Controversial role of fungal laccases in decreasing the antibacterial effect of olive mill waste-waters.

Antibacterial diffusion tests (against Bacillus megaterium) detected both bacterial growth-promoting and growth-inhibiting components in olive mill waste-water (OMW). Mixtures of OMW aromatic components showed antibacterial effects that did not show antibacterial activity when tested as individual compounds. Strains of white rot fungi (WRF) producing different patterns of lignin modifying enzymes (LMEs) have been evaluated for OMW remediation under nutritional conditions affecting the LMEs produced. The decrease of both the content in OMW phenols and in the OMW antibacterial activity was compared with fungal growth and LMEs production. OMW addition to the cultures increased fungal growth and laccase activity irrespectively of the nutritional conditions of the cultures. Laccase was the sole LME activity that increased after OMW addition to the cultures. Neither the increased growth of WRF in OMW-containing cultures, their content in laccase nor the amount of OMW phenols were direct indications of a greater decrease in OMW antibacterial effect. The higher decrease in OMW antibacterial activity was obtained in cultures of Phanerochaete flavido-alba in an N-rich media.