Abstract：
Legionella pneumophila is a natural inhabitant of water systems. From there, it can be transmitted to humans by aerosolization resulting in severe pneumonia. Most large outbreaks are caused by cooling towers colonized with L. pneumophila. The resident microbiota of the cooling tower is a key determinant for the colonization and growth of L. pneumophila. In our preceding study, the genus Pseudomonas correlated negatively with the presence of L. pneumophila in cooling towers, but it was not clear which species was responsible. Therefore, we identified the Pseudomonas species inhabiting 14 cooling towers using a Pseudomonas-specific 16S rRNA amplicon sequencing strategy. We found that cooling towers that are free of L. pneumophila contained a high relative abundance of members from the Pseudomonas alcaliphila/oleovorans phylogenetic cluster. P. alcaliphila JCM 10630 inhibited the growth of L. pneumophila on agar plates. Analysis of the P. alcaliphila genome revealed the presence of a gene cluster predicted to produce toxoflavin. L. pneumophila growth was inhibited by pure toxoflavin and by extracts from P. alcaliphila culture found to contain toxoflavin by liquid chromatography coupled with mass spectrometry. In addition, toxoflavin inhibits the growth of Vermameoba vermiformis, a host cell of L. pneumophila. Our study indicates that P. alcaliphila may be important to restrict growth of L. pneumophila in water systems through the production of toxoflavin. A sufficiently high concentration of toxoflavin is likely not achieved in the bulk water but might have a local inhibitory effect such as near or in biofilms.
摘要：
嗜肺军团菌是水系统的自然居民。从那里,它可以通过雾化传播给人类，导致严重的肺炎。大多数大型疫情是由嗜肺乳杆菌定植的冷却塔引起的。冷却塔的常驻微生物群是嗜肺乳杆菌定植和生长的关键决定因素。在我们之前的研究中,假单胞菌属与冷却塔中嗜肺乳杆菌的存在呈负相关，但不清楚是哪个物种负责。因此,我们使用假单胞菌特异性16SrRNA扩增子测序策略鉴定了居住在14个冷却塔中的假单胞菌属物种。我们发现，不含嗜肺乳杆菌的冷却塔中含有相对丰富的嗜肺假单胞菌/油菌系统发育簇成员。P.alcaliphilaJCM10630抑制嗜肺乳杆菌在琼脂平板上的生长。对alcalaliphila基因组的分析揭示了预测产生毒黄素的基因簇的存在。纯毒素黄素和通过液相色谱与质谱联用发现含有毒素黄素的P.alcaliphila培养物的提取物抑制了嗜肺乳杆菌的生长。此外,毒黄素抑制Vermameoba的生长，嗜肺乳杆菌的宿主细胞。我们的研究表明，P.alcaliphila可能是重要的限制在水系统中的嗜肺乳杆菌的生长通过生产的毒素黄素。在主体水中可能无法实现足够高浓度的弓黄素,但可能具有局部抑制作用,例如在生物膜附近或在生物膜中。
