Bandyopadhyay Purnima, Liu Shuqing, Gabbai Carolina B, Venitelli Zeah, Steinman Howard M
Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Infect Immun. 2007 Feb;75(2):723-35. doi: 10.1128/IAI.00956-06. Epub 2006 Nov 13.
Legionella pneumophila, the causative organism of Legionnaires' disease, is a fresh-water bacterium and intracellular parasite of amoebae. This study examined the effects of incubation in water and amoeba encystment on L. pneumophila strain JR32 and null mutants in dot/icm genes encoding a type IVB secretion system required for entry, delayed acidification of L. pneumophila-containing phagosomes, and intracellular multiplication when stationary-phase bacteria infect amoebae and macrophages. Following incubation of stationary-phase cultures in water, mutants in dotA and dotB, essential for function of the type IVB secretion system, exhibited entry and delay of phagosome acidification comparable to that of strain JR32. Following encystment in Acanthamoeba castellanii and reversion of cysts to amoeba trophozoites, dotA and dotB mutants exhibited intracellular multiplication in amoebae. The L. pneumophila Lvh locus, encoding a type IVA secretion system homologous to that in Agrobacterium tumefaciens, was required for restoration of entry and intracellular multiplication in dot/icm mutants following incubation in water and amoeba encystment and was required for delay of phagosome acidification in strain JR32. These data support a model in which the Dot/Icm type IVB secretion system is conditionally rather than absolutely required for L. pneumophila virulence-related phenotypes. The data suggest that the Lvh type IVA secretion system, previously thought to be dispensable, is involved in virulence-related phenotypes under conditions mimicking the spread of Legionnaires' disease from environmental niches. Since environmental amoebae are implicated as reservoirs for an increasing number of environmental pathogens and for drug-resistant bacteria, the environmental mimics developed here may be useful in virulence studies of other pathogens.
嗜肺军团菌是军团病的致病原，是一种淡水细菌和变形虫的细胞内寄生虫。本研究检测了在水中孵育和变形虫包囊化对嗜肺军团菌JR32菌株以及编码IVB型分泌系统的dot/icm基因缺失突变体的影响，该分泌系统是嗜肺军团菌进入细胞、含嗜肺军团菌吞噬体延迟酸化以及静止期细菌感染变形虫和巨噬细胞时细胞内增殖所必需的。将静止期培养物在水中孵育后，IVB型分泌系统功能所必需的dotA和dotB突变体表现出与JR32菌株相当的进入细胞和吞噬体酸化延迟现象。在卡氏棘阿米巴中包囊化并将包囊转化为变形虫滋养体后，dotA和dotB突变体在变形虫中表现出细胞内增殖。嗜肺军团菌的Lvh基因座编码一种与根癌土壤杆菌中同源的IVA型分泌系统，在水中孵育和变形虫包囊化后，dot/icm突变体恢复进入细胞和细胞内增殖需要该基因座，并且JR32菌株吞噬体酸化延迟也需要该基因座。这些数据支持了一个模型，即Dot/Icm IVB型分泌系统对于嗜肺军团菌毒力相关表型是条件性而非绝对必需的。数据表明，以前认为可有可无的Lvh IVA型分泌系统在模拟军团病从环境生态位传播的条件下参与毒力相关表型。由于环境变形虫被认为是越来越多环境病原体和耐药细菌的储存库，这里开发的环境模拟物可能有助于其他病原体的毒力研究。
