A bacteria-free monoxenic culture of Paramecium bursaria: its growth characteristics and the re-establishment of symbiosis with Chlorella in bacteria-free conditions

A bacteria-free monoxenic culture of Paramecium bursaria has been established. Chlorogonium elongatum was used as the sole food source and large numbers of easily maintained P. bursaria were obtained. Additional enhancement of the growth of P. bursaria was achieved by supplementing the culture medium with soybean lecithin. The ability of monoxenically cultured P. bursaria to re-establish its symbiotic relationship with Chlorella in bacteria-free conditions was examined. Bacteria-free, monoxenic, Chlorella-free (white) P. bursaria, and axenic isolated symbiotic Chlorella cultures were established from bacteria-free monoxenic cultures of Chlorella-bearing (green) P. bursaria. When the white paramecia and isolated Chlorella were mixed in bacteria-free conditions, they re-established a symbiotic relationship, and normal green paramecia were reconstructed. This newly developed bacteria-free monoxenic culturing of P. bursaria will be useful in the study of protozoan symbiosis, as this method provides us with large numbers of cells that possess the ability to reestablish a symbiotic relationship with Chlorella.