RESUMO
Alternative sigma (σ) factors, proteins that recruit RNA polymerase core enzyme to target promoters, are one mechanism by which bacteria transcriptionally regulate groups of genes in response to environmental stimuli. A class of σ(70) proteins, termed extracytoplasmic function (ECF) σ factors, are involved in cellular processes such as bacterial stress responses and virulence. Here, we describe an ECF16 σ factor, EcfS (Blr4928) from the gram-negative soil bacterium Bradyrhizobium japonicum USDA110, that plays a critical role in the establishment of a functional symbiosis with soybean. Nonpolar insertional mutants of ecfS form immature nodules that do not fix nitrogen, a defect that can be successfully complemented by expression of ecfS. Overexpression of the cocistronic gene, tmrS (blr4929), phenocopies the ecfS mutant in planta and, therefore, we propose that TmrS is a negative regulator of EcfS, a determination consistent with the prediction that it encodes an anti-σ factor. Microarray analysis of the ecfS mutant and tmrS overexpressor was used to identify 40 transcripts misregulated in both strains. These transcripts primarily encode proteins of unknown and transport-related functions and may provide insights into the symbiotic defect in these strains.
Assuntos
Bradyrhizobium/metabolismo , Regulação Bacteriana da Expressão Gênica/genética , Glycine max/microbiologia , Fator sigma/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bradyrhizobium/genética , Bradyrhizobium/fisiologia , DNA Complementar/genética , Expressão Gênica/genética , Perfilação da Expressão Gênica , Genes Bacterianos/genética , Teste de Complementação Genética , Mutagênese Insercional , Fixação de Nitrogênio , Análise de Sequência com Séries de Oligonucleotídeos , Fenótipo , Folhas de Planta/microbiologia , RNA Bacteriano/genética , RNA Mensageiro/genética , Nódulos Radiculares de Plantas/microbiologia , Nódulos Radiculares de Plantas/ultraestrutura , Fator sigma/genética , Glycine max/ultraestrutura , Estresse Fisiológico , Simbiose , Transcrição Gênica , TranscriptomaRESUMO
Bordetella avium is a Gram negative upper respiratory tract pathogen of birds. B. avium infection of commercially raised turkeys is an agriculturally significant problem. Here we describe the functional analysis of the first characterized B. avium autotransporter protein, Baa1. Autotransporters comprise a large family of proteins found in all groups of Gram negative bacteria. Although not unique to pathogenic bacteria, autotransporters have been shown to perform a variety of functions implicated in virulence. To test the hypothesis that Baa1 is a B. avium virulence factor, unmarked baa1 deletion mutants (Δbaa1) were created and tested phenotypically. It was found that baa1 mutants have wild-type levels of serum sensitivity and infectivity, yet significantly lower levels of turkey tracheal cell attachment in vitro. Likewise, semi-purified recombinant His-tagged Baa1, expressed in Escherichia coli, was shown to bind specifically to turkey tracheal cells via western blot analysis. Taken together, we conclude that Baa1 acts as a host cell attachment factor and thus plays a role B. avium virulence.
