Anaerobic Regulation of Shigella flexneri Virulence: ArcA Regulates fur and Iron Acquisition Genes

The University of Texas at Austin, Section .
Journal of Bacteriology (Impact Factor: 2.81). 11/2007; 189(19):6957-67. DOI: 10.1128/JB.00621-07
Source: PubMed


Invasion and plaque formation in epithelial monolayers are routinely used to assess the virulence of Shigella flexneri, a causative agent of dysentery. A modified plaque assay was developed to identify factors contributing to the virulence of S. flexneri under the anaerobic conditions present in the colon. This assay demonstrated the importance of the ferrous iron transport system Feo, as well as the global transcription factors Fur, ArcA, and Fnr, for Shigella plaque formation in anoxic environments. Transcriptional analyses of S. flexneri iron transport genes indicated that anaerobic conditions activated feoABC while repressing genes encoding two other iron transport systems, the ABC transporter Sit and the Iuc/Iut aerobactin siderophore synthesis and transport system. The anaerobic transcription factors ArcA and Fnr activated expression of feoABC, while ArcA repressed iucABCD iutA. Transcription of fur, encoding the iron-responsive transcriptional repressor of bacterial iron acquisition, was also repressed anaerobically in an ArcA-dependent manner.

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Available from: Shelley M Payne, Jul 16, 2014
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    • "Genome sequences are available for at least one representative species for more than 20 different genera of enterobacteria ( To our knowledge changes in global gene expression under oxygen limitation have been documented for only five of them (E. coli K-12 MG1655 [19]: Salmonella enterica serovar Typhimurium [20]:, Shigella [21]:, Dickeya dadantii 3937 and Pectobacterium atrosepticum SCRI1043 [22]:). Thus the range of metabolic responses to O2 and the mechanisms that govern them are still incompletely understood for this family of facultative anaerobes. "
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    ABSTRACT: The yersiniae (Enterobacteriaceae) occupy a variety of niches, including some in human and flea hosts. Metabolic adaptations of the yersiniae, which contribute to their success in these specialized environments, remain largely unknown. We report results of an investigation of the transcriptome under aerobic and anaerobic conditions for Y. intermedia, a non-pathogenic member of the genus that has been used as a research surrogate for Y. pestis. Y. intermedia shares characteristics of pathogenic yersiniae, but is not known to cause disease in humans. Oxygen restriction is an important environmental stimulus experienced by many bacteria during their life-cycles and greatly influences their survival in specific environments. How oxygen availability affects physiology in the yersiniae is of importance in their life cycles but has not been extensively characterized. Tiled oligonucleotide arrays based on a draft genome sequence of Y. intermedia were used in transcript profiling experiments to identify genes that change expression in response to oxygen availability during growth in minimal media with glucose. The expression of more than 400 genes, constituting about 10% of the genome, was significantly altered due to oxygen-limitation in early log phase under these conditions. Broad functional categorization indicated that, in addition to genes involved in central metabolism, genes involved in adaptation to stress and genes likely involved with host interactions were affected by oxygen-availability. Notable among these, were genes encoding functions for motility, chemotaxis and biosynthesis of cobalamin, which were up-regulated and those for iron/heme utilization, methionine metabolism and urease, which were down-regulated. This is the first transcriptome analysis of a non-pathogenic Yersinia spp. and one of few elucidating the global response to oxygen limitation for any of the yersiniae. Thus this study lays the foundation for further experimental characterization of oxygen-responsive genes and pathways in this ecologically diverse genus.
    PLoS ONE 10/2013; 8(10):e76567. DOI:10.1371/journal.pone.0076567 · 3.23 Impact Factor
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    • "In E. coli ArcB senses oxygen availability via the quinone redox status (Q/QH2 and menaquinone/menaquinol) and tunes aerobic and anaerobic respiratory metabolism through its phosphorylation of ArcA [42]. ArcA functions as a transcriptional regulator of operons involved in respiratory and fermentative metabolism; ArcA plays a role in virulence in a wide variety of pathogenic bacteria in animals and humans including the enteric pathogens Vibrio cholerae[43] and Shigella flexneri[44]. Mutations in genes encoding respiratory chain complexes also identify components in pathogens essential for virulence. Rat lung fibroblasts exposed to Shigella flexneri with mutations in the cytochrome bd oxidase had lower numbers of plaques than fibroblasts infected with the wild-type parental strain [45]. "
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    ABSTRACT: Background Studies with the nematode model Caenorhabditis elegans have identified conserved biochemical pathways that act to modulate life span. Life span can also be influenced by the composition of the intestinal microbiome, and C. elegans life span can be dramatically influenced by its diet of Escherichia coli. Although C. elegans is typically fed the standard OP50 strain of E. coli, nematodes fed E. coli strains rendered respiratory deficient, either due to a lack coenzyme Q or the absence of ATP synthase, show significant life span extension. Here we explore the mechanisms accounting for the enhanced nematode life span in response to these diets. Results The intestinal load of E. coli was monitored by determination of worm-associated colony forming units (cfu/worm or coliform counts) as a function of age. The presence of GFP-expressing E. coli in the worm intestine was also monitored by fluorescence microscopy. Worms fed the standard OP50 E. coli strain have high cfu and GFP-labeled bacteria in their guts at the L4 larval stage, and show saturated coliform counts by day five of adulthood. In contrast, nematodes fed diets of respiratory deficient E. coli lacking coenzyme Q lived significantly longer and failed to accumulate bacteria within the lumen at early ages. Animals fed bacteria deficient in complex V showed intermediate coliform numbers and were not quite as long-lived. The results indicate that respiratory deficient Q-less E. coli are effectively degraded in the early adult worm, either at the pharynx or within the intestine, and do not accumulate in the intestinal tract until day ten of adulthood. Conclusions The findings of this study suggest that the nematodes fed the respiratory deficient E. coli diet live longer because the delay in bacterial colonization of the gut subjects the worms to less stress compared to worms fed the OP50 E. coli diet. This work suggests that bacterial respiration can act as a virulence factor, influencing the ability of bacteria to colonize and subsequently harm the animal host. Respiratory deficient bacteria may pose a useful model for probing probiotic relationships within the gut microbiome in higher organisms.
    BMC Microbiology 12/2012; 12(1):300. DOI:10.1186/1471-2180-12-300 · 2.73 Impact Factor
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    • "Typically, Fur acts as a transcriptional repressor by binding to regulatory Fur box sequences in the promoters of iron-regulated genes under iron-repleted conditions. This protein also acts as a global regulator controlling the expression of iron acquisition and storage genes as well as the expression of genes involved in the oxidative stress response, virulence genes and small, iron-repressible regulatory RNAs [42], [43], [44]. The activation of the gene azo0644, encoding the Fur protein, in conditioned supernatant would repress the expression of Fur-dependent genes in Azoarcus sp. "
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    ABSTRACT: Bacterial communication is involved in regulation of cellular mechanisms such as metabolic processes, microbe-host interactions or biofilm formation. In the nitrogen-fixing model endophyte of grasses Azoarcus sp. strain BH72, known cell-cell signaling systems have not been identified; however, the pilA gene encoding the structural protein of type IV pili that are essential for plant colonization appears to be regulated in a population density-dependent manner. Our data suggest that pilAB expression is affected by population density, independent of autoinducers typical for gram-negative bacteria, likely depending on unknown secreted molecule(s) that can be produced by different bacterial species. We used transcriptomic and proteomic approaches to identify target genes and proteins differentially regulated in conditioned supernatants in comparison to standard growth conditions. Around 8% of the 3992 protein-coding genes of Azoarcus sp. and 18% of the detected proteins were differentially regulated. Regulatory proteins and transcription factors among the regulated proteins indicated a complex hierarchy. Differentially regulated genes and proteins were involved in processes such as type IV pili formation and regulation, metal and nutrient transport, energy metabolism, and unknown functions mediated by hypothetical proteins. Four of the newly discovered target genes were further analyzed and in general they showed regulation patterns similar to pilAB. The expression of one of them was shown to be induced in plant roots. This study is the first global approach to initiate characterization of cell density-dependent gene regulation mediated by soluble molecule(s) in the model endophyte Azoarcus sp. strain BH72. Our data suggest that the putative signaling molecule(s) are also produced by other Proteobacteria and might thus be used for interspecies communication. This study provides the foundation for the development of robust reporter systems for Azoarcus sp. to analyze mechanisms and molecules involved in the population-dependent gene expression in this endophyte in future.
    PLoS ONE 01/2012; 7(1):e30421. DOI:10.1371/journal.pone.0030421 · 3.23 Impact Factor
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