Intercellular Nanotubes Mediate Bacterial Communication

Gyanendra P. Dubey and Sigal Ben-Yehuda. 2011 Cell 144, 590–600

Speaker: Chung-Han Hsieh (謝宗翰)                           Time: 14:00~15:00, Apr. 27, 2011

Commentator: Dr. Ching-Hao Teng (鄧景浩博士)      Place: Room 601

Abstract:

The bacteria in nature display complex multicellular behaviors that enable them to execute sophisticated tasks. They are also known to communicate primarily via secreted extracellular factors. However, in this study, the authors found a novel intercellular nanotube-mediated bacterial communication mechanism. They first spotted B. subtilis SB444 cells that harbored a chromosomally encoded gfp reporter gene (gfp+) on agar plate alongside B. subtilis PY79 cells that lacked gfp (gfp-). A green fluorescence gradient was observed to emanate from the gfp+ cells toward the gfp-cells, covering a distance of approximately 40 μm. The authors then observed these bacteria under a fluorescence microscope and found some intercellular nanotubes between two bacterial cells. By immuno-electronmicroscopy, they found that GFP actually was transferred to neighbor cells by these nanotubes. They also introduced the chloramphenicol acetyltransferase (Cat) and erythromycin resistance methylase (Erm) genes into B. subtilis chromosome separately, and then examined the growth ability of these strains on antibiotics. They found that when these two strains were co-cultured on LB plate with chloramphenicol (Cm) and lincomycin, both strains could survive , while their genotypes did not change. This result showed that the bacteria could exchange their protein products that could work in the new host. They further tested whether these tubes could also mediate the transfer of DNA. They isolated a strain that contained a nonconjugative plasmid carrying cat and erm and co-incubated this strain with strain P2 (Kanamycin resistant, GFP+). They examined the genotypes of colonies expressing the drug resistance markers of strain P2 and thenonconjugative plasmid, and found that they contained all those three resistance genes. They further showed that this plasmid-transferring mechanism was DNaseI resistant and the transferring frequency of this plasmid was 1,000-fold lower than that of a conjugative plasmid. The latter result, together with the lack of sex pilus, suggests that the transfer of non-conjugative plasmid was not mediated by conjugation. Therefore, the nanotubes could also transfer plasmid. Finally, they co-incubated B. subtilis with Staphylococcus aureus or Escherichia coli, and they found that the intercellular nanotubes also formed between B. subtilis and these two species. In conclusion, this new bacterial communication mechanism could transfer the proteins and DNA in cytoplasm between the same or different species. This phenomenon could be a new area of bacterial research.

References:

1.      Davis et.al.2008  Nat. Rev. Mol. Cell Biol. 9,431–436

2.      Martens, S.et al. H.T. 2008. Nat. Rev. Mol. Cell Biol. 9, 543–556