Expression of bik cluster and production of bikaverin by Fusarium oxysporum f. sp. lycopersici grown using two alternate nitrogen sources

Abstract

The genus Fusarium can be utilized to produce a great variety of secondary metabolites under specific culture conditions, including pigments of increasing biotechnological interest, such as bikaverin. Such pigments are important due to the biological properties they possess, including antitumor and antibiotic activities, among others. In Fusarium fujikuroi, bik1–bik6 have been identified as the genes that are responsible for the synthesis of bikaverin. Therefore, in this study, we screened for the presence of bik genes and examined changes in mRNA levels of the bik genes under the influence of NH₄NO₃ (0.024, 0.048, 0.50, 1.0, and 4.60 g L⁻¹) and NH₄Cl (0.50 and 1.0 g L⁻¹) as nitrogen sources for the phytopathogen Fusarium oxysporum f. sp. lycopersici. Our results indicated the presence of at least six bik (bik1–bik6) genes and showed increased mRNA levels for bik4, bik5, and bik6 in conditions where NH₄NO₃ was used at pH 3.0. The characteristic coloration of bikaverin was obtained in 10 out of 16 culture conditions, except when the fungus was grown with higher concentrations of NH₄NO₃ (1.0 and 4.60 g L⁻¹). The pigment was chloroform-extracted from the culture conditions of NH₄NO₃ (0.024, 0.048, and 0.50 g L⁻¹) and NH₄Cl (0.50 and 1.0 g L⁻¹) with 3 and 9 days of incubation. Analysis via visible spectroscopy and matrix-assisted laser desorption ionization-time of flight mass spectrometry were used for the identification of bikaverin.