open access

https://hdl.handle.net/2115/49712

Ciliates Expel Environmental Legionella-laden Pellets for Stockpiling Food

英語

2012-08

American Society for Microbiology

Applied and Environmental Microbiology

78(15)

5247-5257

When the ciliate Tetrahymena is cultured with Legionella pneumophila, they expel bacteria packaged in free spherical pellets. Why the ciliates expel these pellets remains unclear. Hence, we determined optimal conditions for pellet expulsion, and assessed whether they contribute to maintenance of growth and survival of ciliates. When incubated environmental L. pneumophila, the ciliates maximally expelled the pellets at 2 days after infection. Heat-killed bacteria failed to produce pellets from ciliates, and there was no obvious difference in pellet production among the ciliates or bacterial strains. Morphological studies with assessment of lipid accumulation showed that pellets contained tightly packed bacteria with rapid lipid accumulation and were composed of the layers of membranes; bacterial culturability in the pellets rapidly decreased in contrast to that in ciliate-free culture, although the bacteria maintained membrane integrity in the pellets. Furthermore, ciliates newly cultured with pellets were maintained and grew vigorously compared with those without pellets. In contrast, a human L. pneumophila isolate killed ciliates 7 day post-infection in a Dot/Icm dependent manner and pellets harboring this strain did not support ciliate growth. Also, pellets harboring the human isolate were resuscitated by co-culture with amoebae, depending on Dot/Icm expression. Thus, while ciliates expel pellet-packaged environmental L. pneumophila for stockpiling food, the pellets packaged the human isolate are harmful on ciliate's survival, possibly connecting clinical significance.

学術雑誌論文

Accepted Manuscript

0099-2240

AA00543249