Effect of long-term mercury treatment on composition of rumen protozoan Entodinium caudatum associated bacterial population

Abstract

Upon long term in vitro culture of Entodinium caudatum with increased dose of mercury, the mercury resistance of E. caudatum culture increased from initial level of less than 0.5 microgram per ml to more than 10 micrograms per ml. No changes of mercury chemical status were detected in protozoal culture, indicating the lack of detoxification activities of mercury reductase. Denaturing gradient gel electrophoresis (DGGE) analysis of associated bacterial populations revealed clear shift in eubacterial population structure with hydrogen sulphide producing bacteria overgrowing but very limited changes in archaebacterial population structure. The data obtained indicated that free living bacteria protect protozoan cells and their archaebacterial endosymbionts by eliminating mercury into its insoluble form.