Search

Abstract Bacteria often use multiple transcription factors to regulate specific biological processes. Biosynthesis of heat-stable antifungal factor (HSAF) is regulated by multiple factors in Lysobacter enzymogenes. However, the mechanism of HSAF biosynthesis regulation remains largely unknown. In this study, we screened a potential HSAF biosynthesis regulator, RecX, by a DNA pull-down assay. Deletion of recX resulted in a significant increase in the production of HSAF, and overexpression of recX significantly suppressed HSAF production. Importantly, our results showe that RecX directly binds to the promoter region of the lafB gene to inhibit its transcription and thus decreases HSAF production in L. enzymogenes. These findings reveal the novel mechanism of RecX regulation of antifungal antibiotic production in L. enzymogenes.

Abstract Anthracnose, caused by fungi of the genus Colletotrichum, is a serious disease of chili worldwide. Sterol 14α-demethylation inhibitors (DMIs) are a class of chemical fungicides that can effectively control anthracnose diseases. In this study, 22 Colletotrichum isolates collected from commercial chili fields in Zhangzhou, Fujian Province, China, were identified as Colletotrichum siamense. The sensitivities of the 22 C. siamense isolates to tebuconazole were determined based on the EC50 (50% effective inhibition concentration) value. The results showed that the EC50 values of the two isolates to tebuconazole were 0.039 ± 0.0036 and 0.042 ± 0.0012 mg/L, while the other 20 isolates showed significantly decreased sensitivities to tebuconazole, with EC50 values ranging from 0.61 ± 0.056 to 1.94 ± 0.11 mg/L. Sequence analysis of CYP51A and CYP51B revealed five genotype mutations (i. e., CYP51AV46L, D115V, P163S, R306K, E397D, CYP51AD115V, S164Y, R306K, E397D, CYP51AD115V, R306K, P339T, E397D, CYP51AD115V, R306K, E397D, S400N, and CYP51AD115V, R306K, E397DCYP51BR266H) in the resistant isolates. The tebuconazole-resistant isolates of five genotypes suffered a fitness penalty and exhibited cross-resistance to difenoconazole, prochloraz, and propiconazole. Additionally, the five genotype mutations were validated as being responsible for tebuconazole-resistance in C. siamense by construction of replacement mutants. Overexpression of CYP51A and CYP51B was not detected in the replacement mutants of the five genotypes. Overall, the present study is the first to report DMI resistance in C. siamense and provides significant information for rational use of DMIs to control chili anthracnose.