RESUMO
Listeria monocytogenes is a food-borne pathogen with a high mortality rate that has also emerged as a paradigm for intracellular parasitism. We present and compare the genome sequences of L. monocytogenes (2,944,528 base pairs) and a nonpathogenic species, L. innocua (3,011,209 base pairs). We found a large number of predicted genes encoding surface and secreted proteins, transporters, and transcriptional regulators, consistent with the ability of both species to adapt to diverse environments. The presence of 270 L. monocytogenes and 149 L. innocua strain-specific genes (clustered in 100 and 63 islets, respectively) suggests that virulence in Listeria results from multiple gene acquisition and deletion events.
Assuntos
Proteínas de Bactérias/genética , Genoma Bacteriano , Listeria monocytogenes/genética , Listeria/genética , Adaptação Fisiológica , Motivos de Aminoácidos , Bacillus subtilis/genética , Proteínas de Bactérias/química , Proteínas de Bactérias/fisiologia , Composição de Bases , Proteínas de Transporte/química , Proteínas de Transporte/genética , Cromossomos Bacterianos/genética , DNA Bacteriano/química , DNA Bacteriano/genética , Transferência Genética Horizontal , Genes Bacterianos , Genômica , Listeria/química , Listeria/fisiologia , Listeria monocytogenes/química , Listeria monocytogenes/patogenicidade , Listeria monocytogenes/fisiologia , Proteínas de Membrana/química , Proteínas de Membrana/genética , Análise de Sequência de DNA , Staphylococcus aureus/genética , Fatores de Transcrição/química , Fatores de Transcrição/genética , Virulência/genéticaRESUMO
Bacteria of Shigella spp. are the causative agents of shigellosis. The virulence traits of these pathogens include their ability to enter into epithelial cells and induce apoptosis in macrophages. Expression of these functions requires the Mxi-Spa type III secretion apparatus and the secreted IpaA-D proteins, all of which are encoded by a virulence plasmid. In wild-type strains, the activity of the secretion apparatus is tightly regulated and induced upon contact of bacteria with epithelial cells. To investigate the repertoire of proteins secreted by Shigella flexneri in conditions of active secretion, we determined the N-terminal sequence of 14 proteins that are secreted by a mutant in which secretion was deregulated. Sequencing of the virulence plasmid pWR100 of the S. flexneri strain M90T (serotype 5) has allowed us to identify the genes encoding these secreted proteins and suggests that approximately 25 proteins are secreted by the type III secretion apparatus. Analysis of the G+C content and the relative positions of genes and open reading frames carried by the plasmid, together with information concerning the localization and function of encoded proteins, suggests that pWR100 contains blocks of genes of various origins, some of which were initially carried by four different plasmids.
Assuntos
Proteínas de Bactérias/genética , Plasmídeos/genética , Shigella flexneri/genética , Shigella flexneri/patogenicidade , Sequência de Aminoácidos , Sequência de Bases , Regulação Bacteriana da Expressão Gênica , Genes Bacterianos , Dados de Sequência Molecular , Virulência/genéticaRESUMO
Bacillus subtilis grows in the absence of oxygen using nitrate ammonification and various fermentation processes. Lactate, acetate, and 2,3-butanediol were identified in the growth medium as the major anaerobic fermentation products by using high-performance liquid chromatography. Lactate formation was found to be dependent on the lctEP locus, encoding lactate dehydrogenase and a putative lactate permease. Mutation of lctE results in drastically reduced anaerobic growth independent of the presence of alternative electron acceptors, indicating the importance of NADH reoxidation by lactate dehydrogenase for the overall anaerobic energy metabolism. Anaerobic formation of 2,3-butanediol via acetoin involves acetolactate synthase and decarboxylase encoded by the alsSD operon. Mutation of alsSD has no significant effect on anaerobic growth. Anaerobic acetate synthesis from acetyl coenzyme A requires phosphotransacetylase encoded by pta. Similar to the case for lctEP, mutation of pta significantly reduces anaerobic fermentative and respiratory growth. The expression of both lctEP and alsSD is strongly induced under anaerobic conditions. Anaerobic lctEP and alsSD induction was found to be partially dependent on the gene encoding the redox regulator Fnr. The observed fnr dependence might be the result of Fnr-induced arfM (ywiD) transcription and subsequent lctEP and alsSD activation by the regulator ArfM (YwiD). The two-component regulatory system encoded by resDE is also involved in anaerobic lctEP induction. No direct resDE influence on the redox regulation of alsSD was observed. The alternative electron acceptor nitrate represses anaerobic lctEP and alsSD transcription. Nitrate repression requires resDE- and fnr-dependent expression of narGHJI, encoding respiratory nitrate reductase. The gene alsR, encoding a regulator potentially responding to changes of the intracellular pH and to acetate, is essential for anaerobic lctEP and alsSD expression. In agreement with its known aerobic function, no obvious oxygen- or nitrate-dependent pta regulation was observed. A model for the regulation of the anaerobic fermentation genes in B. subtilis is proposed.
