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Addition of exogenous carbon and nitrogen sources to aphid exuviae modulates synthesis of proteases and chitinase by germinating conidia of Beauveria bassiana

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Abstract

Secretion of catabolic extracellular enzymes (ECE) is the hallmark of the infection of insects through the cuticle by entomopathogenic fungi (EPF). In this paper, we show that germinating conidia of Beauveria bassiana (Bb) regulate the synthesis of ECE through a multiple control mode during the initial stages of germination. We tested Bb conidial growth on aphid exuviae with or without supplementation of additional carbon and/or nitrogen (C/N) compounds. To understand the interrelation between conidial germination during growth, the synthesis of ECE activity, free amino nitrogen (FAN), glucose and fungal dry weight biomass were measured. Immediately (0.25 h) upon incubation of conidia, activity of subtilisin-like Pr1 and trypsin-like Pr2 enzymes and chitinase (NAGase) was observed in the culture filtrates. At 0.25 h, addition of exogenous C-source resulted in higher activities of Pr1 and Pr2, respectively. Conversely at 0.25 h, addition of N-sources repressed the synthesis of Pr2, but that of Pr1. C/N repression was observed only for exponentially growing mycelia. NAGase activity remained at basal level and unaffected by added C/N. We conclude that C/N repression occurs only when it is necessary for the Bb infective structures to establish a nutritional relationship with the host structures.

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Acknowledgments

A Natural Sciences and Engineering Research Council of Canada Research Grant #493 (G. G. Khachatourians) and University of Saskatchewan post-graduate scholarships to SSQ supported this research. We would like to thank Dinka Besic and Dubravko Besic for technical assistance in the preparation of Figs. 1–5.

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Authors and Affiliations

  1. Microbial Biotechnology/Molecular Microbiology Labs, Department of Applied Microbiology and Food Science, College of Agriculture, University of Saskatchewan, Saskatoon, Canada

    Sohail S. Qazi & George G. Khachatourians

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  1. Sohail S. Qazi
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  2. George G. Khachatourians
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Correspondence to Sohail S. Qazi.

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Communicated by Axel Brakhage.

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Qazi, S.S., Khachatourians, G.G. Addition of exogenous carbon and nitrogen sources to aphid exuviae modulates synthesis of proteases and chitinase by germinating conidia of Beauveria bassiana . Arch Microbiol 189, 589–596 (2008). https://doi.org/10.1007/s00203-008-0355-9

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  • DOI: https://doi.org/10.1007/s00203-008-0355-9

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