Examinando por Autor "Saavedra, C.P."

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    Comparative Genomics Analysis of a New Exiguobacterium Strain from Salar de Huasco Reveals a Repertoire of Stress-Related Genes and Arsenic Resistance
    (FRONTIERS MEDIA, 2017-03) Castro-Severyn, J.; Remonsellez, F.; Valenzuela, S.L.; Salinas, C.; Fortt, J.; Aguilar, P.; Pardo-Esté, C.; Dorador, C.; Quatrini, R.; Molina, F.; Aguayo, D.; Castro-Nallar, E.; Saavedra, C.P.
    The Atacama Desert hosts diverse ecosystems including salt flats and shallow Andean lakes. Several heavy metals are found in the Atacama Desert, and microorganisms growing in this environment show varying levels of resistance/tolerance to copper, tellurium, and arsenic, among others. Herein, we report the genome sequence and comparative genomic analysis of a new Exiguobacterium strain, sp. SH31, isolated from an altiplanic shallow athalassohaline lake. Exiguobacterium sp. SH31 belongs to the phylogenetic Group II and its closest relative is Exiguobacterium sp. S17, isolated from the Argentinian Altiplano (95% average nucleotide identity). Strain SH31 encodes a wide repertoire of proteins required for cadmium, copper, mercury, tellurium, chromium, and arsenic resistance. Of the 34 Exiguobacterium genomes that were inspected, only isolates SH31 and S17 encode the arsenic efflux pump Acr3. Strain SH31 was able to grow in up to 10 mM arsenite and 100 mM arsenate, indicating that it is arsenic resistant. Further, expression of the ars operon and acr3 was strongly induced in response to both toxics, suggesting that the arsenic efflux pump Acr3 mediates arsenic resistance in Exiguobacterium sp. SH31.
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    Genomic Variation and Arsenic Tolerance Emerged as Niche Specific Adaptations by Different Exiguobacterium Strains Isolated From the Extreme Salar de Huasco Environment in Chilean – Altiplano
    (Frontiers Media S.A., 2020-07) Castro-Severyn, J.; Pardo-Esté, C.; Mendez, K.N.; Morales, N.; Marquez, S.L.; Molina, F.; Remonsellez, F.; Castro-Nallar, E.; Saavedra, C.P.
    Polyextremophilic bacteria can thrive in environments with multiple stressors such as the Salar de Huasco (SH). Microbial communities in SH are exposed to low atmospheric pressure, high UV radiation, wide temperature ranges, salinity gradient and the presence of toxic compounds such as arsenic (As). In this work we focus on arsenic stress as one of the main adverse factors in SH and bacteria that belong to the Exiguobacterium genus due to their plasticity and ubiquity. Therefore, our aim was to shed light on the effect of niche conditions pressure (particularly arsenic), on the adaptation and divergence (at genotypic and phenotypic levels) of Exiguobacterium strains from five different SH sites. Also, to capture greater diversity in this genus, we use as outgroup five As(III) sensitive strains isolated from Easter Island (Chile) and The Great Salt Lake (United States). For this, samples were obtained from five different SH sites under an arsenic gradient (9 to 321 mg/kg: sediment) and isolated and sequenced the genomes of 14 Exiguobacterium strains, which had different arsenic tolerance levels. Then, we used comparative genomic analysis to assess the genomic divergence of these strains and their association with phenotypic differences such as arsenic tolerance levels and the ability to resist poly-stress. Phylogenetic analysis showed that SH strains share a common ancestor. Consequently, populations were separated and structured in different SH microenvironments, giving rise to multiple coexisting lineages. Hence, this genotypic variability is also evidenced by the COG (Clusters of Orthologous Groups) composition and the size of their accessory genomes. Interestingly, these observations correlate with physiological traits such as growth patterns, gene expression, and enzyme activity related to arsenic response and/or tolerance. Therefore, Exiguobacterium strains from SH are adapted to physiologically overcome the contrasting environmental conditions, like the arsenic present in their habitat. © Copyright © 2020 Castro-Severyn, Pardo-Esté, Mendez, Morales, Marquez, Molina, Remonsellez, Castro-Nallar and Saavedra.
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    SmvA, and not AcrB, is the major efflux pump for acriflavine and related compounds in Salmonella enterica serovar Typhimurium
    (Oxford University Press, 2008-12) Villagra, N.A.; Hidalgo, A.A.; Santiviago, C.A.; Saavedra, C.P.; Mora, G.C.
    Objectives: The aim was to study the role played by SmvA pump in the efflux of quaternary ammonium compounds (QACs) in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium). Methods: Mutants in the smvA, acrB and tolC genes were constructed by the red swap method. P22 was used to transduce tolC to acrB and smvA mutant strains. The susceptibility of these strains to acriflavine and a variety of QACs was determined by MIC assays. Results: In comparison with the Salmonella Typhimurium wild-type strain, the smvA mutant was more susceptible to QACs than the acrB mutant strain. A tolC single mutant was more susceptible than an acrB mutant to QACs, acriflavine, ethidium bromide, malachite green and pyronin B. The tolC - acrB double mutant was as susceptible as the single tolC mutant to QACs. Additionally, the smvA mutant strain was more susceptible to acriflavine than the acrB mutant (MICs = 31.3 versus 125 mg/L, i.e. 4-fold). Finally, the tolC - smvA double mutant (3.9 mg/L) was approximately 10 times more susceptible to acriflavine than either smvA (31.3 mg/L) or tolC (31.3 mg/L) single mutants. Conclusions: It is the SmvA efflux pump, and not AcrB, that plays the major role in the efflux of acriflavine and other QACs from Salmonella Typhimurium. This apparently conflicting report is due to the fact that in Escherichia coli the smvA gene does not exist. Our results suggest that tolC and smvA genes encode components of two different efflux systems with overlapping specificities that work in parallel to export acriflavine and other QACs. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
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    The ArcAB two-component regulatory system promotes resistance to reactive oxygen species and systemic infection by Salmonella Typhimurium
    (Public Library of Science, 2018-09) Pardo-Esté, C.; Hidalgo, A.A.; Aguirre, C.; Inostroza, A.; Briones, A.C.; Cabezas, C.E.; Castro-Severyn, J.; Fuentes, J.A.; Opazo, C.M.; Riedel, C.A.; Otero, C.; Pacheco, R.; Valvano, M.A.; Saavedra, C.P.
    Salmonella enterica Serovar Typhimurium (S. Typhimurium) is an intracellular bacterium that overcomes host immune system barriers for successful infection. The bacterium colonizes the proximal small intestine, penetrates the epithelial layer, and is engulfed by macrophages and neutrophils. Intracellularly, S. Typhimurium encounters highly toxic reactive oxygen species including hydrogen peroxide and hypochlorous acid. The molecular mechanisms of Salmonella resistance to intracellular oxidative stress is not completely understood. The ArcAB two-component system is a global regulatory system that responds to oxygen. In this work, we show that the ArcA response regulator participates in Salmonella adaptation to changing oxygen levels and is also involved in promoting intracellular survival in macrophages and neutrophils, enabling S. Typhimurium to successfully establish a systemic infection. © 2018 Pardo-Esté et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.