Chitinase Expression Due to Reduction in Fusaric Acid Level in an Antagonistic Trichoderma harzianum S17TH
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IGINAL ARTICLE
Chitinase Expression Due to Reduction in Fusaric Acid Level in an Antagonistic Trichoderma harzianum S17TH Vivek Sharma • Pamita Bhandari • Bikram Singh Amita Bhatacharya • Veerubommu Shanmugam
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Received: 26 June 2012 / Accepted: 6 November 2012 / Published online: 22 November 2012 Ó Association of Microbiologists of India 2012
Abstract To study the effect of reduction in phytotoxin level on fungal chitinases, antagonistic Trichoderma spp. were screened for their ability to reduce the level of fusaric acid (FA), the phytotoxin produced by Fusarium spp. A T. harzianum isolate S17TH was able to tolerate high levels of FA (up to 500 ppm) but was unable to reduce the toxin to a significant level (non-toxic) added to minimal synthetic broth (MSB). However, the isolate was able to reduce 400 ppm FA in the liquid medium after 7 days to a non-toxic level and displayed similar level of antagonism over the control (without FA). In studies of the effect of the reduction in FA (400 ppm) level on chitinase gene expression in PCR assays, nag1 was significantly repressed but ech42 expression was only slightly repressed. Chitinase activity was either reduced or absent in the extracellular proteins of MSB supplemented with 400 ppm FA, which could be attributed to the effect of residual FA or its breakdown products through unknown mechanisms. Selection of S17TH as a toxin insensitive isolate that could commensurate the negative effect on chitinase activity makes it a potential antagonist against Fusarium spp. Keywords Fusaric acid Reduction Trichoderma harzianum Chitinase
V. Sharma P. Bhandari B. Singh A. Bhatacharya V. Shanmugam (&) Council of Scientific and Industrial Research-Institute of Himalayan Bioresource Technology, Palampur 176 061, HP, India e-mail: [email protected]
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Introduction Phytotoxins are toxic compounds produced by fungi for selfdefense by suppressing induced resistance or for plant pathogenesis by dissolving cell membranes. Fusaric acid (FA; 5-butyl-picolinic acid; C10H13NO2, Mr: 179.22) is a well-known phytotoxin produced by several Fusarium spp., particularly pathogenic strains of Fusarium oxysporum, the causal agent of wilt diseases in a wide variety of plants [1]. In addition to its toxicity to plants, FA is toxic to microorganisms by inhibiting their growth and metabolism [2]. In biocontrol agents, such toxicity also represses the production of antifungal metabolites [3]. Detoxification or inactivation of phytotoxins is one of the mechanisms by which microbes protect themselves from the toxins [4] and therefore serves as an attractive strategy for decontamination of agricultural commodities and protection of crops from phytotoxic effect of fungal metabolites produced by pathogens. Chitinases are cell wall degrading enzymes that degrade chitin polymers and are key components of mycoparasitism mechanism in select fungi and bacteria. Trichoderma species, which can act as potent biocontrol agents, exhibit mycoparasitism against a wide range of plant pathogens, mainly thro
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