RESUMO
Bacteria of the Bacillus cereus group colonize several ecological niches and infect different hosts. Bacillus cereus, a ubiquitous species causing food poisoning, Bacillus thuringiensis, an entomopathogen, and Bacillus anthracis, which is highly pathogenic to mammals, are the most important species of this group. These species are closely related genetically, and their specific toxins are encoded by plasmids. The infectious cycle of B. thuringiensis in its insect host is regulated by quorum-sensing systems from the RNPP family. Among them, the Rap-Phr systems, which are well-described in Bacillus subtilis, regulate essential processes, such as sporulation. Given the importance of these systems, we performed a global in silico analysis to investigate their prevalence, distribution, diversity and their role in sporulation in B. cereus group species. The rap-phr genes were identified in all selected strains with 30% located on plasmids, predominantly in B. thuringiensis. Despite a high variability in their sequences, there is a remarkable association between closely related strains and their Rap-Phr profile. Based on the key residues involved in RapH phosphatase activity, we predicted that 32% of the Rap proteins could regulate sporulation by preventing the phosphorylation of Spo0F. These Rap are preferentially located on plasmids and mostly related to B. thuringiensis. The predictions were partially validated by in vivo sporulation experiments suggesting that the residues linked to the phosphatase function are necessary but not sufficient to predict this activity. The wide distribution and diversity of Rap-Phr systems could strictly control the commitment to sporulation and then improve the adaptation capacities of the bacteria to environmental changes.
Assuntos
Bacillus cereus/genética , Proteínas de Bactérias/genética , Fosfoproteínas Fosfatases/genética , Percepção de Quorum/genética , Bacillus cereus/enzimologia , Bacillus cereus/metabolismo , Bacillus subtilis/enzimologia , Bacillus subtilis/genética , Bacillus thuringiensis/enzimologia , Bacillus thuringiensis/genética , Proteínas de Bactérias/metabolismo , Análise por Conglomerados , Esterases/genética , Esterases/metabolismo , Peptídeos/química , Fosfoproteínas Fosfatases/metabolismo , Filogenia , Plasmídeos/genética , Plasmídeos/metabolismo , Percepção de Quorum/fisiologia , Esporos Bacterianos/genética , Esporos Bacterianos/metabolismoRESUMO
Bacillus thuringiensis and Bacillus cereus belong to the B. cereus species group. The two species share substantial chromosomal similarity and differ mostly in their plasmid content. The phylogenetic relationship between these species remains a matter of debate. There is genetic exchange both within and between these species, and current evidence indicates that insects are a particularly suitable environment for the growth of and genetic exchange between these species. We investigated the conjugation efficiency of B. thuringiensis var. kurstaki KT0 (pHT73-Em) as a donor and a B. thuringiensis and several B. cereus strains as recipients; we used one-recipient and two-recipient conjugal transfer systems in vitro (broth and filter) and in Bombyx mori larvae, and assessed multiplication following conjugation between Bacillus strains. The B. thuringiensis KT0 strain did not show preference for genetic exchange with the B. thuringiensis recipient strain over that with the B. cereus recipient strains. However, B. thuringiensis strains germinated and multiplied more efficiently than B. cereus strains in insect larvae and only B. thuringiensis maintained complete spore germination for at least 24 h in B. mori larvae. These findings show that there is no positive association between bacterial multiplication efficiency and conjugation ability in infected insects for the used strains.
Assuntos
Bacillus cereus/genética , Bacillus thuringiensis/genética , Conjugação Genética/fisiologia , Especiação Genética , Plasmídeos/genética , Bacillus cereus/crescimento & desenvolvimento , Bacillus thuringiensis/crescimento & desenvolvimento , Conjugação Genética/genética , Especificidade da EspécieRESUMO
In favorable conditions Bacillus thuringiensis spores germinate and vegetative cells multiply, whereas in unfavorable conditions Bacillus thuringiensis sporulates and produces insecticidal crystal proteins. The development of B. thuringiensis strains was investigated in the larvae of insects belonging to the orders Lepidoptera and Diptera. Bacillus thuringiensis strains able to kill the insects did not always multiply in cadavers. Strains with no specificity to kill the insect sometimes multiplied when the insects were killed mechanically. These results indicate that some insect larvae represent an environment that favors the germination of B. thuringiensis spores and the multiplication of vegetative cells; however, there was no correlation between the toxin specificity and the specificity of the host.
Assuntos
Bacillus thuringiensis/fisiologia , Bacillus thuringiensis/patogenicidade , Dípteros/microbiologia , Lepidópteros/microbiologia , Controle Biológico de Vetores , Animais , Bacillus thuringiensis/metabolismo , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/metabolismo , Proteínas de Bactérias/toxicidade , Toxinas Bacterianas/metabolismo , Toxinas Bacterianas/toxicidade , Dípteros/crescimento & desenvolvimento , Endotoxinas/metabolismo , Endotoxinas/toxicidade , Proteínas Hemolisinas , Larva/microbiologia , Lepidópteros/crescimento & desenvolvimento , Esporos Bacterianos/fisiologiaRESUMO
Um fragmento de DNA contendo o gene da -endotoxina de um novo isolado de Bacillus thuringiensis, o SPL407 (serotipo H1), foi clonado usando o vetor pUC18 e um novo vetor, o pHT3101, que contém a regiäo de origem de replicaçäo de um plasmídeo nativo de B. thuringiensis. As clonagens foram feitas a partir do DNA total: na primeira um fragmento de DNA de 12 kb Bam HI/Pst, foi clonado em E. coli usando o pUC18 como vetor, na segunda um fragmento de DNA de 12kb Smal/Pst foi clonado no pHT3101 digerido por Smal/Pst; e na terceira um fragmento de DNA de 7 kb Hpa/Smal foi inserido no pHT3101 digerido no Smal. Os plasmídios construídos usando o pHT3101 foram introduzidos em E. coli e em B. thuringiensis. A análise dos plasmídios dos clones recombinantes de B. thuringiensis indicou que eles näo sofreram rearranjos moleculares e parecem ser estruturalmente estáveis