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The spaceflight environment is relevant to conditions encountered by pathogens during the course of infection and induces novel changes in microbial pathogenesis not observed using conventional methods. It is unclear how microbial cells sense spaceflight-associated changes to their growth environment and orchestrate corresponding changes in molecular and physiological phenotypes relevant to the infection process. Here we report that spaceflight-induced increases in Salmonella virulence are regulated by media ion composition, and that phosphate ion is sufficient to alter related pathogenesis responses in a spaceflight analogue model. Using whole genome microarray and proteomic analyses from two independent Space Shuttle missions, we identified evolutionarily conserved molecular pathways in Salmonella that respond to spaceflight under all media compositions tested. Identification of conserved regulatory paradigms opens new avenues to control microbial responses during the infection process and holds promise to provide an improved understanding of human health and disease on Earth.

AlgR controls numerous virulence factors in Pseudomonas aeruginosa, including alginate, hydrogen cyanide production, and type 1V pilus-mediated twitching motility. In this study, the role of AlgR in biofiims was examined in continuous-flow and static biofilm assays. Strain PSL317 ([DELTA]algR) produced one-third the biofilm biomass of wild-type strain PAP1. Complementation with algR, but notfimTU-pilVWXY1Y2E, restored PSL317 to the wild-type biofilm phenotype. Comparisons of the transcriptional profiles of biofilm-grown PAP1 and PSL317 revealed that a number of quorum-sensing genes were upregulated in the algR deletion strain. Measurement of rhlA::lacZ and rhlI::lacZ promoter fusions confirmed the transcriptional profiling data when PSL317 was grown as a hiofiim, but not planktonically. Increased amounts of rhamnolipids and N-butyryl homoserine iactone were detected in the biofilm effluent but not the planktonic superuatants of the algR mutant. Additionally, AlgR specifically bound to the rhlA and rhlI promoters in mobility shift assays. Moreover, PAP1 containing a chromosomal mutated AlgR binding site in its rhlI promoter formed biofilms and produced increased amounts of rhamnolipids similarly to the algR deletion strain. These observations indicate that AlgR specifically represses the Rhl quorum-sensing system during biofilm growth and that such repression is necessary for normal biofilm development. These data also suggest that AlgR may control transcription in a contact-dependent or biofilm-specific manner.

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic lung infections in cystic fibrosis (CF) patients. One characteristic of P. aeruginosa CF isolates is the overproduction of the exopolysaccharide alginate, controlled by AlgR. Transcriptional profiling analyses comparing mucoid P. aeruginosa strains to their isogenic algR deletion strains showed that the transcription of cyanide-synthesizing genes (hcnAB) was ~3-fold lower in the algR mutants. S1 nuclease protection assays corroborated these findings, indicating that AlgR activates hcnA transcription in mucoid P. aeruginosa. Quantification of hydrogen cyanide (HCN) production from laboratory isolates revealed that mucoid laboratory strains made sevenfold more HCN than their nonmucoid parental strains. In addition, comparison of laboratory and clinically derived nonmucoid strains revealed that HCN was fivefold higher in the nonmucoid CF isolates. Moreover, the average amount of cyanide produced by mucoid clinical isolates was 4.7 [+ or -] 0.85 [micro]mol of HCN/mg of protein versus 2.4 [+ or -] 0.40 [micro]mol of HCN/mg of protein for nonmucoid strains from a survey conducted with 41 P. aeruginosa CF isolates from 24 patients. Our data indicate that (i) mucoid P. aeruginosa regardless of their origin (laboratory or clinically derived) produce more cyanide than their nonmucoid counterparts, (ii) AlgR regulates HCN production in P. aeruginosa, and (iii) P. aeruginosa CF isolates are more hypercyanogenic than nonmucoid laboratory strains. Taken together, cyanide production may be a relevant virulence factor in CF lung disease, the production of which is regulated, in part, by AlgR.

An estimated one-third of the world's population is latently infected with Mycobacterium tuberculosis, the etiologic agent of tuberculosis. Here, we demonstrate that, unlike wild-type M. tuberculosis, a strain of M. tuberculosis disrupted in the mce 1 operon was unable to enter a stable persistent state of infection in mouse lungs. Instead, the mutant continued to replicate and killed the mice more rapidly than did the wild-type strain. Histological examination of mouse lungs infected with the mutant strain revealed diffusely organized granulomas with aberrant inflammatory cell migration. Murine macrophages infected ex vivo with the mutant strain were reduced in their ability to produce tumor necrosis factor [alpha], IL-6, monocyte chemoattractant protein 1, and nitric oxide (NO), but not IL-4. The mce 1 mutant strain complemented with the mce 1 genes stimulated tumor necrosis factor [alpha] and NO production by murine macrophages at levels stimulated by the wild-type strain. These observations indicate that the mce 1 operon mutant is unable to stimulate T helper 1-type immunity in mice. The hypervirulence of the mutant strain may have resulted from its inability to stimulate a proinflammatory response that would otherwise induce organized granuloma formation and control the infection without killing the organism. The mce 1 operon of M. tuberculosis may be involved in modulating the host inflammatory response in such a way that the bacterium can enter a persistent state without being eliminated or causing disease in the host.

Abstract Background Lyme neuroborreliosis (LNB) may present as meningitis, cranial neuropathy, acute radiculoneuropathy or, rarely, as encephalomyelitis. We hypothesized that glia, upon exposure to Borrelia burgdorferi, the Lyme disease agent, produce inflammatory mediators that promote the acute cellular infiltration of early LNB. This inflammatory context could potentiate glial and neuronal apoptosis. Methods We inoculated live B. burgdorferi into the cisterna magna of rhesus macaques and examined the inflammatory changes induced in the central nervous system (CNS), and dorsal root nerves and ganglia (DRG). Results ELISA of the cerebrospinal fluid (CSF) showed elevated IL-6, IL-8, CCL2, and CXCL13 as early as one week post-inoculation, accompanied by primarily lymphocytic and monocytic pleocytosis. In contrast, onset of the acquired immune response, evidenced by anti-B. burgdorferi C6 serum antibodies, was first detectable after 3 weeks post-inoculation. CSF cell pellets and CNS tissues were culture-positive for B. burgdorferi. Histopathology revealed signs of acute LNB: severe multifocal leptomeningitis, radiculitis, and DRG inflammatory lesions. Immunofluorescence staining and confocal microscopy detected B. burgdorferi antigen in the CNS and DRG. IL-6 was observed in astrocytes and neurons in the spinal cord, and in neurons in the DRG of infected animals. CCL2 and CXCL13 were found in microglia as well as in endothelial cells, macrophages and T cells. Importantly, the DRG of infected animals showed significant satellite cell and neuronal apoptosis. Conclusion Our results support the notion that innate responses of glia to B. burgdorferi initiate/mediate the inflammation seen in acute LNB, and show that neuronal apoptosis occurs in this context.