Bacillus anthracis diverges from related clades of the Bacillus cereus group in 16S-23S ribosomal DNA intergenic transcribed spacers containing tRNA genes

Ultrasensitive Detection of Bacillus anthracis by Real-Time PCR Targeting a Polymorphism in Multi-Copy 16S rRNA Genes and Their Transcripts

The anthrax pathogen Bacillus anthracis poses a significant threat to human health. Identification of B. anthracis is challenging because of the bacterium's close genetic relationship to other Bacillus cereus group species. Thus, molecular detection is founded on species-specific PCR targeting single-copy genes. Here, we validated a previously recognized multi-copy target, a species-specific single nucleotide polymorphism (SNP) present in 2-5 copies in every B. anthracis genome analyzed. For this, a hydrolysis probe-based real-time PCR assay was developed and rigorously tested. The assay was specific as only B. anthracis DNA yielded positive results, was linear over 9 log10 units, and was sensitive with a limit of detection (LoD) of 2.9 copies/reaction. Though not exhibiting a lower LoD than established single-copy PCR targets (dhp61 or PL3), the higher copy number of the B. anthracis-specific 16S rRNA gene alleles afforded ≤2 unit lower threshold (Ct) values. To push the detection limit even further, the assay was adapted for reverse transcription PCR on 16S rRNA transcripts. This RT-PCR assay was also linear over 9 log10 units and was sensitive with an LoD of 6.3 copies/reaction. In a dilution series of experiments, the 16S RT-PCR assay achieved a thousand-fold higher sensitivity than the DNA-targeting assays. For molecular diagnostics, we recommend a real-time RT-PCR assay variant in which both DNA and RNA serve as templates (thus, no requirement for DNase treatment). This can at least provide results equaling the DNA-based implementation if no RNA is present but is superior even at the lowest residual rRNA concentrations.

A comparative GC-MS analysis of bioactive secondary metabolites produced by halotolerant Bacillus spp. isolated from the Great Sebkha of Oran

The reemergence of infectious diseases and resistant pathogens represents a serious problem for human life. Hence, the screening for new or alternative antimicrobial compounds is still urgent. Unusual ecosystems such as saline habitats are considered promising environments for the purposes of isolating bacterial strains able to produce potent natural products. The aim of this study is the identification of bioactive compounds biosynthesized by three halotolerant strains isolated from the Sebkha of Oran (Algeria) using gas chromatography coupled to mass spectrometry. Primary screening investigation of antimicrobial activities were performed against reference bacterial and fungal strains and revealed a broad-spectrum activity. Secondary metabolite extraction was carried out using ethyl acetate and chloroform. Crude extracts were tested for bioactivity using the disc diffusion method and subjected to GC-MS analysis. The extracts showed an important inhibitory effect against all tested strains. Fifty-six compounds were identified; they include tert-butyl phenol compounds, fatty acid methyl esters due to the methylation procedure, hydrocarbons, aldehydes, benzoquinones, pyrrols, and terpenes. Literature reports such compounds to have wide biological and pharmaceutical applications. The molecular identification of the three isolates was achieved using the 16S-23S rRNA gene intergenic spacer region (ITS) and 16S rRNA sequencing. Partial 16S rRNA gene sequencing showed very high similarity with many species of Bacillus. This study provided insights on the potential of halotolerant Bacillus as drug research target for bioactive metabolites. The findings suggest that the Great Sebkha of Oran is a valuable source of strains exhibiting variety of beneficial attributes that can be utilized in the development of biological antibiotics.

Unravelling the characteristics of a heteropolysaccharide-protein from an Haloarchaeal strain with flocculation effectiveness in heavy metals and dyes removal

The production, characterization and potential application in heavy metals and dyes removal of a novel heteropolysaccharide-protein named, gpHb, produced by an Haloarchaeal strain Halogeometricum borinquense strain A52 were investigated. The highest gpHb yield of 13.96 ± 0.32 g/L was produced under optimized conditions by response surface methodology. We focused on the characteristics and flocculation performance of gpHb. An important attribute of protein with 16 protein types identified that occupied a total content of 50.2% in the gpHb. Additionally, carbohydrate that occupied 30.4% of the total bioflocculant content consisted of three monosaccharides. Fourier transform-infrared spectroscopy indicated the presence of carboxyl, hydroxyl, amine, amide, and sulphate groups. To further study flocculation activities, factors such as bioflocculant dosage, temperature, pH, salinity and cations addition were tested. In comparison to the chemical flocculant polyaluminium chloride, gpHb maintain high activity at large range of salinity and its flocculation activity was higher on both sides of pH 7. Addition of trivalent cation mainly Fe³⁺ enhances the flocculating rate indicating that the bioflocculant is negatively charged. Its practical applicability was established for heavy metals and dyes removal from saline aqueous solutions. The highest removal efficiency was observed with Cr³⁺ (91.4%) and Ni²⁺ (89.60%) and with basic blue 3 (83.8%) and basic red (78.6%). The excellent flocculation activity of gpHb under saline condition suggests its potential industrial utility for treatment of textile and tannery wastewaters.

Ribosomal background of the Bacillus cereus group thermotypes

In this study we reconstructed the architecture of Bacillus cereus sensu lato population based on ribosomal proteins, and identified a link between the ribosomal proteins’ variants and thermal groups (thermotypes) of the bacilli. The in silico phyloproteomic analysis of 55 ribosomal proteins (34 large and 21 small subunit r-proteins) of 421 strains, representing 14 well-established or plausible B. cereus sensu lato species, revealed several ribosomal clusters (r-clusters), which in general were well correlated with the strains’ affiliation to phylogenetic/thermal groups I–VII. However, a conformity and possibly a thermal characteristic of certain phylogenetic groups, e.g. the group IV, were not supported by a distribution of the corresponding r-clusters, and consequently neither by the analysis of cold-shock proteins (CSPs) nor by a content of heat shock proteins (HSPs). Furthermore, a preference for isoleucine and serine over valine and alanine in r-proteins along with a lack of HSP16.4 were recognized in non-mesophilic thermotypes. In conclusion, we suggest that the observed divergence in ribosomal proteins may be connected with an adaptation of B. cereus sensu lato members to various thermal niches.

Whole genomic sequence analysis of Bacillus infantis: defining the genetic blueprint of strain NRRL B-14911, an emerging cardiopathogenic microbe

Background

We recently reported the identification of Bacillus sp. NRRL B-14911 that induces heart autoimmunity by generating cardiac-reactive T cells through molecular mimicry. This marine bacterium was originally isolated from the Gulf of Mexico, but no associations with human diseases were reported. Therefore, to characterize its biological and medical significance, we sought to determine and analyze the complete genome sequence of Bacillus sp. NRRL B-14911.

Results

Based on the phylogenetic analysis of 16S ribosomal RNA (rRNA) genes, sequence analysis of the 16S-23S rDNA intergenic transcribed spacers, phenotypic microarray, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry, we propose that this organism belongs to the species Bacillus infantis, previously shown to be associated with sepsis in a newborn child. Analysis of the complete genome of Bacillus sp. NRRL B-14911 revealed several virulence factors including adhesins, invasins, colonization factors, siderophores and transporters. Likewise, the bacterial genome encodes a wide range of methyl transferases, transporters, enzymatic and biochemical pathways, and insertion sequence elements that are distinct from other closely related bacilli.

Conclusions

The complete genome sequence of Bacillus sp. NRRL B-14911 provided in this study may facilitate genetic manipulations to assess gene functions associated with bacterial survival and virulence. Additionally, this bacterium may serve as a useful tool to establish a disease model that permits systematic analysis of autoimmune events in various susceptible rodent strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2900-2) contains supplementary material, which is available to authorized users.

The worldwide distribution of genetically and phylogenetically diverse Bacillus cereus isolates harbouring Bacillus anthracis-like plasmids

Bacillus cereus is a close relative of B. anthracis, the causative agent of anthrax whose pathogenic determinants are located on pXO1 and pXO2 plasmids. Bacillus anthracis-like plasmids have been also noted among B. cereus, however, genetic features of B. cereus harbouring these elements remain largely undescribed, especially from the global perspective. Herein, we present the genetic polymorphism, population structure and phylogeny of B. cereus with pXO1-/pXO2-like plasmids originating from Argentina, Kazakhstan, Kenya and Poland. The plasmids were found in about 17% of the isolates, but their frequencies and expression of replicons differed within and between populations. In the multi-locus sequence typing, the bacteria exhibited high genetic polymorphism reflected by 116 sequencing types, including 84 singletons and 10 clonal complexes, which mainly consisted of isolates of the same origin. The phylogenetic analysis of pXO1-/pXO2-like positive B. cereus isolates revealed six independent clades; in certain clades individual populations predominated. Generally, B. cereus with pXO1-/pXO2-like plasmids did not indicate the genetic relationship with B. anthracis, and cannot be classified into an evolutionary independent anthrax line within the B. cereus group. Our report is of a crucial importance for discovering the genetic specificity and evolution of B. cereus bacilli.

Cultivation-dependent assessment, diversity, and ecology of haloalkaliphilic bacteria in arid saline systems of southern Tunisia

Haloalkaliphiles are polyextremophiles adapted to grow at high salt concentrations and alkaline pH values. In this work, we isolated 122 haloalkaliphilic bacteria upon enrichments of 23 samples from 5 distinct saline systems of southern Tunisia, growing optimally in media with 10% salt and at pH 10. The collection was classified into 44 groups based on the amplification of the 16S-23S rRNA internal transcribed spacers (ITS-PCR). Phylogenetic analysis and sequencing of the 16S rRNA genes allowed the identification of 13 genera and 20 distinct species. Three gram-positive isolates showing between 95 and 96% of 16S rRNA sequence homology with Bacillus saliphilus could represent new species or genus. Beside the difference in bacterial diversity between the studied sites, several species ecological niches correlations were demonstrated such as Oceanobacillus in salt crust, Nesterenkonia in sand, and Salinicoccus in the rhizosphere of the desert plant Salicornia. The collection was further evaluated for the production of extracellular enzymes. Activity tests showed that gram-positive bacteria were mostly active, particularly for protease, lipase, DNase, and amylase production. Our overall results demonstrate the huge phenotypic and phylogenetic diversity of haloalkaliphiles in saline systems of southern Tunisia which represent a valuable source of new lineages and metabolites.

Uneven distribution of Halobacillus trueperi species in arid natural saline systems of Southern Tunisian Sahara

The genetic diversity of a collection of 336 spore-forming isolates recovered from five salt-saturated brines and soils (Chott and Sebkhas) mainly located in the hyper-arid regions of the southern Tunisian Sahara has been assessed. Requirements and abilities for growth at a wide range of salinities\ showed that 44.3 % of the isolates were extremely halotolerant, 23 % were moderate halotolerant, and 32.7 % were strict halophiles, indicating that they are adapted to thrive in these saline ecosystems. A wide genetic diversity was documented based on 16S-23S rRNA internal transcribed spacer fingerprinting profiles (ITS) and 16S rRNA gene sequences that clustered the strains into seven genera: Bacillus, Gracilibacillus, Halobacillus, Oceanobacillus, Paenibacillus, Pontibacillus, and Virgibacillus. Halobacillus trueperi was the most encountered species in all the sites and presented a large intraspecific diversity with a multiplicity of ITS types. The most frequent ITS type included 42 isolates that were chosen for assessing of the intraspecific diversity by BOX-PCR fingerprinting. A high intraspecific microdiversity was documented by 14 BOX-PCR genotypes whose distribution correlated with the strain geographic origin. Interestingly, H. trueperi isolates presented an uneven geographic distribution among sites with the highest frequency of isolation from the coastal sites, suggesting a marine rather than terrestrial origin of the strains. The high frequency and diversity of H. trueperi suggest that it is a major ecosystem-adapted microbial component of the Tunisian Sahara harsh saline systems of marine origin.

Microdiversity of deep-sea Bacillales isolated from Tyrrhenian sea sediments as revealed by ARISA, 16S rRNA gene sequencing and BOX-PCR fingerprinting

With respect to their terrestrial relatives, marine Bacillales have not been sufficiently investigated. In this report, the diversity of deep-sea Bacillales, isolated from seamount and non-seamount stations at 3,425 to 3,580 m depth in the Tyrrhenian Sea, was investigated using PCR fingerprinting and 16S rRNA sequence analysis. The isolate collection (n=120) was de-replicated by automated ribosomal intergenic spacer analysis (ARISA), and phylogenetic diversity was analyzed by 16S rRNA gene sequencing of representatives of each ARISA haplotype (n=37). Phylogenetic analysis of isolates showed their affiliation to six different genera of low G+C% content Gram-positive Bacillales: Bacillus, Staphylococcus, Exiguobacterium, Paenibacillus, Lysinibacillus and Terribacillus. Bacillus was the dominant genus represented by the species B. licheniformis, B. pumilus, B. subtilis, B. amyloliquefaciens and B. firmus, typically isolated from marine sediments. The most abundant species in the collection was B. licheniformis (n=85), which showed seven distinct ARISA haplotypes with haplotype H8 being the most dominant since it was identified by 63 isolates. The application of BOX-PCR fingerprinting to the B. licheniformis sub-collection allowed their separation into five distinct BOX genotypes, suggesting a high level of intraspecies diversity among marine B. licheniformis strains. This species also exhibited distinct strain distribution between seamount and non-seamount stations and was shown to be highly prevalent in non-seamount stations. This study revealed the great microdiversity of marine Bacillales and contributes to understanding the biogeographic distribution of marine bacteria in deep-sea sediments.

Intra- and intergenomic variation of ribosomal RNA operons in concurrent Alteromonas macleodii strains

Biodiversity estimates based on ribosomal operon sequence diversity rely on the premise that a sequence is characteristic of a single specific taxon or operational taxonomic unit (OTU). Here, we have studied the sequence diversity of 14 ribosomal RNA operons (rrn) contained in the genomes of two isolates (five operons in each genome) and four metagenomic fosmids, all from the same seawater sample. Complete sequencing of the isolate genomes and the fosmids establish that they represent strains of the same species, Alteromonas macleodii, with average nucleotide identity (ANI) values >97 %. Nonetheless, we observed high levels of intragenomic heterogeneity (i.e., variability between operons of a single genome) affecting multiple regions of the 16S and 23S rRNA genes as well as the internally transcribed spacer 1 (ITS-1) region. Furthermore, the ribosomal operons exhibited intergenomic heterogeneity (i.e., variability between operons located in separate genomes) in each of these regions, compounding the variability. Our data reveal the extensive heterogeneity observed in natural populations of A. macleodii at a single point in time and support the idea that distinct lineages of A. macleodii exist in the deep Mediterranean. These findings highlight the potential of rRNA fingerprinting methods to misrepresent species diversity while simultaneously failing to recognize the ecological significance of individual strains.

Paenibacillus larvae 16S-23S rDNA intergenic transcribed spacer (ITS) regions: DNA fingerprinting and characterization

Paenibacillus larvae is the causative agent of American foulbrood in honey bee (Apis mellifera) larvae. PCR amplification of the 16S-23S ribosomal DNA (rDNA) intergenic transcribed spacer (ITS) regions, and agarose gel electrophoresis of the amplified DNA, was performed using genomic DNA collected from 134 P. larvae strains isolated in Connecticut, six Northern Regional Research Laboratory stock strains, four strains isolated in Argentina, and one strain isolated in Chile. Following electrophoresis of amplified DNA, all isolates exhibited a common migratory profile (i.e., ITS-PCR fingerprint pattern) of six DNA bands. This profile represented a unique ITS-PCR DNA fingerprint that was useful as a fast, simple, and accurate procedure for identification of P. larvae. Digestion of ITS-PCR amplified DNA, using mung bean nuclease prior to electrophoresis, characterized only three of the six electrophoresis bands as homoduplex DNA and indicating three true ITS regions. These three ITS regions, DNA migratory band sizes of 915, 1010, and 1474 bp, signify a minimum of three types of rrn operons within P. larvae. DNA sequence analysis of ITS region DNA, using P. larvae NRRL B-3553, identified the 3' terminal nucleotides of the 16S rRNA gene, 5' terminal nucleotides of the 23S rRNA gene, and the complete DNA sequences of the 5S rRNA, tRNA(ala), and tRNA(ile) genes. Gene organization within the three rrn operon types was 16S-23S, 16S-tRNA(ala)-23S, and l6S-5S-tRNA(ile)-tRNA(ala)-23S and these operons were named rrnA, rrnF, and rrnG, respectively. The 23S rRNA gene was shown by I-CeuI digestion and pulsed-field gel electrophoresis of genomic DNA to be present as seven copies. This was suggestive of seven rrn operon copies within the P. larvae genome. Investigation of the 16S-23S rDNA regions of this bacterium has aided the development of a diagnostic procedure and has helped genomic mapping investigations via characterization of the ITS regions.

Characterization of an environmental strain of Bacillus thuringiensis from a hot spring in Western Himalayas

Bacillus anthracis, the etiological agent of anthrax, is responsible for a serious and often fatal disease of mammalian livestock and humans and is an important biological warfare agent. Bacillus sp. AKG was isolated from a hot spring in western Himalayas and species-specific primers targeting gyrB gene identified the strain as B. anthracis within cereus-group. Cloning, sequencing, and phylogenetic analysis of the partial gyrB sequence from strain AKG indicated a close affiliation with B. anthracis and a few recently isolated strains of B. thuringiensis (e.g., strain Al Hakam and serovar konkukian). Phylogenetic analysis of two other housekeeping genes, clpC and gdpD yielded similar results. This observation is further substantiated by phylogenetic reconstruction using concatenated sequences (1680 bases) of the three genes (gyrB, clpC, and gdpD). Phenotypic features indicated a non-anthracis affiliation for the strain AKG. A novel strategy to distinguish among strains of B. anthracis, B. cereus, and B. thuringiensis based on whole proteome comparison was developed and tested for the identification of this environmental strain. Proteome comparison was used to establish the identity of this unknown environmental strain. Group of replicate 2DE gels for whole cell proteome were generated for each of the three species and strain AKG. Protein spots unique to each group and those showing match between the groups, in a pair-wise comparison, indicated strain AKG as a member of B. thuringiensis. This strategy can be used to assign strains of B. cereus group to their respective species.

Gammaproteobacteria occurrence and microdiversity in Tyrrhenian Sea sediments as revealed by cultivation-dependent and -independent approaches

Bacterial diversity in Tyrrhenian Sea sediments was assessed using cultivation-dependent and -independent approaches. Samples collected from the different sediment layers (up to 30cm) relative to four seamount and non-seamount stations, at depths from 3425 to 3580m, were subjected to DNA extraction and 16S rRNA amplification targeting the V3 region. Denaturing gradient gel electrophoresis (DGGE) showed several heterogeneous profiles and 27 single bands were excised and sequenced. Sequence analysis revealed the presence of Firmicutes, Actinobacteria and Chloroflexi in 26% of the DGGE bands and a predominance of sequences affiliated to cultivable and uncultivable clones of Gammaproteobacteria (55%). To corroborate these findings, cultivation attempts were performed that allowed the isolation of 87 strains assigned to the proteobacterial classes. Identification was achieved by means of automated ribosomal intergenic spacer analysis (ARISA) and by 16S rDNA sequencing. The isolates were related to the gamma, alpha and beta subclasses of Proteobacteria with respective percentages of 77, 17 and 6%. The most predominant Gammaproteobacteria isolates, assigned to the Psychrobacter marincola and P. submarinus clade (n=53) and to Halomonas aquamarina (n=14), showed a huge intraspecific diversity with 29 distinct ARISA haplotypes. The detection by both approaches of these psychrophilic and moderately halophilic species and their extensive microdiversity indicated their predominance in Tyrrhenian Sea sediments where they constituted the indigenous microflora.

Diversity and phylogeny of culturable spore-forming Bacilli isolated from marine sediments

Members of the genus Bacillus and related genera are ubiquitous in nature. However, Bacillus species isolated from marine sediments have attracted less interest respect to their terrestrial relatives. Here, we report the phylogenetic diversity of a collection of 96 Bacilli, isolated from 17 distinct stations of 5 oceanographic campaigns. The diversity was analysed by phenotypic and molecular approaches based on the amplified rDNA restriction analysis (ARDRA), amplification of the internal transcribed spacers (ITS-PCR) and on 16S rRNA sequencing. Intra-specific polymorphism was efficiently detected by biochemical analysis and ARDRA while results of ITS-PCR were in agreement with 16S rRNA sequencing. The identification results assigned 68% of the isolates to the species B. subtilis, B. licheniformis, B. pumilus and B. cereus. Phylogenetic analysis allowed the separation of 9 isolates in a clade that may represent a group of obligate marine Bacillus since they clustered with B. firmus, B. foraminis and marine isolates with metal oxidation and bioaccumulation capabilities. The remaining isolates showed a close affiliation to the genera Virgibacillus, Gracilibacillus and Paenibacillus. The widespread of Bacilli and their high diversity level observed in this work point out the need of more extensive studies to understand their distribution and ecology in deep-sea environments.

The small acid soluble proteins (SASP alpha and SASP beta) of Bacillus weihenstephanensis and Bacillus mycoides group 2 are the most distinct among the Bacillus cereus group

The Bacillus cereus group includes Bacillus anthracis, B. cereus, Bacillus thuringiensis, Bacillus mycoides and Bacillus weihenstephanensis. The small acid soluble spore protein (SASP) beta has been previously demonstrated to be among the biomarkers differentiating B. anthracis and B. cereus; SASP beta of B. cereus most commonly exhibits one or two amino acid substitutions when compared to B. anthracis. SASP alpha is conserved in sequence among these two species. Neither SASP alpha nor beta for B. thuringiensis, B. mycoides and B. weihenstephanensis have been previously characterized as taxonomic discriminators. In the current work molecular weight (MW) variation of these SASPs were determined by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for representative strains of the 5 species within the B. cereus group. The measured MWs also correlate with calculated MWs of translated amino acid sequences generated from whole genome sequencing projects. SASP alpha and beta demonstrated consistent MW among B. cereus, B. thuringiensis, and B. mycoides strains (group 1). However B. mycoides (group 2) and B. weihenstephanensis SASP alpha and beta were quite distinct making them unique among the B. cereus group. Limited sequence changes were observed in SASP alpha (at most 3 substitutions and 2 deletions) indicating it is a more conserved protein than SASP beta (up to 6 substitutions and a deletion). Another even more conserved SASP, SASP alpha-beta type, was described here for the first time.

Unusual intragenomic and interspecific variability of Geobacillus 16S-23S rRNA internal transcribed spacers

The aim of this study was to evaluate the inter-and intraspecific as well as intragenomic variability of Geobacillus 16S–23S rRNA internal transcribed spacers without tRNA genes and to compare these sequences with sequences bearing tRNA genes. In this study the structural analysis was performed in a unique way because the length and the sequence of the structural blocks were adjusted to fit the structure of 16S–23S rRNA internal transcribed spacers of five different Geobacillus species. Our study demonstrated the mosaic-like structure of 16S–23S rRNA internal transcribed spacers in Geobacillus. Some characteristics of these spacers of geobacilli were not previously reported for other bacteria: unusually short conserved sequence in the 5′ end region, some identical conserved blocks in both 5′ and 3′ regions of 16S–23S rRNA internal transcribed spacers, the same sequence blocks in both 16S–23S and 23S–5S rRNA intergenic spacers. Our study demonstrated quite uniform arrangement of the sequence blocks in Geobacillus thermodenitrificans. This species diverged early in the phylogenetic tree of the genus Geobacillus. For the phylogenetically recent species Geobacillus kaustophilus and Geobacillus lituanicus the low inter-and intraspecific, but high intragenomic variability, as a consequence of recent phylogenetic events, was established.

Genotypic and phenotypic diversity of Bacillus spp. isolated from steel plant waste

BACKGROUND

Molecular studies of Bacillus diversity in various environments have been reported. However, there have been few investigations concerning Bacillus in steel plant environments. In this study, genotypic and phenotypic diversity and phylogenetic relationships among 40 bacterial isolates recovered from steel plant waste were investigated using classical and molecular methods.

RESULTS

16S rDNA partial sequencing assigned all the isolates to the Bacillus genus, with close genetic relatedness to the Bacillus subtilis and Bacillus cereus groups, and to the species Bacillus sphaericus. tDNA-intergenic spacer length polymorphisms and the 16S-23S intergenic transcribed spacer region failed to identify the isolates at the species level. Genomic diversity was investigated by molecular typing with rep (repetitive sequence) based PCR using the primer sets ERIC2 (enterobacterial repetitive intergenic consensus), (GTG)5, and BOXAIR. Genotypic fingerprinting of the isolates reflected high intraspecies and interspecies diversity. Clustering of the isolates using ERIC-PCR fingerprinting was similar to that obtained from the 16S rRNA gene phylogenetic tree, indicating the potential of the former technique as a simple and useful tool for examining relationships among unknown Bacillus spp. Physiological, biochemical and heavy metal susceptibility profiles also indicated considerable phenotypic diversity. Among the heavy metal compounds tested Zn, Pb and Cu were least toxic to the bacterial isolates, whereas Ag inhibited all isolates at 0.001 mM.

CONCLUSION

Isolates with identical 16S rRNA gene sequences had different genomic fingerprints and differed considerably in their physiological capabilities, so the high levels of phenotypic diversity found in this study are likely to have ecological relevance.

Glycosyltransferase: a specific marker for the discrimination of Bacillus anthracis from the Bacillus cereus group

Bacillus anthracis, the aetiological agent of anthrax, has been taxonomically classified with the Bacillus cereus group, which comprises B. cereus, Bacillus thuringiensis, Bacillus mycoides, Bacillus pseudomycoides and Bacillus weihenstephanensis. Although the pathogenesis and ecological manifestations may be different, B. anthracis shares a high degree of DNA sequence similarity with its group member species. As a result, the discrimination of B. anthracis from its close relatives in the B. cereus group is still quite difficult. Suppression subtractive hybridization (SSH) was performed to search for genomic differences between a B. anthracis Korean isolate CR and the most closely related B. cereus type strain KCTC 3624(T). Two-hundred and five B. anthracis CR clones obtained by SSH underwent Southern hybridization, and comparative sequences were analysed using the blast program from the National Center for Biotechnology Information (NCBI). Subsequently, primer sets based on the glycosyltransferase group 1 family protein gene specific to B. anthracis were designed from the sequences of subtracted clones, and their specificities were evaluated using eight B. anthracis, 33 B. cereus, 10 B. thuringiensis, six B. mycoides, one B. pseudomycoides, one B. weihenstephanensis and 19 strains from 11 other representative Bacillus species. PCR primers specific for the glycosyltransferase group 1 family protein gene did not amplify the desired products from any of the Bacillus strains under examination, except B. anthracis alone. These findings may be useful in the future development of efficient diagnostic tools for the rapid identification of B. anthracis from other members of the B. cereus group.

Discrimination of Bacillus anthracis and closely related microorganisms by analysis of 16S and 23S rRNA with oligonucleotide microarray

Analysis of 16S rRNA sequences is a commonly used method for the identification and discrimination of microorganisms. However, the high similarity of 16S and 23S rRNA sequences of Bacillus cereus group organisms (up to 99-100%) and repeatedly failed attempts to develop molecular typing systems that would use DNA sequences to discriminate between species within this group have resulted in several suggestions to consider B. cereus and B. thuringiensis, or these two species together with B. anthracis, as one species. Recently, we divided the B. cereus group into seven subgroups, Anthracis, Cereus A and B, Thuringiensis A and B, and Mycoides A and B, based on 16S rRNA, 23S rRNA and gyrB gene sequences and identified subgroup-specific makers in each of these three genes. Here we for the first time demonstrated discrimination of these seven subgroups, including subgroup Anthracis, with a 3D gel element microarray of oligonucleotide probes targeting 16S and 23S rRNA markers. This is the first microarray enabled identification of B. anthracis and discrimination of these seven subgroups in pure cell cultures and in environmental samples using rRNA sequences. The microarray bearing perfect match/mismatch (p/mm) probe pairs was specific enough to discriminate single nucleotide polymorphisms (SNPs) and was able to identify targeted organisms in 5min. We also demonstrated the ability of the microarray to determine subgroup affiliations for B. cereus group isolates without rRNA sequencing. Correlation of these seven subgroups with groupings based on multilocus sequence typing (MLST), fluorescent amplified fragment length polymorphism analysis (AFLP) and multilocus enzyme electrophoresis (MME) analysis of a wide spectrum of different genes, and the demonstration of subgroup-specific differences in toxin profiles, psychrotolerance, and the ability to harbor some plasmids, suggest that these seven subgroups are not based solely on neutral genomic polymorphisms, but instead reflect differences in both the genotypes and phenotypes of the B. cereus group organisms.

In silico comparison of bacterial strains using mutual information

Fast-sequencing throughput methods have increased the number of completely sequenced bacterial genomes to about 400 by December 2006, with the number increasing rapidly. These include several strains. In silico methods of comparative genomics are of use in categorizing and phylogenetically sorting these bacteria. Various word-based tools have been used for quantifying the similarities and differences between entire genomes. The simple di-nucleotide frequency comparison, codon specificity and k-mer repeat detection are among some of the well-known methods. In this paper, we show that the Mutual Information function, which is a measure of correlations and a concept from Information Theory, is very effective in determining the similarities and differences among genome sequences of various strains of bacteria such as the plant pathogen Xylella fastidiosa, marine Cyanobacteria Prochlorococcus marinus or animal and human pathogens such as species of Ehrlichia and Legionella. The short-range three-base periodicity, small sequence repeats and long-range correlations taken together constitute a genome signature that can be used as a technique for identifying new bacterial strains with the help of strains already catalogued in the database. There have been several applications of using the Mutual Information function as a measure of correlations in genomics but this is the first whole genome analysis done to detect strain similarities and differences.

Development of rapid real-time PCR and most-probable-number real-time PCR assays to quantify enterotoxigenic strains of the species in the Bacillus cereus group

Members of the Bacillus cereus group may produce diarrheal enterotoxins and could be potential hazards if they enter the food chain. Therefore, a method capable of detecting all the species in the B. cereus group rather than B. cereus alone is important. We selected nhe as the target and developed a real-time PCR assay to quantify enterotoxigenic strains of the B. cereus group. The real-time PCR assay was evaluated with 60 B. cereus group strains and 28 others. The assay was also used to construct calibration curves for different food matrices and feces. The assay has an excellent quantification capacity, as proved by its linearity (R2 > 0.993), wide dynamic quantification range (10(2) to 10(7) CFU/g for cooked rice and chicken, 10(3) to 10(7) CFU/ml for milk, and 10(4) to 10(7) CFU/g for feces), and adequate relative accuracy (85.5 to 101.1%). For the low-level contaminations, a most-probable-number real-time PCR assay was developed that could detect as low as 10(0) CFU/ml. Both assays were tested with real food samples and shown to beconsiderably appropriate for B. cereus group detection and quantification.

Genetic distribution of 295 Bacillus cereus group members based on adk-screening in combination with MLST (Multilocus Sequence Typing) used for validating a primer targeting a chromosomal locus in B. anthracis

The genetic distribution of 295 Bacillus cereus group members has been investigated by using a modified Multilocus Sequence Typing method (MLST). By comparing the nucleic acid sequence of the adk gene fragment, isolates of B. cereus group members most related to B. anthracis may be easily identified. The genetic distribution, with focus on the B. anthracis close neighbours, was used to evaluate a new primer set for specific identification of B. anthracis. This primer set, BA5510-1/2, targeted the putative B. anthracis specific gene BA5510. Real-time PCR using BA5510-1/2 amplified the target fragment from all B. anthracis strains tested and only two (of 289) non-B. anthracis strains analysed. This is one of the most thoroughly validated chromosomal B. anthracis markers for real-time PCR identification, in which the screened collection contained several very closely related B. anthracis strains.

Genomic diversity and relationship of Bacillus thuringiensis and Bacillus cereus by multi-REP-PCR fingerprinting

The genomic diversity and relationship among 56 Bacillus thuringiensis and Bacillus cereus type strains were investigated by multi-REP-PCR fingerprinting consisting of three PCR reactions targeting the enterobacterial ERIC1 and ERIC2 and the streptococcal BOXA1R consensus sequences. A total of 113 polymorphic bands were generated in the REP-PCR profiles that allowed tracing of a single dendrogram with three major groups. Bacillus cereus strains clustered together in the A and B groups. Most of the B. thuringiensis strains clustered in group C, which included groups of serovars with a within-group similarity higher than 40% as follows: darmstadiensis, israelensis, and morrisoni; aizawai, kenyae, pakistani, and thompsoni; canadensis, entomocidus, galleriae, kurstaki, and tolworthi; alesti, dendrolimus, and kurstaki; and finitimus, sotto, and thuringiensis. Multi-REP-PCR fingerprinting clustered B. thuringiensis serovars in agreement with previously developed multilocus sequence typing schemes, indicating that it represents a rapid shortcut for addressing the genetic relationship of unknown strains with the major known serovars.

The Bacillus cereus group: novel aspects of population structure and genome dynamics

AIMS

To provide new insights into the population and genomic structure of the Bacillus cereus group of bacteria.

METHODS AND RESULTS

The genetic relatedness among B. cereus group strains was assessed by multilocus sequence typing (MLST) using an optimized scheme based on seven chromosomal housekeeping genes. A set of 48 strains from different clinical sources was included, and six clonal complexes containing several genetically similar isolates from unrelated patients were identified. Interestingly, several clonal groups contained strains that were isolated from similar human sources. Furthermore, comparative whole genome sequence analysis of 16 strains led to the discovery of novel ubiquitous genome features of the B. cereus group, such as atypical group II introns, IStrons, and hitherto uncharacterized repeated elements.

CONCLUSIONS

The B. cereus group constitutes a coherent population unified by the presence of ubiquitous and specific genetic elements which do not show any pattern, either in their sequences or genomic locations, which allows to differentiate between the member species of the group. Nevertheless, the population is very dynamic, as particular lineages of clinical origin can evolve to form clonal complexes. At the genome level, the dynamic behaviour is indicated by the presence of numerous mobile and repeated elements.

SIGNIFICANCE AND IMPACT OF THE STUDY

The B. cereus group of bacteria comprises species that are of medical and economic importance. The MLST data, along with the primers and protocols used, will be available in a public, web-accessible database (http://mlstoslo.uio.no).

Differentiation between Bacillus thuringiensis strains by gyrB PCR-Sau3Al fingerprinting

gyrB DNA fragments of seven Bacillus thuringiensis local collection family representatives were amplified by PCR and sequenced. Several differences in their corresponding sequences were evidenced. Both in silico and in vitro restriction maps of gyrB sequences and fragments respectively confirmed that EcoRI and Sau3AI could be used to differentiate between B. thuringiensis strains. However, the phylogeny analysis showed that only the gyrB PCR-Sau3AI allows a strains classification that correlates very well with that obtained on the basis of the sequences analysis. Thus, these finds show that gyrB PCR- Sau3AI digestion could be considered as an efficient, rapid, and easy method to make a distinction, not only between strains belonging to the Bacillus cereus group, but also between those belonging to B. thuringiensis.

Differential identification of Bacillus anthracis from environmental Bacillus species using microarray analysis

AIMS

To determine whether microarray analysis could be employed for the differential identification of a range of environmental Bacillus sp. from four strains of Bacillus anthracis.

METHODS AND RESULTS

Oligonucleotide probes were designed that were specific to virulence factor genes of B. anthracis (pag, lef and cap), the variable number tandem repeat region of the B. anthracis vrrA gene and to the 16S-23S rRNA intergenic transcribed spacer region (ITS) and pleiotropic regulator (plcR) regions of the Bacillus cereus subgroup species. Generic probes were also designed to hybridize with conserved regions of the 16S rRNA genes of Bacillus (as a positive control), Neisseria sp., Pseudomonas sp., Streptococcus sp., Mycobacterium sp. and to all members of the Enterobacteriaceae to allow simultaneous detection of these bacteria. Identification of B. anthracis was found to rely entirely on hybridization of DNA specific to regions of the pag, lef and cap genes. Cross-reaction was observed between B. anthracis and other Bacillus species with all the other Bacillus probes tested. Results obtained using microarray hybridizations were confirmed using conventional microbiological techniques and found to have very high comparability.

CONCLUSIONS

Microarray-based assays are an effective method for the identification of B. anthracis from mixed-culture environmental samples without problems of false-positivity that have been observed with conventional PCR assays.

SIGNIFICANCE AND IMPACT OF THE STUDY

Identification of environmental Bacillus sp. by conventional PCR is prone to potential for reporting false-positives. This study provides a method for the exclusion of such isolates.

Diversity of 16S rRNA gene, ITS region and aclB gene of the Aquificales

The Aquificales are prevalent members of the microbial communities inhabiting many marine and terrestrial hydrothermal systems. Numerous new strains were obtained from deep-sea and terrestrial hydrothermal systems. In order to resolve the phylogenetic relationships within this group, three different phylogenetic datasets were used, namely the 16S rRNA gene, the intergenic transcribed spacer region between the 16S rRNA and 23S rRNA genes (ITS) and the gene coding for the ATP citrate lyase (aclB), a key enzyme in the reductive TCA cycle. The data were analyzed using neighbor-joining, parsimony and maximum likelihood. The resulting phylogenies appeared to be consistent between the three markers. The three genes confirmed the presence of isolates that merit further characterization and descriptions as new species and perhaps even new genera. The detailed phylogenetic interrelationships of these isolates are described here.

Strategy for identification of Bacillus cereus and Bacillus thuringiensis strains closely related to Bacillus anthracis

Bacillus cereus strains that are genetically closely related to B. anthracis can display anthrax-like virulence traits (A. R. Hoffmaster et al., Proc. Natl. Acad. Sci. USA 101:8449-8454, 2004). Hence, approaches that rapidly identify these "near neighbors" are of great interest for the study of B. anthracis virulence mechanisms, as well as to prevent the use of such strains for B. anthracis-based bioweapon development. Here, a strategy is proposed for the identification of near neighbors of B. anthracis based on single nucleotide polymorphisms (SNP) in the 16S-23S rRNA intergenic spacer (ITS) containing tRNA genes, characteristic of B. anthracis. By using restriction site insertion-PCR (RSI-PCR) the presence of two SNP typical of B. anthracis was screened in 126 B. cereus group strains of different origin. Two B. cereus strains and one B. thuringiensis strain showed RSI-PCR profiles identical to that of B. anthracis. The sequencing of the entire ITS containing tRNA genes revealed two of the strains to be identical to B. anthracis. The strict relationship with B. anthracis was confirmed by multilocus sequence typing (MLST) of four other independent loci: cerA, plcR, AC-390, and SG-749. The relationship to B. anthracis of the three strains described by MLST was comparable and even higher to that of four B. cereus strains associated with periodontitis in humans and previously reported as the closest known strains to B. anthracis. SNP in ITS containing tRNA genes combined with RSI-PCR provide a very efficient tool for the identification of strains closely related to B. anthracis.

The autolytic phenotype of the Bacillus cereus group

AIM

To determine the autolytic phenotype of five species in the Bacillus cereus group.

METHODS AND RESULTS

The autolytic rate of 96 strains belonging to five species in the B. cereus group was examined under starvation conditions at pH 6, 6.5 and 8.5 in different buffers. The autolytic rate was strain-dependent with a wide variability at pH 6, but higher and more uniform at pH 6.5. At pH 8.5, and respect to the extent of autolysis at pH 6.5, it was relatively low for most of the strains with the lowest values between 13 and 52% in Bacillus mycoides and Bacillus pseudomycoides. Peptidoglycan hydrolase patterns evaluated by renaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis using cells of Bacillus thuringiensis ssp. tolworthi HD125 as an indicator, revealed complex profiles with lytic bands of about 90, 63, 46, 41, 38, 32, 28 and 25 kDa in B. cereus, B. thuringiensis and Bacillus weihenstephanensis. Bacillus mycoides and B. pseudomycoides had simpler profiles with lytic bands of 63, 46 and 38 kDa. Changes in the autolytic pattern were observed for cells harvested at the stationary phase of growth (72 h) showing an increase in the intensity of the 25 kDa band in the case of B. cereus, B. thuringiensis and B. weihenstephanensis, while no changes were observed for B. mycoides. Using Micrococcus lysodeicticus and Listeria monocytogenes as indicators lytic activity was retained by proteins of 63, 46, 38, 32 and 25 kDa and a new one of about 20 kDa in B. mycoides. Growth in the different media did not affect the autolytic pattern. NaCl abolished the activity of all the peptidoglycan hydrolases except for those of B. mycoides and B. weihenstephanensis. Lytic activity was retained in the presence of MgCl(2), MnCl(2) and EDTA and increased at basic pH.

CONCLUSIONS

Bacillus cereus/B. thuringiensis/B. weihenstephanensis showed a high extent of autolysis around neutral pH, even though they presented relatively complex autolysin profiles at alkaline pH. Bacillus mycoides/B. pseudomycoides had a higher extent of autolysis at acidic pH and a simpler autolysin pattern.

SIGNIFICANCE AND IMPACT OF THE STUDY

Information on the autolytic phenotype expand the phenotypic characterization of the different species in the B. cereus group.

Comparison of minisatellite polymorphisms in the Bacillus cereus complex: a simple assay for large-scale screening and identification of strains most closely related to Bacillus anthracis

Polymorphism of five tandem repeats that are monomorphic in Bacillus anthracis was investigated in 230 isolates of the B. cereus group and in 5 sequenced B. cereus genomes in search for markers allowing identification of B. cereus and B. thuringiensis strains most closely related to B. anthracis. Using this multiple-locus variable number of tandem repeat analysis (MLVA), a cluster of 30 strains was selected for further characterization. Eventually, six of these were characterized by multilocus sequence type analysis. One of the strains is only six point mutations (of almost 3,000 bp) away from B. anthracis and was also proposed to be closest to B. anthracis by MLVA analysis. However, this strain remains separated from B. anthracis by a number of significant genetic events observed in B. anthracis, including the loss of the hemolysin activity, the presence of four prophages, and the presence of the two virulence plasmids, pXO1 and pXO2. One particular minisatellite marker provides an efficient assay to identify the subset of B. cereus and B. thuringiensis strains closely related to B. anthracis. Based on these results, a very simple assay is proposed that allows the screening of hundreds of strains from the B. cereus complex, with modest equipment and at a low cost, to eventually fill the gap with B. anthracis and better understand the origin and making of this dangerous pathogen.

Establishment of a novel multiplex PCR assay and detection of toxigenic strains of the species in the Bacillus cereus group

Five different enterotoxins and one emetic toxin of Bacillus cereus have been characterized. To amplify all of the enterotoxin and emetic-specific sequences of the species in the B. cereus group, a multiplex PCR with 12 primer pairs was established. In developing the assay method, a common terminal sequence at the 3' ends of all primers was chosen and a hot start Taq polymerase was used to overcome primer dimer formation. The assay was successfully applied to analyze the toxigenic potential of 162 food-poisoning and food-related strains. Results showed that there were 10 toxigenic patterns for all the test strains. All of the B. cereus strains carried at least one toxin gene. More than 70% of Bacillus mycoides strains carried no known toxin genes. The toxin profiles and toxin genes of B. mycoides strains were significantly different from B. cereus strains (P < 0.05), although the two species were closely related. The results suggest that many B. mycoides strains might be less prone to cause food poisoning. They also indicate the importance of detecting the toxin genes together with the detection of the species in the B. cereus group.

Development of a rapid detection and enumeration method for thermophilic bacilli in milk powders

Thermophilic strains of Geobacillus, Anoxybacillus and Bacillus that are able to grow at 55 degrees C and above are recognized as commonly occurring contaminants during the production of milk powders. In particular, Anoxybacillus flavithermus strain C and Bacillus licheniformis strain F are often the most prevalent. We describe here the development of a TaqMan-based real-time-PCR assay using a small amplicon of the ribosomal 16S rRNA gene for the selective and quantitative detection of thermophilic bacilli in milk powders. We further present an effective, rapid and inexpensive method for the isolation of total bacterial DNA from milk powder for quantitative PCR analysis within 20 min. With this method, the detection of thermophilic bacilli in milk powder can be accomplished within 1 h. The detection limit for reconstituted and inoculated milk was 8 vegetative cfu ml(-1) and 64 spores ml(-1), respectively.

Microarray-based resequencing of multiple Bacillus anthracis isolates

Custom-designed resequencing arrays were used to generate 3.1 Mb of genomic sequence from a panel of 56 Bacillus anthracis strains. Sequence quality was shown to be very high by replication and by comparison to independently generated shotgun sequence

We used custom-designed resequencing arrays to generate 3.1 Mb of genomic sequence from a panel of 56 Bacillus anthracis strains. Sequence quality was shown to be very high by replication (discrepancy rate of 7.4 × 10^-7) and by comparison to independently generated shotgun sequence (discrepancy rate < 2.5 × 10^-6). Population genomics studies of microbial pathogens using rapid resequencing technologies such as resequencing arrays are critical for recognizing newly emerging or genetically engineered strains.

Comparison of different primer sets for use in automated ribosomal intergenic spacer analysis of complex bacterial communities

ITSF and ITSReub, constituting a new primer set designed for the amplification of the 16S-23S rRNA intergenic transcribed spacers, have been compared with primer sets consisting of 1406F and 23Sr (M. M. Fisher and E. W. Triplett, Appl. Environ. Microbiol. 65:4630-4636, 1999) and S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 (L. Ranjard et al., Appl. Environ. Microbiol. 67:4479-4487, 2001), previously proposed for automated ribosomal intergenic spacer analysis (ARISA) of complex bacterial communities. An agricultural soil and a polluted soil, maize silage, goat milk, a small marble sample from the facade of the Certosa of Pavia (Pavia, Italy), and brine from a deep hypersaline anoxic basin in the Mediterranean Sea were analyzed with the three primer sets. The number of peaks in the ARISA profiles, the range of peak size (width of the profile), and the reproducibility of results were used as indices to evaluate the efficiency of the three primer sets. The overall data showed that ITSF and ITSReub generated the most informative (in term of peak number) and reproducible profiles and yielded a wider range of spacer sizes (134 to 1,387) than the other primer sets, which were limited in detecting long fragments. The minimum amount of DNA template and sensitivity in detection of minor DNA populations were evaluated with artificial mixtures of defined bacterial species. ITSF and ITSReub amplified all the bacteria at DNA template concentrations from 280 to 0.14 ng microl(-1), while the other primer sets failed to detect the spacers of one or more bacterial strains. Although the primer set consisting of ITSF and ITSReub and that of S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 showed similar sensitivities for the DNA of Allorhizobium undicula mixed with the DNA of other species, the S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 primer set failed to detect the DNA of Pseudomonas stutzeri.

Oligonucleotide microarray for identification ofBacillus anthracisbased on intergenic transcribed spacers in ribosomal DNA

We developed a DNA microarray for identification of Bacillus anthracis and other phylogenetic groupings within the "Bacillus cereus group". Nucleotide sequences of 16S-23S ribosomal DNA internal transcribed spacers containing genes for tRNA(Ile) from 52 B. anthracis strains were found to be identical to sequences from seven strains published previously and different from all other bacteria. When 42 oligonucleotide probes targeting polymorphic sites were immobilized on glass slides and hybridized to fluorescently labeled PCR amplification products, one or more mismatches could be discriminated in all but one cases. Hence, hybridization events were highly specific and identification of B. anthracis was straightforward.

Invertebrates as a source of emerging human pathogens

Despite their importance, little is known about the origins of many emerging human pathogens. However, given the age and current predominance of invertebrates, it is likely that bacteria-invertebrate interactions are not only a present source of human pathogens but have also shaped their evolution. Pathogens of invertebrate and unicellular organisms represent an extensive reservoir of bacterial strains equipped with virulence factors that evolved to overcome the innate immune responses of their hosts. This reservoir might represent a source of new human pathogenic strains and might also foster the spread of novel virulence factors into existing human commensal or pathogenic bacteria. This article examines the available evidence for this concept by examining pairs of closely related bacteria, one of which is benign, but insect associated, and one of which is a human pathogen.

Population structure of the Bacillus cereus group as determined by sequence analysis of six housekeeping genes and the plcR Gene

The population structure of the Bacillus cereus group (52 strains of B. anthracis, B. cereus, and B. thuringiensis) was investigated by sequencing seven gene fragments (rpoB, gyrB, pycA, mdh, mbl, mutS, and plcR). Most of the strains were classifiable into two large subgroups in six housekeeping gene trees but not in the plcR tree. In addition, several consistent clusters were identified, which were unrelated to species distinction. Moreover, interrelationships among these clusters were incongruent in each gene tree. The incongruence length difference test and split decomposition analyses also showed incongruences between genes, suggesting horizontal gene transfer. The plcR gene was observed to have characteristics that differed from those of the other genes in terms of phylogenetic topology and pattern of sequence diversity. Thus, we suggest that the evolutionary history of the PlcR regulon differs from those of the other chromosomal genes and that recombination of the plcR gene may be frequent. The homogeneity of B. anthracis, which is depicted as an independent lineage in phylogenetic trees, is suggested to be of recent origin or to be due to the narrow taxonomic definition of species.

Detection and characterization of the novel bacteriocin entomocin 9, and safety evaluation of its producer, Bacillus thuringiensis ssp. entomocidus HD9

AIMS

To identify and characterize new bacteriocins from a collection of 41 strains belonging to 27 subspecies of Bacillus thuringiensis, and to evaluate the safety of the producers.

METHODS AND RESULTS

Bacillus thuringiensis ssp. entomocidus HD9 produced in the culture supernatant an antimicrobial activity against Gram-positive bacteria including Listeria monocytogenes, one of four pathogenic Pseudomonas aeruginosa and several fungi. Production of the antibacterial activity, named entomocin 9, started during mid-logarithmic growth reaching its maximum at the early stationary phase. Entomocin 9 retained more than 72% of activity after incubation for 20 min at 121 degrees C. Activity was lost after proteinase K treatment, it was stable in a pH range between 3 and 9, and resistant to lyophilization. After partial purification with ammonium sulphate precipitation followed by gel-filtration and anion-exchange chromatography, an active protein of ca 12.4 kDa was isolated. The mode of action of entomocin 9 was bactericidal and caused cell lysis of growing cells. Despite the presence of a range of virulence related genes, including haemolysin BL, nonhaemolytic enterotoxin, cytotoxin K and several hydrolytic activities, B. thuringiensis HD9 was not toxic against Vero cells.

CONCLUSIONS

Entomocin 9 is a novel heat-stable, bacteriocin produced by B. thuringiensis HD9. The absence of toxicity against Vero cells suggests the suitability of strain HD9 for a safe application in antimicrobial treatments.

SIGNIFICANCE AND IMPACT OF THE STUDY

New finding on entomocin 9 would make B. thuringiensis attractive in biotechnological applications as an antimicrobial agent in agriculture and food industry.

Nature of polymorphisms in 16S-23S rRNA gene intergenic transcribed spacer fingerprinting of Bacillus and related genera

The intergenic transcribed spacers (ITS) between the 16S and 23S rRNA genetic loci are frequently used in PCR fingerprinting to discriminate bacterial strains at the species and intraspecies levels. We investigated the molecular nature of polymorphisms in ITS-PCR fingerprinting of low-G+C-content spore-forming bacteria belonging to the genera Bacillus, Brevibacillus, Geobacillus, and Paenibacillus: We found that besides the polymorphisms in the homoduplex fragments amplified by PCR, heteroduplex products formed during PCR between amplicons from different ribosomal operons, with or without tRNA genes in the ITS, contribute to the interstrain variability in ITS-PCR fingerprinting patterns obtained in polyacrylamide-based gel matrices. The heteroduplex nature of the discriminating bands was demonstrated by fragment separation in denaturing polyacrylamide gels, by capillary electrophoresis, and by cloning, sequencing, and recombination of purified short and tRNA gene-containing long ITS. We also found that heteroduplex product formation is enhanced by increasing the number of PCR cycles. Homoduplex-heteroduplex polymorphisms (HHP) in a conserved region, such as the 16S and 23S rRNA gene ITS, allowed discrimination of closely related strains and species undistinguishable by other methods, indicating that ITS-HHP analysis is an easy and reproducible additional tool for strain typing.

Genetic relationship in the 'Bacillus cereus group' by rep-PCR fingerprinting and sequencing of a Bacillus anthracis-specific rep-PCR fragment

AIMS

To evaluate the genetic relationship in the Bacillus cereus group by rep-PCR fingerprinting.

METHODS AND RESULTS

A collection of 112 strains of the six species of the B. cereus group was analysed by rep-PCR fingerprinting using the BOX-A1R primer. A relative genetic distinctness was found among the species. Cluster analysis of the rep-PCR patterns showed clusters of B. thuringiensis strains quite separate from those of B. cereus strains. The B. anthracis strains represented an independent lineage in a B. cereus cluster. The B. mycoides, B. pseudomycoides and B. weihenstephanensis strains were clustered into three groups at some distance from the other species. Comparison of sequences of AC-390, a typical B. anthracis rep-PCR fragment, from 27 strains of B. anthracis, B. cereus, B. thuringiensis and B. weihenstephanensis, representative of different clusters identified by rep-PCR fingerprinting, confirmed that B. anthracis diverges from its related species.

CONCLUSIONS

The genetic relationship deduced from the rep-PCR patterns indicates a relatively clear separation of the six species, suggesting that they can indeed be considered as separate units.

SIGNIFICANCE AND IMPACT OF THE STUDY

rep-PCR fingerprinting can make a contribution in the clarification of the genetic relationships between the species of the B. cereus group.