Advances and Obstacles in the Genetic Dissection of Chlamydial Virulence

Abstract

Obligate intracellular pathogens in the family Chlamydiaceae infect taxonomically diverse eukaryotes ranging from amoebae to mammals. However, many fundamental aspects of chlamydial cell biology and pathogenesis remain poorly understood. Genetic dissection of chlamydial biology has historically been hampered by a lack of genetic tools. Exploitation of the ability of chlamydia to recombine genomic material by lateral gene transfer (LGT) ushered in a new era in chlamydia research. With methods to map mutations in place, genetic screens were able to assign functions and phenotypes to specific chlamydial genes. Development of an approach for stable transformation of chlamydia also provided a mechanism for gene delivery and platforms for disrupting chromosomal genes. Here, we explore how these and other tools have been used to test hypotheses concerning the functions of known chlamydial virulence factors and discover the functions of completely uncharacterized genes. Refinement and extension of the existing genetic tools to additional Chlamydia spp. will substantially advance understanding of the biology and pathogenesis of this important group of pathogens.

A Genital Infection-Attenuated Chlamydia muridarum Mutant Infects the Gastrointestinal Tract and Protects against Genital Tract Challenge

“…We screened a subset of heavily EMS-mutagenized Cm isolates using the murine GI and genital tract models of infection and identified a mutant, GIAM-1, that exhibited those characteristics. Unfortunately, the large number of nonsense mutations in GIAM-1 and the mutant's lack of a strong counterselectable in vitro phenotype have prevented us from identifying the attenuating mutations using markerless lateral gene transfer and/or complementation (49,50). Nonetheless, although we have screened only a small number of heavily mutagenized Cm isolates in the GI and genital tract infection models, those screens have identified the genital tract infection-attenuated GIAM-1 mutant and other mutants that are specifically attenuated for GI infection (28).…”

Ptr/CTL0175 Is Required for the Efficient Recovery of Chlamydia trachomatis From Stress Induced by Gamma-Interferon

“…Several studies have shown that the transcriptional responses triggered in Chlamydia are not the same across different stress models, suggesting that specific Chlamydia genes participate in regulating the response to different stressful stimuli (Mathews et al, 2001; Belland et al, 2003; Gerard et al, 2004; Goellner et al, 2006; Ouellette et al, 2006; Maurer et al, 2007; Brinkworth et al, 2018). Due to Chlamydia being refractory to genetic manipulation until recently (reviewed in McClure et al, 2017; Brothwell et al, 2018; Rahnama and Fields, 2018), the genes involved in such response remain largely unknown. Notably, Muramatsu et al (2016) carried out a genetic screen aimed at identifying C. trachomatis mutants defective for recovery from IFNγ-induced persistence.…”

Chlamydiae from Down Under: The Curious Cases of Chlamydial Infections in Australia

“…The diverse members of the phylum Chlamydiae constantly remain in the global spotlight, attracting attention not just as successful and enigmatic human and animal pathogens [1], but also by cutting-edge biological and "omics" research involving Chlamydiae [2,3]. From a global public perspective, Chlamydiae in Australia are perhaps best known as the notorious pathogens of the iconic marsupial, koala (Phascolarctos cinereus).…”