Journal of Microbiology

Hyon E. Choy

13 Articles

Amino acid residues in the Ler protein critical for derepression of the LEE5 promoter in enteropathogenic E. coli: Su-Mi Choi , Jae-Ho Jeong , Hyon E. Choy , Minsang Shin; J. Microbiol. 2016;54(8):559-564. Published online August 2, 2016; DOI: https://doi.org/10.1007/s12275-016-6027-6

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Enteropathogenic E. coli causes attaching and effacing (A/E) intestinal lesions. The genes involved in the formation of A/E lesions are encoded within a chromosomal island comprising of five major operons, LEE1-5. The global regulator H-NS represses the expression of these operons. Ler, a H-NS homologue, counteracts the H-NS–mediated repression. Using a novel genetic approach, we identified the amino acid residues in Ler that are involved in the interaction with H-NS: I20 and L23 in the C-terminal portion of α-helix 3, and I42 in the following unstructured linker region.

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Structural basis of the oligomerization of anti-silencer Ler from enterohemorrhagic E. coli (EHEC)
Guanghao Wang, Bo Duan, Bin Xia
Structural Dynamics.2026;[Epub] CrossRef
Regulation of the Locus of Enterocyte Effacement in Attaching and Effacing Pathogens
R. Christopher D. Furniss, Abigail Clements, William Margolin
Journal of Bacteriology.2018;[Epub] CrossRef

Effect of promoter-upstream sequence on σ38-dependent stationary phase gene transcription: Hyung-Ju Lim , Kwangsoo Kim , Minsang Shin , Jae-Ho Jeong , Phil Youl Ryu , Hyon E. Choy; J. Microbiol. 2015;53(4):250-255. Published online April 8, 2015; DOI: https://doi.org/10.1007/s12275-015-4681-8

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σ38 in Escherichia coli is required for expression of a subset of stationary phase genes. However, the promoter elements for σ38-dependent genes are virtually indistinguishable from that for σ70-dependent house-keeping genes. hdeABp is a σ38-dependent promoter and LEE5p is a σ70-dependent promoter, but both are repressed by H-NS, a bacterial histone- like protein, which acts at promoter upstream sequence. We swapped the promoter upstream sequences of the two promoters and found that the σ dependency was switched. This was further verified using lacUV5 core promoter. The
results
suggested that the determinant for σ38-dependent promoter lies in the promoter upstream sequence.

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Sequence-dependent model of genes with dual σ factor preference
Ines S.C. Baptista, Vinodh Kandavalli, Vatsala Chauhan, Mohamed N.M. Bahrudeen, Bilena L.B. Almeida, Cristina S.D. Palma, Suchintak Dash, Andre S. Ribeiro
Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms.2022; 1865(3): 194812. CrossRef
Function Enhancement of a Metabolic Module via Endogenous Promoter Replacement for Pseudomonas sp. JY-Q to Degrade Nicotine in Tobacco Waste Treatment
Jun Li, Fengmei Yi, Guoqing Chen, Fanda Pan, Yang Yang, Ming Shu, Zeyu Chen, Zeling Zhang, Xiaotong Mei, Weihong Zhong
Applied Biochemistry and Biotechnology.2021; 193(9): 2793. CrossRef
Recent advances in genetic engineering tools based on synthetic biology
Jun Ren, Jingyu Lee, Dokyun Na
Journal of Microbiology.2020; 58(1): 1. CrossRef

Identification of High-Specificity H-NS Binding Site in LEE5 Promoter of Enteropathogenic Esherichia coli (EPEC): Abhay Prasad Bhat , Minsang Shin , Hyon E. Choy; J. Microbiol. 2014;52(7):626-629. Published online March 7, 2014; DOI: https://doi.org/10.1007/s12275-014-3562-x

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Histone-like nucleoid structuring protein (H-NS) is a small but abundant protein present in enteric bacteria and is involved in compaction of the DNA and regulation of the transcription. Recent reports have suggested that H-NS binds to a specific AT rich DNA sequence than to intrinsically curved DNA in sequence independent manner. We detected two high-specificity H-NS binding sites in LEE5 promoter of EPEC centered at -110 and -138, which were close to the proposed consensus H-NS binding motif. To identify H-NS binding sequence in LEE5 promoter, we took a random mutagenesis approach and found the mutations at around -138 were specifically defective in the regulation byH-NS. It was concluded that H-NS exertsmaximumrepression via the specific sequence at around -138 and ubsequently contacts α subunit of RNAP through oligomerization.

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Horizontally Acquired Homologs of Xenogeneic Silencers: Modulators of Gene Expression Encoded by Plasmids, Phages and Genomic Islands
Alejandro Piña-Iturbe, Isidora D. Suazo, Guillermo Hoppe-Elsholz, Diego Ulloa-Allendes, Pablo A. González, Alexis M. Kalergis, Susan M. Bueno
Genes.2020; 11(2): 142. CrossRef
Recent advances in genetic engineering tools based on synthetic biology
Jun Ren, Jingyu Lee, Dokyun Na
Journal of Microbiology.2020; 58(1): 1. CrossRef
Regulation of the Locus of Enterocyte Effacement in Attaching and Effacing Pathogens
R. Christopher D. Furniss, Abigail Clements, William Margolin
Journal of Bacteriology.2018;[Epub] CrossRef
Bacterial-Chromatin Structural Proteins Regulate the Bimodal Expression of the Locus of Enterocyte Effacement (LEE) Pathogenicity Island in Enteropathogenic Escherichia coli
Hervé Leh, Ahmad Khodr, Marie-Christine Bouger, Bianca Sclavi, Sylvie Rimsky, Stéphanie Bury-Moné, Susan Gottesman
mBio.2017;[Epub] CrossRef
Alternative Synthesis Route of Biocompatible Polyvinylpyrrolidone Nanoparticles and Their Effect on Pathogenic Microorganisms
Vedran Milosavljevic, Pavlina Jelinkova, Ana Maria Jimenez Jimenez, Amitava Moulick, Yazan Haddad, Hana Buchtelova, Sona Krizkova, Zbynek Heger, Lukas Kalina, Lukas Richtera, Pavel Kopel, Vojtech Adam
Molecular Pharmaceutics.2017; 14(1): 221. CrossRef
H-NS and RNA polymerase: a love–hate relationship?
Robert Landick, Joseph T Wade, David C Grainger
Current Opinion in Microbiology.2015; 24: 53. CrossRef
Effect of promoter-upstream sequence on σ38-dependent stationary phase gene transcription
Hyung-Ju Lim, Kwangsoo Kim, Minsang Shin, Jae-Ho Jeong, Phil Youl Ryu, Hyon E. Choy
Journal of Microbiology.2015; 53(4): 250. CrossRef

Effect of Salmonella Treatment on an Implanted Tumor (CT26) in a Mouse Model: Misun Yun , SangO Pan , Sheng- Nan Jiang , Vu Hong Nguyen , Seung-Hwan Park , Che-Hun Jung , Hyung-Seok Kim , Jung-Joon Min , Hyon E. Choy , Yeongjin Hong; J. Microbiol. 2012;50(3):502-510. Published online June 30, 2012; DOI: https://doi.org/10.1007/s12275-012-2090-9

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The use of bacteria has contributed to recent advances in targeted cancer therapy especially for its tumor-specific accumulation and proliferation. In this study, we investigated the molecular events following bacterial therapy using an attenuated Salmonella Typhimurium defective in ppGpp synthesis (ΔppGpp), by analyzing those proteins differentially expressed in tumor tissues from treated and untreated mice. CT26 murine colon cancer cells were implanted in BALB/c mice and allowed to form tumors. The tumor-bearing mice were treated with the attenuated Salmonella Typhimurium. Tumor tissues were analyzed by 2D-PAGE. Fourteen differentially expressed proteins were identified by mass spectrometry. The analysis revealed that cytoskeletal components, including vimentin, drebrin-like protein, and tropomyosinalpha 3, were decreased while serum proteins related to heme or iron metabolism, including transferrin, hemopexin, and haptoglobin were increased. Subsequent studies revealed that the decrease in cytoskeletal components occurred at the transcriptional level and that the increase in heme and iron metabolism proteins occurred in liver. Most interestingly, the same pattern of increased expression of transferrin, hemopexin, and haptoglobin was observed following radiotherapy at the dosage of 14 Gy.

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Constitutive Expression of a Cytotoxic Anticancer Protein in Tumor-Colonizing Bacteria
Phuong-Thu Mai, Daejin Lim, EunA So, Ha Young Kim, Taner Duysak, Thanh-Quang Tran, Miryoung Song, Jae-Ho Jeong, Hyon E. Choy
Cancers.2023; 15(5): 1486. CrossRef
Emerging applications of cancer bacteriotherapy towards treatment of pancreatic cancer
Emily A. Henderson, Slawomir Lukomski, Brian A. Boone
Frontiers in Oncology.2023;[Epub] CrossRef
Recombinant Attenuated Salmonella enterica as a Delivery System of Heterologous Molecules in Cancer Therapy
Elayne Irene Becerra-Báez, Sergio Enrique Meza-Toledo, Paola Muñoz-López, Luis Fernando Flores-Martínez, Karla Fraga-Pérez, Kevin Jorge Magaño-Bocanegra, Uriel Juárez-Hernández, Armando Alfredo Mateos-Chávez, Rosendo Luria-Pérez
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Engineered Attenuated Salmonella typhimurium Expressing Neoantigen Has Anticancer Effects
Jungheun Hyun, Soyeong Jun, Hyeonseob Lim, Hyunjun Cho, Sung-Hwan You, Sang-Jun Ha, Jung-Joon Min, Duhee Bang
ACS Synthetic Biology.2021; 10(10): 2478. CrossRef
Cancer Immunotherapy: Priming the Host Immune Response with Live Attenuated Salmonella enterica
Marco Antonio Hernández-Luna, Rosendo Luria-Pérez
Journal of Immunology Research.2018; 2018: 1. CrossRef
Salmonella-Mediated Cancer Therapy: Roles and Potential
Vu Hong Nguyen, Jung-Joon Min
Nuclear Medicine and Molecular Imaging.2017; 51(2): 118. CrossRef
Tumour‐targeting bacteria‐based cancer therapies for increased specificity and improved outcome
Sebastian Felgner, Vinay Pawar, Dino Kocijancic, Marc Erhardt, Siegfried Weiss
Microbial Biotechnology.2017; 10(5): 1074. CrossRef
Local application of bacteria improves safety ofSalmonella-mediated tumor therapy and retains advantages of systemic infection
Dino Kocijancic, Sebastian Felgner, Tim Schauer, Michael Frahm, Ulrike Heise, Kurt Zimmermann, Marc Erhardt, Siegfried Weiss
Oncotarget.2017; 8(30): 49988. CrossRef
Therapy of solid tumors using probiotic Symbioflor-2 - restraints and potential
Dino Kocijancic, Sebastian Felgner, Michael Frahm, Ronja-Melinda Komoll, Aida Iljazovic, Vinay Pawar, Manfred Rohde, Ulrike Heise, Kurt Zimmermann, Florian Gunzer, Juliane Hammer, Katja Crull, Sara Leschner, Siegfried Weiss
Oncotarget.2016; 7(16): 22605. CrossRef
Salmonella enterica: un aliado en la terapia contra el cáncer
Hilda Chávez-Navarro, Daniel Dimitri Hernández-Cueto, Ariel Vilchis-Estrada, David César Bermúdez-Pulido, Gabriela Antonio-Andrés, Rosendo Luria-Pérez
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Immune Response Induced by ppGpp-Defective Salmonella enterica serovar Gallinarum in Chickens: Sang-Ik Park , Jae-Ho Jeong , Hyon E. Choy , Joon Haeng Rhee , Hee-Sam Na , Tae-Hoon Lee , Moon Her , Kyoung-Oh Cho , Yeongjin Hong; J. Microbiol. 2010;48(5):674-681. Published online November 3, 2010; DOI: https://doi.org/10.1007/s12275-010-0179-6

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To protect chickens from typhoid caused by Salmonella enterica serovar Gallinarum (S. Gallinarum), the attenuated 9R strain has been used in the field as a vaccine. However, safety concerns have been raised because the mutations in 9R are undefined while its efficacy is still a question under debate. A global regulator, ppGpp, synthesized by RelA and SpoT, has been shown to induce various virulence genes in S. Gallinarum (Jeong et al., 2008). In this study, two mutant strains defective in ppGpp-synthesis were constructed in wild-type S. Gallinarum (∆ppGpp) and 9R strain (9R-∆ppGpp) backgrounds and tested as live vaccines in chickens. After oral inoculation, the LD50 values of ∆ppGpp and 9R-∆ppGpp were approximately 5×1010 colony forming unit (CFU) similarly as 9R strain, which was ~105-fold higher than that of the wildtype S. Gallinarum strain. Immunological analyses revealed immunization with either of the two attenuated ppGpp-defective strains induced significant antibody responses, the production of antibody-secreting B cells in blood, proliferation of CD4+ and CD8+ T cells in the spleen, and splenic expression of proinflammatory cytokines, such as IFN-γ and TGF-β4, at levels comparable to the 9R strain. Chickens immunized with the mutants (1×108 CFU) were 80% protected against oral challenge with 1×109 wild-type virulent bacteria (4,000-fold LD50 dose), similar to the level of protection achieved by 9R immunization. Based on these data, live attenuated ∆ppGpp-defective strains may serve as novel vaccines to control fowl typhoid in chickens.

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Shivani Kundra, Cristina Colomer-Winter, José A. Lemos
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О. М. Sen, О. О. Saliy, V. I. Mazurkevych, Y. A. Sobko
Regulatory Mechanisms in Biosystems.2020; 11(4): 506. CrossRef
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Gayeon Won, Atul A. Chaudhari, John Hwa Lee
Clinical and Experimental Vaccine Research.2016; 5(2): 148. CrossRef
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Generation of a safety enhanced Salmonella Gallinarum ghost using antibiotic resistance free plasmid and its potential as an effective inactivated vaccine candidate against fowl typhoid
Chetan V. Jawale, Atul A. Chaudhari, John Hwa Lee
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Molecular Cloning and Characterization of clyA Genes in Various Serotypes of Salmonella enterica: Lan Ji Huang , Jinghua Cui , Hong Hua Piao , Yeongjin Hong , Hyon E. Choy , Phil Youl Ryu; J. Microbiol. 2010;48(5):663-667. Published online November 3, 2010; DOI: https://doi.org/10.1007/s12275-010-9268-9

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Cytolysin A (ClyA) is a pore-forming hemolytic protein encoded by the clyA gene. It has been identified in Salmonella enterica serovars Typhi and Paratyphi A. To identify and characterize the clyA genes in various Salmonella enterica strains, 21 different serotypes of strains isolated from clinical specimens were presently examined. Full-length clyA genes were found in S. enterica serovar Brandenburg, Indiana, Panama, and Schwarzengrund strains by polymerase chain reaction amplification. The ClyA proteins from these four strains showed >97% amino acid identity to that of S. enterica serovar Typhi. Although all four serovars expressed detectable levels of ClyA as determined by Western blot analysis, they did not show a strong hemolytic effect on blood agar, indicating that ClyA may not be efficiently expressed or secreted. Escherichia coli transformed with clyA genes from the four serovars enhanced production of ClyA proteins and hemolytic activities to a level similar to S. enterica serovar Typhi ClyA. The present results suggest that ClyA may play a role in the pathogenesis of S. enterica serovar Brandenburg, Indiana, Panama and Schwarzengrund.

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Plasmid profile and role in virulence of salmonella enterica serovars isolated from food animals and humans in Lagos Nigeria
Ajayi Abraham, Smith Stella Ifeanyi, Fowora Muinah, Bode-Sojobi Ibidunni Oreoluwa, Kalpy Julien Coulibaly, Adeleye Isaac Adeyemi
Pathogens and Global Health.2019; 113(6): 282. CrossRef
Assembly mechanism of the α-pore–forming toxin cytolysin A from Escherichia coli
Daniel Roderer, Rudi Glockshuber
Philosophical Transactions of the Royal Society B: Biological Sciences.2017; 372(1726): 20160211. CrossRef
Soluble Oligomers of the Pore-forming Toxin Cytolysin A from Escherichia coli Are Off-pathway Products of Pore Assembly
Daniel Roderer, Stephan Benke, Benjamin Schuler, Rudi Glockshuber
Journal of Biological Chemistry.2016; 291(11): 5652. CrossRef
The assembly dynamics of the cytolytic pore toxin ClyA
Stephan Benke, Daniel Roderer, Bengt Wunderlich, Daniel Nettels, Rudi Glockshuber, Benjamin Schuler
Nature Communications.2015;[Epub] CrossRef
Eha, a transcriptional regulator of hemolytic activity ofEdwardsiella tarda
Daqing Gao, Jing Cheng, Enjin Zheng, Yuhong Li, Zeye Shao, Zeyan Xu, Chengping Lu
FEMS Microbiology Letters.2014; 353(2): 132. CrossRef
Elevated recombinant clyA gene expression in the uropathogenic Escherichia coli strain 536, a clue to explain pathoadaptive mutations in a subset of extraintestinal E. coli strains
Constance Oben Ayuk Enow, Jan Oscarsson, Nikola Zlatkov, Marie Westermark, Marylise Duperthuy, Sun Nyunt Wai, Bernt Eric Uhlin
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Immunological Responses Induced by asd and wzy/asd Mutant Strains of Salmonella enterica serovar Typhimurium in BALB/c Mice: Hong Hua Piao , Vo Thi Minh Tam , Hee Sam Na , Hyun Ju Kim , Phil Youl Ryu , Soo Young Kim , Joon Haeng Rhee , Hyon E. Choy , Suhng Wook Kim , Yeongjin Hong; J. Microbiol. 2010;48(4):486-495. Published online August 20, 2010; DOI: https://doi.org/10.1007/s12275-010-0023-z

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Attenuated bacteria have long been developed as vaccine candidates but can have some disadvantages, such as the potential for damage to immune organs due to insufficient clearance. To minimize these disadvantages, we generated Salmonella enterica serovar Typhimurium mutants SHJ2104 (asd::cm) and HTSaYA (wzy::km, asd::cm). The wzy gene codes for the O-antigen polymerase, which is involved in lipopolysaccharide (LPS) biosynthesis, and asd codes for aspartate ß- semialdehyde dehydrogenase, which participates in cell wall formation. The strains synthesized LPS with a short-chain length, and showed lower cytotoxicity and reduced intracellular proliferation in animal cells compared to wild-type bacteria. After oral infection, the mutants were cleared in immune tissues, including the Peyer’s patch, mesenteric lymph node, and spleen, within 5 days. The LD50 of the mutants in Balb/c mice was estimated to be 106 higher than wild-type bacteria when administered either via an oral or i.p. route, indicating that the two strains are highly attenuated. To compare the immune response to and protective effects of the mutants against wild-type bacterial infection, we inoculated the mutants into mice via an oral (1×1010 CFU) or i.p. (1×107 CFU) route once or twice at a two week interval. All immune responses, such as serum IgG and secretory IgA levels, cytokine production, and delayed hypersensitivity, were highly induced by two rounds of immunization. HTSaYA and SHJ2104 induced similar immune responses, and mice immunized with HTSaYA or SHJ2104 via an i.p. route were protected against wild-type Salmonella infection even at 100-fold of the LD50 (5×106 CFU). Taken together, these data indicate that HTSaYA and SHJ2104 could be developed as live attenuated Salmonella vaccine candidates.

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The Evolution of Vaccines Development across Salmonella Serovars among Animal Hosts: A Systematic Review
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Identification of Genes That Are Dispensable for Animal Infection by Salmonella typhimurium: Hyun-Ju Kim , Hyon E. Choy; J. Microbiol. 2010;48(3):399-403. Published online June 23, 2010; DOI: https://doi.org/10.1007/s12275-010-9332-5

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In the current study, we generated a pool of Salmonella typhimurium mutants using the Tn10d-cam minitransposon. This pool of mutants was administered to BALB/c mice through the oral route, and bacteria were recovered from the spleen 3 days post-infection. After three rounds of serial passage, we observed enrichment of two insertion mutants, a yddG insertion and an amyA insertion. These two genes have been implicated in growth on plant products (amyA) and survival in the presence of paraquat (yddG), both of which are natural environments for Salmonella. Thus, while in vivo expression technology has identified S. typhimurium genes that are absolutely necessary for animal infection, other genes involved in vegetative growth also appear to play role in the establishment of pathogenesis.

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Novel Determinants of Intestinal Colonization of Salmonella enterica Serotype Typhimurium Identified in Bovine Enteric Infection
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ppGpp-Mediated Stationary Phase Induction of the Genes Encoded by Horizontally Acquired Pathogenicity Islands and cob/pdu Locus in Salmonella enterica serovar Typhimurium: Miryoung Song , Hyun-Ju Kim , Sangryeol Ryu , Hyunjin Yoon , Jiae Yun , Hyon E. Choy; J. Microbiol. 2010;48(1):89-95. Published online March 11, 2010; DOI: https://doi.org/10.1007/s12275-009-0179-6

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Salmonella enterica is highly diverse in terms of genome structure, which is at least partly due to the horizontal transfer of genetic elements from various sources. In this study, we examined the expression profiles of such genes in Salmonella Pathogenicity Islands (SPIs) and the cob/pdu locus, horizontally acquired large DNA segments, during growth under standard growth conditions. Transcripts from exponentially growing and early stationary phase Salmonellae were compared using various methods including cDNA microarray analysis. Nearly all genes encoded by SPIs and the cob/pdu locus were induced at the onset of the stationary phase in a stringent molecule ppGpp-dependent but stationary phase σ, σ38-independent manner. Although, it has been suggested that ppGpp acts in concert with DksA, we found the stationary phase induction of those SPI genes was not DksA dependent. It is suggested that ppGpp stimulates the expression of these stress-inducible genes encoded by horizontally acquired DNA, by itself or in concert with DksA.

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DksA inhibitors against intracellular and persistent Salmonella are effective in acute models of infection
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Protective Effect of Polygoni Cuspidati Radix and Emodin on Vibrio vulnificus Cytotoxicity and Infection: Jong Ro Kim , Dool-Ri Oh , Mi Hye Cha , Byoung Sik Pyo , Joon Haeng Rhee , Hyon E. Choy , Won Keun Oh , Young Ran Kim; J. Microbiol. 2008;46(6):737-743. Published online December 24, 2008; DOI: https://doi.org/10.1007/s12275-008-0232-x

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Abstract PDF

Vibrio vulnificus, a good model organism of bacterial septicemia, causes fatal septicemia manifesting a fulminating course and a high mortality rate within days. In order to identify new natural substances preventing V. vulnificus infection, a plant library was screened for inhibiting cytotoxicity to host cells by using Trypan blue staining and LDH assay. We found that Polygoni Cuspidati Radix potently suppressed the acute death of HeLa and RAW264.7 cells in a dose dependent manner. Further studies revealed that Polygoni Cuspidati Radix inhibited V. vulnificus growth and survival in HI broth and seawater, respectively. We confirmed that Polygoni Cuspidati Radix contained high level of emodin by thin layer chromatography (TLC). Emodin showed direct antibacterial activity against V. vulnificus. In addition, emodin prevented the morphologic damages and acute death of HeLa cells caused from V. vulnificus. The safety of Polygoni Cuspidati Radix and emodin to host cells was confirmed by MTT assay. Polygoni Cuspidati Radix and emodin protected mice from V. vulnificus infection.

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Initial Characterization of yliH in Salmonella typhimurium: Kyung-Hwa Park , Miryung Song , Hyon E. Choy; J. Microbiol. 2007;45(6):558-565.; DOI: https://doi.org/2608 [pii]

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Abstract PDF: Using microarray analysis, we determined those Salmonella genes induced at the entry of stationary phase, and subsequently discovered that uncharacterized yliH was induced most dramatically. We set out to establish the molecular mechanism underlying the stationary phase induction of yliH under the standard culture condition, LB with vigorous aeration, by analyzing its promoter activity in various mutant backgrounds, lacking stationary phase σ, RpoS-, or stringent signal molecules ppGpp, ΔrelA ΔspoT. It was found that the stationary phase induction of yliHp was partially dependent on rpoS but entirely dependent on ppGpp. DNA sequence analysis revealed that the Salmonella yliH gene is composed of 381 base-pair nucleotides, with overall amino acid sequence revealing 76.38% amino acid identity and 88.98% similarity with Escherichia coli yliH, although no motif from data base was noted for its possible role. Recently however, it has been reported that yliH in E. coli was implicated in biofilm formation and motility by repressing these activities (Domka et al., 2006). We have constructed a mutant Salmonella deleting yliH gene by allele replacement and examined its phenotype, and found that the yliH in Salmonella more or less affects motility and adherence by enhancing these activities. The effect on biofilm formation in Salmonella was uncertain. Moreover, addition of cloned yliH of E. coli into Salmonella did not reduce motility or adherence. Taken together, it appears that the pathways implicating yliH for biofilm formation and motility in E. coli and in Salmonella are somewhat different.

Use of Clostridium septicum Alpha Toxins for Isolation of Various Glycosylphosphatidylinositol-Deficient Cells: Dong-Jun Shin , Hyon E. Choy , Yeongjin Hong; J. Microbiol. 2005;43(3):266-271.; DOI: https://doi.org/2214 [pii]

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Abstract PDF: In eukaryotic cells, various proteins are anchored to the plasma membrane through glycosylphosphatidylinositol (GPI). To study the biosynthetic pathways and modifications of GPI, various mutant cells have been isolated from the cells of Chinese hamster ovaries (CHO) supplemented with several exogenous genes involved in GPI biosynthesis using aerolysin, a toxin secreted from gram-negative bacterium Aeromonas hydrophila. Alpha toxin from Gram-positive bacterium Clostridium septicum is homologous to large lobes (LL) of aerolysin, binds GPI-anchored proteins and possesses a cell-destroying mechanism similar to aerolysin. Here, to determine whether alpha toxins can be used as an isolation tool of GPI-mutants, like aerolysin, CHO cells stably transfected with several exogenous genes involved in GPI biosynthesis were chemically mutagenized and cultured in a medium containing alpha toxins. We isolated six mutants highly resistant to alpha toxins and deficient in GPI biosynthesis. By genetic complementation, we determined that one mutant cell was defective of the second subunit of dolichol phosphate mannose synthase (DPM2) and other five cells were of a putative catalytic subunit of inositol acyltransferase (PIG-W). Therefore, C. septicum alpha toxins are a useful screening probe for the isolation of various GPI-mutant cells.

Factors Influencing Preferential Utilization of RNA Polymerase Containing Sigma-38 in Stationary-Phase Gene Expression in Escherichia coli: Eun Young Kim , Min-Sang Shin , Joon Haeng Rhee , Hyon E. Choy; J. Microbiol. 2004;42(2):103-110.; DOI: https://doi.org/2037 [pii]

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Abstract PDF: In order to understand the molecular basis of selective expression of stationary-phase genes by RNA polymerase containing [sigma]^38 (E[sigma]^38) in Escherichia coli, we examined transcription from the stationaryphase promoters, katEP, bolAP, hdeABP, csgBAP, and mcbP, in vivo and in vitro. Although these promoters are preferentially recognized in vivo by E[sigma]^38, they are transcribed in vitro by both E[sigma]^38 and E[sigma]^70 containing the major exponential [sigma], [sigma]^70. In the presence of high concentrations of glutamate salts, however, only E[sigma]^38 was able to efficiently transcribe from these promoters, which supports the concept that the promoter selectivity of [sigma]^38 -containing RNA polymerase is observed only under specific reaction conditions. The examination of 6S RNA, which is encoded by the ssr1 gene in vivo, showed that it reduced E[sigma]^70 activity during the stationary phase, but this reduction of activity did not result in the elevation of E[sigma]^38 activity. Thus, the preferential expression of stationary-phase genes by E[sigma]^38 is unlikely the consequence of selective inhibition of E[sigma]^70 by 6S RNA.

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