Strombidium purpureum Kahl, an anaerobic ciliate with endosymbiotic
purple non-sulphur bacteria
Bernard, C.1 and Fenchel, T.2
1University of Western Sydney Nepean, Kingswood, Australia
2Marine Biological Laboratory, University of Copenhagen, Helsingør, Denmark
Mitochondria are believed to be descended from endosymbiotic bacteria of the a-group of the proteobacteria [3]. Woese (1982) suggested that among them, the phototrophic non-sulphur bacteria were the most likely ancestors, and that their significance in terms of respiration arose later. Strombidium purpureum Kahl is an oligotrichous ciliate, isolated from anaerobic, sulphide-containing marine sands [1,2]. The ciliate always harbours purple non-sulphur endosymbiotic bacteria. These bacteria contain photosynthetic membranes containing bacteriochlorophyll a, the carotenoid spirilloxanthin and storage vacuoles with poly-b-hydroxybutyrate, and multiply by budding, suggesting a relation with phototrophic non-sulphur bacteria. Strombidium purpureum could be grown under strictly anaerobic conditions in the light, but in the dark, the cells accumulated under microaerobic conditions (1-4% atm. sat.) suggesting that the symbionts had secondarily transformed the ciliate into an aerobic organism in the dark. Strombidium purpureum showed a photosensory behaviour controlled by the metabolic activity of the symbionts. This symbiotic relationship represents an analogy to the origin of mitochodria from photosynthetic bacteria. It shows how such association can be mutualistic under anaerobic conditions and how it can gradually convert an anaerobic host to aerobic life.
[1] Fenchel T. & Bernard C. (1992) Nature 362: 300
[2] Fenchel T. & Bernard C. (1993) FEMS Microbiol. Lett. 110: 21-25
[3] Young D. et al. (1985) Proc. Natl. Acad. Sci. U.S.A. 82: 4443-4447
[4] Woese C.R. (1982) J. Mol. Evol. 10: 93-96
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Wednesday, April 8 |
08:30 am |