TasA-tasB, a new putative toxin-antitoxin (TA) system from Bacillus thuringiensis pGI1 plasmid is a widely distributed composite mazE-doc TA system

BACKGROUND: Post-segregational killing systems are present in a large variety of microorganisms. When found on plasmids, they are described as addiction systems that act to maintain the plasmid during the partitioning of the cell. The plasmid to be maintained through the generations harbours a group of two genes, one coding for a stable toxin and the other coding for an unstable antitoxin that inhibits the effects of the toxin. If, during cell division, the plasmid is lost, the toxin and antitoxin proteins present in the cytosol cease to be newly expressed. The level of unstable antitoxin protein then rapidly decreases, leaving the toxin free to act on the cellular target, leading to cell death. Consequently, only cells harbouring the plasmid can survive. RESULTS: The pGI1 plasmid of Bacillus thuringiensis H1.1 harbours a group of two genes, one showing similarities with the Doc toxin of the phd-doc toxin-antitoxin system, potentially coding for a toxin-antitoxin system. Attempts were made to clone this putative system in the Gram-negative host Escherichia coli. The putative antitoxin tasA was easily cloned in E. coli. However, although several combinations of DNA fragment were used in the cloning strategy, only clones containing a mutation in the toxin gene could be recovered, suggesting a toxic activity of TasB. An exhaustive search was carried out in order to index genes homologous to those of the putative tasA-tasB system among microorganisms. This study revealed the presence of this system in great number and in a large variety of microorganisms, either as tasA-tasB homologues or in association with toxins (or antitoxins) from other TA systems. CONCLUSION: In this work, we showed that the pGI1 plasmid of B. thuringiensis H1.1 harbours genes resembling a toxin-antitoxin system, named tasA-tasB for thuringiensis addiction system. This system appeared to be functional but unregulated in E. coli. Bioinformatics studies showed that the tasAB system is present on plasmids or chromosomes of a large variety of microorganisms. Moreover, the association between TasA antitoxin with toxins other than TasB (and vice versa) revealed the composite and modular nature of bacterial TA systems

IS4 family goes genomic

<p>Abstract</p> <p>Background</p> <p>Insertion sequences (ISs) are small, mobile DNA entities able to expand in prokaryotic genomes and trigger important rearrangements. To understand their role in evolution, accurate IS taxonomy is essential. The IS<it>4 </it>family is composed of ~70 elements and, like some other families, displays extremely elevated levels of internal divergence impeding its classification. The increasing availability of complete genome sequences provides a valuable source for the discovery of additional IS<it>4 </it>elements. In this study, this genomic database was used to update the structural and functional definition of the IS<it>4 </it>family.</p> <p>Results</p> <p>A total of 227 IS<it>4</it>-related sequences were collected among more than 500 sequenced bacterial and archaeal genomes, representing more than a three fold increase of the initial inventory. A clear division into seven coherent subgroups was discovered as well as three emerging families, which displayed distinct structural and functional properties. The IS<it>4 </it>family was sporadically present in 17 % of analyzed genomes, with most of them displaying single or a small number of IS<it>4 </it>elements. Significant expansions were detected only in some pathogens as well as among certain extremophiles, suggesting the probable involvement of some elements in bacterial and archaeal adaptation and/or evolution. Finally, it should be noted that some IS<it>4 </it>subgroups and two emerging families occurred preferentially in specific phyla or exclusively inside a specific genus.</p> <p>Conclusion</p> <p>The present taxonomic update of IS<it>4 </it>and emerging families will facilitate the classification of future elements as they arise from ongoing genome sequencing. Their narrow genomic impact and the existence of both IS-poor and IS-rich thriving prokaryotes suggested that these families, and probably ISs in general, are occasionally used as a tool for genome flexibility and evolution, rather than just representing self sustaining DNA entities.</p

Conjugative plasmid pAW63 brings new insights into the genesis of the Bacillus anthracis virulence plasmid pXO2 and of the Bacillus thuringiensis plasmid pBT9727

BACKGROUND: Bacillus cereus, Bacillus anthracis and Bacillus thuringiensis belong to the genetically close-knit Bacillus cereus sensu lato group, a family of rod-shaped Gram-positive bacteria. pAW63 is the first conjugative plasmid from the B. cereus group to be completely sequenced. RESULTS: The 71,777 bp nucleotide sequence of pAW63 reveals a modular structure, including a 42 kb tra region encoding homologs of the Type IV secretion systems components VirB11, VirB4 and VirD4, as well as homologs of Gram-positive conjugation genes from Enterococcus, Lactococcus, Listeria, Streptococcus and Staphylococcus species. It also firmly establishes the existence of a common backbone between pAW63, pXO2 from Bacillus anthracis and pBT9727 from the pathogenic Bacillus thuringiensis serovar konkukian strain 97-27. The alignment of these three plasmids highlights the presence of well conserved segments, in contrast to distinct regions of high sequence plasticity. The study of their specific differences has provided a three-point reference framework that can be exploited to formulate solid hypotheses concerning the functionalities and the molecular evolution of these three closely related plasmids. This has provided insight into the chronology of their divergence, and led to the discovery of two Type II introns on pAW63, matching copies of the mobile element IS231L in different loci of pXO2 and pBT9727, and the identification on pXO2 of a 37 kb pathogenicity island (PAI) containing the anthrax capsule genes. CONCLUSION: The complete sequence determination of pAW63 has led to a functional map of the plasmid yielding insights into its conjugative apparatus, which includes T4SS-like components, as well as its resemblance to other large plasmids of Gram-positive bacteria. Of particular interest is the extensive homology shared between pAW63 and pXO2, the second virulence plasmid of B. anthracis, as well as pBT9727 from the pathogenic strain B. thuringiensis serovar konkukian strain 97-27

Whole-Genome Sequences of 94 Environmental Isolates of Bacillus cereus Sensu Lato

Bacillus cereus sensu lato is a species complex that includes the anthrax pathogen Bacillus anthracis and other bacterial species of medical, industrial, and ecological importance. Their phenotypes of interest are typically linked to large plasmids that are closely related to the anthrax plasmids pXO1 and pXO2. Here, we present the draft genome sequences of 94 isolates of B. cereus sensu lato, which were chosen for their plasmid content and environmental origins

Circuitry rewiring directly couples competence to predation in the gut dweller Streptococcus salivarius

Small distortions in transcriptional networks might lead to drastic phenotypical changes, especially in cellular developmental programs such as competence for natural transformation. Here, we report a pervasive circuitry rewiring for competence and predation interplay in commensal streptococci. Canonically, in streptococci paradigms such as Streptococcus pneumoniae and Streptococcus mutans, the pheromone-based two-component system BlpRH is a central node that orchestrates the production of antimicrobial compounds (bacteriocins) and incorporates signal from the competence activation cascade. However, the human commensal Streptococcus salivarius does not contain a functional BlpRH pair, while the competence signaling system ComRS directly couples bacteriocin production and competence commitment. This network shortcut might underlie an optimal adaptation against microbial competitors and explain the high prevalence of S. salivarius in the human digestive tract. Moreover, the broad spectrum of bacteriocin activity against pathogenic bacteria showcases the commensal and genetically tractable S. salivarius species as a user-friendly model for competence and bacterial predation

Aislamiento y caracterización de cepas de Bacillus asociadas al cultivo del arroz (Oryza sativa L.)

El presente trabajo muestra el aislamiento y la caracterización de bacterias del género Bacillus provenientes de la rizosfera del cultivo del arroz (Oryza sativa L.) variedad J-104 utilizando el modelo microcosmos. Se realizaron además aislamientos directos del suelo que se encontraba cultivado con la variedad INCA LP-5. Se llevó a cabo la caracterización fisiológica de 13 aislados en cuanto a la producción de compuestos indólicos, la determinación de antagonismo frente a hongos fitopatógenos Del arroz (Alternaria solani, Pyricularia grisea, Fusarium sp. y Curvularia sp.), la capacidad de solubilización de fosfatos y la determinación cualitativa de la fijación de nitrógeno. Teniendo en cuenta los resultados obtenidos se seleccionaron a través de un análisis de conglomerado (cluster), los aislados más promisorios para su identificación utilizando las pruebas morfológicas, tintoriales y bioquímicas propuestas por el Manual de Bergey y la secuenciación del ADN ribosómico 16S

Molecular characterization of a DNA fragment harboring the replicon of pBMB165 from Bacillus thuringiensis subsp. tenebrionis

BACKGROUND: Bacillus thuringiensis belongs to the Bacillus cereus sensu lato group of Gram-positive and spore-forming bacteria. Most isolates of B. thuringiensis can bear many endogenous plasmids, and the number and size of these plasmids can vary widely among strains or subspecies. As far as we know, the replicon of the plasmid pBMB165 is the first instance of a plasmid replicon being isolated from subsp. tenebrionis and characterized. RESULTS: A 20 kb DNA fragment containing a plasmid replicon was isolated from B. thuringiensis subsp. tenebrionis YBT-1765 and characterized. By Southern blot analysis, this replicon region was determined to be located on pBMB165, the largest detected plasmid (about 82 kb) of strain YBT-1765. Deletion analysis revealed that a replication initiation protein (Rep165), an origin of replication (ori165) and an iteron region were required for replication. In addition, two overlapping ORFs (orf6 and orf10) were found to be involved in stability control of plasmid. Sequence comparison showed that the replicon of pBMB165 was homologous to the pAMβ1 family replicons, indicating that the pBMB165 replicon belongs to this family. The presence of five transposable elements or remnants thereof in close proximity to and within the replicon control region led us to speculate that genetic exchange and recombination are potentially responsible for the divergence among the replicons of this plasmid family. CONCLUSION: The replication and stability features of the pBMB165 from B. thuringiensis subsp. tenebrionis YBT-1765 were identified. Of particular interest is the homology and divergence shared between the pBMB165 replicon and other pAMβ1 family replicons

Revisiting a pollen-transmitted ilarvirus previously associated with angular mosaic of grapevine

We report the characterization of a novel tri-segmented RNA virus infecting Mercurialis annua, a common crop weed and model species in plant science. The virus, named "Mercurialis latent virus" (MeLaV) was first identified in a mixed infection with the recently described Mercurialis orthotospovirus 1 (MerV1) on symptomatic plants grown in glasshouses in Lausanne (Switzerland). Both viruses were found to be transmitted by Thrips tabaci, which presumably help the inoculation of infected pollen in the case of MeLaV. Complete genome sequencing of the latter revealed a typical ilarviral architecture and close phylogenetic relationship with members of the Ilarvirus subgroup 1. Surprisingly, a short portion of MeLaV replicase was found to be identical to the partial sequence of grapevine angular mosaic virus (GAMV) reported in Greece in the early 1990s. However, we have compiled data that challenge the involvement of GAMV in angular mosaic of grapevine, and we propose alternative causal agents for this disorder. In parallel, three highly-conserved MeLaV isolates were identified in symptomatic leaf samples in The Netherlands, including a herbarium sample collected in 1991. The virus was also traced in diverse RNA sequencing datasets from 2013-2020, corresponding to transcriptomic analyses of M. annua and other plant species from five European countries, as well as metaviromics analyses of bees in Belgium. Additional hosts are thus expected for MeLaV, yet we argue that infected pollen grains have likely contaminated several sequencing datasets and may have caused the initial characterization of MeLaV as GAMV