# Fermentation and Immobilization of Insect-Derived Deltamethrin-Degrading Strain, Microbacterium sp

## TL;DR

A new strain of bacteria from insects is immobilized to effectively and repeatedly remove deltamethrin, a harmful pesticide, from contaminated environments.

## Contribution

A novel immobilization method enhances the deltamethrin degradation efficiency and reusability of a Microbacterium sp. strain.

## Key findings

- Immobilized Microbacterium sp. removed over 50% deltamethrin even after five reuse cycles.
- Immobilized bacteria showed 1.4 times higher deltamethrin removal in contaminated soil and water compared to free bacteria.
- Optimal immobilization conditions included 2% sodium alginate and 3% CaCl2 cross-linking for 4 hours.

## Abstract

In agricultural production, the extensive use of insecticides has led to the persistent presence of residues such as deltamethrin in the environment, posing threats to ecosystems and human health. Utilizing microbes for environmental bioremediation presents a feasible approach. Studies have found that insects with strong insecticide tolerance often harbor gut bacteria capable of degrading insecticides. These gut bacteria are becoming an excellent reservoir of insecticide-degrading bacteria with bioremediation potential. However, in practical applications, the activity of free bacterial cells is easily affected by environmental factors, limiting the stability of their remediation efficacy. This study focused on a Microbacterium sp. strain isolated from insects. By optimizing culture conditions and the sodium alginate immobilization process, the remediation efficiency of the immobilized strain in contaminated soil and water was investigated. The results demonstrated that the immobilized strain significantly outperformed free bacteria in deltamethrin degradation performance in both contaminated soil and water, while also exhibiting good stability and reusability. This research provides an effective method for the remediation of deltamethrin-contaminated environments.

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, Microbacterium sp., previously isolated from the gut of Tribolium castaneum (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. Microbacterium 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 Microbacterium 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 Microbacterium sp. still reached over 50%. When Microbacterium 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 Microbacterium sp.-containing CAMs possess an excellent deltamethrin removal capability and good reusability, showing great potential for the remediation of deltamethrin-contaminated environments.