Pure cultures of obligate methanotrophic bacteria were isolated from natural habitats and cultivated on media containing silica gel which provided more elective conditions than media with agar. According to their morphology, fine structure, cultural, physiological and biochemical properties, the bacteria were identified as Methylosinus trichosporium, Methylosinus trichosporium var. methanolicum, Methylocystis parvus, Methylocytis parvus var. fuscus, Methylomonas methanica.