Legionella pneumophila Utilizes the Same Genes To Multiply within Acanthamoeba castellanii and Human Macrophages

Abstract

ABSTRACT In previous reports we described a 22-kb Legionella pneumophila chromosomal locus containing 18 genes. Thirteen of these genes ( icmT , - R , - Q , - P , - O , - M , - L , - K , - E , - C , - D , - J , and - B ) were found to be completely required for intracellular growth and killing of human macrophages. Three genes ( icmS , - G , and - F ) were found to be partially required, and two genes ( lphA and tphA ) were found to be dispensable for intracellular growth and killing of human macrophages. Here, we analyzed the requirement of these genes for intracellular growth in the protozoan host Acanthamoeba castellanii , a well-established important environmental host of L. pneumophila . We found that all the genes that are completely required for intracellular growth in human macrophages are also completely required for intracellular growth in A. castellanii . However, the genes that are partially required for intracellular growth in human macrophages are completely required for intracellular growth in A. castellanii . In addition, the lphA gene, which was shown to be dispensable for intracellular growth in human macrophages, is partially required for intracellular growth in A. castellanii . Our results indicate that L. pneumophila utilizes the same genes to grow intracellularly in both human macrophages and amoebae.