Pneumococcal Gene Complex Involved in Resistance to Extracellular Oxidative Stress

Streptococcus pneumoniae is a Gram-positive bacterium which is a member of the normal human nasopharyngeal flora but can also cause serious disease such as pneumonia, bacteremia, and meningitis. Throughout its life cycle, S. pneumoniae is exposed to significant oxidative stress derived from endogenously produced hydrogen peroxide (H2O2) and from the host through the oxidative burst. How S. pneumoniae, an aerotolerant anaerobic bacterium that lacks catalase, protects itself against hydrogen peroxide stress is still unclear. Bioinformatic analysis of its genome identified a hypothetical open reading frame belonging to the thiol-specific antioxidant (TlpA/TSA) family, located in an operon consisting of three open reading frames. For all four strains tested, deletion of the gene resulted in an approximately 10-fold reduction in survival when strains were exposed to external peroxide stress. However, no role for this gene in survival of internal superoxide stress was observed. Mutagenesis and complementation analysis demonstrated that all three genes are necessary and sufficient for protection against oxidative stress. Interestingly, in a competitive index mouse pneumonia model, deletion of the operon had no impact shortly after infection but was detrimental during the later stages of disease. Thus, we have identified a gene complex involved in the protection of S. pneumoniae against external oxidative stress, which plays an important role during invasive disease.

Alternative Oxidase Mediates Pathogen Resistance in Paracoccidioides brasiliensis Infection

Thermally dimorphic pathogenic fungi are responsible for potentially life-threatening diseases of immunocompetent and immunocompromised individuals. These microorganisms grow as conidia-producing mycelia in the environment, which when inhaled by the host convert to the pathogenic yeast form at 37°C. During adaptation and growth, fungi interact with host immune cells and must cope with defense mechanisms such as imposed-oxidative stress (e.g., reactive oxygen species; ROS). Alternative oxidase (AOX) is an enzyme recently implicated in the reduction of ROS production by the mitochondria when triggered by external stimuli, such as temperature and ROS. During this work we have evaluated the relevance of AOX during infection with Paracoccidioides brasiliensis, the etiological agent of one of the most prevalent mycoses in Latin America, paracoccidioidomycosis. We show that PbAOX gene expression is stimulated after interaction with alveolar macrophages or in the presence of H2O2 and is essential for survival against fungicidal activity of both the immune cells and the ROS compound. Moreover, decreasing PbAOX gene expression in P. brasiliensis led to increased survival of infected mice. Altogether, our data supports a relevant role for AOX in the virulence of P. brasiliensis

Function and Regulation of Vibrio campbellii Proteorhodopsin: Acquired Phototrophy in a Classical Organoheterotroph

Proteorhodopsins (PRs) are retinal-binding photoproteins that mediate light-driven proton translocation across prokaryotic cell membranes. Despite their abundance, wide distribution and contribution to the bioenergy budget of the marine photic zone, an understanding of PR function and physiological significance in situ has been hampered as the vast majority of PRs studied to date are from unculturable bacteria or culturable species that lack the tools for genetic manipulation. In this study, we describe the presence and function of a horizontally acquired PR and retinal biosynthesis gene cluster in the culturable and genetically tractable bioluminescent marine bacterium Vibrio campbellii. Pigmentation analysis, absorption spectroscopy and photoinduction assays using a heterologous over-expression system established the V. campbellii PR as a functional green light absorbing proton pump. In situ analyses comparing PR expression and function in wild type (WT) V. campbellii with an isogenic ΔpR deletion mutant revealed a marked absence of PR membrane localization, pigmentation and light-induced proton pumping in the ΔpR mutant. Comparative photoinduction assays demonstrated the distinct upregulation of pR expression in the presence of light and PR-mediated photophosphorylation in WT cells that resulted in the enhancement of cellular survival during respiratory stress. In addition, we demonstrate that the master regulator of adaptive stress response and stationary phase, RpoS1, positively regulates pR expression and PR holoprotein pigmentation. Taken together, the results demonstrate facultative phototrophy in a classical marine organoheterotrophic Vibrio species and provide a salient example of how this organism has exploited lateral gene transfer to further its adaptation to the photic zone

The anti-sigma factor RsrA responds to oxidative stress by reburying its hydrophobic core

Redox-regulated effector systems that counteract oxidative stress are essential for all forms of life. Here we uncover a new paradigm for sensing oxidative stress centred on the hydrophobic core of a sensor protein. RsrA is an archetypal zinc-binding anti-sigma factor that responds to disulfide stress in the cytoplasm of Actinobacteria. We show that RsrA utilizes its hydrophobic core to bind the sigma factor σ R preventing its association with RNA polymerase, and that zinc plays a central role in maintaining this high-affinity complex. Oxidation of RsrA is limited by the rate of zinc release, which weakens the RsrA-σ R complex by accelerating its dissociation. The subsequent trigger disulfide, formed between specific combinations of RsrA's three zinc-binding cysteines, precipitates structural collapse to a compact state where all σ R-binding residues are sequestered back into its hydrophobic core, releasing σ R to activate transcription of anti-oxidant genes

Carotenoids Play a Positive Role in the Degradation of Heterocycles by Sphingobium yanoikuyae

BACKGROUND: Microbial oxidative degradation is a potential way of removing pollutants such as heterocycles from the environment. During this process, reactive oxygen species or other oxidants are inevitably produced, and may cause damage to DNA, proteins, and membranes, thereby decreasing the degradation rate. Carotenoids can serve as membrane-integrated antioxidants, protecting cells from oxidative stress. FINDINGS: Several genes involved in the carotenoid biosynthetic pathway were cloned and characterized from a carbazole-degrading bacterium Sphingobium yanoikuyae XLDN2-5. In addition, a yellow-pigmented carotenoid synthesized by strain XLDN2-5 was identified as zeaxanthin that was synthesized from β-carotene through β-cryptoxanthin. The amounts of zeaxanthin and hydrogen peroxide produced were significantly and simultaneously enhanced during the biodegradation of heterocycles (carbazole < carbazole + benzothiophene < carbazole + dibenzothiophene). These higher production levels were consistent with the transcriptional increase of the gene encoding phytoene desaturase, one of the key enzymes for carotenoid biosynthesis. CONCLUSIONS/SIGNIFICANCE: Sphingobium yanoikuyae XLDN2-5 can enhance the synthesis of zeaxanthin, one of the carotenoids, which may modulate membrane fluidity and defense against intracellular oxidative stress. To our knowledge, this is the first report on the positive role of carotenoids in the biodegradation of heterocycles, while elucidating the carotenoid biosynthetic pathway in the Sphingobium genus

Regulation of Plant Developmental Processes by a Novel Splicing Factor

Serine/arginine-rich (SR) proteins play important roles in constitutive and alternative splicing and other aspects of mRNA metabolism. We have previously isolated a unique plant SR protein (SR45) with atypical domain organization. However, the biological and molecular functions of this novel SR protein are not known. Here, we report biological and molecular functions of this protein. Using an in vitro splicing complementation assay, we showed that SR45 functions as an essential splicing factor. Furthermore, the alternative splicing pattern of transcripts of several other SR genes was altered in a mutant, sr45-1, suggesting that the observed phenotypic abnormalities in sr45-1 are likely due to altered levels of SR protein isoforms, which in turn modulate splicing of other pre-mRNAs. sr45-1 exhibited developmental abnormalities, including delayed flowering, narrow leaves and altered number of petals and stamens. The late flowering phenotype was observed under both long days and short days and was rescued by vernalization. FLC, a key flowering repressor, is up-regulated in sr45-1 demonstrating that SR45 influences the autonomous flowering pathway. Changes in the alternative splicing of SR genes and the phenotypic defects in the mutant were rescued by SR45 cDNA, further confirming that the observed defects in the mutant are due to the lack of SR45. These results indicate that SR45 is a novel plant-specific splicing factor that plays a crucial role in regulating developmental processes

Genomic analysis of Acinetobacter baumannii prophages reveals remarkable diversity and suggests significant impact on bacterial virulence and fitness

[Abstract] Bacterial genomics has revealed substantial amounts of prophage DNA in bacterial genomes. This integrated viral DNA has been shown to play important roles in the evolution of bacterial pathogenicity. Acinetobacter baumannii has shown a fast progression as a nosocomial multi-resistant pathogen in recent years, and is now considered one of the most dangerous microorganisms in hospital environments. The role of prophages in the evolution of A. baumannii pathogenicity has not yet been explored. In this context, we aimed at evaluating the impact of prophages on A. baumannii genomic diversity and pathogenicity. [...]info:eu-repo/semantics/publishedVersio