Identification of thermoacidophilic bacteria and a new Alicyclobacillus genomic species isolated from acidic environments in Japan

Sixty strains of thermoacidophilic bacteria have been isolated from soil and water samples obtained from various acidic environments in Japan. An initial comparative sequence analysis of the hypervariable regions of the 16S rDNA revealed that all strains could be assigned to the Alicyclobacillus acidocaldarius- Alicyclobacillus genomic species 1 group, which could be further subdivided into three clusters (Clusters I-III). On the basis of phenotypic characteristics, chemotaxonomic profiles, and phylogenetic data of six selected strains, five strains were identified as either A. acidocaldarius or Alicyclobacillus genomic species 1; however, one strain (MIH 332) could not be determined to belong to either of these species. 16S rDNA sequence homology values between strain MIH 332 and the reference strains of A. acidocaldarius (ATCC 27009(T)) and Alicyclobacillus genomic species 1 (DSM 11984) were 98.8% and 99.1%, respectively, which were higher than the corresponding similarity between the reference strains (98.4%). On the other hand, DNA-DNA hybridization levels between strain MIH 332 and the reference strains were 39% and 44%, respectively, which were lower than the value between the reference strains (59% or 65%). However, the phenotype of strain MIH 332 was also similar to those of the reference strains, and a typical phenotype could not be found for the strain, thus indicating that the strain may be a new genomic species of A. acidocaldarius, for which the name Alicyclobacillus genomic species 2 is tentatively proposed. The results of this study suggest that A. acidocaldarius and its related species are widely distributed in acidic environments in Japan, with slight regional variations in morphological and genotypic characteristics.     

Phylogenetic characterization of a new thermoacidophilic bacterium isolated from hot springs in Japan

Three strains of thermophilic-acidophilic bacteria isolated previously from different hot springs in Japan were characterized by molecular genetic methods. The strategy taken involved PCR amplification, sequencing and restriction pattern analysis of 16S rDNA, 16S-23S rDNA spacer polymorphism analysis and genomic DNA-DNA hybridization. A phylogenetic analysis based on 16S rDNA sequences showed that the new thermoacidophilic isolates formed a genetically coherent group at the species level and fell into a major cluster together with members of the genera Alicyclobacillus and Sulfobacillus with A. acidocaldarius and A. acidoterrestris as their closest relatives. The levels of binary sequence similarity between the isolates and the two Alicyclobacillus species were 97.6 to 97.9%, values considered low enough to warrant placement of the isolates in a distinct species of the genus Alicyclobacillus. The 16S rDNA restriction pattern analysis, but not 16S-23S rDNA spacer polymorphism analysis, was useful for differentiating the isolates from the established Alicyclobacillus species. DNA-DNA hybridization assays demonstrated a distinct phylogenetic position of our isolates as a genospecies within the genus Alicyclobacillus. On the basis of these results, the thermoacidophilic isolates should be classified into a new species of Alicyclobacillus. The results of this study suggest that this new genospecies of Alicyclobacillus is widely distributed in hot springs in Japan.     

Structure and patterns of sequence variation in the mitochondrial DNA control region of the great cats

Mitochondrial DNA control region structure and variation were determined in the five species of the genus Panthera. Comparative analyses revealed two hypervariable segments, a central conserved region, and the occurrence of size and sequence heteroplasmy. As observed in the domestic cat, but not commonly seen in other animals, two repetitive sequence arrays (RS-2 with an 80-bp motif and RS-3 with a 6-10-bp motif) were identified. The 3' ends of RS-2 and RS-3 were highly conserved among species, suggesting that these motifs have different functional constraints. Control region sequences provided improved phylogenetic resolution grouping the sister taxa lion (Panthera leo) and leopard (Panthera pardus), with the jaguar (Panthera onca).     

Nucleotide sequence diversity of rDNA internal transcribed spacers extracted from conidia and cleistothecia of several powdery mildew fungi

An improved protocol, including DNA extraction with Chelex, two amplifications with a nested primer set, and DNA purification by electrophoresis, made it possible to analyze nuclear rDNA sequences of powdery mildew fungi using at most several hundred conidia or 20 cleistothecia. Nucleotide sequence diversity of the nuclear rDNA region containing the two internal transcribed spacers (ITS1 and ITS2) and 5.8S rRNA gene derived from conidia and cleistothecia was investigated for four kinds of powdery mildew fungi including two isolates of the same species. The results showed that the nucleotide sequences of the nuclear rDNA region were highly conserved between the teleomorph and the anamorph. Thus, the nucleotide sequence data obtained from either developmental stage can be used for phylogenetic studies of powdery mildew fungi. The nucleotide sequences of the 5.8S rRNA genes of the four species were highly conserved, but those of their ITS regions were variable. This suggests that the nuclear rDNA region is not suitable for phylogenetic studies of distantly related powdery mildew fungi, because too much sequence diversity exists, within the ITS, and too little phylogenetic information is contained within the 5.8S rRNA gene. However, the ITS region will be useful for phylogenetic comparison of closely related species or intraspecies. Contribution No. 132 from the Laboratory of Plant Pathology, Mie University.     

Bacterial phylogenetic clusters revealed by genome structure.

Current bacterial taxonomy is mostly based on phenotypic criteria, which may yield misleading interpretations in classification and identification. As a result, bacteria not closely related may be grouped together as a genus or species. For pathogenic bacteria, incorrect classification or misidentification could be disastrous. There is therefore an urgent need for appropriate methodologies to classify bacteria according to phylogeny and corresponding new approaches that permit their rapid and accurate identification. For this purpose, we have devised a strategy enabling us to resolve phylogenetic clusters of bacteria by comparing their genome structures. These structures were revealed by cleaving genomic DNA with the endonuclease I-CeuI, which cuts within the 23S ribosomal DNA (rDNA) sequences, and by mapping the resulting large DNA fragments with pulsed-field gel electrophoresis. We tested this experimental system on two representative bacterial genera: Salmonella and Pasteurella. Among Salmonella spp., I-CeuI mapping revealed virtually indistinguishable genome structures, demonstrating a high degree of structural conservation. Consistent with this, 16S rDNA sequences are also highly conserved among the Salmonella spp. In marked contrast, the Pasteurella strains have very different genome structures among and even within individual species. The divergence of Pasteurella was also reflected in 16S rDNA sequences and far exceeded that seen between Escherichia and Salmonella. Based on this diversity, the Pasteurella haemolytica strains we analyzed could be divided into 14 phylogenetic groups and the Pasteurella multocida strains could be divided into 9 groups. If criteria for defining bacterial species or genera similar to those used for Salmonella and Escherichia coli were applied, the striking phylogenetic diversity would allow bacteria in the currently recognized species of P. multocida and P. haemolytica to be divided into different species, genera, or even higher ranks. On the other hand, strains of Pasteurella ureae and Pasteurella pneumotropica are very similar to those of P. multocida in both genome structure and 16S rDNA sequence and should be regarded as strains within this species. We conclude that large-scale genome structure can be a sensitive indicator of phylogenetic relationships and that, therefore, I-CeuI-based genomic mapping is an efficient tool for probing the phylogenetic status of bacteria.     

Structural conservation and variation in the mitochondrial control region of fringilline finches (Fringilla spp.) and the greenfinch (Carduelis chloris)

We sequenced the entire control region and portions of flanking genes (tRNA(Phe), tRNA(Glu), and ND6) in the common chaffinch (Fringilla coelebs), blue chaffinch (F. teydea), brambling (F. montifringilla), and greenfinch (Carduelis chloris). In these finches the control region is similar in length (1,223-1,237 bp) and has the same flanking gene order as in other birds, and contains a putative TAS element and the highly conserved CSB-1 and F, D, and C boxes recognizable in most vertebrates. Cloverleaf-like structures associated with the TAS element at the 5' end and CSB-1 at the 3' end of the control region may be involved with the stop and start of D-loop synthesis, respectively. The pattern of nucleotide and substitution bias is similar to that in other vertebrates, and consequently the finch control region can be subdivided into a central, conserved G-rich domain (domain II) flanked by hypervariable 5'-C-rich (domain I) and 3'-AT-rich (domain III) segments. In pairwise comparisons among finch species, the central domain has unusually low transition/transversion ratios, which suggests that increased G + T content is a functional constraint, possibly for DNA primase efficiency. In finches the relative rates of evolution vary among domains according to a ratio of 4.2 (domain III) to 2.2 (domain I) to 1 (domain II), and extensively among sites within domains I and II. Domain I and III sequences are extremely useful in recovering intraspecific phylogeographic splits between populations in Africa and Europe, Madeira, and a basal lineage in Nefza, Tunisia. Domain II sequences are highly conserved, and are therefore only useful in conjunction with sequences from domains I and III in phylogenetic studies of closely related species.      

Coevolution of symbiotic spirochete diversity in lower termites.

The phylogenetic relationships of symbiotic spirochetes from five dry-wood feeding lower termites (Cryptotermes cavifrons, Heterotermes tenuis, Kalotermes flavicollis, Neotermes mona, and Reticulitermes grassei) was compared to those described in previous reports. The 16S rDNA bacterial genes were PCR-amplified from DNA isolated from intestinal samples using a spirochete-selective primer, and the 16S amplicons were cloned into Escherichia coli. Sequences of the cloned inserts were then used to determine closest relatives by comparison with published sequences. Clones sharing more than 97% sequence identity were grouped into the same phylotype. Forty-three new phylotypes were identified. These termite whole-gut-spirochetes fell into two previous defined clusters, designated as Treponema Clusters I and II, and one new Cluster III. Thirty-seven phylotypes were grouped in Cluster I. Cluster II comprised three phylotypes, two from Reticulitermes grassei (LJ029 and LJ012) and one from Heterotermes tenuis (LQ016). Three phylotypes, LK057, LK050 and LK028, were affiliated to Cluster III. Members of Cluster I showed the following characteristics: (i) spirochete phylotypes from a particular species of termite were more closely related to each other than to phylotypes of other termite species; (ii) spirochetes obtained from different genera of the same family, such as Cryptotermes sp., Kalotermes sp., and Neotermes sp., all from the family Kalotermitidae, were also related to each other. It was therefore concluded that spirochetes are specific symbionts that have coevolved with their respective species of termites, are stably harbored, and are closely related to members of the same termite family.     

广西不同时期IBV分离株S1基因高变区Ⅰ的遗传变异分析

对广西1985-2007年间分离到的22株传染性支气管炎病毒（IBV）的S1基因高变区I（HVRI）进行序列测定,并与发表的其他IBV参考株及鸽子分离的冠状病毒株的基因序列进行比较和分析。系统进化关系显示毒株可分为5个基因群,其中有16个广西分离株属第1群,它们与鸽子冠状病毒分离株的氨基酸序列同源性较高,与Massachusetts（Mass）型疫苗株的同源性较低。有15个分离株在33-34位和34～35之间分别有4个和3个氨基酸残基的插入,GX-NN6在33～34位和34～35位之间则均有4个氨基酸残基的插入;GX-YL1、GX-NN2与常用的Mass型疫苗株的亲缘关系最近,同属于第Ⅱ群;GX-G、GX-XD与日本同一时期分离的毒株JP Miyazaki 89亲缘关系最近,属于第Ⅲ群;GX-YL6、GX-NN7与欧洲毒株4／91亲缘关系较近,属于第V群。结果表明广西存在着多种类型IBV毒株的流行,毒株S1基因HVRI碱基的突变或插入比较普遍,可导致其氨基酸序列的变化,绝大部分毒株与目前常用的Mass型疫苗株的亲缘关系较低。同一时期的分离株同源性较高,但无明显的地域性差异。     

Cloning and characterization of cDNAs encoding S-RNases from almond (Prunus dulcis): primary structural features and sequence diversity of the S-RNases in Rosaceae

cDNAs encoding three S-RNases of almond (Prunus dulcis), which belongs to the family Rosaceae, were cloned and sequenced. The comparison of amino acid sequences between the S-RNases of almond and those of other rosaceous species showed that the amino acid sequences of the rosaceous S-RNases are highly divergent, and intra-subfamilial similarities are higher than inter-subfamilial similarities. Twelve amino acid sequences of the rosaceous S-RNases were aligned to characterize their primary structural features. In spite of?their high level of diversification, the rosaceous S-RNases were found to have five conserved regions, C1, C2, C3, C5, and RC4 which is Rosaceae-specific conserved region. Many variable sites fall into one region, named RHV. RHV is located at a similar position to that of the hypervariable region a (HVa) of the solanaceous S-RNases, and is assumed to be involved in recognizing S-specificity of pollen. On the other hand, the region corresponding to another solanaceous hypervariable region (HVb) was not variable in the rosaceous S-RNases. In the phylogenetic tree of the T2/S type RNase, the rosaceous S-RNase fall into two subfamily-specific groups (Amygdaloideae and Maloideae). The results of sequence comparisons and phylogenetic analysis imply that the present S-RNases of Rosaceae have diverged again relatively recently, after the divergence of subfamilies.     

Application of the partial 16S rDNA sequence as an index for rapid identification of species in the genus Bacillus

A comparison of 16S rRNA gene (rDNA) sequences was made among type strains of 69 Bacillus species approved in the International Journal of Systematic Bacteriology (IJSB) until 1998. The results suggested that 5' end region (approx. 275 bp) was the hypervariant region (HV region) in the gene and was highly specific for each type strain. Furthermore, a sequence analysis of the HV region of Bacillus strains revealed that this region was highly conserved within the species. These results indicate that the HV region is a useful index for the identification or grouping of Bacillus species.     

Molecular Organization of 5S rDNAs in Rajidae (Chondrichthyes): Structural Features and Evolution of Piscine 5S rRNA Genes and Nontranscribed Intergenic Spacers

The genomic and gene organisation of 5S rDNA clusters have been extensively characterized in bony fish and eukaryotes, providing general issues for understanding the molecular evolution of this multigene DNA family. By contrast, the 5S rDNA features have been rarely investigated in cartilaginous fish (only three species). Here, we provide evidence for a dual 5S rDNA gene system in the Rajidae by sequence analysis of the coding region (5S) and adjacent nontranscribed spacer (NTS) in five Mediterranean species of rays (Rajidae), and in a large number of piscine taxa including lampreys and bony fish. As documented in several bony fish, two functional 5S rDNA types were found here also in the rajid genome: a short one (I) and a long one (II), distinguished by distinct 5S and NTS sequences. That the ancestral piscine genome had these two 5S rDNA loci might be argued from the occurrence of homologous dual gene systems that exist in several fish taxa and from 5S phylogenetic relationships. An extensive analysis of NTS-II sequences of Rajidae and Dasyatidae revealed the occurrence of large simple sequence repeat (SSR) regions that are formed by microsatellite arrays. The localization and organization of SSR within the NTS-II are conserved in Rajiformes since the Upper Cretaceous. The direct correlation between the SSRs extension and the NTS length indicated that they might play a role in the maintenance of the larger 5S rDNA clusters in rays. The phylogenetic analysis indicated that NTS-II is a valuable systematic tool limited to distantly related taxa of Rajiformes. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Rafael Zardoya]     

免培养法对一热泉细菌多样性的初步研究

应用免培养法（Cultureindependent）对云南腾冲热海大滚锅高温热泉中细菌的多样性进行初步的分析。经过克隆筛选,测定了5个克隆的16S rDNA插入片段的近全序列,系统发育分析的结果表明,它们分属于Bacillus、Hydrogenobacter和Pseudomonas,有一个克隆尚难确定其分类地位,它属于Thermodesulfobacteriaceae科,介于Geothermbacterium属和Thermodesulfobacteria属之间。经PCR扩增出上述5个克隆16S rDNA插入序列中及环境样品总DNA中的16S rDNA V8高变区约600bp片段,进行变性梯度电泳（DGGE）。所得电泳图谱和5个序列的系统发育树不仅表明该高温热泉存在着丰富的细菌多样性,还显示了它们是该高温热泉中细菌的优势物种。     

The phylogenetic diversity of thermophilic members of the genus Bacillus as revealed by 16S rDNA analysis

Abstract Sixteen thermophilic strains of the genus Bacillus , representing eight validly described and six invalidly described species, as well as one unassigned strain, were investigated by comparative 16S rDNA analyses and the sequences compared to the existing database for the genera Bacillus and Alicyclobacillus . The majority of strains were found to cluster in two groups represented by B. stearothermophilus and B. pallidus. Bacillus smithii, B. thermocloacae , and B. thermoruber are phylogenetically well separated and cluster within the radiation of mesophilic bacilli. The as yet undescribed taxon 'B. flavothermus' warrants species status. B. schlegelii and B. tusciae group peripherally with members of Alicyclobacillus and may be reclassified when more phenotypic data support their phylogenetic position.     

Heterogeneity of ITS1 sequences in the biting midge Culicoides impunctatus (Goetghebuer) suggests a population in Argyll, Scotland, may be genetically distinct.

Ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1) is a useful genomic region for understanding evolutionary and genetic relationships. In the current study, variation in ITS1 from eight Culicoides species was analysed by PCR, DNA restriction analysis, cloning, and sequencing. ITS1 variants were essentially homogenized within a species, as sequences were identical or closely related. However, Culicoides impunctatus ITS1 sequences derived from one (Argyll) of five populations contained considerable genomic diversity. The secondary structure of each ITS1 was computed. The structure aided the production of an accurate alignment and the identification of a large indel. A phylogenetic analysis was performed. Some of the sequences from the diverse Argyll C. impunctatus population were more related to Culicoides imicola, a vector of animal pathogens in the Old World, than they were to the other C. impunctatus sequences. Thus, the rDNA ITS1 regions of individuals in the Argyll C. impunctatus population were not conforming to the general theory of rDNA homogenization through molecular drive.     

Genetic diversity of Paramecium species on the basis of multiple loci analysis and ITS secondary structure models

Among ciliates, Paramecium has become a privileged model for the study of “species problem” particularly in the case of the “Paramecium aurelia complex” that has been intensely investigated. Despite extensive studies, the taxonomy of Paramecium is still challenging. The major problem is an uneven sampling of Paramecium with relatively few representatives of each species. To investigate species from the less discovered region (Pakistan), 10 isolates of Paramecium species including a standing-alone FT8 strain previously isolated by some of us were subjected to molecular characterization. Fragments of 18S recombinant DNA (rDNA), ITS1-5.8S-ITS2-5′LSU rDNA, cytochrome c oxidase subunit II, and hsp70 genes were used as molecular markers for phylogenetic analysis of particular isolates. The nucleotide sequences of polymerase chain reaction products of all markers were compared with the available sequences of relevant markers of other Paramecium species from GenBank. Phylogenetic trees based on all molecular markers showed that all the nine strains had a very close relationship with Paramecium primaurelia except for the FT8 strain. FT8 consistently showed its unique position in comparison to all other species in the phylogenetic trees. Available sequences of internal transcribed spacer 1 (ITS1) and ITS2 and some other ciliate sequences from GenBank were used for the construction of secondary models. Two highly conserved helices supported by compensatory base changes among all ciliates of ITS2 secondary structures were found similar to other eukaryotes. Therefore, the most conserved 120 to 180 base pairs regions were identified for their comparative studies. We found that out of the three helices in ITS1 structure, helix B was more conserved in Paramecium species. Despite various substitutions in the primary sequence, it was observed that secondary structures of ITS1 and ITS2 could be helpful in interpreting the phylogenetic relationships both at species as well as at generic level.     

PCR assay of the groEL gene for detection and differentiation of Bacillus cereus group cells

Strains of species in the Bacillus cereus group are potentially enterotoxic. Thus, the detection of all B. cereus group strains is important. As 16S ribosomal DNA sequence analysis cannot adequately differentiate species of the B. cereus group, we explored the potential of the groEL gene as a phylogenetic marker. A phylogenetic analysis of the groEL sequences of 78 B. cereus group strains revealed that the B. cereus group strains were split into two major clusters, one including six B. mycoides and one B. pseudomycoides (cluster II) and the other including two B. mycoides and the rest of the B. cereus group strains (cluster I). Cluster I was further differentiated into two subclusters, Ia and Ib. The sodA gene sequences of representative strains from different clusters were also compared. The phylogenetic tree constructed from the sodA sequences showed substantial similarity to the tree constructed from the groEL sequences. Based on the groEL sequences, a PCR assay for detection and identification of B. cereus group strains was developed. Subsequent restriction fragment length polymorphism (RFLP) analysis verified the PCR amplicons and the differentiation of the B. cereus group strains. RFLP with MboI was identical for all the B. cereus group strains analyzed, while RFLP with MfeI or PstI classified all B. cereus and B. thuringiensis strains into two groups. All cluster II B. mycoides and B. pseudomycoides strains could be discriminated from other B. cereus group bacteria by restriction analysis with TspRI.     

Cloning and characterization of cDNAs encoding S-RNases from almond ( Prunus dulcis ): primary structural features and sequence diversity of the S-RNases in Rosaceae

cDNAs encoding three S-RNases of almond (Prunus dulcis), which belongs to the family Rosaceae, were cloned and sequenced. The comparison of amino acid sequences between the S-RNases of almond and those of other rosaceous species showed that the amino acid sequences of the rosaceous S-RNases are highly divergent, and intra-subfamilial similarities are higher than inter-subfamilial similarities. Twelve amino acid sequences of the rosaceous S-RNases were aligned to characterize their primary structural features. In spite of␣their high level of diversification, the rosaceous S-RNases were found to have five conserved regions, C1, C2, C3, C5, and RC4 which is Rosaceae-specific conserved region. Many variable sites fall into one region, named RHV. RHV is located at a similar position to that of the hypervariable region a (HVa) of the solanaceous S-RNases, and is assumed to be involved in recognizing S-specificity of pollen. On the other hand, the region corresponding to another solanaceous hypervariable region (HVb) was not variable in the rosaceous S-RNases. In the phylogenetic tree of the T2/S type RNase, the rosaceous S-RNase fall into two subfamily-specific groups (Amygdaloideae and Maloideae). The results of sequence comparisons and phylogenetic analysis imply that the present S-RNases of Rosaceae have diverged again relatively recently, after the divergence of subfamilies. Received: 28 May 1998 / Accepted: 13 August 1998     

紫芝基因组rDNA序列特征及ITS2二级结构比较

紫芝栽培品种‘紫芝S2’(武芝2号)的ITS序列与NCBI数据库中5个紫芝菌株/分离株相似度高达99.79%-100%,在系统进化树上相聚成一类。本研究预测‘紫芝S2’基因组与参考基因组中的rRNA基因簇,分析rDNA结构及各构件序列间的多态性。从高质量‘紫芝S2’基因组中挖掘得到完整rDNA,序列全长40.377 kb,由4组串联重复的(18S、5.8S、28S、5S) rRNA基因簇组成,并含有完整的基因内间隔区(ITS1、ITS2)和基因间间隔区(IGS1、IGS2)。在紫芝S2的rDNA中,高度保守的28S rRNA基因间出现3个SNP和2个插入(1 bp,10 bp)位点;虽然第4条ITS2中有1个SNP位点,但紫芝S2的4条ITS2在二级结构上的分子形态高度一致,与ITS2数据库中其他紫芝菌株仅存在螺旋区间夹角的微小差异。由‘紫芝S2’基因组rDNA的ITS2生成的DNA条形码与二维码,可以作为该栽培品种鉴定与同源物种其他菌株鉴别的分子标记。     

Genotypic differentiation of twelve Clostridium species by polymorphism analysis of the triosephosphate isomerase (tpi) gene

Housekeeping genes encoding metabolic enzymes may provide alternative markers to 16S ribosomal DNA (rDNA) for genotypic and phylogenetic characterization of bacterial species. We have developed a PCR-restriction fragment length polymorphism (PCR-RFLP) assay, targeting the triosephosphate isomerase (tpi) gene, which allows the differentiation of twelve pathogenic Clostridium species. Degenerate primers constructed from alignments of tpi sequences of various gram-positive bacteria allowed the amplification of a 501 bp target region in the twelve Clostridium type strains. A phylogenetic tree constructed from the nucleotidic sequences of these tpi amplicons was well correlated with that inferred from analysis of 16S rDNA gene sequences. The analysis of tpi sequences revealed restriction sites of enzyme AluI that could be species-specific. Indeed, AluI digestion of amplicons from the twelve type strains provided distinct restriction patterns. A total of 127 strains (three to sixteen strains for each species) was further analyzed by PCR-RFLP of the tpi gene, and confirmed that each species could be characterized by one to three restriction types (RTs). The differences between RTs within species could be explained by point mutations in AluI restriction sites of the tpi sequences. PCR-restriction analysis of the tpi gene offers an accurate tool for species identification within the genus Clostridium, and provides an alternative marker to 16S rDNA for phylogenetic analyses.     

Identification of Escherichia coli O157:H7 genomic regions conserved in strains with a genotype associated with human infection

Beta-glucuronidase-negative, sorbitol-nonfermenting isolates of Shiga toxin-producing Escherichia coli O157 comprise part of a clone complex of related enterohemorrhagic E. coli isolates. High-resolution genotyping shows that the O157 populations have diverged into two different lineages that appear to have different ecologies. To identify genomic regions unique to the most common human-associated genotype, suppression subtractive hybridization was used to identify DNA sequences present in two clinical strains representing the human lineage I O157:H7 strains but absent from two bovine-derived lineage II strains. PCR assays were then used to test for the presence of these regions in 10 lineage I strains and 20 lineage II strains. Twelve conserved regions of genomic difference for lineage I (CRD(I)) were identified that were each present in at least seven of the lineage I strains but absent in most of the lineage II strains tested. The boundaries of the lineage I conserved regions were further delimited by PCR. Eleven of these CRD(I) were associated with E. coli Sakai S-loops 14, 16, 69, 72, 78, 82, 83, 91 to 93, 153, and 286, and the final CRD(I) was located on the pO157 virulence plasmid. Several potential virulence factors were identified within these regions, including a putative hemolysin-activating protein, an iron transport system, and several possible regulatory genes. Cluster analysis based on lineage I conserved regions showed that the presence/absence of these regions was congruent with the inferred phylogeny of the strains.