Possible Use in Soil Bioremediation of the Bacterial Strain Bacillus Sphaericus NM-1 Capable of Simultaneously Degrading Promethrin and Acetochlor

Abstract

Prometryn and acetochlor are herbicides used to control weeds in farmlands and other areas. They enter the soil through direct application, residual accumulation in crops, and atmospheric deposition. The pollution of their residues in the environment has attracted people's attention. Bioremediation is one of the main methods to solve such problems. In this study, the effects of prometryn and acetochlor-degrading strain NM-1 on soil enzymes, soil microbial communities, and physiological indexes of soybean seedlings during soil remediation were studied, and the relationship between them was discussed. The results showed that 81.54% of prometryn (50 mg·L^-1) and 89.47% of acetochlor (50 mg·L^-1) were degraded within 15 days after NM-1 inoculation in soil. NM-1 positively affected soil enzyme activities and soil microbial communities, and the abundance of beneficial bacteria in soil increased. More importantly, the inoculation of strain NM-1 under prometryn and acetochlor stress significantly increased plant height, root length, root volume, water content, chlorophyll concentration, and root activity of soybean. The results of these studies showed that the NM-1 strain showed significant potential in bioremediation in order to provide technical support for solving the problem of prometryn and acetochlor pollution.

Keywords: acetochlor; microbial bioremediation; prometryn; soil enzyme activity; soil microbial community; soybean seedlings.

Figure 1

(a) Chemical structure of prometryn; (b) chemical structure of acetochlor.

Figure 2

Residue of prometryn (A) and acetochlor (B) in soil.

Figure 3

Effect of strain NM-1 on the activity of catalase (A), urease (B), cellulase (C), and sucrase (D) in soil treated with prometryn and acetochlor. (p < 0.05). The error bars represent the standard deviation (SD). Lowercase letters (a, b, c) above the bars indicate significant differences between treatment groups at the same time point, as determined by one-way analysis of variance (ANOVA) followed by post-hoc tests. Values with different lowercase letters are significantly different (p < 0.05), while those with the same lowercase letter are not significantly different.

Figure 4

Relative abundance of soil bacterial community at phylum level (A) and genus level (B).

Figure 5

Effects of strain NM-1 on plant height (A), root length (B), root volume (C), water content (D), root activity (E), and chlorophyll content (F) of soybean plants during soil remediation (p < 0.05). The error bars represent the standard deviation (SD). Lowercase letters (e.g., a, b, c) above the bars indicate significant differences among different treatment groups at the same time point, as analyzed by one-way analysis of variance (ANOVA). Values marked with different lowercase letters are significantly different (p < 0.05), while those with the same lowercase letter show no significant difference.

Figure 6

Redundant analysis of relationships between soil enzymes, bacteria, strain NM-1, prometryn, and acetochlor (p < 0.05).

Figure 7

A double-matrix correlation analysis of the relationship between soil enzymes, soil microorganisms, prometryn and acetochlor residues, and soybean plants (p < 0.05) (X-axis: plant physiological indicators; Y-axis: soil dominant bacteria and soil enzymes. Red color represents positive correlation and blue color represents negative correlation.).