Isolation of a Methanogenic Endosymbiont of the Sapropelic Amoeba Pelomyxa palustris Greeff

Abstract

ABSTRACT. One of the two methanogenic endosymbionts of the giant sapropelic amoeba Pelomyxa palustris was isolated in pure culture. The cells were slender non‐motile rods (3 × 0.4 μm), sometimes occurring in chains of 3–4 cells. Ultrathin sections revealed a Gram‐positive cell wall and conically pointed ends with mesosome‐like structures in the cytoplasm. The isolate had a generation time of 10 and 12 h during growth on H2/CO2 and formate, respectively. The optimum growth temperature was 40°C and the optimum pH was 7.8. The G+C content of its DNA was found to be 37.7% mole percent. The isolate was identified as Methanobacterium formicicum.