ABSTRACT
Stenocarpella maydis from different maize growing regions in South Africa were collected and screened for the presence of diplodiatoxin. The presence of diplodiatoxin in these isolates was detected by thin layer chromatography and further confirmed by atomic pressure chemical ionization mass spectrometry. Samples containing diplodiatoxin showed a strong positive ion at m/z=307. MC34, MC35, MC43 and MC50 isolates of Potchefstroom region produced high amount of diplodiatoxin, whereas some of the isolates from Potchefstroom (D72, D74, D78, D79 and D80) and Cedara (CH3 and U3H) regions did not contain diplodiatoxin. Experiments were conducted to optimize in vitro production of diplodiatoxin using the isolate MC 43. A varied range of pH (3.0 to 5.0) and various culture media viz., PDB, CME, CLM and MSM were tested. Growth of mycelium and production of diplodiatoxin was maximum in PDB media at pH 4.5 and it was observed that diplodiatoxin was produced in detectable quantity in the cultures older than 6 weeks in this media. Further, diplodiatoxin was isolated and purified from 8-weeks-old cultures of MC43 isolate and confirmed by nuclear mass resolution. The standard and the compound purified showed similar NMR spectrum. Sixty-gram (fresh weight) mycelium yielded 19.52 mg of diplodiatoxin. Effect of diplodiatoxin on the growth of various bacterial strains in agar-gelled LB media was studied. They showed different range of tolerance to diplodiatoxin. The increasing order of tolerance to diplodiatoxin was Stenocarpella maydis < B. cereus < B. subtulus < P. fluorescense < E. coli. Further, the effect of different concentrations (4.88-49.70 microg/mL) of diplodiatoxin on the growth of S. aureus in LB liquid media was studied. Presence of diplodiatoxin in the media reduced cell growth as compared to the control thus, confirming anti-bacterial activity of diplodiatoxin.