Multi-sited mutations of beta-tubulin are involved in benzimidazole resistance and thermotolerance of fungal biocontrol agent Beauveria bassiana

Authors

  • Gen Zou,

    1. Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, People’s Republic of China.
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  • Sheng-Hua Ying,

    1. Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, People’s Republic of China.
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  • Zhi-Chen Shen,

    1. Institute of Insect Sciences, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, 310029, People’s Republic of China.
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  • Ming-Guang Feng

    Corresponding author
    1. Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, People’s Republic of China.
    2. Institute of Insect Sciences, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, 310029, People’s Republic of China.
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*E-mail mgfeng@zju.edu.cn; Tel. (+86) 571 8697 1129; Fax (+86) 571 8697 1129.

Summary

Fungicide resistance and thermotolerance of biocontrol agents in mitosporic fungi are of merits for enhancing fungal formulations against insect pests in the field. Among 20 wild strains of Beauveria bassiana (a well-known fungal biocontrol agent) tested in this study, 19 were sensitive or highly sensitive to carbendazim (methyl 2-benzimidazole carbamate), a typical benzimidazole fungicide, despite low resistance found in one strain. Sequential mutagenesis of a carbendazim-sensitive wild strain [minimal inhibitory concentration (MIC) = 1.32 µg ml−1] under artificial selection pressure generated 11 mutants sharing a common MIC of > 1000 µg ml−1 without visible variation in colony growth and conidiation capacity. This represents at least 758-fold enhancement of the resistance among the mutants. However, accompanied with the enhanced resistance, all the mutants became less thermotolerable. Stressed at 48°C, conidial LT50s of the mutants varied from 1.8 to 9.6 min and were lower than the parental LT50 (36 min). Moreover, the contents of hydrophobin-like proteins in conidial walls declined significantly among the mutants compared with that of the wild parent. Mutations commonly relating to benzimidazole resistance in fungi were located at Q134, F167 and/or E198 around the taxol-binding site of beta-tubulin by sequencing the beta-tubulin of the mutants. Also, mutations of other 37 amino acid residues in the sequences (each having one to five residues mutated) were found for the first time and they were diverse in spatial structure. All mutations restricted to the half of beta-tubulin close to alpha-tubulin were likely involved in variation in each of the traits concerned but their interactions were complicated.

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