Isolation And Identification Of The Qinling Mountains Rana Pathogens

Amphibians play an important role in maintenance of ecological balance, control pests and so on, and they have important economic and medicinal value. The Rana chensinensis as a unique amphibian species in China, also has very important value. In recent years, the population of Rana chensinensis has declined rapidly on account of the environmental damage and the over hunt by human.The Rana chensinensis widely distributed in Qinling Mountains were liable to be infected in Dayukou (region A,109°6'52"E,34°0'56"N) than Shibianyu (region B,108°56'33"E,34°0'20"N). Six microorganisms were isolated from the infected Rana chensinensis at region A. The isolated strains were Acinetobacter johnsonii, Pseudomonas sp., Morganella morganii, Rhodococcus erythropolis, Flavobacterium sp. And Aeromonas hydrophila by the identification of physiological biochemical experiment and 16S rDNA sequence analysis. The sixth strain which was identified to be Aeromonas hydrophila has strong pathogenicity to Rana chensinensis according to the data from artificial infections. Acinetobacter johnsonii and Rhodococcus erythropolis can enhance the pathogenic ability of Aeromonas hydrophila to Rana chensinensis. It indicated that the disease of Rana chensinensis was caused by the infection of bacteria in the environment.The bacteria-community structures of two regions were analyzed by PCR based denaturing gradient gel electrophoresis (PCR-DGGE). A rich bacteria diversity was found in the soil and water from both region A and B, but there had significant differences between A and B. The bacteria-community structure of the water in region A was distinct from other environments. It's bacteria-community structure has been changed significantly caused by human activities. The content of six strains isolated from Rana chensinensis in A and B was dissimilar as well, and the population of Aeromonas hydrophila in region A was richer than region B by the DGGE analysis. The content of Acinetobacter johnsonii in region A is also higher than region B. Particularly, several strains isolated at region A were highly homologous with the stains identified from sewerage which were the pathogens to human and animals. So, the higher level of pathogens at region A was assumed to be the major causation for the infection of the wild Rana chensinensis.The environment of region A was influenced seriously by human activeities. There are lots of garbage around the river of region A. And the water quality of region A is lower than region B examined by Shaanxi Provincial Department of Hydrology and Water Resources. Meanwhile the pollutant in the environment at region A may weaken the immunity of Rana chensinensis. That would lead to the Rana chensinensis more susceptible to pathogens. And it is more likely that the infection of Rana chensinensis was caused by the comprehensive action among various factors which comes from the human activities. So we must reduce the disturbance and destroy to the environment in order to protect the wide Rana chensinensis.