Insight into the ecology of vaginal bacteria through integrative analyses of metagenomic and metatranscriptomic data

Background

Vaginal bacterial communities dominated by Lactobacillus species are associated with a reduced risk of various adverse health outcomes. However, somewhat unexpectedly, many healthy women have microbiota that are not dominated by lactobacilli. To determine the factors that drive vaginal community composition we characterized the genetic composition and transcriptional activities of vaginal microbiota in healthy women.

Results

We demonstrate that the abundance of a species is not always indicative of its transcriptional activity and that impending changes in community composition can be predicted from metatranscriptomic data. Functional comparisons highlight differences in the metabolic activities of these communities, notably in their degradation of host produced mucin but not glycogen. Degradation of mucin by communities not dominated by Lactobacillus may play a role in their association with adverse health outcomes. Finally, we show that the transcriptional activities of L. crispatus, L. iners, and Gardnerella vaginalis vary with the taxonomic composition of the communities in which they reside. Notably, L. iners and G. vaginalis both demonstrate lower expression of their cholesterol-dependent cytolysins when co-resident with Lactobacillus spp. and higher expression when co-resident with other facultative and obligate anaerobes. The pathogenic potential of these species may depend on the communities in which they reside and thus could be modulated by interventional strategies.

Conclusions

Our results provide insight to the functional ecology of the vaginal microbiota, demonstrate the diagnostic potential of metatranscriptomic data, and reveal strategies for the management of these ecosystems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02635-9.

VALENCIA: a nearest centroid classification method for vaginal microbial communities based on composition

BACKGROUND

Taxonomic profiles of vaginal microbial communities can be sorted into a discrete number of categories termed community state types (CSTs). This approach is advantageous because collapsing a hyper-dimensional taxonomic profile into a single categorical variable enables efforts such as data exploration, epidemiological studies, and statistical modeling. Vaginal communities are typically assigned to CSTs based on the results of hierarchical clustering of the pairwise distances between samples. However, this approach is problematic because it complicates between-study comparisons and because the results are entirely dependent on the particular set of samples that were analyzed. We sought to standardize and advance the assignment of samples to CSTs.

RESULTS

We developed VALENCIA (VAginaL community state typE Nearest CentroId clAssifier), a nearest centroid-based tool which classifies samples based on their similarity to a set of reference centroids. The references were defined using a comprehensive set of 13,160 taxonomic profiles from 1975 women in the USA. This large dataset allowed us to comprehensively identify, define, and characterize vaginal CSTs common to reproductive age women and expand upon the CSTs that had been defined in previous studies. We validated the broad applicability of VALENCIA for the classification of vaginal microbial communities by using it to classify three test datasets which included reproductive age eastern and southern African women, adolescent girls, and a racially/ethnically and geographically diverse sample of postmenopausal women. VALENCIA performed well on all three datasets despite the substantial variations in sequencing strategies and bioinformatics pipelines, indicating its broad application to vaginal microbiota. We further describe the relationships between community characteristics (vaginal pH, Nugent score) and participant demographics (race, age) and the CSTs defined by VALENCIA.

CONCLUSION

VALENCIA provides a much-needed solution for the robust and reproducible assignment of vaginal community state types. This will allow unbiased analysis of both small and large vaginal microbiota datasets, comparisons between datasets and meta-analyses that combine multiple datasets. Video abstract.

Chromatin accessibility dynamics of Chlamydia-infected epithelial cells

Chlamydia are Gram-negative, obligate intracellular bacterial pathogens responsible for a broad spectrum of human and animal diseases. In humans, Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection worldwide and is the causative agent of trachoma (infectious blindness) in disadvantaged populations. Over the course of its developmental cycle, Chlamydia extensively remodels its intracellular niche and parasitises the host cell for nutrients, with substantial resulting changes to the host cell transcriptome and proteome. However, little information is available on the impact of chlamydial infection on the host cell epigenome and global gene regulation. Regions of open eukaryotic chromatin correspond to nucleosome-depleted regions, which in turn are associated with regulatory functions and transcription factor binding. We applied formaldehyde-assisted isolation of regulatory elements enrichment followed by sequencing (FAIRE-Seq) to generate temporal chromatin maps of C. trachomatis-infected human epithelial cells in vitro over the chlamydial developmental cycle. We detected both conserved and distinct temporal changes to genome-wide chromatin accessibility associated with C. trachomatis infection. The observed differentially accessible chromatin regions include temporally-enriched sets of transcription factors, which may help shape the host cell response to infection. These regions and motifs were linked to genomic features and genes associated with immune responses, re-direction of host cell nutrients, intracellular signalling, cell-cell adhesion, extracellular matrix, metabolism and apoptosis. This work provides another perspective to the complex response to chlamydial infection, and will inform further studies of transcriptional regulation and the epigenome in Chlamydia-infected human cells and tissues.

A comprehensive non-redundant gene catalog reveals extensive within-community intraspecies diversity in the human vagina

Analysis of metagenomic and metatranscriptomic data is complicated and typically requires extensive computational resources. Leveraging a curated reference database of genes encoded by members of the target microbiome can make these analyses more tractable. In this study, we assemble a comprehensive human vaginal non-redundant gene catalog (VIRGO) that includes 0.95 million non-redundant genes. The gene catalog is functionally and taxonomically annotated. We also construct a vaginal orthologous groups (VOG) from VIRGO. The gene-centric design of VIRGO and VOG provides an easily accessible tool to comprehensively characterize the structure and function of vaginal metagenome and metatranscriptome datasets. To highlight the utility of VIRGO, we analyze 1,507 additional vaginal metagenomes, and identify a high degree of intraspecies diversity within and across vaginal microbiota. VIRGO offers a convenient reference database and toolkit that will facilitate a more in-depth understanding of the role of vaginal microorganisms in women’s health and reproductive outcomes.

Reference databases are essential for studies on host-microbiota interactions. Here, the authors present the construction of VIRGO, a human vaginal non-redundant gene catalog, which represents a comprehensive resource for taxonomic and functional profiling of vaginal microbiomes from metagenomic and metatranscriptomic datasets.

Early Transcriptional Landscapes of Chlamydia trachomatis-Infected Epithelial Cells at Single Cell Resolution

Chlamydia are Gram-negative obligate intracellular bacterial pathogens responsible for a variety of disease in humans and animals worldwide. Chlamydia trachomatis causes trachoma in disadvantaged populations, and is the most common bacterial sexually transmitted infection in humans, causing reproductive tract disease. Antibiotic therapy successfully treats diagnosed chlamydial infections, however asymptomatic infections are common. High-throughput transcriptomic approaches have explored chlamydial gene expression and infected host cell gene expression. However, these were performed on large cell populations, averaging gene expression profiles across all cells sampled and potentially obscuring biologically relevant subsets of cells. We generated a pilot dataset, applying single cell RNA-Seq (scRNA-Seq) to C. trachomatis infected and mock-infected epithelial cells to assess the utility, pitfalls and challenges of single cell approaches applied to chlamydial biology, and to potentially identify early host cell biomarkers of chlamydial infection. Two hundred sixty-four time-matched C. trachomatis-infected and mock-infected HEp-2 cells were collected and subjected to scRNA-Seq. After quality control, 200 cells were retained for analysis. Two distinct clusters distinguished 3-h cells from 6- and 12-h. Pseudotime analysis identified a possible infection-specific cellular trajectory for Chlamydia-infected cells, while differential expression analyses found temporal expression of metallothioneins and genes involved with cell cycle regulation, innate immune responses, cytoskeletal components, lipid biosynthesis and cellular stress. We find that changes to the host cell transcriptome at early times of C. trachomatis infection are readily discernible by scRNA-Seq, supporting the utility of single cell approaches to identify host cell biomarkers of chlamydial infection, and to further deconvolute the complex host response to infection.

The Cervicovaginal Microbiota-Host Interaction Modulates Chlamydia trachomatis Infection

The mechanism(s) by which Lactobacillus-dominated cervicovaginal microbiota provide a barrier to Chlamydia trachomatis infection remain(s) unknown. Here we evaluate the impact of different Lactobacillus spp. identified via culture-independent metataxonomic analysis of C. trachomatis-infected women on C. trachomatis infection in a three-dimensional (3D) cervical epithelium model. Lactobacillus spp. that specifically produce d(-) lactic acid were associated with long-term protection against C. trachomatis infection, consistent with reduced protection associated with Lactobacillus iners, which does not produce this isoform, and with decreased epithelial cell proliferation, consistent with the observed prolonged protective effect. Transcriptomic analysis revealed that epigenetic modifications involving histone deacetylase-controlled pathways are integral to the cross talk between host and microbiota. These results highlight a fundamental mechanism whereby the cervicovaginal microbiota modulates host functions to protect against C. trachomatis infection.IMPORTANCE The vaginal microbiota is believed to protect women against Chlamydia trachomatis, the etiologic agent of the most prevalent sexually transmitted infection (STI) in developed countries. The mechanism underlying this protection has remained elusive. Here, we reveal the comprehensive strategy by which the cervicovaginal microbiota modulates host functions to protect against chlamydial infection, thereby providing a novel conceptual mechanistic understanding. Major implications of this work are that (i) the impact of the vaginal microbiota on the epithelium should be considered in future studies of chlamydial infection and other STIs and (ii) a fundamental understanding of the cervicovaginal microbiota's role in protection against STIs may enable the development of novel microbiome-based therapeutic strategies to protect women from infection and improve vaginal and cervical health.

Bioinformatic analysis of bacteria and host cell dual RNA-sequencing experiments

Bacterial pathogens subvert host cells by manipulating cellular pathways for survival and replication; in turn, host cells respond to the invading pathogen through cascading changes in gene expression. Deciphering these complex temporal and spatial dynamics to identify novel bacterial virulence factors or host response pathways is crucial for improved diagnostics and therapeutics. Dual RNA sequencing (dRNA-Seq) has recently been developed to simultaneously capture host and bacterial transcriptomes from an infected cell. This approach builds on the high sensitivity and resolution of RNA sequencing technology and is applicable to any bacteria that interact with eukaryotic cells, encompassing parasitic, commensal or mutualistic lifestyles. Several laboratory protocols have been presented that outline the collection, extraction and sequencing of total RNA for dRNA-Seq experiments, but there is relatively little guidance available for the detailed bioinformatic analyses required. This protocol outlines a typical dRNA-Seq experiment, based on a Chlamydia trachomatis-infected host cell, with a detailed description of the necessary bioinformatic analyses with currently available software tools.

Dual RNA-Seq of Chlamydia and Host Cells

During the infection of a host cell by a bacterial pathogen, a cascading series of gene expression changes occurs as each organism manipulates or responds to the other via defense or survival strategies. Unraveling this complex interplay is key for our understanding of bacterial virulence and host response pathways for the development of novel therapeutics. Dual RNA sequencing (dual RNA-Seq) has recently been developed to simultaneously capture host and bacterial transcriptomes from an infected cell. Leveraging the sensitivity and resolution allowed by RNA-seq, dual RNA-Seq can be applied to any bacteria-eukaryotic host interaction. We pioneered dual RNA-Seq to simultaneously capture Chlamydia and host expression profiles during an in vitro infection as proof of principle. Here we provide a detailed laboratory protocol and bioinformatics analysis guidelines for dual RNA-seq experiments focusing on Chlamydia as the organism of interest.

A Laboratory Methodology for Dual RNA-Sequencing of Bacteria and their Host Cells In Vitro

Dual RNA-Sequencing leverages established next-generation sequencing (NGS)-enabled RNA-Seq approaches to measure genome-wide transcriptional changes of both an infecting bacteria and host cells. By simultaneously investigating both organisms from the same biological sample, dual RNA-Seq can provide unique insight into bacterial infection processes and reciprocal host responses at once. However, the difficulties involved in handling both prokaryotic and eukaryotic material require distinct, optimized procedures. We previously developed and applied dual RNA-Seq to measure prokaryotic and eukaryotic expression profiles of human cells infected with bacteria, using in vitro Chlamydia-infected epithelial cells as proof of principle. Here we provide a detailed laboratory protocol for in vitro dual RNA-Seq that is readily adaptable to any host-bacteria system of interest.

Group B Streptococcus and the Vaginal Microbiota

Background

Streptococcus agalactiae (group B Streptococcus [GBS]) is an important neonatal pathogen and emerging cause of disease in adults. The major risk factor for neonatal disease is maternal vaginal colonization. However, little is known about the relationship between GBS and vaginal microbiota.

Methods

Vaginal lavage samples from nonpregnant women were tested for GBS, and amplicon-based sequencing targeting the 16S ribosomal RNA V3-V4 region was performed.

Results

Four hundred twenty-eight of 432 samples met the high-quality read threshold. There was no relationship between GBS carriage and demographic characteristics, α-diversity, or overall vaginal microbiota community state type (CST). Within the non-Lactobacillus-dominant CST IV, GBS positive status was significantly more prevalent in CST IV-A than CST IV-B. Significant clustering by GBS status was noted on principal coordinates analysis, and 18 individual taxa were found to be significantly associated with GBS carriage by linear discriminant analysis. After adjusting for race/ethnicity, 4 taxa were positively associated with GBS, and 6 were negatively associated.

Conclusions

Vaginal microbiota CST and α-diversity are not related to GBS status. However, specific microbial taxa are associated with colonization of this important human pathogen, highlighting a potential role for the microbiota in promotion or inhibition of GBS colonization.

Association of HPV infection and clearance with cervicovaginal immunology and the vaginal microbiota

Cervical human papillomavirus (HPV) infection may increase HIV risk. Since other genital infections enhance HIV susceptibility by inducing inflammation, we assessed the impact of HPV infection and clearance on genital immunology and the cervico-vaginal microbiome. Genital samples were collected from 65 women for HPV testing, immune studies and microbiota assessment; repeat HPV testing was performed after 6 months. All participants were HIV-uninfected and free of bacterial STIs. Cytobrush-derived T cell and dendritic cell subsets were assessed by multiparameter flow cytometry. Undiluted cervico-vaginal secretions were used to determine cytokine levels by multiplex ELISA, and to assess bacterial community composition and structure by 16S rRNA gene sequence analysis. Neither HPV infection nor clearance were associated with broad differences in cervical T cell subsets or cytokines, although HPV clearance was associated with increased Langerhans cells and HPV infection with elevated IP-10 and MIG. Individuals with HPV more frequently had a high diversity cervico-vaginal microbiome (community state type IV) and were less likely to have an L. gasseri predominant microbiome. In summary, HPV infection and/or subsequent clearance was not associated with inflammation or altered cervical T cell subsets, but associations with increased Langerhans cells and the composition of the vaginal microbiome warrant further exploration.

Distinct Effects of the Cervicovaginal Microbiota and Herpes Simplex Type 2 Infection on Female Genital Tract Immunology

Background

Genital inflammation is a key determinant of human immunodeficiency virus (HIV) transmission, and may increase HIV-susceptible target cells and alter epithelial integrity. Several genital conditions that increase HIV risk are more prevalent in African, Caribbean, and other black (ACB) women, including bacterial vaginosis and herpes simplex virus type-2 (HSV-2) infection. Therefore, we assessed the impact of the genital microbiota on mucosal immunology in ACB women and microbiome-HSV-2 interactions.

Methods

Cervicovaginal secretions and endocervical cells were collected by cytobrush and Instead Softcup, respectively. T cells and dendritic cells were assessed by flow cytometry, cytokines by multiplex enzyme-linked immunosorbent assay (ELISA), and the microbiota by 16S ribosomal ribonucleic acid gene sequencing.

Results

The cervicovaginal microbiota of 51 participants were composed of community state types (CSTs) showing diversity (20/51; 39%) or predominated by Lactobacillus iners (22/51; 42%), L. crispatus (7/51; 14%), or L. gasseri (2/51; 4%). High-diversity CSTs and specific bacterial phyla (Gardnerella vaginalis and Prevotella bivia) were strongly associated with cervicovaginal inflammatory cytokines, but not with altered endocervical immune cells. However, cervical CD4+ T-cell number was associated with HSV-2 infection and a distinct cytokine profile.

Conclusions

This suggests that the genital microbiota and HSV-2 infection may influence HIV susceptibility through independent biological mechanisms.

Molecular Characterization of the Human Stomach Microbiota in Gastric Cancer Patients

Helicobacter pylori (Hp) is the primary cause of gastric cancer but we know little of its relative abundance and other microbes in the stomach, especially at the time of gastric cancer diagnosis. Here we characterized the taxonomic and derived functional profiles of gastric microbiota in two different sets of gastric cancer patients, and compared them with microbial profiles in other body sites. Paired non-malignant and tumor tissues were sampled from 160 gastric cancer patients with 80 from China and 80 from Mexico. The 16S rRNA gene V3-V4 region was sequenced using MiSeq platform for taxonomic profiles. PICRUSt was used to predict functional profiles. Human Microbiome Project was used for comparison. We showed that Hp is the most abundant member of gastric microbiota in both Chinese and Mexican samples (51 and 24%, respectively), followed by oral-associated bacteria. Taxonomic (phylum-level) profiles of stomach microbiota resembled oral microbiota, especially when the Helicobacter reads were removed. The functional profiles of stomach microbiota, however, were distinct from those found in other body sites and had higher inter-subject dissimilarity. Gastric microbiota composition did not differ by Hp colonization status or stomach anatomic sites, but did differ between paired non-malignant and tumor tissues in either Chinese or Mexican samples. Our study showed that Hp is the dominant member of the non-malignant gastric tissue microbiota in many gastric cancer patients. Our results provide insights on the gastric microbiota composition and function in gastric cancer patients, which may have important clinical implications.

Abstract 3257: Molecular characterization of the human stomach microbiota in gastric cancer patients

Background Helicobacter pylori (Hp) is the primary cause of gastric cancer but we know little of its relative abundance and other microbes in the stomach, especially at the time of gastric cancer diagnosis. Here we characterized the taxonomic and derived functional profiles of gastric microbiota in 157 non-malignant gastric tissue samples from two different sets of gastric cancer patients, and compared them with microbial profiles of oral, stool, nasal, vagina and skin samples from Human Microbiome Project.

Results We show that Hp is the most abundant member of gastric microbiota in both Chinese and Mexican samples (51% and 24% respectively), followed by the genera commonly seen in the oral microbiota. Taxonomic (phylum) profiles of stomach microbiota largely resembled oral microbiota when the Helicobacter reads were removed. The functional profiles of stomach microbiota, however, were distinct from those found in other body sites and had higher inter-subject dissimilarity. Gastric microbiota composition did not differ by Hp colonization status or stomach anatomic site, but did differ between paired non-malignant and tumor tissues in either Chinese or Mexican samples.

Conclusions Our study is the first to show that Hp is the dominant member of the gastric microbiota in many gastric cancer patients rather than diminished or depleted as traditionally believed. Our results provide insights on the gastric microbiota composition and function in gastric cancer patients, which may have important clinical implications.

Citation Format: Guoqin Yu, Javier Torres, Nan Hu, Rafael Medrano-Guzman, Roberto Herrera-Goepfert, Michael S. Humphrys, Lemin Wang, Chaoyu Wang, Ti Ding, Jacques Ravel, Philip R. Taylor, Christian Abnet, Alisa Goldstein. Molecular characterization of the human stomach microbiota in gastric cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3257. doi:10.1158/1538-7445.AM2017-3257

The effect of cigarette smoking on the oral and nasal microbiota

BACKGROUND

The goal of the study was to investigate whether cigarette smoking alters oral and nasal microbial diversity, composition, and structure. Twenty-three current smokers and 20 never smokers were recruited. From each subject, nine samples including supra and subgingiva plaque scrapes, saliva, swabs from five soft oral tissue sites, and one nasal swab from both the anterior nares were collected. 16S rRNA V3-V4 region was sequenced for microbial profiles.

RESULTS

We found that alpha diversity was lower in smokers than in nonsmokers in the buccal mucosa, but in other sample sites, microbial diversity and composition were not significantly different by smoking status. Microbial profiles differed significantly among eight oral sites.

CONCLUSIONS

This study investigates the effect of cigarette smoking on different sites of the oral cavity and shows a potential effect of cigarette smoking on the buccal mucosa microbiota. The marked heterogeneity of the oral microbial ecosystem that we found may contribute to the stability of the oral microbiota in most sites when facing environmental perturbations such as that caused by cigarette smoking.

Chlamydia caviae infection alters abundance but not composition of the guinea pig vaginal microbiota

In humans, the vaginal microbiota is thought to be the first line of defense again pathogens including Chlamydia trachomatis. The guinea pig has been extensively used as a model to study chlamydial infection because it shares anatomical and physiological similarities with humans, such as a squamous vaginal epithelium as well as some of the long-term outcomes caused by chlamydial infection. In this study, we aimed to evaluate the guinea pig-C. caviae model of genital infection as a surrogate for studying the role of the vaginal microbiota in the early steps of C. trachomatis infection in humans. We used culture-independent molecular methods to characterize the relative and absolute abundance of bacterial phylotypes in the guinea pig vaginal microbiota in animals non-infected, mock-infected or infected by C. caviae. We showed that the guinea pig and human vaginal microbiotas are of different bacterial composition and abundance. Chlamydia caviae infection had a profound effect on the absolute abundance of bacterial phylotypes but not on the composition of the guinea pig vaginal microbiota. Our findings compromise the validity of the guinea pig-C. caviae model to study the role of the vaginal microbiota during the early steps of sexually transmitted infection.

The vaginal microbiota of the guinea pig differs from that of humans and cannot prevent chlamydial infections efficiently.

Environmental surveillance for toxigenic Vibrio cholerae in surface waters of Haiti

Epidemic cholera was reported in Haiti in 2010, with no information available on the occurrence or geographic distribution of toxigenic Vibrio cholerae in Haitian waters. In a series of field visits conducted in Haiti between 2011 and 2013, water and plankton samples were collected at 19 sites. Vibrio cholerae was detected using culture, polymerase chain reaction, and direct viable count methods (DFA-DVC). Cholera toxin genes were detected by polymerase chain reaction in broth enrichments of samples collected in all visits except March 2012. Toxigenic V. cholerae was isolated from river water in 2011 and 2013. Whole genome sequencing revealed that these isolates were a match to the outbreak strain. The DFA-DVC tests were positive for V. cholerae O1 in plankton samples collected from multiple sites. Results of this survey show that toxigenic V. cholerae could be recovered from surface waters in Haiti more than 2 years after the onset of the epidemic.

Simultaneous transcriptional profiling of bacteria and their host cells

We developed an RNA-Seq-based method to simultaneously capture prokaryotic and eukaryotic expression profiles of cells infected with intracellular bacteria. As proof of principle, this method was applied to Chlamydia trachomatis-infected epithelial cell monolayers in vitro, successfully obtaining transcriptomes of both C. trachomatis and the host cells at 1 and 24 hours post-infection. Chlamydiae are obligate intracellular bacterial pathogens that cause a range of mammalian diseases. In humans chlamydiae are responsible for the most common sexually transmitted bacterial infections and trachoma (infectious blindness). Disease arises by adverse host inflammatory reactions that induce tissue damage & scarring. However, little is known about the mechanisms underlying these outcomes. Chlamydia are genetically intractable as replication outside of the host cell is not yet possible and there are no practical tools for routine genetic manipulation, making genome-scale approaches critical. The early timeframe of infection is poorly understood and the host transcriptional response to chlamydial infection is not well defined. Our simultaneous RNA-Seq method was applied to a simplified in vitro model of chlamydial infection. We discovered a possible chlamydial strategy for early iron acquisition, putative immune dampening effects of chlamydial infection on the host cell, and present a hypothesis for Chlamydia-induced fibrotic scarring through runaway positive feedback loops. In general, simultaneous RNA-Seq helps to reveal the complex interplay between invading bacterial pathogens and their host mammalian cells and is immediately applicable to any bacteria/host cell interaction.

NsrR targets in the Escherichia coli genome: new insights into DNA sequence requirements for binding and a role for NsrR in the regulation of motility

The Escherichia coli NsrR protein is a nitric oxide-sensitive repressor of transcription. The NsrR-binding site is predicted to comprise two copies of an 11 bp motif arranged as an inverted repeat with 1 bp spacing. By mutagenesis we confirmed that both 11 bp motifs are required for maximal NsrR repression of the ytfE promoter. We used chromatin immunoprecipitation and microarray analysis (ChIP-chip) to show that NsrR binds to 62 sites close to the 5' ends of genes. Analysis of the ChIP-chip data suggested that a single 11 bp motif (with the consensus sequence AANATGCATTT) can function as an NsrR-binding site in vivo. NsrR binds to sites in the promoter regions of the fliAZY, fliLMNOPQR and mqsR-ygiT transcription units, which encode proteins involved in motility and biofilm development. Reporter fusion assays confirmed that NsrR negatively regulates the fliA and fliL promoters. A mutation in the predicted 11 bp NsrR-binding site in the fliA promoter impaired repression by NsrR and prevented detectable binding in vivo. Assays on soft-agar confirmed that NsrR is a negative regulator of motility in E. coli K12 and in a uropathogenic strain; surface attachment assays revealed decreased levels of attached growth in the absence of NsrR.