Effect of pH on the radial growth rate and pigment production of two strains of Pycnoporus Mendoza García Marlen 1,2 , Hernández Nava Rosa Mariela 1,2 , Elba Cristina Villegas Villarreal 3 , Quiroz Díaz Montserrat 4 , Acosta-Urdapilleta Ma. de Lourdes 1 , Díaz- Godínez Gerardo 5 , Téllez-Téllez Maura 1 1 Centro de Investigaciones Biológicas Universidad Autónoma del Estado de Morelos; 2 Facultad de Ciencias Biológicas Licenciatura de Biología, UAEM; 3 Centro de Investigación en Biotecnología, UAEM, 4 Escuela de Biología, de la Benemérita Universidad Autónoma de Puebla. 4 Centro de Investigación en Ciencias Biológicas, 5 Universidad Autónoma de Tlaxcala; E-mail: tllezm@gmaill.com Abstract: The genus Pycnoporus includes saprophytes and basidiomycetes fungi common in tropical and subtropical areas of the world. These fungi have a great potential in the production of metabolites. In this study, two strains of Pycnoporus spp HEMIM-55 and 80 were investigated. The effect of pH culture media (4.5, 5.5, 6.5, 7.5 and 8.5) on radial growth rate and pigment production of two strains of Pycnoporus HEMIM-55 and 80 were evaluated. Optimal pH value for growth and pigmentation were 5.5 and 6.5. HEMIM-80 strain showed higher pigment coloration than HEMIM-55, but HEMIM-55 had a faster radial growth rate. In general, cells internal pH is neutral, but microorganisms have a mechanism for controlling inlet and outlet protons and cations flow, throughout the membrane, then they are capable to develop over different pH range. The culture media pH is an important factor for growth and pigment production in these fungi, however, the best pH conditions responsible for growth and pigment formation for Pycnoporus have been scarcely investigated. Keywords: pH ● White-rot fungi● mycelium ●growth Introduction: The genus Pycnoporus (Polyporaceae) is constituted by four species, Pycnoporus sanguineus (L. Fr.) Murr., P. cinnabarinus (Jacq. Fr.) Karst., P. puniceus (Fr.) Ryv., and P. coccineus (Fr.) Bondartsev and Singer (1980). Pycnoporus is a wild that grows on wood, both on fallen branches and stumps, preferring deciduous trees such as beech or oak. It can appear almost any time of year. Fungi of the genus Pycnoporus are white rot basidiomycetes, classified as microorganisms cosmetic and food grade. Pycnoporus is not edible in Europe, but belongs to the traditional pharmacopoeia of the countries of Africa and South America, which have been used to treat various diseases and skin lesions. It also produces cinnabarine that has shown antiviral activity and against bacteria undesirable in food (Smânia et al., 1995) and human pathogenic bacteria such as Klebsiella pneumonia and Salmonella typhi (Smânia et al., 2004) and others of clinical importance such as: Bacillis subtillis (Eherenberg) Cohn, Escherichia coli (Mingula) Castellani and Chalmers, Listeria monocytogenes Pirie. Shigella flexneri Castellani and Chalmers, Salmonella typhi (Schroeter) Warren and Scott, Staphylococcus aeureus Rosenbach, Streptococcus agalactiae Lehmann and Neumann (Sullivan and Henry, 1971). On the other hand, ergosterol with leishmanicidal activity was isolated from Pycnoporus sanguineus (Acosta- Urdapilleta et al., 2010). The genus is characterized by an orange-red color on the surface, pileus and pores. This color arises from the synthesis of various pigments such as cinnabarin, cinnabarinic acid and 194