Víctor Manuel Gómez-Reyes

Typing and selection of wild strains of Trichoderma spp. producers of extracellular laccase

Using the ITS region and the gene tef1, 23 strains of the genus Trichoderma were identified as belonging to the species T. harzianum (n = 14), T. olivascens (n = 1), T. trixiae (n = 1), T. viridialbum (n = 1), T. tomentosum (n = 2), T. koningii (n = 1), T. atroviride (n = 1), T. viride (n = 1), and T. gamsii (n = 1). Strains expressing extracellular laccase activity were selected by decolorization/oxidation assays in solid media, using azo, anthraquinone, indigoid, and triphenylmethane dyes, and the phenolic substances tannic acid and guaiacol. No strain decolorized Direct Blue 71 or Chicago Blue 6B, but all of them weakly oxidized guaiacol, decolorized Methyl Orange, and efficiently oxidized tannic acid. Based in decolorization/oxidation assays, strains CMU‐1 (T. harzianum), CMU‐8 (T. atroviride), CMU‐218 (T. viride), and CMU‐221 (T. tomentosum) were selected for evaluating their extracellular laccase activity in liquid media. Strain CMU‐8 showed no basal laccase activity, while strains CMU‐1, CMU‐218, and CMU‐221 had a basal laccase activity of 1,313.88 mU/mL, 763.88 mU/mL, and 799.53 mU/mL, respectively. Addition of sorghum straw inhibited laccase activity in strain CMU‐1 by 34%, relative to the basal culture, while strains CMU‐8, CMU‐21, and CMU‐221 increased their laccase activity by 1,321.5%, 64%, and 47%, respectively. These results show that assayed phenolic substrates are good tools for selecting laccase producer strains in Trichoderma. These same assays indicate the potential use of studied strains for bioremediation processes. Straw laccase induction suggests that analyzed strains have potential for straw delignification in biopulping and other biotechnological applications.