No abstract

SignificanceBacterial infection is still a global threat to human health. Gene expression profiling of pathogenic bacteria during infection may aid in a better understanding of the pathophysiological events. Here, we present a reporter-based technology to identify in vivo repressed (ivr) genes of Vibrio cholerae. Our data demonstrate that constitutive expression of ivr genes reduces colonization fitness, indicating a pivotal role of gene silencing. A comprehensive characterization of an H+/Cl− transporter revealed a defined spatiotemporal expression pattern, being induced in the stomach to facilitate survival under low pH, but silenced under alkaline pH in the lower gastrointestinal tract to avoid detrimental effects. Thus, previously understudied ivr genes could reveal new insights into host–pathogen interaction and alternative therapeutic strategies.

The facultative human pathogen Vibrio cholerae transits between the gastrointestinal tract of its host and aquatic reservoirs. V. cholerae adapts to different situations by the timely coordinated expression of genes during its life cycle. We recently identified a subclass of genes that are induced at late stages of infection. Initial characterization demonstrated that some of these genes facilitate the transition of V. cholerae from host to environmental conditions. Among these genes are uptake systems lacking detailed characterization or correct annotation. In this study, we comprehensively investigated the function of the VCA0682-to-VCA0687 gene cluster, which was previously identified as in vivo induced. The results presented here demonstrate that the operon encompassing open reading frames VCA0685 to VCA0687 encodes an ABC transport system for hexose-6-phosphates with K m values ranging from 0.275 to 1.273 M for glucose-6P and fructose-6P, respectively. Expression of the operon is induced by the presence of hexose-6P controlled by the transcriptional activator VCA0682, representing a UhpA homolog. Finally, we provide evidence that the operon is essential for the utilization of hexose-6P as a C and P source. Thereby, a physiological role can be assigned to hexose-6P uptake, which correlates with increased fitness of V. cholerae after a transition from the host into phosphate-limiting environments.T he life cycle of the facultative human pathogen Vibrio cholerae is marked by repetitive transitions between aquatic environments and the host gastrointestinal tract. Besides many other variable conditions, V. cholerae has to adjust to different qualities and quantities of nutrient sources. This variability is emphasized by the fact that utilization of nutrients under laboratory conditions, such as in full broth or a chemically defined minimal medium, represents no growth limitation for clinical V. cholerae isolates (1).In the open sea, bacteria such as V. cholerae face C, N, and P limitation and are restricted to limited nutrients on a picomolar or nanomolar scale, whereby substrates become available and accessible only in specific habitats (2). Therefore, marine bacteria are found close to organic particles ranging from micrometer-to millimeter-sized aggregates. These organic particles derive from different sources, such as lysed or dead phytoplankton, zooplankton, or fecal pellets. They deliver organic and inorganic substrates in concentrations that are up to 4 orders of magnitude greater than those found in particle-free open seawater (for a recent review, see reference 2). Therefore, many plants and animals in the ocean serve as microbial niches for V. cholerae (3-6). For example, copepods or other crustaceans contain or are covered with chitin, a ␤,1-4-linked polymer of 2-acetamido-2-deoxy-␤-D-glucopyranoside (GlcNAc) n and its deacetylated form, chitosan. These substrates are utilized by Vibrio sp. as C and N sources (7-9). In addition, biofilm formation on chitinous surfaces plays a crucial role in V. choler...