AUTHOR=Wang Li , Hou YingLan , Yuan HongXia , Chen Hongliang 

TITLE=The role of tryptophan in Chlamydia trachomatis persistence

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.931653

DOI=10.3389/fcimb.2022.931653

ISSN=2235-2988

ABSTRACT=<p><italic>Chlamydia trachomatis</italic> (<italic>C. trachomatis</italic>) is the most common etiological agent of bacterial sexually transmitted infections (STIs) and a worldwide public health issue. The natural course with <italic>C. trachomatis</italic> infection varies widely between individuals. Some infections clear spontaneously, others can last for several months or some individuals can become reinfected, leading to severe pathological damage. Importantly, the underlying mechanisms of <italic>C. trachomatis</italic> infection are not fully understood. <italic>C. trachomatis</italic> has the ability to adapt to immune response and persist within host epithelial cells. Indoleamine-2,3-dioxygenase (IDO) induced by interferon-gamma (IFN-γ) degrades the intracellular tryptophan pool, to which <italic>C. trachomatis</italic> can respond by converting to a non-replicating but viable state. <italic>C. trachomatis</italic> expresses and encodes for the tryptophan synthase (TS) genes (<italic>trpA</italic> and <italic>trpB</italic>) and tryptophan repressor gene (<italic>trpR</italic>). Multiple genes interact to regulate tryptophan synthesis from exogenous indole, and persistent <italic>C. trachomatis</italic> can recover its infectivity by converting indole into tryptophan. In this review, we discuss the characteristics of chlamydial infections, biosynthesis and regulation of tryptophan, the relationship between tryptophan and <italic>C. trachomatis</italic>, and finally, the links between the tryptophan/IFN-γ axis and <italic>C. trachomatis</italic> persistence.</p>