RESUMEN
The optimal growth of mesophilic methanotrophic bacteria (collection strains of the genera Methylocystis, Methylomonas, Methylosinus, and Methylobacter) occurred within temperature ranges of 31-34 degrees C and 23-25 degrees C. None of the strains studied were able to grow at 1.5 or 4 degrees C. Representatives of six methanotrophic species (strains Mcs. echinoides 2, Mm. methanica 12, Mb. bovis 89, Mcs. pyriformis 14, Mb. chroococcum 90, and Mb. vinelandii 87) could grow at 10 degrees C (with a low specific growth rate). The results obtained suggest that some mesophilic methane-oxidizing bacteria display psychrotolerant (psychrotrophic) but not psychrophilic properties. In general, the Rosso model, which describes bacterial growth rate as a function of temperature, fits well the experimental data, although, for most methanotrophs, with symmetrical approximations for optimal temperature.