scholarly journals Transcriptional Activation of Agrobacterium tumefaciens Virulence Gene Promoters in Escherichia coli Requires the A. tumefaciens rpoA Gene, Encoding the Alpha Subunit of RNA Polymerase

1999 ◽  
Vol 181 (15) ◽  
pp. 4533-4539 ◽  
Author(s):  
S. M. Lohrke ◽  
S. Nechaev ◽  
H. Yang ◽  
K. Severinov ◽  
S. J. Jin
Keyword(s):  
Escherichia Coli ◽  
Agrobacterium Tumefaciens ◽  
Rna Polymerase ◽  
Virulence Genes ◽  
Virulence Gene ◽  
Dependent Manner ◽  
Gene Promoters ◽  
Gene Encoding ◽  
Α Subunit ◽  
E Coli

ABSTRACT The two-component regulatory system, composed of virAand virG, is indispensable for transcription of virulence genes within Agrobacterium tumefaciens. However,virA and virG are insufficient to activate transcription from virulence gene promoters within Escherichia coli cells, indicating a requirement for additional A. tumefaciens genes. In a search for these additional genes, we have identified the rpoA gene, encoding the α subunit of RNA polymerase (RNAP), which confers significant expression of avirB promoter (virBp)::lacZ fusion in E. coli in the presence of an active transcriptional regulatorvirG gene. We conducted in vitro transcription assays using either reconstituted E. coli RNAP or hybrid RNAP in which the α subunit was derived from A. tumefaciens. The two forms of RNAP were equally efficient in transcription from a ς70-dependent E. coli galP1 promoter; however, only the hybrid RNAP was able to transcribe virBpin a virG-dependent manner. In addition, we provide evidence that the α subunit from A. tumefaciens, but not from E. coli, is able to interact with the VirG protein. These data suggest that transcription of virulence genes requires specific interaction between VirG and the α subunit of A. tumefaciens and that the α subunit from E. coli is unable to effectively interact with the VirG protein. This work provides the basis for future studies designed to examinevir gene expression as well as the T-DNA transfer process in E. coli.

scholarly journals Reconstitution of Acetosyringone-Mediated Agrobacterium tumefaciens Virulence Gene Expression in the Heterologous Host Escherichia coli

2001 ◽  
Vol 183 (12) ◽  
pp. 3704-3711 ◽  
Author(s):  
Scott M. Lohrke ◽  
Hongjiang Yang ◽  
Shouguang Jin
Keyword(s):  
Gene Expression ◽  
Escherichia Coli ◽  
Agrobacterium Tumefaciens ◽  
Virulence Genes ◽  
Virulence Gene ◽  
Dependent Manner ◽  
Gene Encoding ◽  
Virulence Gene Expression ◽  
E Coli ◽  
Glucose Binding

ABSTRACT The ability to utilize Escherichia coli as a heterologous system in which to study the regulation ofAgrobacterium tumefaciens virulence genes and the mechanism of transfer DNA (T-DNA) transfer would provide an important tool to our understanding and manipulation of these processes. We have previously reported that the rpoA gene encoding the alpha subunit of RNA polymerase is required for the expression of lacZ gene under the control of virB promoter (virBp::lacZ) in E. colicontaining a constitutively active virG gene [virG(Con)]. Here we show that an RpoA hybrid containing the N-terminal 247 residues from E. coli and the C-terminal 89 residues from A. tumefaciens was able to significantly express virBp::lacZ in E. coli in a VirG(Con)-dependent manner. Utilization oflac promoter-driven virA and virGin combination with the A. tumefaciens rpoA construct resulted in significant inducer-mediated expression of thevirBp::lacZ fusion, and the level ofvirBp::lacZ expression was positively correlated to the copy number of the rpoA construct. This expression was dependent on VirA, VirG, temperature, and, to a lesser extent, pH, which is similar to what is observed in A. tumefaciens. Furthermore, the effect of sugars on virgene expression was observed only in the presence of thechvE gene, suggesting that the glucose-binding protein ofE. coli, a homologue of ChvE, does not interact with the VirA molecule. We also evaluated other phenolic compounds in induction assays and observed significant expression with syringealdehyde, a low level of expression with acetovanillone, and no expression with hydroxyacetophenone, similar to what occurs in A. tumefaciens strain A348 from which the virA clone was derived. These data support the notion that VirA directly senses the phenolic inducer. However, the overall level of expression of thevir genes in E. coli is less than what is observed in A. tumefaciens, suggesting that additional gene(s) from A. tumefaciens may be required for the full expression of virulence genes in E. coli.

scholarly journals Molecular characterisation of antimicrobial resistance and virulence genes in Escherichia coli strains isolated from diarrhoeic and healthy rabbits in Tunisia

2020 ◽  
Vol 28 (2) ◽  
pp. 81
Author(s):  
Raouia Ben Rhouma ◽  
Ahlem Jouini ◽  
Amira Klibi ◽  
Safa Hamrouni ◽  
Aziza Boubaker ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Virulence Genes ◽  
Antimicrobial Agents ◽  
Antibiotic Resistance Genes ◽  
Virulence Gene ◽  
Diffusion Method ◽  
Class 1 Integron ◽  
E Coli ◽  
Class 1

The purpose of this study was to identify <em>Escherichia coli</em> isolates in diarrhoeic and healthy rabbits in Tunisia and characterise their virulence and antibiotic resistance genes. In the 2014-2015 period, 60 faecal samples from diarrhoeic and healthy rabbits were collected from different breeding farms in Tunisia. Susceptibility to 14 antimicrobial agents was tested by disc diffusion method and the mechanisms of gene resistance were evaluated using polymerase chain reaction and sequencing methods. Forty <em>E. coli</em> isolates were recovered in selective media. High frequency of resistance to tetracycline (95%) was detected, followed by different levels of resistance to sulphonamide (72.5%), streptomycin (62.5%), trimethoprim-sulfamethoxazole (60%), nalidixic acid (32.5%), ampicillin (37.5%) and ticarcillin (35%). <em>E. coli</em> strains were susceptible to cefotaxime, ceftazidime and imipenem. Different variants of bla<sub>TEM</sub>, <em>tet</em>, <em>sul</em> genes were detected in most of the strains resistant to ampicillin, tetracycline and sulphonamide, respectively. The presence of class 1 integron was studied in 29 sulphonamide-resistant <em>E. coli</em> strains from which 15 harboured class 1 integron with four different arrangements of gene cassettes, <em>dfrA17</em>+<em>aadA5</em> (n=9), <em>dfrA1</em> + <em>aadA1</em> (n=4), <em>dfrA12</em> + <em>addA2</em> (n=1), <em>dfrA12</em>+<em>orf</em>+<em>addA2</em> (n=1). The <em>qnrB</em> gene was detected in six strains out of 13 quinolone-resistant <em>E. coli</em> strains. Seventeen <em>E. coli</em> isolates from diarrhoeic rabbits harboured the enteropathogenic eae genes associated with different virulence genes tested (<em>fimA</em>, <em>cnf1</em>, <em>aer</em>), and affiliated to B2 (n=8) and D (n=9) phylogroups. Isolated <em>E. coli</em> strains from healthy rabbit were harbouring <em>fim A</em> and/or <em>cnf1</em> genes and affiliated to A and B1 phylogroups. This study showed that <em>E. coli</em> strains from the intestinal tract of rabbits are resistant to the widely prescribed antibiotics in medicine. Therefore, they constitute a reservoir of antimicrobial-resistant genes, which may play a significant role in the spread of antimicrobial resistance. In addition, the eae virulence gene seemed to be implicated in diarrhoea in breeder rabbits in Tunisia.

scholarly journals Isolation and Characterization of Potentially Pathogenic Antimicrobial-Resistant Escherichia coli Strains from Chicken and Pig Farms in Spain

2010 ◽  
Vol 76 (9) ◽  
pp. 2799-2805 ◽  
Author(s):  
Pilar Cortés ◽  
Vanessa Blanc ◽  
Azucena Mora ◽  
Ghizlane Dahbi ◽  
Jesús E. Blanco ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Virulence Genes ◽  
Phylogenetic Analyses ◽  
Virulence Gene ◽  
E Coli ◽  
Isolation And Characterization ◽  
Zoonotic Risk ◽  
Poultry Farms ◽  
Pig Farms ◽  
Genes Encoding

ABSTRACT To ascertain whether on animal farms there reside extended-spectrum β-lactamase (ESBL) and plasmidic class C β-lactamase-producing Escherichia coli isolates potentially pathogenic for humans, phylogenetic analyses, pulsed-field gel electrophoresis (PFGE) typing, serotyping, and virulence genotyping were performed for 86 isolates from poultry (57 isolates) and pig (29 isolates) farms. E. coli isolates from poultry farms carried genes encoding enzymes of the CTX-M-9 group as well as CMY-2, whereas those from pig farms mainly carried genes encoding CTX-M-1 enzymes. Poultry and pig isolates differed significantly in their phylogenetic group assignments, with phylogroup A predominating in pig isolates and phylogroup D predominating in avian isolates. Among the 86 farm isolates, 23 (26.7%) carried two or more virulence genes typical of extraintestinal pathogenic E. coli (ExPEC). Of these, 20 were isolated from poultry farms and only 3 from pig farms. Ten of the 23 isolates belonged to the classic human ExPEC serotypes O2:H6, O2:HNM, O2:H7, O15:H1, and O25:H4. Despite the high diversity of serotypes and pulsotypes detected among the 86 farm isolates, 13 PFGE clusters were identified. Four of these clusters contained isolates with two or more virulence genes, and two clusters exhibited the classic human ExPEC serotypes O2:HNM (ST10) and O2:H6 (ST115). Although O2:HNM and O2:H6 isolates of human and animal origins differed with respect to their virulence genes and PFGE pulsotypes, the O2:HNM isolates from pigs showed the same sequence type (ST10) as those from humans. The single avian O15:H1 isolate was compared with human clinical isolates of this serotype. Although all were found to belong to phylogroup D and shared the same virulence gene profile, they differed in their sequence types (ST362-avian and ST393-human) and PFGE pulsotypes. Noteworthy was the detection, for the first time, in poultry farms of the clonal groups O25b:H4-ST131-B2, producing CTX-M-9, and O25a-ST648-D, producing CTX-M-32. The virulence genes and PFGE profiles of these two groups were very similar to those of clinical human isolates. While further studies are required to determine the true zoonotic potential of these clonal groups, our results emphasize the zoonotic risk posed especially by poultry farms, but also by pig farms, as reservoirs of ESBL- and CMY-2-encoding E. coli.

scholarly journals Virulence gene profiles of avian pathogenic Escherichia coli isolated from chickens with colibacillosis in Bulawayo, Zimbabwe

2015 ◽  
Vol 82 (1) ◽  
Author(s):  
Joshua Mbanga ◽  
Yvonne O. Nyararai
Keyword(s):  
Escherichia Coli ◽  
Virulence Genes ◽  
Virulence Gene ◽  
Economic Losses ◽  
Avian Pathogenic Escherichia Coli ◽  
Pcr Assay ◽  
E Coli ◽  
Gene Profiles ◽  
Pathogenic Escherichia Coli ◽  
Polymerase Chain

Colibacillosis, a disease caused by avian pathogenic Escherichia coli (APEC), is one of the main causes of economic losses in the poultry industry worldwide. This study was carried out in order to determine the APEC-associated virulence genes contained by E. coli isolates causing colibacillosis in chickens. A total of 45 E. coli isolates were obtained from the diagnostics and research branch of the Central Veterinary Laboratories, Bulawayo, Zimbabwe. These isolates were obtained from chickens with confirmed cases of colibacillosis after postmortem examination. The presence of the iutA, hlyF, ompT, frz, sitD, fimH, kpsM, sitA, sopB, uvrY, pstB and vat genes were investigated by multiplex polymerase chain reaction (PCR) assay. Of the 45 isolates, 93% were positive for the presence of at least one virulence gene. The three most prevalent virulence genes were iutA (80%), fimH (33.3%) and hlyF (24.4%). The kpsM, pstB and ompT genes had the lowest prevalence, having been detected in only 2.2% of the isolates. All 12 virulence genes studied were detected in the 45 APEC isolates. Virulence gene profiles were constructed for each APEC isolate from the multiplex data. The APEC isolates were profiled as 62.2% fitting profile A, 31.1% profile B and 6.7% profile C. None of the isolates had more than seven virulence genes. Virulence profiles of Zimbabwean APEC isolates are different from those previously reported. Zimbabwean APEC isolates appear to be less pathogenic and may rely on environmental factors and stress in hosts to establish infection.

scholarly journals Virulence and antibiotic resistance profile of avian Escherichia coli strains isolated from colibacillosis lesions in central of Algeria

2019 ◽  
Vol 12 (11) ◽  
pp. 1840-1848 ◽  
Author(s):  
Nacima Meguenni ◽  
Nathalie Chanteloup ◽  
Angelina Tourtereau ◽  
Chafika Ali Ahmed ◽  
Saliha Bounar-Kechih ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antibiotic Resistance ◽  
Virulence Factors ◽  
Virulence Genes ◽  
Iron Acquisition ◽  
Virulence Gene ◽  
Resistance Profile ◽  
E Coli ◽  
Antibiotic Resistance Profile ◽  
Embryo Lethality

Background and Aim: Avian pathogenic Escherichia coli cause extensive mortality in poultry flocks, leading to extensive economic losses. To date, in Algeria, little information has been available on virulence potential and antibiotics resistance of avian E. coli isolates. Therefore, the aim of this study was the characterization of virulence genes and antibiotic resistance profile of Algerian E. coli strains isolated from diseased broilers. Materials and Methods: In this study, 43 avian E. coli strains isolated from chicken colibacillosis lesions at different years were analyzed to determine their contents in 10 virulence factors by polymerase chain reaction, antimicrobial susceptibility to 22 antibiotics belonging to six different chemical classes and genomic diversity by pulsed-field gel electrophoresis (PFGE). Results: Mainly E. coli isolates (58.1%) carried two at six virulence genes and the most frequent virulence gene association detected were ompT (protectin), hlyF (hemolysin) with 55.8% (p<0.001), and iroN, sitA (iron acquisition/uptake systems), and iss (protectin) with 41.8% (p<0.001). Some strains were diagnosed as virulent according to their virulence gene profile. Indeed, 23.25% of the isolates harbored iroN, ompT, hlyF, iss, and sitA combination, 14% ompT, hlyF, and frzorf4 (sugar metabolism), and 11,6% iroN, hlyF, ompT, iss, iutA (iron acquisition/uptake systems), and frzorf4. The chicken embryo lethality assay performed on five isolates confirmed the potential virulence of these strains. All isolates submitted to PFGE analysis yielded different genetic profiles, which revealed their diversity. Overall, 97.2% of the isolates were resistant to at least one antibiotic and 53.5% demonstrated multi-antimicrobial resistance to three different antimicrobial classes. The highest resistance levels were against nalidixic acid (83.4%), amoxicillin and ampicillin (83.3%), ticarcillin (80.5%), pipemidic acid (75%), and triméthoprim-sulfamethoxazole (66.6%). For beta-lactam class, the main phenotype observed belonged to broad-spectrum beta-lactamases. However, extended-spectrum beta-lactamase associated with three at six virulence factors was also detected in 13 isolates. Two of them were attested virulent as demonstrated in the embryo lethality test which constitutes a real public threat. Conclusion: It would be imperative in avian production to discourage misuse while maintaining constant vigilance guidelines and regulations, to limit and rationalize antimicrobial use.

scholarly journals Antibiotic resistance and virulence of Escherichia coli strains isolated from animal rendering plant

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Gabriela Gregova ◽  
Vladimir Kmet
Keyword(s):  
Escherichia Coli ◽  
Antibacterial Agents ◽  
Virulence Genes ◽  
Gene Encoding ◽  
Antibiotic Resistant ◽  
Beta Lactamases ◽  
E Coli ◽  
Animal Wastes ◽  
Extended Spectrum Beta Lactamases ◽  
High Level

Abstract Processing of animal carcasses and other animal wastes in rendering plants is a significant source of antibiotic resistant microorganisms. The main goal of this study was to investigate the resistance to 18 antibacterial agents including β-lactams, fluoroquinolones, colistin and virulence factors (iss, tsh, cvaC, iutA, papC, kps and ibeA genes) in 88 Escherichia coli strains isolated from a rendering plant over 1 year period. ESBL (Extended-spectrum beta-lactamases) and plasmid-mediated Amp were screened by interpretative reading of MIC. ESBL phenotype was detected in 20.4% of samples and high level of resistance to fluoroquinolone was found in 27.2% of strains. Cephalosporinase CTX-M1, cephamycinase CMY-2, integrase 1 and transposon 3 genes were detected by PCR. Furthermore, there were found three CMY-2 producing E. coli with O25b-ST131, resistant to the high level of enrofloxacin and containing the gene encoding the ferric aerobactin receptor (iutA). One enrofloxacin resistant E. coli strain possessed iss, ibeA, kps and papC virulence genes also with CMY-2, integrase1 and Tn3. ST131 E. coli with CMY-2 has a zoonotic potential and presents a serious health risk to humans.

Characterisation of multidrug resistant Escherichia coli isolated from two commercial lettuce and spinach supply chains

2021 ◽  
Author(s):  
Muneiwa T. Ratshilingano ◽  
Erika Margarete du Plessis ◽  
Stacey Duvenage ◽  
Lise Korsten
Keyword(s):  
Escherichia Coli ◽  
Antibiotic Resistance ◽  
Irrigation Water ◽  
Virulence Genes ◽  
Disease Outbreaks ◽  
Virulence Gene ◽  
Multidrug Resistant ◽  
Water Sources ◽  
Point Of Sale ◽  
E Coli

ABSTRACT Leafy green vegetables have increasingly been reported as a reservoir of multidrug-resistant pathogenic Enterobacteriaceae; with Shiga toxin- producing Escherichia coli frequently implicated in disease outbreaks worldwide.  This study aimed to determine the presence and characteristics of antibiotic resistance, diarrheagenic virulence genes and phylogenetic groupings of E. coli isolates (n=51) from commercially produced lettuce and spinach from the farm, through processing and at the point of sale.  Multidrug resistance was observed in 33 of the 51 E. coli isolates (64.7%); with 35.7% (n=10/28) being generic and 100% (n=23/23) Extended Spectrum β-lactamase/AmpC- producing.  Resistance of E. coli isolates was observed against neomycin (100%; n=51/51), ampicillin (70.6%; n=36/51), amoxycilin (68.6%; n=35/51), tetracycline (45%; n=23/51), trimethoprim/ sulfamethoxazole (43%; n=22/51), chloramphenicol (25.5%; n=13/51), augmentin (11.8%; n=6/51) and gentamicin (7.8%; n=4/51); with 100% (n=51/51) susceptibility to imipenem. Virulence gene eae was detected in two E. coli isolates from irrigation water sources only, while none of the other virulence genes tested for were detected.   Most of the E. coli strains belonged to phylogenetic group B2 (25.5%; n=13), B1 (19.6%; n=10) and A (17.6%; n=9); with D (5.9%; n=3) less distributed. Although diarrheagenic E. coli were not detected, antibiotic resistance in E. coli prevalent in the supply chain was evident. Additionally, a clear link between E. coli isolates from irrigation water sources and leafy green vegetables through DNA fingerprinting was established which indicates the potential transfer of E. coli from irrigation water to minimally processed leafy green vegetables.

IDENTIFICATION OF THE AVIAN PATHOTYPE OF ESCHERICHIA COLI ON LAYER FLOCKS BY MULTIPLEX PCR

2019 ◽  
Vol 7 ◽  
pp. 905-911
Author(s):  
Marilena Burtan ◽  
Virgilia Popa ◽  
Maria Rodica Gurau ◽  
Doina Danes
Keyword(s):  
Escherichia Coli ◽  
Multiplex Pcr ◽  
Virulence Genes ◽  
Virulence Gene ◽  
Economic Losses ◽  
Ompa Gene ◽  
Avian Pathogenic Escherichia Coli ◽  
E Coli ◽  
Pathogenic Escherichia Coli

Introduction: Colibacillosis in poultry is determined by avian pathogenic Escherichia coli (APEC) and represents an important source of economic losses  in the poultry industry. APEC’s pathogenicity relies on the presence and expression of different virulence factors. The genes ompA , iss  and  fimH, encoding the outer membrane protein, the protein inducing resistance to complement and the synthesis of type 1 fimbria are present in APEC strains. Objective: Escherichia coli strains isolated from layers were analysed to assess the pathotype they belong to. Methods: In order to detect the three genes associated with APEC strains, 16 E. coli isolates were investigated for virulence associated genes ompA, iss and fimH, using multiplex PCR. Results: From the 16 E.coli strains submitted, multiplex PCR assessment revealed that 14 (87.5%) of the E. coli strains isolated contained at least one virulence gene, while 2 (12.5%) strains did not harbour any of the virulence genes tested. The fimH gene was noted in 13 (81.25%) of the strains tested, the ompA gene has been present in 12 (75%) strains and the iss gene was present in 9 (56.25%) strains. Eight (50%) strains were found to present all three investigated genes. Conclusion: Presence of these genes is a strong indicatory to consider those strains as belonging to the APEC pathotype.

scholarly journals Virulence Factor Gene Profiles of Escherichia coli Isolates from Clinically Healthy Pigs

2006 ◽  
Vol 72 (10) ◽  
pp. 6680-6686 ◽  
Author(s):  
Peter Schierack ◽  
Hartmut Steinrück ◽  
Sylvia Kleta ◽  
Wilfried Vahjen
Keyword(s):  
Escherichia Coli ◽  
Virulence Factor ◽  
Virulence Genes ◽  
Clinical Signs ◽  
Virulence Gene ◽  
Bacterial Populations ◽  
Factor Gene ◽  
E Coli ◽  
Gene Profiles ◽  
Virulence Factor Gene

ABSTRACT Nonpathogenic, intestinal Escherichia coli (commensal E. coli) supports the physiological intestinal balance of the host, whereas pathogenic E. coli with typical virulence factor gene profiles can cause severe outbreaks of diarrhea. In many reports, E. coli isolates from diarrheic animals were classified as putative pathogens. Here we describe a broad variety of virulence gene-positive E. coli isolates from swine with no clinical signs of intestinal disease. The isolation of E. coli from 34 pigs from the same population and the testing of 331 isolates for genes encoding heat-stable enterotoxins I and II, heat-labile enterotoxin I, Shiga toxin 2e, and F4, F5, F6, F18, and F41 fimbriae revealed that 68.6% of the isolates were positive for at least one virulence gene, with a total of 24 different virulence factor gene profiles, implying high rates of horizontal gene transfer in this E. coli population. Additionally, we traced the occurrence of hemolytic E. coli over a period of 1 year in this same pig population. Hemolytic isolates were differentiated into seven clones; only three were found to harbor virulence genes. Hemolytic E. coli isolates without virulence genes or with only the fedA gene were found to be nontypeable by slide agglutination tests with OK antisera intended for screening live cultures against common pathogenic E. coli serogroups. The results appear to indicate that virulence gene-carrying E. coli strains are a normal part of intestinal bacterial populations and that high numbers of E. coli cells harboring virulence genes and/or with hemolytic activity do not necessarily correlate with disease.

ELECTROSTATIC PROPERTIES OF PROMOTER RECOGNIZED BYE. COLIRNA POLYMERASE Eσ70

2006 ◽  
Vol 04 (02) ◽  
pp. 455-467 ◽  
Author(s):  
ANATOLY A. SOROKIN ◽  
ALEXANDR A. OSYPOV ◽  
TIMUR R. DZHELYADIN ◽  
PETR M. BESKARAVAINY ◽  
SVETLANA G. KAMZOLOVA
Keyword(s):  
Escherichia Coli ◽  
Comparative Analysis ◽  
Rna Polymerase ◽  
Α Subunit ◽  
Promoter Sequences ◽  
E Coli ◽  
Adp Ribosylation ◽  
Electrostatic Properties ◽  
Differential Recognition ◽  
T4 Phage

A comparative analysis of electrostatic patterns for 359 σ70-specific promoters and 359 nonpromoter regions on electrostatic map of Escherichia coli genome was carried out. It was found that DNA is not a uniformly charged molecule. There are some local inhomogeneities in its electrostatic profile which correlate with promoter sequences. Electrostatic patterns of promoter DNAs can be specified due to the presence of some distinctive motifs which differ for different promoter groups and may be involved as signal elements in differential recognition of various promoters by the enzyme. Some specific electrostatic elements which are responsible for modulating promoter activities due to ADP-ribosylation of RNA polymerase α-subunit were found in far upstream regions of T4 phage early promoters and E. coli ribosomal promoters.

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