B25 for 24 h, or culture with B22 for 36 h. [Conclusion] The gut of D. baccarum L. harbors rich culturable bacteria and 37% of the isolates can produce cellulose, which can assist in food digestion and influence the host health. Both fermentation time and medium pH influence the cellulase production of functional strains. Strain B22 with strong cellulase-producing ability should be further developed and utilized.