| Uropathogenic Escherchia coli (UPEC) is the causative agent of urinary tract infections. Nitric oxide (NO) is a toxic water-soluble gas that is encountered by UPEC in the urinary tract. Therefore, UPEC likely requires mechanisms to detoxify NO in the host environment. Thus far, flavohemoglobin (Hmp), an NO denitrosylase, is the only demonstrated NO detoxification system in UPEC. Here we show that, in strain CFT073, the NADH-dependent NO reductase flavorubredoxin (FlRd) also plays a major role in NO scavenging. We generated a mutant that lacks all known and candidate NO detoxification pathways (Hmp, FlRd and the respiratory nitrite reductase, NrfA). When grown anaerobically, this mutant expresses an NO-inducible NO scavenging activity, pointing to the existence of a novel detoxification mechanism. Expression of this activity is inducible by both NO and nitrate, and the enzyme is membrane associated. The activity shows a complex pattern of regulation by NsrR, FNR, NarL and NarP. Genome wide transcriptional profiling of UPEC grown under anaerobic conditions in the presence of a source of NO highlights various aspects of the response of the pathogen to NO. Our data suggest that exposure to a source of NO causes a reprogramming of energy metabolism in UPEC, and may contribute to increased expression of virulence-associated genes. Thus, virulence determinants may be expressed by UPEC in response to a host-generated signal, and NO may act as a signal of a suitable host environment.;Inactivation of genes encoding essential proteins makes bacteria auxotrophic for compounds that are products of reactions catalyzed by these proteins. One such gene is lpd, encoding dihydrolipoamide dehydrogenase, deletion of which creates a requirement for acetate and succinate during aerobic growth of E. coli K-12 in glucose minimal media. In addition to lpd, CFT073 has an lpd homolog in its genome. We tried to identify the role, if any, of the lpd homolog. We also isolated suppressors of CFT073 lacking lpd and its homolog that did not require supplements for growth. Here, we describe our effort to identify these suppressor mutations and provide probable explanations for adaptations in a CFT073 lpd deletion strain that enable it to overcome the metabolic stress imposed by the lack of Lpd. |
