Aoki Hiroaki, Wu Hong, Nakano Takashi, Ooi Yukimasa, Daikoku Eriko, Kohno Takehiro, Matsushita Tomoyo, Sano Kouichi
Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan.
Med Mol Morphol. 2009 Mar;42(1):40-6. doi: 10.1007/s00795-008-0431-x. Epub 2009 Mar 18.
Vibrio cholerae (V. cholerae) cholera toxin (CT), which causes a severe watery diarrheal illness, is secreted via the type II secretion machinery; it remains unclear, however, how this toxin is transported toward the machinery. In this study, we determined that the pH-dependent intrabacterial transport system correlates with the priming of CT secretion by V. cholerae. The secretion and production of V. cholerae treated at different pHs were examined by enzyme immunoassay. The localization of the CT was analyzed by immunoelectron microscopy. The CT secretion level rapidly increases in the alkaline-pH-treated V. cholerae but does so more slowly in neutral- and acidic-pH-treated V. cholerae. The CT was found to be densely localized near the membrane in the alkaline-pH-treated bacterial cytoplasm, suggesting that the CT shifts from the center to the peripheral portion of the cytoplasm following an extracellular rise in pH. The shift was observed in V. cholerae treated at alkaline pH for more than 10 min. The pH treatment did not enhance CT production at the same stage at which secretion and intrabacterial transport of the CT were enhanced. We propose that V. cholerae possesses a pH-dependent intrabacterial nanotransportation system that probably accelerates priming for CT secretion.
霍乱弧菌的霍乱毒素（CT）可引发严重的水样腹泻疾病，它通过II型分泌机制进行分泌；然而，这种毒素如何被转运至该机制仍不清楚。在本研究中，我们确定了pH依赖的细菌内转运系统与霍乱弧菌对CT分泌的启动相关。通过酶免疫测定法检测了在不同pH值下处理的霍乱弧菌的分泌和产生情况。通过免疫电子显微镜分析了CT的定位。在经碱性pH处理的霍乱弧菌中，CT分泌水平迅速增加，但在经中性和酸性pH处理的霍乱弧菌中增加较为缓慢。在经碱性pH处理的细菌细胞质中，发现CT密集地定位在膜附近，这表明随着细胞外pH值升高，CT从细胞质中心转移到周边部分。在经碱性pH处理超过10分钟的霍乱弧菌中观察到了这种转移。pH处理在增强CT分泌和细菌内转运的同一阶段并未增强CT的产生。我们提出霍乱弧菌拥有一种pH依赖的细菌内纳米转运系统，该系统可能加速CT分泌的启动。
