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The largest bacterium


THE large, morphologically peculiar microorganism Epulopiscium fishelsoni1,2 inhabits the intestinal tract of Acanthurus nigrofuscus, a brown surgeon fish (family Acanthuridae) from the Red Sea. Similar microorganisms have been found in surgeonfish species from the Great Barrier Reef3. As these microorganisms have only been seen in surgeonfish and no free-living forms have been found, they are considered to be specific symbionts of surgeonfish, although the nature of the symbiosis is unclear1–4. Initial reports considered them to be eukaryotic protists, based primarily on their size1–4, with individuals being larger than 600 μm by 80 μm. But their cellular morphology in the electron microscope is more like that of bacterial than eukaryotic cells1,2,54. To resolve the nature of these symbionts, we have isolated the genes encoding the small subunit ribosomal RNA from two morphotypes and used them in a phylogenetic analysis. In situ hybridization with oligonucleotide probes based on the cloned rRNA sequences confirmed the source of the rRNA genes. Our results identify the symbionts as members of the low-(G + C) Gram-positive group of bacteria. They are therefore the largest bacteria to be described so far.

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  1. Fishelsen, L. Montgomery, W. L. & Myrberg, A. A. Jr Science 229, 49–51 (1985).

    Article  ADS  Google Scholar 

  2. Montgomery, W. L. & Pollak, P. E. J. Protozool. 35, 565–569 (1988).

    Article  Google Scholar 

  3. Clements, K. D., Sutton, D. C. & Choat, J. H. Mar. Biol. 102, 403–412 (1989).

    Article  Google Scholar 

  4. Montgomery, W. L. & Pollak, P. E. Mar. Ecol. Prog. Ser. 44, 7–13 (1988).

    Article  ADS  Google Scholar 

  5. Clements, K. D. & Bullivant, S. J. Bact. 173, 5359–5362 (1991).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Saiki, R. K. et al. Science 239, 487–491 (1988).

    Article  CAS  ADS  PubMed  Google Scholar 

  7. Olsen, G. J. et al. Nucleic Acids Res. 20, 2199–2200 (1992).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  8. Olsen, G. J. Meth. Enzym. 164, 793–812 (1988).

    Article  CAS  PubMed  Google Scholar 

  9. Woese, C. R. Microbiol. Rev. 51, 221–271 (1987).

    CAS  PubMed  PubMed Central  Google Scholar 

  10. Felsenstein, J. Evolution 37, 783–791 (1985).

    Article  Google Scholar 

  11. DeLong, E. F., Wickham, G. S. & Pace, N. R. Science 243, 1360–1363 (1989).

    Article  CAS  ADS  PubMed  Google Scholar 

  12. Woese, C. R., Kandler, O. & Wheelis, M. L. Proc. natn. Acad. Sci. U.S.A. 87, 4576–4579 (1990).

    Article  CAS  ADS  Google Scholar 

  13. Blakemore, R. P. & Canale-Parola, E. Arch. Mikrobiol. 89, 273–289 (1973).

    Article  CAS  PubMed  Google Scholar 

  14. Delaporte, B. Ann. Inst. Pasteur, Paris 107, 246–262 (1964).

    CAS  Google Scholar 

  15. Starr, M. P. & Schmidt, J. M. in The Prokaryotes (eds Starr, M. P., Stolp, H. Trüper, H. G., Balows, A. & Schlegel, H. G.) 3–42 (Springer, New York, 1981).

    Google Scholar 

  16. Jannasch, H. W., Nelson, D. C. & Wirsen, C. O. Nature 342, 834–836 (1989).

    Article  CAS  ADS  Google Scholar 

  17. Ward, D. M., Bateson, M. M., Weller, R. & Ruff-Roberts, A. L. in Advances in Microbial Ecology (ed. Marshall, K. C.) Vol. 12 219–286 (Plenum, New York, 1992).

    Book  Google Scholar 

  18. Sambrook, J., Fritsch, E. F. & Maniatis, T. Molecular Cloning: A Laboratory Manual 2nd edn (Cold Spring Harbor Laboratory, New York, 1989).

    Google Scholar 

  19. Biggin, M. D., Gibson, T. J. & Hong, G. F. Proc. natn. Acad. Sci. U.S.A. 80, 3963–3965 (1983).

    Article  CAS  ADS  Google Scholar 

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Angert, E., Clements, K. & Pace, N. The largest bacterium. Nature 362, 239–241 (1993).

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