Molecular genetic identification and extracellular laccase activity of two wild fungal isolates from Mexico
Fungal strains BM-1 and BG-2 were isolated from rotting stemwood of the Ipomoea murucoides tree. Both strains were assigned to Botryosphaeria rhodina (teleomorph)/Lasiodiplodia theobromae (anamorph) complex by the internal transcribed spacer (ITS) sequence of Nuclear Ribosomal Unit. BM-1 produced 4.39 ± 0.35 μg/mL, and BG-2 3.61 ± 0.28 μg/mL of extracellular protein in non-induced culture. BM-1 increases this amount by 93% when CuSO4 (150 μM) is added to medium, and by 73% after addition of ethanol (10% v/v). Corresponding increases for BG-2 were of less than 40%. Basal activity of extracellular laccase had a maximum value of 0.379 ± 0.042 U/mL for BM-1 and of 0.312 ± 0.130 U/mL for BG-2. CuSO4 (150 μM) addition to the culture increased the maximum activity of laccase up to 3.964 ± 0.385 U/mL in BM-1 and up to 5.270 ± 0.0.793U/mL in BG-2. Ethanol addition (10% v/v) to the culture increased the maximum activity of laccase to 3.639 ± 0.506 U/mL in BM-1 and to 11.397 ± 0.440 U/mL in BG-2. The physiological differences observed between strains BM-1 and BG-2, stresses the importance of characterizing wild isolates from new substrates with the objective of finding strains of biotechnological potential.
Key words: Botryosphaeria wild strains, ITS DNA sequence, extracellular laccase.