DAO 84:115-121 (2009)  -  DOI: https://doi.org/10.3354/dao02033

Characterization of proteins secreted from a Type III secretion system of Edwardsiella tarda and their roles in macrophage infection

Jun Okuda1, 4,*, Makoto Kiriyama1, Etsuko Suzaki2, Katsuko Kataoka2, Mitsuaki Nishibuchi3, Toshihiro Nakai1

1Graduate School of Biosphere Science, Hiroshima University, 1-4-4, Kagamiyama, Higashi-Hiroshima 739-8528, Japan
2Graduate School of Biomedical Science, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan
3Centre for Southeast Asian Studies, Kyoto University, Kyoto 606-8501, Japan
4Present address: Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto 607-8414, Japan

ABSTRACT: The Type III secretion system is essential for intracellular replication of Edwardsiella tarda in phagocytes of fish and mammals. We identified the secreted proteins of the Type III secretion system by comparing the wild-type strain and the Type III mutant mET1229. The wild-type strain secreted 55, 25, and 22 kDa proteins into the culture supernatant, whereas the Type III mutant did not. These proteins were identified as EseB, EseC, and EseD and are similar in sequence to Salmonella SseB, SseC, and SseD that function as a translocon. The EseB, EseC, and EseD knockout mutants did not replicate in murine macrophages, suggesting that these proteins are essential for intracellular replication of E. tarda. Highest secretion of EseBCD proteins was observed when bacterial cells were cultured in neutral and alkaline pHs but not in acidic pH. When the pH of the phagosomes was examined using an acidotropic probe, the phagosomes containing the wild-type strain showed neutral pH, whereas those containing the Type III mutant exhibited acidic pH. These results suggest that the Type III-dependent interference with formation of the acidic environment in phagosomes is essential for intracellular replication of bacteria in murine macrophages.


KEY WORDS: Edwardsiella tarda · EseBCD proteins · Translocon · Phagosomal pH · Macrophage


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Cite this article as: Okuda J, Kiriyama M, Suzaki E, Kataoka K, Nishibuchi M, Nakai T (2009) Characterization of proteins secreted from a Type III secretion system of Edwardsiella tarda and their roles in macrophage infection. Dis Aquat Org 84:115-121. https://doi.org/10.3354/dao02033

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