RESUMEN
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.
Asunto(s)
Bacillus cereus/genética , Proteínas Bacterianas/genética , Fosfoproteínas Fosfatasas/genética , Percepción de Quorum/genética , Bacillus cereus/enzimología , Bacillus cereus/metabolismo , Bacillus subtilis/enzimología , Bacillus subtilis/genética , Bacillus thuringiensis/enzimología , Bacillus thuringiensis/genética , Proteínas Bacterianas/metabolismo , Análisis por Conglomerados , Esterasas/genética , Esterasas/metabolismo , Péptidos/química , Fosfoproteínas Fosfatasas/metabolismo , Filogenia , Plásmidos/genética , Plásmidos/metabolismo , Percepción de Quorum/fisiología , Esporas Bacterianas/genética , Esporas Bacterianas/metabolismoRESUMEN
Bacillus thuringiensis is an important microbial control agent against insect pests. The draft genome sequence of the Brazilian strain BR58 described here contains the insecticidal genes cry4A, cry4B, cry10A, cry11A, cry60A, cry60B, and cyt1A, which show toxicity to both Aedes aegypti and Hypothenemus hampei larvae.
RESUMEN
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.
Asunto(s)
Bacillus cereus/genética , Bacillus thuringiensis/genética , Conjugación Genética/fisiología , Especiación Genética , Plásmidos/genética , Bacillus cereus/crecimiento & desarrollo , Bacillus thuringiensis/crecimiento & desarrollo , Conjugación Genética/genética , Especificidad de la EspecieRESUMEN
The bacterial strain Bacillus cereus is closely related to Bacillus thuringiensis, although any genetic relationship between the two strains is still in debate. Using rep-PCR genomic fingerprinting, we established the genetic relationships between Brazilian sympatric populations of B. cereus and B. thuringiensis simultaneously collected from two geographically separate sites. We observed the formation of both B. thuringiensis and B. cereus clusters, as well as strains of B. cereus that are more closely related to B. thuringiensis than to other B. cereus strains. In addition, lower genetic variability was observed among B. thuringiensis clusters compared to B. cereus clusters, indicating that either the two species should be categorized as separate or that B. thuringiensis may represent a clone from a B. cereus background.
Asunto(s)
Bacillus cereus/genética , Bacillus thuringiensis/genética , Dermatoglifia del ADN/métodos , Variación Genética/genética , Reacción en Cadena de la Polimerasa/métodos , Bacillus cereus/aislamiento & purificación , Bacillus thuringiensis/aislamiento & purificación , Análisis por Conglomerados , Microbiología del SueloRESUMEN
The bacterial strain Bacillus cereus is closely related to Bacillus thuringiensis, although any genetic relationship between the two strains is still in debate. Using rep-PCR genomic fingerprinting, we established the genetic relationships between Brazilian sympatric populations of B. cereus and B. thuringiensis simultaneously collected from two geographically separate sites. We observed the formation of both B. thuringiensis and B. cereus clusters, as well as strains of B. cereus that are more closely related to B. thuringiensis than to other B. cereus strains. In addition, lower genetic variability was observed among B. thuringiensis clusters compared to B. cereus clusters, indicating that either the two species should be categorized as separate or that B. thuringiensis may represent a clone from a B. cereus background.
Asunto(s)
Bacillus cereus/genética , Bacillus thuringiensis/genética , Dermatoglifia del ADN/métodos , Variación Genética , Reacción en Cadena de la Polimerasa/métodos , Bacillus cereus/aislamiento & purificación , Bacillus thuringiensis/aislamiento & purificación , Análisis por Conglomerados , Microbiología del SueloRESUMEN
Um mutante (407-P) da linhagem Bacillus thuringiensis subsp. thuringiensis 407 produtor de melanina foi obtido após tratamento com o agente mutagênico etil-metano-sulfonato. Diversas propriedades microbiológicas e bioquímicas das duas linhagens foram analisadas e os resultados foram similares. O mutante 407-P foi incorporado em amostras de solo não esterilizado, recuperado, facilmente identificado e quantificado, possibilitando seu uso em estudos de ecologia de B. thuringiensis.