ORIGINAL PAPER Isolation of Oxalic acid tolerating fungi and decipherization of its potential to control Sclerotinia sclerotiorum through oxalate oxidase like protein Shivani Yadav • Alok K. Srivastava • Dhanajay P. Singh • Dilip K. Arora Received: 11 February 2012 / Accepted: 11 July 2012 / Published online: 4 August 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Oxalic acid plays major role in the pathogen- esis by Sclerotinia sclerotiorum; it lowers the pH of nearby environment and creates the favorable condition for the infection. In this study we examined the degradation of oxalic acid through oxalate oxidase and biocontrol of Sclerotinia sclerotiorum. A survey was conducted to col- lect the rhizospheric soil samples from Indo-Gangetic Plains of India to isolate the efficient fungal strains able to tolerate oxalic acid. A total of 120 fungal strains were isolated from root adhering soils of different vegetable crops. Out of 120 strains a total of 80 isolates were able to grow at 10 mM of oxalic acid whereas only 15 isolates were grow at 50 mM of oxalic acid concentration. Then we examined the antagonistic activity of the 15 isolates against Sclerotinia sclerotiorum. These strains potentially inhibit the growth of the test pathogen. A total of three potential strains and two standard cultures of fungi were tested for the oxalate oxidase activity. Strains S7 showed the maxi- mum degradation of oxalic acid (23 %) after 60 min of incubation with fungal extract having oxalate oxidase activity. Microscopic observation and ITS (internally transcribed spacers) sequencing categorized the potential fungal strains into the Aspergillus, Fusarium and Tricho- derma. Trichoderma sp. are well studied biocontrol agent and interestingly we also found the oxalate oxidase type activity in these strains which further strengthens the potentiality of these biocontrol agents. Keywords Biocontrol Á ITS Á Oxalate oxidase Á Oxalic acid Introduction Oxalic acid is an organic compound with the formula H 2 C 2 O 4 . It occurs ubiquitously in nature, sometimes as a free acid, but more commonly as soluble potassium or sodium oxalate or as insoluble calcium oxalate. Oxalic acid and oxalates are produced by many fungi, bacteria, actinomy- cetes and plants and whereas it occurs naturally in animals. It has been suggested that it inhibit the growth of fungi that are more sensitive to acidity or oxalate, thus having an impact on competition between fungal species. Role of oxalic acid has been reported by the many researchers in invasion of host tissue by phytopathogenic fungi (Bateman and Beer 1965; Maxwell and Bateman 1968). Oxalic acid produced by Sclerotinia sclerotiorum, during pathogenesis acts syner- gistically with endopolygalacturonase, lowering the pH of the infected tissues to a level optimal for the activity of this enzyme. Oxalic acid strongly chelates the calcium present in the structural pectates as a result plant tissues becomes more susceptible to invasion by Sclerotinia sclerotiorum (Punja and Jenkins 1984). Three different oxalate-degrading enzymes have been reported in fungi, bacteria and plants: oxalate decarboxy- lases (ODC, EC 4.1.1.2), oxalate oxidases (OXO, EC 1.2.3.4) and oxalyl-CoA decarboxylases (OXC, EC 4.1.1.8) (Svedruzic et al. 2005)). Oxalate decorboxylase is a Mn- containing enzyme that decomposes oxalic acid to formic acid and CO 2 in a reaction that requires O 2 (Reinhardt et al. 2003). Oxalate oxidase have a greater extent of protein sequence similarity with oxalate decoroxylase is accord- ingly at first oxidized by O 2 . However, upon catalysis, OXO cleaves oxalic acid to two CO 2 molecules together with generation of H 2 O 2 . Oxalate oxidase activity has extensively studied in plants, and as an intracellular enzyme. On the other hand, it has been also studied in two S. Yadav (&) Á A. K. Srivastava Á D. P. Singh Á D. K. Arora National Bureau of Agriculturally Important Microorganisms, Mau Nath Bhanjan, Uttar Pradesh 275101, India e-mail: shivaniyadav09@gmail.com 123 World J Microbiol Biotechnol (2012) 28:3197–3206 DOI 10.1007/s11274-012-1130-2