Fermentation and Immobilization of Insect-Derived Deltamethrin-Degrading Strain, <i>Microbacterium</i> sp.

Abstract

Extensive application of deltamethrin on agricultural products results in serious contamination of the environment. Its negative impact on environmental and public health necessitates the development of environmental remediation technologies. Detailed investigations of microbial degradation of deltamethrin may be useful for the development of bioremediation strategies. In this study, the deltamethrin removal capability of a bacterial strain, <i>Microbacterium</i> sp., previously isolated from the gut of <i>Tribolium castaneum</i> (Herbst) (Coleoptera: Tenebrionidae) was first investigated. When 3 mL of the bacterial solution (OD₆₀₀ = 1) was inoculated into 97 mL of MS media containing 200 μg/mL deltamethrin, it could remove 45.7% deltamethrin after 64 h of incubation. This strain grew fastest in LB media with an inoculum volume of 3% in pH 7 at 175 rpm, 25 °C. To enhance its environmental tolerance, this strain was immobilized with sodium alginate. <i>Microbacterium</i> sp.-containing calcium alginate microspheres (CAMs) exhibited an enhanced deltamethrin removal capability compared to free bacteria, and CAMs generated by immobilization with 2% sodium alginate and 3% CaCl₂ cross-linking for 4 h possessed the maximum deltamethrin removal capability. The ultrastructure of <i>Microbacterium</i> sp.-containing CAMs prepared under optimal conditions was a three-dimensional mesh structure with pores and dense features, and the bacteria grew well in the immobilized carrier. After being reused five times, the deltamethrin removal rate of immobilized <i>Microbacterium</i> sp. still reached over 50%. When <i>Microbacterium</i> sp. was inoculated into deltamethrin-contaminated water or soil for 48 h, the deltamethrin removal rate of immobilized bacteria was 1.4 times higher than that of free bacteria. These results suggest that <i>Microbacterium</i> sp.-containing CAMs possess an excellent deltamethrin removal capability and good reusability, showing great potential for the remediation of deltamethrin-contaminated environments.