Examinando por Autor "Montt, Fernanda"

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    Participation of two sRNA RyhB homologs from the fish pathogen Yersinia ruckeri in bacterial physiology
    (Microbiological Research, Volume 242January 2021 Article number 126629, 2021) Acuña, Lillian G.; Barros, M. José; Montt, Fernanda; Peñaloza, Diego; Núñez, Paula; Valdés, Iván; Gil, Fernando; Fuentes, Juan A.; Calderón, Iván L.
    Small noncoding RNAs (sRNAs) are important regulators of gene expression and physiology in bacteria. RyhB is an iron-responsive sRNA well characterized in Escherichia coli and conserved in other Enterobacteriaceae. In this study, we identified and characterized two RyhB homologs (named RyhB-1 and RyhB-2) in the fish pathogen Yersinia ruckeri. We found that, as in other Enterobacteriaceae, both RyhB-1 and RyhB-2 are induced under iron starvation, repressed by the Fur regulator, and depend on Hfq for stability. Despite these similarities in expression, the mutant strains of Y. ruckeri lacking RyhB-1 (ΔryhB-1) or RyhB-2 (ΔryhB-2) exhibited differential phenotypes. In comparison with the wild type, the ΔryhB-1 strain showed a hypermotile phenotype, reduced biofilm formation, increased replication rate, faster growth, and increased ATP levels in bacterial cultures. By contrast, in salmon cell cultures, the ΔryhB-1 strain exhibited an increased survival. On the other hand, the ΔryhB-2 strain was non-motile and showed augmented biofilm formation as compared to the wild type. The expression of a subset of RyhB conserved targets, selected from different bacterial species, was analyzed by quantitative RT-PCR in wild type, ΔryhB-1, ΔryhB-2, and ΔryhB-1 ΔryhB-2 strains cultured in iron-depleted media. RyhB-1 negatively affected the expression of most analyzed genes (sodB, acnA, sdhC, bfr, fliF, among others), whose functions are related to metabolism and motility, involving iron-containing proteins. Among the genes analyzed, only sdhC and bfr appeared as targets for RyhB-2. Taken together, these results indicate that Y. ruckeri RyhB homologs participate in the modulation of the bacterial physiology with non-redundant roles. © 2020 Elsevier GmbH
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    The RNA Chaperone Hfq Participates in Persistence to Multiple Antibiotics in the Fish Pathogen Yersinia ruckeri
    (MDPI AG, 2021-06) Calderón, Iván; Barros, María José; Montt, Fernanda; Gil, Fernando; Fuentes, Juan; Acuña, Lillian
    Yersinia ruckeri causes outbreaks of enteric redmouth disease in salmon aquaculture all over the world. The transient antibiotic tolerance exhibited by bacterial persisters is commonly thought to be responsible for outbreaks; however, the molecular factors underlying this behavior have not been explored in Y. ruckeri. In this study, we investigated the participation of the RNA chaperone Hfq from Y. ruckeri in antibiotic persistence. Cultures of the hfq-knockout mutant (∆hfq) exhibited faster replication, increased ATP levels and a more reductive environment than the wild type. The growth curves of bacteria exposed to sublethal concentrations of ampicillin, oxolinic acid, ciprofloxacin and polymyxin B revealed a greater susceptibility for the ∆hfq strain. The time-kill curves of bacteria treated with the antibiotics mentioned above and florfenicol, using inoculums from exponential, stationary and biofilm cultures, demonstrated that the ∆hfq strain has significant defects in persister cells production. To shed more light on the role of Hfq in antibiotic persistence, we analyzed its dependence on the (p)ppGpp synthetase RelA by determining the persister cells production in the absence of the relA gene. The ∆relA and ∆relA∆hfq strains displayed similar defects in persister cells formation, but higher than ∆hfq strain. Similarly, stationary cultures of the ∆relA and ∆relA∆hfq strains exhibited comparable levels of ATP but higher than that of the ∆hfq strain, indicating that relA is epistatic over hfq. Taken together, our findings provide valuable information on antibiotic persistence in Y. ruckeri, shedding light on the participation of Hfq in the persistence phenomenon. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.