THE EFFECT OF ENDOSYMBIOTIC METHANOGENS ON THE GROWTH AND METABOLIC PROFILE OF THE ANAEROBIC FREE-LIVING CILIATE TRIMYEMA-COMPRESSUM

We examined the influence of endosymbiotic methanogens on the growth a nd metabolic profile of the anaerobic ciliate Trimyema compressum. Whe n we isolated the ciliate, it possessed a large number of endosymbioti c Methanobacterium-like methanogens inside the cell. The culture was t ransferred to fresh medium with Lactobacillus sp. cells as food bacter ia. T. compressum grew to give a maximum cell number of 3300 cells/ml without loss of the endosymbionts over 30 passages of transfer. Acetat e and methane were major end products with smaller amounts of propiona te and butyrate. However, after further continued cultivation, the num ber of endosymbiotic methanogens started to decrease and they eventual ly disappeared. The growth and metabolic profile of the ciliate were c hanged significantly as the symbiotic association deteriorated. The ma jor fermentation products were shifted to butyrate. These results sugg est that the endosymbiotic methanogens which function as hydrogen scav engers are not indispensable for the growth and survival of T. compres sum, although the growth yield decreased slightly in the absence of me thanogens, and the ciliate is capable of fermenting food bacteria with out endosymbiotic methanogens by changing its metabolic pathway.