RESUMO
Bacteroides fragilis, an opportunistic pathogen and commensal bacterium in the gut, is one the most aerotolerant species among strict anaerobes. However, the mechanisms that control gene regulation in response to oxidative stress are not completely understood. In this study, we show that the MarR type regulator, BmoR, regulates the expression of genes involved in the homeostasis of intracellular redox state. Transcriptome analysis showed that absence of BmoR leads to altered expression in total of 167 genes. Sixteen of these genes had a 2-fold or greater change in their expression. Most of these genes are related to LPS biosynthesis and carbohydrates metabolism, but there was a significant increase in the expression of genes related to the redox balance inside the cell. A pyridine nucleotide-disulfide oxidoreductase located directly upstream of bmoR was shown to be repressed by direct binding of BmoR to the promoter region. The expression of two other genes, coding for a thiosulphate:quinone-oxidoreductase and a thioredoxin, are indirectly affected by bmoR mutation during oxygen exposure. Phenotypic assays showed that BmoR is important to maintain the thiol/disulfide balance in the cell, confirming its relevance to B. fragilis response to oxidative stress.
Assuntos
Bacteroides fragilis , Dissulfetos/metabolismo , Deleção de Genes , Regulação Bacteriana da Expressão Gênica , Estresse Oxidativo/genética , Proteínas Repressoras , Compostos de Sulfidrila/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bacteroides fragilis/genética , Bacteroides fragilis/metabolismo , Perfilação da Expressão Gênica , Oxirredução , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismoRESUMO
Bacteroides fragilis is a minor component of the intestinal microbiota and the most frequently isolated from intra-abdominal infections and bacteremia. Previously, our group has shown that molecules involved in laminin-1 (LMN-1) recognition were present in outer membrane protein extracts of B. fragilis MC2 strain. One of these proteins was identified and showed 98% similarity to a putative B. fragilis plasminogen-binding protein precursor, deposited in the public database. Thus, the objective of this work was to overexpress and further characterize this novel adhesin. The ability of B. fragilis MC2 strain and purified protein to convert plasminogen into plasmin was tested. Our results showed that B. fragilis strain MC2 strain adhered to both LMN-1 and plasminogen and this adhesion was inhibited by either LMN-1 or plasminogen. Regarding the plasminogen activation activity, both the whole bacterial cell and the purified protein converted plasminogen into plasmin similar to streptokinase used as a positive control. Bacterial receptors that recognize plasminogen bind to it and enhance its activation, transforming a nonproteolytic bacterium into a proteolytic one. We present in vitro evidence for a pathogenic function of the plasminogen receptor in promoting adherence to laminin and also the formation of plasmin by B. fragilis.