Cell Biology and Bacteriology of Chlamydia, Rickettsia, and Coxiella

Due to their strict intracellular growth requirements, obligate intracellular bacterial pathogens have historically been one of the most challenging groups of pathogens to study. In many cases, the bacteria have dispensed with key metabolic genes or even entire biosynthetic pathways, instead relying on the host cell for key nutrients. Further, intricate mechanisms of host cell manipulation are required to form their highly specialized intracellular niches. This is certainly true of Chlamydia, Rickettsia, and Coxiella, three genera of major obligate intracellular bacterial pathogens that are a significant cause of morbidity and mortality worldwide. While bacteria of each genera replicate in different environments within the cell, they have many common characteristics. All three possess mechanisms to secrete effector molecules into the host cell, thereby manipulating processes such as vesicular trafficking, apoptosis, and the innate immune response. Manipulation of the host cell is an essential step is establishing the intracellular niche, which further enables access to essential nutrients. With the recent development of a host cell-free culture system and genetic tools for Coxiella, this field is quickly moving forward in identifying and characterizing new virulence factors. Likewise, recent advances in methods to genetically manipulate Chlamydia and Rickettsia is leading to significant insight into the pathogenesis of these bacteria. In this Research Topic, we explore the recent advances made in our understanding of the complex biology and host-pathogen relationships of these unique and highly specialized pathogens.