Clinical Persistence of Chlamydia trachomatis Sexually Transmitted Strains Involves Novel Mutations in the Functional αββα Tetramer of the Tryptophan Synthase Operon

Abstract

Clinical persistence of Chlamydia trachomatis (Ct) sexually transmitted infections (STIs) is a major public health concern. In vitro persistence is known to develop through interferon gamma (IFN-γ) induction of indoleamine 2,3-dioxygenase (IDO), which catabolizes tryptophan, an essential amino acid for Ct replication. The organism can recover from persistence by synthesizing tryptophan from indole, a substrate for the enzyme tryptophan synthase. The majority of Ct strains, except for reference strain B/TW-5/OT, contain an operon comprised of α and β subunits that encode TrpA and TrpB, respectively, and form a functional αββα tetramer. However, trpA mutations in ocular Ct strains, which are responsible for the blinding eye disease known as trachoma, abrogate tryptophan synthesis from indole. We examined serial urogenital samples from a woman who had recurrent Ct infections over 4 years despite antibiotic treatment. The Ct isolates from each infection episode were genome sequenced and analyzed for phenotypic, structural, and functional characteristics. All isolates contained identical mutations in trpA and developed aberrant bodies within intracellular inclusions, visualized by transmission electron microscopy, even when supplemented with indole following IFN-γ treatment. Each isolate displayed an altered αββα structure, could not synthesize tryptophan from indole, and had significantly lower trpBA expression but higher intracellular tryptophan levels compared with those of reference Ct strain F/IC-Cal3. Our data indicate that emergent mutations in the tryptophan operon, which were previously thought to be restricted only to ocular Ct strains, likely resulted in in vivo persistence in the described patient and represents a novel host-pathogen adaptive strategy for survival. IMPORTANCE Chlamydia trachomatis (Ct) is the most common sexually transmitted bacterium with more than 131 million cases occurring annually worldwide. Ct infections are often asymptomatic, persisting for many years despite treatment. In vitro recovery from persistence occurs when indole is utilized by the organism’s tryptophan synthase to synthesize tryptophan, an essential amino acid for replication. Ocular but not urogenital Ct strains contain mutations in the synthase that abrogate tryptophan synthesis. Here, we discovered that the genomes of serial isolates from a woman with recurrent, treated Ct STIs over many years were identical with a novel synthase mutation. This likely allowed long-term in vivo persistence where active infection resumed only when tryptophan became available. Our findings indicate an emerging adaptive host-pathogen evolutionary strategy for survival in the urogenital tract that will prompt the field to further explore chlamydial persistence, evaluate the genetics of mutant Ct strains and fitness within the host, and their implications for disease pathogenesis.

The Immune Characteristics of the Epididymis and the Immune Pathway of the Epididymitis Caused by Different Pathogens

“…IFN-γ has a dual function of inhibiting the growth of CT (110) in mice and inducing Th1 immune responses in CT-infected women (111). Studies have shown that IFN-γ activates host cells to restrict intracellular growth of CT by induction of IDO (112), as shown in Figure 3. The depletion of tryptophan by IDO has been proved to deprive CT of 5-hydroxytryptophan, which is essential for its differentiation into an infectious elementary body (112,113).…”

“…Studies have shown that IFN-γ activates host cells to restrict intracellular growth of CT by induction of IDO (112), as shown in Figure 3. The depletion of tryptophan by IDO has been proved to deprive CT of 5-hydroxytryptophan, which is essential for its differentiation into an infectious elementary body (112,113). If IFN-γ is removed from the host cell, tryptophan synthesis will subsequently recover, and CT quickly forms into an infectious elementary body (114).…”

Genomics and Chlamydial Persistence In Vivo

“…We read with interest the recent paper by Somboonna and colleagues, addressing changes to tryptophan synthase in a single Chlamydia trachomatis strain that had an aberrant growth phenotype in vitro (1). This strain was isolated four times, over 4 years, from a patient who was apparently persistently infected.…”

“…Mutations in trpR (A), trpB (B), and trpA (C) in five persistent strains from patients in sexual health clinics in King County, Washington (patients 1, 2, 3, 6, and 7) discussed in reference 2 and the F/I strain discussed in reference 1. The figure is formatted similarly to data in reference 1. Positions in each coding sequence are indicated at the top of each panel (the numbers are centered on the base), and amino acid sequence and changes are indicated below each DNA sequence.…”

“…Positions in each coding sequence are indicated at the top of each panel (the numbers are centered on the base), and amino acid sequence and changes are indicated below each DNA sequence. Mutant bases and amino acids are indicated by boldface type as in reference 1.…”