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PubMed1985

New class of limited-host-range Agrobacterium mega-tumor-inducing plasmids lacking homology to the transferred DNA of a wide-host-range, tumor-inducing plasmid.

Biotype 1 and 2 strains of Agrobacterium tumefaciens were isolated from crown gall tumors of Lippia canescens plants growing as ground cover in Arizona. The isolates were agrocin 84 sensitive, did not catabolize octopine, nopaline, agropine, or mannopine, and were limited in their tumorigenic host range. One biotype 2 strain, AB2/73, showed the most limited host range; it incited tumors only on Lippia strains, the cucurbit family of plants, and Nicotiana glauca. Megaplasmids were detected in the isolates by vertical agarose gel electrophoresis. The unusual host range, as well as sensitivity to agrocin 84, were plasmid specified since they were conjugally cotransferred with plasmids from donor strain AB2/73. Correlation of deletions with concomitant loss of virulence and agrocin 84 sensitivity identified the megaplasmid pAtAB2/73d as the virulence element in strain AB2/73. The estimated size of this tumor-inducing plasmid was 500 kilobases. Axenic growth of tumor tissue incited by strains carrying pAtAB2/73d was phytohormone independent. Although the limited-host-range megaplasmid pAtAB2/73d lacked any detectable homology to the phytohormone-biosynthetic genes in wide-host-range transferred DNA (tms-1, tms-2, tmr), it showed homology to the wide-host-range virB, virC, virD, and virG loci. Therefore, pAtAB2/73d represents a new class of tumor-inducing plasmids distinguished by its large size, the absence of determinants for the catabolism of several known opines, the presence of agrocin 84 sensitivity, and its lack of homology to wide-host-range transferred DNA contrasted with its conservation of sequences from the wise-host-range vir region.

Adenine Nucleotides↗

PubMed2005

Transcriptional program of early sporulation and stationary-phase events in Clostridium acetobutylicum.

DNA microarray analysis of Clostridium acetobutylicum was used to examine the genomic-scale gene expression changes during the shift from exponential-phase growth and acidogenesis to stationary phase and solventogenesis. Self-organizing maps were used to identify novel expression patterns of functional gene classes, including aromatic and branched-chain amino acid synthesis, ribosomal proteins, cobalt and iron transporters, cobalamin biosynthesis, and lipid biosynthesis. The majority of pSOL1 megaplasmid genes (in addition to the solventogenic genes aad-ctfA-ctfB and adc) had increased expression at the onset of solventogenesis, suggesting that other megaplasmid genes may play a role in stationary-phase phenomena. Analysis of sporulation genes and comparison with published Bacillus subtilis results indicated conserved expression patterns of early sporulation genes, including spo0A, the sigF operon, and putative canonical genes of the sigma(H) and sigma(F) regulons. However, sigE expression could not be detected within 7.5 h of initial spo0A expression, consistent with the observed extended time between the appearance of clostridial forms and endospore formation. The results were compared with microarray comparisons of the wild-type strain and the nonsolventogenic, asporogenous M5 strain, which lacks the pSOL1 megaplasmid. While some results were similar, the expression of primary metabolism genes and heat shock proteins was higher in M5, suggesting a difference in metabolic regulation or a butyrate stress response in M5. The results of this microarray platform and analysis were further validated by comparing gene expression patterns to previously published Northern analyses, reporter assays, and two-dimensional protein electrophoresis data of metabolic genes (including all major solventogenesis genes), sporulation genes, heat shock proteins, and other solventogenesis-induced gene expression.

Amino Acids↗

PubMed2003

Simple sequence repeats and compositional bias in the bipartite Ralstonia solanacearum GMI1000 genome.

BACKGROUND: Ralstonia solanacearum is an important plant pathogen. The genome of R. solananearum GMI1000 is organised into two replicons (a 3.7-Mb chromosome and a 2.1-Mb megaplasmid) and this bipartite genome structure is characteristic for most R. solanacearum strains. To determine whether the megaplasmid was acquired via recent horizontal gene transfer or is part of an ancestral single chromosome, we compared the abundance, distribution and composition of simple sequence repeats (SSRs) between both replicons and also compared the respective compositional biases. RESULTS: Our data show that both replicons are very similar in respect to distribution and composition of SSRs and presence of compositional biases. Minor variations in SSR and compositional biases observed may be attributable to minor differences in gene expression and regulation of gene expression or can be attributed to the small sample numbers observed. CONCLUSIONS: The observed similarities indicate that both replicons have shared a similar evolutionary history and thus suggest that the megaplasmid was not recently acquired from other organisms by lateral gene transfer but is a part of an ancestral R. solanacearum chromosome.

Base Composition↗

PubMed2000

Genetic snapshots of the Rhizobium species NGR234 genome.

BACKGROUND: In nitrate-poor soils, many leguminous plants form nitrogen-fixing symbioses with members of the bacterial family Rhizobiaceae. We selected Rhizobium sp. NGR234 for its exceptionally broad host range, which includes more than I 12 genera of legumes. Unlike the genome of Bradyrhizobium japonicum, which is composed of a single 8.7 Mb chromosome, that of NGR234 is partitioned into three replicons: a chromosome of about 3.5 Mb, a megaplasmid of more than 2 Mb (pNGR234b) and pNGR234a, a 536,165 bp plasmid that carries most of the genes required for symbioses with legumes. Symbiotic loci represent only a small portion of all the genes coded by rhizobial genomes, however. To rapidly characterize the two largest replicons of NGR234, the genome of strain ANU265 (a derivative strain cured of pNGR234a) was analyzed by shotgun sequencing. RESULTS: Homology searches of public databases with 2,275 random sequences of strain ANU265 resulted in the identification of 1,130 putative protein-coding sequences, of which 922 (41%) could be classified into functional groups. In contrast to the 18% of insertion-like sequences (ISs) found on the symbiotic plasmid pNGR234a, only 2.2% of the shotgun sequences represent known ISs, suggesting that pNGR234a is enriched in such elements. Hybridization data also indicate that the density of known transposable elements is higher in pNGR234b (the megaplasmid) than on the chromosome. Rhizobium-specific intergenic mosaic elements (RIMEs) were found in 35 shotgun sequences, 6 of which carry RIME2 repeats previously thought to be present only in Rhizobium meliloti. As non-overlapping shotgun sequences together represent approximately 10% of ANU265 genome, the chromosome and megaplasmid may carry a total of over 200 RIMEs. CONCLUSIONS: 'Skimming' the genome of Rhizobium sp. NGR234 sheds new light on the fine structure and evolution of its replicons, as well as on the integration of symbiotic functions in the genome of a soil bacterium. Although most putative coding sequences could be distributed into functional classes similar to those in Bacillus subtilis, functions related to transposable elements were more abundant in NGR234. In contrast to ISs that accumulated in pNGR234a and pNGR234b, the hundreds of RIME elements seem mostly attributes of the chromosome.

Bacterial Proteins↗

PubMed1983

Physical and genetic characterization of Rhizobium meliloti symbiotic mutants.

A set of 19 symbiotic mutants of Rhizobium meliloti obtained by a Tn5 "suicide plasmid" mutagenesis procedure was characterized genetically and physically. As part of this characterization, we showed that R. meliloti strain 1021, like other R. meliloti strains, contains a very large indigenous plasmid (greater than 300 Md) that carries the structural genes for nitrogenase (nifHDK genes). Among the 19 symbiotic mutations studied, at least six were shown to reside on the megaplasmid. By a "walking procedure" we obtained from a cosmid clone bank a set of overlapping cosmids that contained megaplasmid sequences contiguous to nifHDK. A 90 kb region of contiguous DNA from these cosmids was used to probe the mutant strains for rearrangements within this region. The same six mutations that were located on the megaplasmid mapped within the 90 kb region examined, which included the structural genes for nitrogenase (nifHDK). A majority of the mutations characterized in this study could not be correlated with a bona fide Tn5 insertion into a symbiotic gene.

DNA, Bacterial↗

PubMed2005

Precipitation of silver-thiosulfate complex and immobilization of silver by Cupriavidus metallidurans CH34.

Cupriavidus metallidurans CH34 is a facultative chemolithotrophic bacterium that possesses two megaplasmids (pMOL28 and pMOL30) that confer resistance to eleven metals. The ability of Cupriavidus metallidurans CH34 to resist silver is described here. Electronic microscopy, energy-dispersive X-ray (EDX) and X-ray diffractometry (DRX) observations revealed that C. metallidurans CH34 strongly associated silver with the outer membrane, under chloride chemical form. Using derivate strains of C. metallidurans CH34, which carried only one or no megaplasmid, we show that this resistance seems to be carried by pMOL30.

Bioreactors↗

PubMed2003

Predicting gene expression levels from codon biases in alpha-proteobacterial genomes.

Predicted highly expressed (PHX) genes in five currently available high G+C complete alpha-proteobacterial genomes are analyzed. These include: the nitrogen-fixing plant symbionts Sinorhizobium meliloti (SINME) and Mesorhizobium loti (MESLO), the nonpathogenic aquatic bacterium Caulobacter crescentus (CAUCR), the plant pathogen Agrobacterium tumefaciens (AGRTU), and the mammalian pathogen Brucella melitensis (BRUME). Three of these genomes, SINME, AGRTU, and BRUME, contain multiple chromosomes or megaplasmids (>1 Mb length). PHX genes in these genomes are concentrated mainly in the major (largest) chromosome with few PHX genes found in the secondary chromosomes and megaplasmids. Tricarboxylic acid cycle and aerobic respiration genes are strongly PHX in all five genomes, whereas anaerobic pathways of glycolysis and fermentation are mostly not PHX. Only in MESLO (but not SINME) and BRUME are most glycolysis genes PHX. Many flagellar genes are PHX in MESLO and CAUCR, but mostly are not PHX in SINME and AGRTU. The nonmotile BRUME also carries many flagellar genes but these are generally not PHX and all but one are located in the second chromosome. CAUCR stands out among available prokaryotic genomes with 25 PHX TonB-dependent receptors. These are putatively involved in uptake of iron ions and other nonsoluble compounds.

Agrobacterium tumefaciens↗

PubMed2004

Nosocomial bacteremia and urinary tract infections caused by extended-spectrum beta -lactamase-producing Klebsiella pneumoniae with plasmids carrying both SHV-5 and TLA-1 genes.

We describe the prevalence and molecular characteristics of extended-spectrum beta -lactamase (ESBL)-producing Klebsiella pneumoniae causing nosocomial bacteremia and urinary tract infections in a Mexican general hospital. We analyzed 82 episodes of bacteremia (approximately 60% of episodes) and urinary tract infection (approximately 40% of episodes) due to K. pneumoniae during a 23-month surveillance period. The neonatal intensive care unit accounted for 49% of all episodes. All strains were imipenem susceptible; 62.2% of the strains were resistant to ceftazidime, cefotaxime, and aztreonam; 69.5% were resistant to amikacin; 58.5% were resistant to gentamicin; and 7.3% were resistant to ciprofloxacin. All strains were associated with 28 pulsed-field gel electrophoresis patterns, and dissemination of 2 ceftazidime-resistant clones produced 44% of the cases. The ESBL phenotype in these clones was transferred by identical or highly related megaplasmids. The ESBL activity corresponded to SHV-5 and TLA-1. Cross-transmission of 2 ceftazidime-resistant clones and the horizontal spread of identical or highly related megaplasmids explain the high prevalence of ESBL phenotype in these infections.

Bacteremia↗

PubMed1992

Rhizobium meliloti genes involved in sulfate activation: the two copies of nodPQ and a new locus, saa.

The nitrogen-fixing symbiont Rhizobium meliloti establishes nodules on leguminous host plants. Nodulation (nod) genes used for this process are located in a cluster on the pSym-a megaplasmid of R. meliloti. These genes include nodP and nodQ (here termed nodPQ), which encode ATP sulfurylase and APS kinase, enzymes that catalyze the conversion of ATP and SO(4)2- into the activated sulfate form 3'-phosphoadenosine 5'-phosphosulfate (PAPS), an intermediate in cysteine synthesis. In Rhizobium, PAPS is also a precursor for sulfated and N-acylated oligosaccharide Nod-factor signals that cause symbiotic responses on specific host plants such as alfalfa. We previously found a highly conserved second copy of nodPQ in R. meliloti. We report here the mapping and cloning of this second copy, and its location on the second megaplasmid, pSym-b. The function of nodP2Q2 is equivalent to that of nodP1Q1 in complementation tests of R. meliloti and Escherichia coli mutants in ATP sulfurylase and adenosine 5'-phosphosulfate (APS) kinase. Mutations in nodP2Q2 do not have as severe an effect on symbiosis or plant host range as do those in nodP1Q1, however, possibly reflecting differences in expression and/or channeling of metabolites to specific enzymes involved in sulfate transfer. Strains mutated or deleted for both copies of nodQ are severely defective in symbiotic phenotypes, but remain prototrophic. This suggests the existence in R. meliloti of a third locus for ATP sulfurylase and APS kinase activities. We have found a new locus saa (sulfur amino acid), which may also encode these activities.

Chromosome Mapping↗

PubMed1997

A new nos gene downstream from nosDFY is essential for dissimilatory reduction of nitrous oxide by Rhizobium (Sinorhizobium) meliloti.

Rhizobium (Sinorhizobium) meliloti strains capable of dissimilatory nitrous oxide reduction (Nos+) carry a nosRZDFY gene cluster on a 10.1 kb EcoRI fragment of the nod megaplasmid near the fixGHIS genes. These nos genes are arranged in three complementation groups and the 10.1 kb EcoRI fragment is sufficient to confer Nos activity to R. meliloti strains lacking such activity. An overlapping HindIII fragment containing the nosRZDFY genes but missing a 0-6 kb HindIII-EcoRI downstream segment was found incapable of imparting Nos activity to strains unable to reduce nitrous oxide, suggesting the presence of other nos gene(s) in this region. Tn5 introduced near the HindIII site resulted in mutants with a Nos- phenotype. Complete sequence analysis of nosY showed that it was well-conserved with respect to that of Pseudomonas stutzeri. Two previously unreported genes downstream of nosY in R. meliloti were also revealed. Contiguous with nosY was a sequence showing 63% identity with the ORFL protein of P. stutzeri. It appeared to be in the same operon as nosDFY and was predicted to encode a membrane lipoprotein similar to the putative NosL of P. stutzeri. Unlike the latter protein, however, amino acid sequences typical of metal-binding sites and cysteine residues indicative of the active site of protein disulphide isomerase were absent in the predicted NosL of R. mellioti. The Tn5 mutations resulting in a Nos- phenotype were localized within a 966 nucleotide gene 31 nucleotides downstream of nosDFYL with the same orientation. The new gene, nosX, was determined to be in a separate complementation group. It encoded a periplasmic protein with homology in the C-terminal domain with Rnff of Rhodobacter capsulatus and with a hypothetical Escherichia coli protein, YOJK. It was concluded that there are seven genes constituting the nos cluster in R. meliloti. They are organized in four complementation groups and in the same orientation, spanning a distance of about 9 kb on the nod megaplasmid.

Amino Acid Sequence↗

PubMed2006

Transcriptomic and proteomic analyses of the pMOL30-encoded copper resistance in Cupriavidus metallidurans strain CH34.

The four replicons of Cupriavidus metallidurans CH34 (the genome sequence was provided by the US Department of Energy-University of California Joint Genome Institute) contain two gene clusters putatively encoding periplasmic resistance to copper, with an arrangement of genes resembling that of the copSRABCD locus on the 2.1 Mb megaplasmid (MPL) of Ralstonia solanacearum, a closely related plant pathogen. One of the copSRABCD clusters was located on the 2.6 Mb MPL, while the second was found on the pMOL30 (234 kb) plasmid as part of a larger group of genes involved in copper resistance, spanning 17 857 bp in total. In this region, 19 ORFs (copVTMKNSRABCDIJGFLQHE) were identified based on the sequencing of a fragment cloned in an IncW vector, on the preliminary annotation by the Joint Genome Institute, and by using transcriptomic and proteomic data. When introduced into plasmid-cured derivatives of C. metallidurans CH34, the cop locus was able to restore the wild-type MIC, albeit with a biphasic survival curve, with respect to applied Cu(II) concentration. Quantitative-PCR data showed that the 19 ORFs were induced from 2- to 1159-fold when cells were challenged with elevated Cu(II) concentrations. Microarray data showed that the genes that were most induced after a Cu(II) challenge of 0.1 mM belonged to the pMOL30 cop cluster. Megaplasmidic cop genes were also induced, but at a much lower level, with the exception of the highly expressed MPL copD. Proteomic data allowed direct observation on two-dimensional gel electrophoresis, and via mass spectrometry, of pMOL30 CopK, CopR, CopS, CopA, CopB and CopC proteins. Individual cop gene expression depended on both the Cu(II) concentration and the exposure time, suggesting a sequential scheme in the resistance process, involving genes such as copK and copT in an initial phase, while other genes, such as copH, seem to be involved in a late response phase. A concentration of 0.4 mM Cu(II) was the highest to induce maximal expression of most cop genes.

Amino Acid Sequence↗

PubMed2003

Natural genomic design in Sinorhizobium meliloti: novel genomic architectures.

The complete nucleotide sequence of the genome of Sinorhizobium meliloti, the symbiont of alfalfa, was reported in 2001 by an international consortium of laboratories. The genome comprises a chromosome of 3.65 megabases (Mb) and two megaplasmids, pSymA and pSymB, of 1.35 Mb and 1.68 Mb, respectively. Based on the nucleotide sequence of the whole genome, we designed a pathway of consecutive rearrangements leading to novel genomic architectures. In a first step we obtained derivative strains containing two replicons; in a second step we obtained a strain containing the genetic information in one single replicon of 6.68 MB. From this last architecture we isolated revertants containing two replicons, and from these we could return to the original architecture showing the three replicons. We found that the relative frequency of excision of cointegrated replicons is higher at the site used for the cointegration than at other sites. This might conciliate two apparently opposed facts: the highly dynamic state of genomic architecture in S. meliloti and the common observation that different isolates and derived cellular clones of S. meliloti usually present the architecture of one chromosome and two distinct megaplasmids. Different aspects that must be considered to obtain full advantage of the strategy of natural genomic design are discussed.

DNA Transposable Elements↗

PubMed1999

Genome sequence of the radioresistant bacterium Deinococcus radiodurans R1.

The complete genome sequence of the radiation-resistant bacterium Deinococcus radiodurans R1 is composed of two chromosomes (2,648,638 and 412,348 base pairs), a megaplasmid (177,466 base pairs), and a small plasmid (45,704 base pairs), yielding a total genome of 3,284, 156 base pairs. Multiple components distributed on the chromosomes and megaplasmid that contribute to the ability of D. radiodurans to survive under conditions of starvation, oxidative stress, and high amounts of DNA damage were identified. Deinococcus radiodurans represents an organism in which all systems for DNA repair, DNA damage export, desiccation and starvation recovery, and genetic redundancy are present in one cell.

Bacterial Proteins↗

PubMed1985

General method for the identification of plasmid species in fast-growing soil microorganisms.

Using a horizontal gel electrophoresis method, we demonstrated reproducibly the presence of indigenous plasmids in different Rhizobium, Agrobacterium, and Pseudomonas strains. The method yields a large amount of plasmid DNA and is sensitive in detecting megaplasmids with molecular weights higher than 5 x 10. In two Rhizobium meliloti strains, a megaplasmid other than the low-mobility plasmid already known was detected.

Journal Article↗

PubMed1991

High-Level Nickel Resistance in Alcaligenes xylosoxydans 31A and Alcaligenes eutrophus KTO2.

Two new nickel-resistant strains of Alcaligenes species were selected from a large number (about 400) of strains isolated from ecosystems polluted by heavy metals and were studied on the physiological and molecular level. Alcaligenes xylosoxydans 31A is a heterotrophic bacterium, and Alcaligenes eutrophus KTO2 is an autotrophic aerobic hydrogen-oxidizing bacterium. Both strains carry-among other plasmids-a megaplasmid determining resistance to 20 to 50 mM NiCl(2) and 20 mM CoCl(2) (when growing in defined Tris-buffered media). Megaplasmids pTOM8, pTOM9 from strain 31A, and pGOE2 from strain KTO2 confer nickel resistance to the same degree to transconjugants of all strains of A. eutrophus tested but were not transferred to Escherichia coli. However, DNA fragments carrying the nickel resistance genes, cloned into broad-hostrange vector pVDZ'2, confer resistance to A. eutrophus derivatives as well as E. coli. The DNA fragments of both bacteria, TBA8, TBA9, and GBA (14.5-kb BamHI fragments), appear to be identical. They share equal size, restriction maps, and strong DNA homology but are largely different from fragment HKI of nickel-cobalt resistance plasmid pMOL28 of A. eutrophus CH34.

Journal Article↗

PubMed1994

Electroporation of Alcaligenes eutrophus with (mega) plasmids and genomic DNA fragments.

Electroporation was used as a tool to explore the genetics of the heavy-metal-resistant strain Alcaligenes eutrophus CH34. A 12.9-kb A. eutrophus-Escherichia coli shuttle vector, pMOL850, was constructed to optimize electroporation conditions. This vector is derived from the E. coli plasmid pSUP202 and contains the replication region of the A. eutrophus megaplasmid pMOL28. Electroporation was used to transform A. eutrophus CH34 derivatives with megaplasmids (sizes up to 240 kb), and transformants were selected for resistance to heavy metals. Electroporation was also performed with endonuclease-digested genomic DNA. Transformation of markers affecting lysine biosynthesis (lysA194) and biosynthesis of the siderophore alcaligin E were observed. Transfer of the nonselected markers pheB332 and aro-333, linked to lysA194, confirmed the intervention of homologous recombination. However, during transformation of ale::Tn5-Tc, illegitimate recombination and transposition were also observed as an alternative for the inheritance of the Tn5-Tc markers.

Alcaligenes↗

PubMed2006

Sequence analysis of the 144-kilobase accessory plasmid pSmeSM11a, isolated from a dominant Sinorhizobium meliloti strain identified during a long-term field release experiment.

The genome of Sinorhizobium meliloti type strain Rm1021 consists of three replicons: the chromosome and two megaplasmids, pSymA and pSymB. Additionally, many indigenous S. meliloti strains possess one or more smaller plasmids, which represent the accessory genome of this species. Here we describe the complete nucleotide sequence of an accessory plasmid, designated pSmeSM11a, that was isolated from a dominant indigenous S. meliloti subpopulation in the context of a long-term field release experiment with genetically modified S. meliloti strains. Sequence analysis of plasmid pSmeSM11a revealed that it is 144,170 bp long and has a mean G+C content of 59.5 mol%. Annotation of the sequence resulted in a total of 160 coding sequences. Functional predictions could be made for 43% of the genes, whereas 57% of the genes encode hypothetical or unknown gene products. Two plasmid replication modules, one belonging to the repABC replicon family and the other belonging to the plasmid type A replicator region family, were identified. Plasmid pSmeSM11a contains a mobilization (mob) module composed of the type IV secretion system-related genes traG and traA and a putative mobC gene. A large continuous region that is about 42 kb long is very similar to a corresponding region located on S. meliloti Rm1021 megaplasmid pSymA. Single-base-pair deletions in the homologous regions are responsible for frameshifts that result in nonparalogous coding sequences. Plasmid pSmeSM11a carries additional copies of the nodulation genes nodP and nodQ that are responsible for Nod factor sulfation. Furthermore, a tauD gene encoding a putative taurine dioxygenase was identified on pSmeSM11a. An acdS gene located on pSmeSM11a is the first example of such a gene in S. meliloti. The deduced acdS gene product is able to deaminate 1-aminocyclopropane-1-carboxylate and is proposed to be involved in reducing the phytohormone ethylene, thus influencing nodulation events. The presence of numerous insertion sequences suggests that these elements mediated acquisition of accessory plasmid modules.

Agrobacterium tumefaciens↗

PubMed2001

Characterization of Saa, a novel autoagglutinating adhesin produced by locus of enterocyte effacement-negative Shiga-toxigenic Escherichia coli strains that are virulent for humans.

The capacity of Shiga toxigenic Escherichia coli (STEC) to adhere to the intestinal mucosa undoubtedly contributes to pathogenesis of human disease. The majority of STEC strains isolated from severe cases produce attaching and effacing lesions on the intestinal mucosa, a property mediated by the locus of enterocyte effacement (LEE) pathogenicity island. This element is not essential for pathogenesis, as some cases of severe disease, including hemolytic uremic syndrome (HUS), are caused by LEE-negative STEC strains, but the mechanism whereby these adhere to the intestinal mucosa is not understood. We have isolated a gene from the megaplasmid of a LEE-negative O113:H21 STEC strain (98NK2) responsible for an outbreak of HUS, which encodes an auto-agglutinating adhesin designated Saa (STEC autoagglutinating adhesin). Introduction of saa cloned in pBC results in a 9.7-fold increase in adherence of E. coli JM109 to HEp-2 cells and a semilocalized adherence pattern. Mutagenesis of saa in 98NK2, or curing the wild-type strain of its megaplasmid, resulted in a significant reduction in adherence. Homologues of saa were found in several unrelated LEE-negative STEC serotypes, including O48:H21 (strain 94CR) and O91:H21 (strain B2F1), which were also isolated from patients with HUS. Saa exhibits a low degree of similarity (25% amino acid [aa] identity) with YadA of Yersinia enterocolitica and Eib, a recently described phage-encoded immunoglobulin binding protein from E. coli. Saa produced by 98NK2 is 516 aa long and includes four copies of a 37-aa direct repeat sequence. Interestingly, Saa produced by other STEC strains ranges in size from 460 to 534 aa as a consequence of variation in the number of repeats and/or other insertions or deletions immediately proximal to the repeat domain.

Adhesins, Bacterial↗