Diversity of culturable bacterial communities in the intestinal tracts of goldfish (Carassius auratus) and their ability to produce N-acyl homoserine lactone
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Intestinal bacteria isolated from goldfish (Carassius auratus) were identified based on 16 ribosomal RNA (rRNA) gene sequences and screened for their ability to produce N-acyl homoserine lactone (AHL), an autoinducer of the quorum sensing (QS) system. The 230 aerobes/facultative anaerobes that were isolated comprised members of the genera Aeromonas (184 isolates), Citrobacter (11), Enterobacter (2), Shewanella (28), Vagococcus (1), and Vibrio (4). Among these genera, the two most abundant species were Aeromonas veronii (163 isolates) and Shewanella xiamenensis (27). In addition, 142 obligate anaerobes consisting of Cetobacterium somerae (139 isolates), Clostridium frigidicarnis (2), and Cetobacterium sp. (1) were also isolated. One hundred seventy isolates (74.2%) belonging to the genera Aeromonas, Citrobacter, Enterobacter, Shewanella, and Vibrio produced AHL, while 155 (67.7%) and 91 (39.7%) isolates possessed the luxR and luxI gene homologs, respectively. None of the obligate anaerobes produced AHL or possessed luxRI homologs. Total viable counts ranged from 1.2 × 107 to 2.2 × 109 CFU/g, which were accounted for 0.8 to 15.2% of direct counts. Aeromonas veronii, S. xiamenensis, and C. somerae were detected from five goldfish at densities ranging from 4.0 × 106 to 1.7 × 109 CFU/g, indicating that these bacteria are dominant components of the culturable gut flora in goldfish. In addition, members of the genera Aeromonas and Shewanella appeared to communicate with each other by using the QS system to some extent when the concentration of AHL reaches a certain threshold. It is therefore suggested that bacteria with the ability to disrupt AHL secretion in intestinal environments are potential candidates for probionts for preventing opportunistic infections in freshwater fish such as goldfish.
KeywordsAeromonas Shewanella Cetobacterium goldfish intestinal bacteria gut flora AHL Quorum sensing
This research was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
- McClean KH, Winson MK, Fish L, Taylor A, Chhabra SR, Camara M, Daykin M, Lamb JH, Swift S, Bycroft BW, Stewart GS, Williams P (1997) Quorum sensing and Chromobacterium violaceum: exploitation of violacein production and inhibition for the detection of N-acylhomoserine lactones. Microbiology 143:3703–3711CrossRefPubMedGoogle Scholar
- Ogawa M, Chen CH, Itoi S, Sugita H (2011) N-acyl homoserine lactone-producing bacteria isolated from the intestinal tracts of cultured ayu Plecoglossus altivelis altivelis. Aquaculture Sci 59:599–604Google Scholar
- Swift S, Karlyshev AV, Fish L, Durant EL, Winson MK, Chhabra SR, Williams P, Macintyre S, Stewart GS (1997) Quorum sensing in Aeromonas hydrophila and Aeromonas salmonicida: identification of the lux RI homologs AhyRI and AsaRI and their cognate N-acylhomoserine lactone signal molecules. J Bacteriol 179:5271–5281CrossRefPubMedPubMedCentralGoogle Scholar
- Yarza P, Richter M, Peplies J, Euzeby J, Amann R, Schleifer KH, Ludwig W, Glöckner FO, Rosselló-Móra R (2008) The all-species living tree project: a 16S rRNA-based phylogenetic tree of all sequenced type strains. Syst Appl Microbiol 31:241–2450. doi: 10.1016/j.syapm.2008.07.001 CrossRefPubMedGoogle Scholar