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[This corrects the article DOI: 10.1371/journal.ppat.1002629.].
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How pathogenic bacteria infect and kill their host is currently widely investigated. In comparison, the fate of pathogens after the death of their host receives less attention. We studied Bacillus thuringiensis (Bt) infection of an insect host, and show that NprR, a quorum sensor, is active after death of the insect and allows Bt to survive in the cadavers as vegetative cells. Transcriptomic analysis revealed that NprR regulates at least 41 genes, including many encoding degradative enzymes or proteins involved in the synthesis of a nonribosomal peptide named kurstakin. These degradative enzymes are essential in vitro to degrade several substrates and are specifically expressed after host death suggesting that Bt has an active necrotrophic lifestyle in the cadaver. We show that kurstakin is essential for Bt survival during necrotrophic development. It is required for swarming mobility and biofilm formation, presumably through a pore forming activity. A nprR deficient mutant does not develop necrotrophically and does not sporulate efficiently in the cadaver. We report that necrotrophism is a highly regulated mechanism essential for the Bt infectious cycle, contributing to spore spreading.
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Bacillus thuringiensis/fisiologia , Proteínas de Bactérias/metabolismo , Interações Hospedeiro-Patógeno/fisiologia , Insetos/microbiologia , Percepção de Quorum/fisiologia , Animais , Proteínas de Bactérias/genética , MutaçãoRESUMO
Bacillus cereus can use swarming to move over and colonize solid surfaces in different environments. This kind of motility is a collective behavior accompanied by the production of long and hyperflagellate swarm cells. In this study, the genome-wide transcriptional response of B. cereus ATCC 14579 during swarming was analyzed. Swarming was shown to trigger the differential expression (>2-fold change) of 118 genes. Downregulated genes included those required for basic cellular metabolism. In accordance with the hyperflagellate phenotype of the swarm cell, genes encoding flagellin were overexpressed. Some genes associated with K(+) transport, phBC6A51 phage genes, and the binding component of the enterotoxin hemolysin BL (HBL) were also induced. Quantitative reverse transcription-PCR (qRT-PCR) experiments indicated an almost 2-fold upregulation of the entire hbl operon during swarming. Finally, BC1435 and BC1436, orthologs of liaI-liaH that are known to be involved in the resistance of Bacillus subtilis to daptomycin, were upregulated under swarming conditions. Accordingly, phenotypic assays showed reduced susceptibility of swarming B. cereus cells to daptomycin, and P(spac)-induced hyper-expression of these genes in liquid medium highlighted the role of BC1435 and BC1436 in the response of B. cereus to daptomycin.
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Bacillus cereus/citologia , Flagelos/genética , Flagelina/biossíntese , Flagelina/genética , Bacillus cereus/genética , Bacillus cereus/fisiologia , Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/genética , Proteínas de Bactérias/fisiologia , Daptomicina/farmacologia , Farmacorresistência Bacteriana/genética , Enterotoxinas/biossíntese , Expressão Gênica , Perfilação da Expressão Gênica , Genótipo , Proteínas Hemolisinas/biossíntese , Proteínas Hemolisinas/genética , Análise em Microsséries , Testes de Sensibilidade Microbiana , Fenótipo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Microbiologia do SoloRESUMO
PlcR is a Bacillus cereus transcriptional regulator, which activates gene expression by binding to a nucleotidic sequence called the 'PlcR box'. To build a list of all genes included in the PlcR regulon, a consensus sequence was identified by directed mutagenesis. The reference strain ATCC14579 sequenced genome was searched for occurrences of this consensus sequence to produce a virtual regulon. PlcR control of these genes was confirmed by comparing gene expression in the reference strain and its isogenic Delta-plcR strain using DNA microarrays, lacZ fusions and proteomics methods. The resulting list included 45 genes controlled by 28 PlcR boxes. Forty of the PlcR controlled proteins were exported, of which 22 were secreted in the extracellular medium and 18 were bound or attached to cell wall structures (membrane or peptidoglycan layer). The functions of these proteins were related to food supply (phospholipases, proteases, toxins), cell protection (bacteriocins, toxins, transporters, cell wall biogenesis) and environment-sensing (two-component sensors, chemotaxis proteins, GGDEF family regulators). Four genes coded for cytoplasmic regulators. The PlcR regulon appears to integrate a large range of environmental signals, including food deprivation and self cell-density, and regulate the transcription of genes designed to overcome obstacles that hinder B. cereus growth within the host: food supply, host barriers, host immune defenses, and competition with other bacterial species. PlcR appears to be a key component in the efficient adaptation of B. cereus to its host environment.
