title: Protozoal ciliate promotes bacterial autoinducer-2 accumulation in mixed culture with Escherichia coli.
abstract: We have previously demonstrated conjugation of Escherichia coli into vacuoles of the protozoal ciliate (Tetrahymena thermophila). This indicated a possible role of ciliates in evoking bacterial quorum sensing, directly connecting bacterial survival via accumulation in the ciliate vacuoles. We therefore assessed if ciliates promoted bacterial autoinducer (AI)-2 accumulation with vacuole formation, which controls quorum sensing. E. coli AI-2 accumulation was significantly enhanced in the supernatants of a mixed culture of ciliates and bacteria, likely depending on ciliate density rather than bacterial concentration. As expected, AI-2 production was significantly correlated with vacuole formation. The experiment with E. coli luxS mutants showed that ciliates failed to enhance bacterial AI-2 accumulation, denying a nonspecific phenomenon. Fluorescence microscopy revealed accumulation of fragmented bacteria in ciliate vacuoles, and, more importantly, expulsion of the vacuoles containing disrupted bacteria into the culture supernatant. There was no increase in the expression of luxS (encoding AI-2) or ydgG (a transporter for controlling bacterial export of AI-2). We conclude that ciliates promote bacterial AI-2 accumulation in a mixed culture, via accumulation of disrupted bacteria in ciliate vacuoles followed by expulsion of the vacuoles, independently of luxS or ydgG gene induction. This is believed to be the first demonstration of a relationship between E. coli AI-2 dynamics and ciliates. In the natural environment, ciliate biotopes may provide a survival advantage to bacteria inhabiting such biotopes, via evoking quorum sensing.
authors.affiliation: Hokkaido University Hospital.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Oguri
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hanawa
authors.forename: Junji
authors.initials: J
authors.lastname: Matsuo
authors.forename: Kasumi
authors.initials: K
authors.lastname: Ishida
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Shinji
authors.initials: S
authors.lastname: Nakamura
authors.forename: Torahiko
authors.initials: T
authors.lastname: Okubo
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Fukumoto
authors.forename: Kouzi
authors.initials: K
authors.lastname: Akizawa
authors.forename: Chikara
authors.initials: C
authors.lastname: Shimizu
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kamiya
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamaguchi
mesh_terms: D016798:Ciliophora / Q000254:growth & development*; D006714:Homoserine / Q000031:analogs & derivatives* / Q000378:metabolism; D007783:Lactones / Q000378:metabolism*; D056265:Microbial Interactions; D001678:Organelle Biogenesis; D016808:Tetrahymena thermophila / Q000254:growth & development* / Q000378:metabolism*; D014617:Vacuoles / Q000382:microbiology
chemical_list: D007783:Lactones; C091088:N-octanoylhomoserine lactone; D006714:Homoserine