Molecular basis of indole production catalyzed by tryptophanase in the genus Prevotella

Abstract

Indole is most commonly known as a diagnostic marker and a malodorous chemorepellent. More recently, it has been recognized that indole also functions as an extracellular signaling molecule that controls bacterial physiology and virulence. The gene (tnaA) for tryptophanase, which produces indole, ammonia, and pyruvate via β-elimination of L-tryptophan, was cloned from Prevotella intermedia ATCC 25611 and recombinant TnaA was purified and enzymatically characterized. Analysis by reverse transcriptase-mediated PCR showed that the gene was not cotranscribed with flanking genes in P. intermedia. The results of gel-filtration chromatography suggested that P. intermedia TnaA forms homodimers, unlike other reported TnaA proteins. Recombinant TnaA exhibited a K(m) of 0.23 ± 0.01 mM and k(cat) of 0.45 ± 0.01 s(-1). Of 22 Prevotella species tested, detectable levels of indole were present in the culture supernatants of six, including P. intermedia. Southern hybridization showed that tnaA-positive signals were present in the genomic DNA from the six indole-producing strains, but not the other 16 strains tested. The indole-producing strains, with the exception of Prevotella micans, formed a phylogenetic cluster based on trees constructed using 16S rRNA gene sequences, which suggested that tnaA in P. micans might have been transferred from other Prevotella species relatively recently.

Influence of the tryptophan-indole-IFNγ axis on human genital Chlamydia trachomatis infection: role of vaginal co-infections

“…First, we know that some members of the BV microbiome can express a functional tryptophanase to produce indole from tryptophan (Sasaki-Imamura et al, 2011), thus providing genital serovars of C. trachomatis with a means to obtain tryptophan via indole salvage. We also know from our recent studies that indole is present in the vaginal secretions of patients with BV (Lewis et al, 2014).…”

Beyond Tryptophan Synthase: Identification of Genes That Contribute to Chlamydia trachomatis Survival during Gamma Interferon-Induced Persistence and Reactivation

“…Interestingly, the incidence of C. trachomatis infection is also elevated in women with bacterial vaginosis (BV) (28), and the microbiomes of these women are often enriched with bacterial taxa that contain indole producers, including Prevotella spp. (25,(28)(29)(30). Moreover, indole can be detected in vaginal secretions from women with BV and aberrant RBs were observed in cervical scrapings from one patient with C. trachomatis (3).…”

“…All reference C. trachomatis strains are inhibited by IFN-␥ in human epithelial cells (19), but only the genital strains encode functional tryptophan synthase enzymes that can synthesize tryptophan from serine and indole (20)(21)(22)(23)(24). Neither C. trachomatis bacteria nor humans produce indole, but various microorganisms that colonize the genital tract do (25)(26)(27). Interestingly, the incidence of C. trachomatis infection is also elevated in women with bacterial vaginosis (BV) (28), and the microbiomes of these women are often enriched with bacterial taxa that contain indole producers, including Prevotella spp.…”

Chlamydia trachomatis: the Persistent Pathogen

“…Indole is not present in genital tract secretions when lactobacilli predominate. However, when non-lactobacilli are numerically dominant, as occurs in the common condition known as bacterial vaginosis (42), indole can be readily detected (28,43). In addition, recent evidence has reported the existence of microorganisms in the uterus and fallopian tubes of apparently healthy asymptomatic women (44,45).…”