Journal of Microbiology

Journal Articles

Investigation of Bottleneck Enzyme Through Flux Balance Analysis to Improve Glycolic Acid Production in Escherichia coli.: Jungyeon Kim, Ye-Bin Kim, Ju-Young Kim, Min-Ju Seo, Soo-Jin Yeom, Bong Hyun Sung; J. Microbiol. 2024;62(11):1023-1033. Published online October 28, 2024; DOI: https://doi.org/10.1007/s12275-024-00175-4

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Abstract: Amid rising environmental concerns, attempts have been made to produce glycolic acid (GA) using microbial processes with renewable carbon resources instead of using chemicals. The Dahms pathway for GA production uses xylose as a substrate and consists of relatively simple enzymatic steps. However, employing it leads to a decrease in cell growth and GA productivity. Systematically identifying and addressing metabolic bottlenecks in the Dahms pathway are essential for efficient glycolic acid (GA) production have not yet been performed. Through metabolic flux balance analysis, we found that insufficient aldehyde dehydrogenase (AldA) activity lowers GA production and negatively affects cell growth due to reduced energy production. Thus, we discovered a novel AldA isolated from Buttiauxella agrestis (BaAldA) demonstrated a 1.69-fold lower K_M and a 1.49-fold higher turnover rate (k_cat/K_M) than AldA from Escherichia coli (EcAldA). GA production in E. coli harboring BaAldA was 1.59 times higher than in the original strain. Fed-batch fermentation of E. coli harboring BaAldA produced 22.70 g/L GA with a yield of 0.497 g/g_xylose (98.2% of the theoretical maximum yield in the Dahms pathway), showing a higher final yield for GA than previously reported in E. coli. Our novel BaAldA enzyme shows great potential for the production of GA using microorganisms or enzymes. Furthermore, our approach to identifying metabolic bottlenecks using flux balance analysis could be utilized to enhance the microbial production of various desirable products in future studies.

The putative polysaccharide synthase AfCps1 regulates Aspergillus fumigatus morphogenesis and conidia immune response in mouse bone marrow-derived macrophages: Sha Wang , Anjie Yuan , Liping Zeng , Sikai Hou , Meng Wang , Lei Li , Zhendong Cai , Guowei Zhong; J. Microbiol. 2021;59(1):64-75. Published online November 17, 2020; DOI: https://doi.org/10.1007/s12275-021-0347-x

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Abstract: Aspergillus fumigatus is a well-known opportunistic pathogen that causes invasive aspergillosis (IA) infections with high mortality in immunosuppressed individuals. Morphogenesis, including hyphal growth, conidiation, and cell wall biosynthesis is crucial in A. fumigatus pathogenesis. Based on a previous random insertional mutagenesis library, we identified the putative polysaccharide synthase gene Afcps1 and its paralog Afcps2. Homologs of the cps gene are commonly found in the genomes of most fungal and some bacterial pathogens. Afcps1/cpsA is important in sporulation, cell wall composition, and virulence. However, the precise regulation patterns of cell wall integrity by Afcps1/cpsA and further effects on the immune response are poorly understood. Specifically, our in-depth study revealed that Afcps1 affects cell-wall stability, showing an increased resistance of ΔAfcps1 to the chitinmicrofibril destabilizing compound calcofluor white (CFW) and susceptibility of ΔAfcps1 to the β-(1,3)-glucan synthase inhibitor echinocandin caspofungin (CS). Additionally, deletion of Afcps2 had a normal sporulation phenotype but caused hypersensitivity to Na+ stress, CFW, and Congo red (CR). Specifically, quantitative analysis of cell wall composition using high-performance anion exchange chromatography- pulsed amperometric detector (HPAEC-PAD) analysis revealed that depletion of Afcps1 reduced cell wall glucan and chitin contents, which was consistent with the downregulation of expression of the corresponding biosynthesis genes. Moreover, an elevated immune response stimulated by conidia of the ΔAfcps1 mutant in marrow-derived macrophages (BMMs) during phagocytosis was observed. Thus, our study provided new insights into the function of polysaccharide synthase Cps1, which is necessary for the maintenance of cell wall stability and the adaptation of conidia to the immune response of macrophages in A. fumigatus.

Review

REVIEW] Recent paradigm shift in the assembly of bacterial tripartite efflux pumps and the type I secretion system: Inseong Jo , Jin-Sik Kim , Yongbin Xu , Jaekyung Hyun , Kangseok Lee , Nam-Chul Ha; J. Microbiol. 2019;57(3):185-194. Published online February 26, 2019; DOI: https://doi.org/10.1007/s12275-019-8520-1

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9 Citations

Abstract: Tripartite efflux pumps and the type I secretion system of Gram-negative bacteria are large protein complexes that span the entire cell envelope. These complexes expel antibiotics and other toxic substances or transport protein toxins from bacterial cells. Elucidating the binary and ternary complex structures at an atomic resolution are crucial to understanding the assembly and working mechanism. Recent advances in cryoelectron microscopy along with the construction of chimeric proteins drastically shifted the assembly models. In this review, we describe the current assembly models from a historical perspective and emphasize the common assembly mechanism for the assembly of diverse tripartite pumps and type I secretion systems.

Journal Article

Contribution of EmrAB efflux pumps to colistin resistance in Acinetobacter baumannii: Ming-Feng Lin , Yun-You Lin , Chung-Yu Lan; J. Microbiol. 2017;55(2):130-136. Published online January 26, 2017; DOI: https://doi.org/10.1007/s12275-017-6408-5

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71 Citations

Abstract: Efflux pumps play an important role in antimicrobial resistance for Acinetobacter baumannii. However, the function of the Emr pump system and the relationship between Emr and drug resistance has not been characterized in A. baumannii. In this study, four possible groups of emr-like genes were found by searching a genome database. Among them, A1S_ 1772 (emrB) and A1S_1773 (emrA) were demonstrated to be co-transcribed as a single operon. Moreover, during osmotic stress, A1S_1772 showed the largest change in gene expression compared to the other emrB-like genes, and deletion of A1S_1772 (AB ΔemrB) significantly slowed cell growth in 20% sucrose. Using a phenotypic microarray analysis, the AB ΔemrB mutant was more susceptible to colistin and nafcillin, paromomycin, spiramycin, and D,L-serine hydroxmate than the wild type. The spot assay, time kill assay and minimal inhibition concentration determination also indicated that the wild type could tolerate colistin better than the AB ΔemrB mutant. Finally, the increased expression levels of all emrBlike genes, including A1S_0775, A1S_0909, A1S_1772, and A1S_1799, in colistin resistance-induced A. baumannii further supported the possible involvement of the emrB genes in A. baumannii colistin resistance. Together, the Emr pump systems in A. baumannii contribute to adaptation to osmotic stress and resistance to colistin.

Research Support, Non-U.S. Gov't

Mutational inactivation of OprD in carbapenem-resistant Pseudomonas aeruginosa isolates from Korean hospitals: Chi Hyun Kim , Hee Young Kang , Bo Ra Kim , Hyejin Jeon , Yoo Chul Lee , Sang Hwa Lee , Je Chul Lee; J. Microbiol. 2016;54(1):44-49. Published online January 5, 2016; DOI: https://doi.org/10.1007/s12275-016-5562-5

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21 Citations

Abstract: This study investigated the mechanisms underlying the carbapenem resistance of bloodstream isolates of Pseudomonas aeruginosa obtained from two Korean hospitals. Of the 79 P. aeruginosa isolates, 22 and 21 were resistant to imipenem and meropenem, respectively. The 22 imipenem-resistant P. aeruginosa isolates were classified into 7 sequence types (STs) and 13 pulsotypes. Twelve imipenem-resistant isolates from one hospital were found to belong to the international clone ST111. Two imipenem-resistant P. aeruginosa ST235 isolates carried the blaIMP-6 gene, but the remaining 20 isolates did not produce carbapenemases. Mutations in the oprD gene and a related decrease in gene expression were found in 21 and 5 isolates, respectively. However, all imipenemresistant P. aeruginosa isolates showed no significant expression of OprD in the outer membrane as compared with that of carbapenem-susceptible PAO1 strain. Overexpression of genes associated with efflux pumps, including mexB, mexD, mexF, and mexY, was not found in any imipenem-resistant isolate. One imipenem-resistant P. aeruginosa isolate overexpressed the ampC gene. Our results show that the low permeability of drugs due to the mutational inactivation of OprD is primarily responsible for carbapenem resistance in bloodstream isolates of P. aeruginosa from Korean hospitals.

Reviews

MINIREVIEW] Multidrug efflux pumps in Staphylococcus aureus and their clinical implications: Soojin Jang; J. Microbiol. 2016;54(1):1-8. Published online January 5, 2016; DOI: https://doi.org/10.1007/s12275-016-5159-z

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86 Citations

Abstract: Antibiotic resistance is rapidly spreading among bacteria such as Staphylococcus aureus, an opportunistic bacterial pathogen that causes a variety of diseases in humans. For the last two decades, bacterial multidrug efflux pumps have drawn attention due to their potential association with clinical multidrug resistance. Numerous researchers have demonstrated efflux-mediated resistance in vitro and in vivo and found novel multidrug transporters using advanced genomic information about bacteria. This article aims to provide a concise summary of multidrug efflux pumps and their important clinical implications, focusing on recent findings concerning S. aureus efflux pumps.

MINIREVIEW] Molecular architecture of the bacterial tripartite multidrug efflux pump focusing on the adaptor bridging model: Saemee Song , Jin-Sik Kim , Kangseok Lee , Nam-Chul Ha; J. Microbiol. 2015;53(6):355-364. Published online May 30, 2015; DOI: https://doi.org/10.1007/s12275-015-5248-4

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12 Citations

Abstract: Gram-negative bacteria expel a wide range of toxic substances through tripartite drug efflux pumps consisting of an inner membrane transporter, an outer membrane channel protein, and a periplasmic adaptor protein. These pumps form tripartite assemblies which can span the entire cell envelope, including the inner and outer membranes. There have been controversial findings regarding the assembly of the individual components in tripartite drug efflux pumps. Recent structural and functional studies have advanced our understanding of the assembly and working mechanisms of the pumps. Here, we re-evaluate the assembly models based on recent structural and functional studies. In particular, this study focuses on the ‘adaptor bridging model’, highlighting the intermeshing cogwheel-like interactions between the tip regions of the outer membrane channel protein and the periplasmic adaptor protein in the hexameric assembly.

Research Support, Non-U.S. Gov'ts

Effect of carbonyl cyanide 3-chlorophenylhydrazone (CCCP) on killing Acinetobacter baumannii by colistin: Young Kyoung Park , Kwan Soo Ko; J. Microbiol. 2015;53(1):53-59. Published online January 4, 2015; DOI: https://doi.org/10.1007/s12275-015-4498-5

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47 Citations

Abstract: We investigated the effect of cyanide 3-chlorophenylhydrazone (CCCP) and other efflux pump inhibitors (EPIs) on the colistin susceptibility in Acinetobacter baumannii. While minimum inhibitory concentrations (MICs) of colistin in all colistin-resistant strains decreased significantly with 25 μM of CCCP and 2,4-dinitrophenol (DNP), phenyl-arginine-β- naphthylamide (PAβN), and reserpine did not decrease the colistin MICs. However, CCCP and DNP as well as PAβN and reserpine did not have a significant effect on the MICs of the other agents. Efflux pump gene expressions in colistinresistant strains were not increased compared with those in colistin-susceptible strains. When only 5X MIC of colistin (5 mg/L) was provided to a colistin-susceptible A. baumannii strain, the bacterial cell number was reduced by 9 h after exposure to colistin, but regrowth was observed. When CCCP was added to colistin, bacterial cells were completely killed after 24 to 48 h of incubation, which was not due to the toxicity of CCCP itself. Colistin resistance in A. baumannii may not be due to efflux pumps. Our present study suggests that bacterial cells with reduced metabolic activity by CCCP are more susceptible to colistin in A. baumannii. It may show the possibility that combined therapy with colistin and other antimicrobial agents could effective against A. baumannii infections.

Analysis of cepA Encoding an Efflux Pump-like Protein in Corynebacterium glutamicum: Soo-Yeon Sim , Eun-Ji Hong , Younhee Kim , Heung-Shick Lee; J. Microbiol. 2014;52(4):278-283. Published online February 17, 2014; DOI: https://doi.org/10.1007/s12275-014-3461-1

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4 Citations

Abstract: A gene encoding a homolog of purine efflux proteins of Escherichia coli and Bacillus subtilis was identified in the genome of Corynebacterium glutamicum and designated as cepA. The gene encoded a putative protein product, containing 12 transmembrane helixes, which is a typical feature of integral membrane transport proteins. To elucidate the function of the gene, we constructed a cepA deletion mutant (ΔcepA) and a cepA-overexpressing strain and analyzed their physiological characteristics. The cepA gene could be deleted with no critical effect on cell growth. However, the cell yield of a ΔcepA strain was decreased by 10% as compared to that of a strain carrying a cepA-overexpression plasmid (P180-cepA). Further analysis identified increased resistance of the P180-cepA strain to the purine analogues 6-mercaptopurine and 6-mercaptoguanine, but not to 2-aminopurine and purine nucleoside analogues. Moreover, this strain showed increased resistance to the antibiotics nalidixic acid and ampicillin. Collectively, these data suggest that cepA is a novel multidrug resistance gene and probably functions in the efflux of toxic substances from the inside of cells to the environment, thus allowing cells to reach a higher cell yield.

Interaction between the α-Barrel Tip of Vibrio vulnificus TolC Homologs and AcrA Implies the Adapter Bridging Model: Seunghwa Lee , Saemee Song , Minho Lee , Soonhye Hwang , Ji-Sun Kim , Nam-Chul Ha , Kangseok Lee; J. Microbiol. 2014;52(2):148-153. Published online February 1, 2014; DOI: https://doi.org/10.1007/s12275-014-3578-2

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11 Citations

Abstract: The AcrAB-TolC multidrug efflux pump confers resistance to Escherichia coli against many antibiotics and toxic compounds. The TolC protein is an outer membrane factor that participates in the formation of type I secretion systems. The genome of Vibrio vulnificus encodes two proteins homologous to the E. coli TolC, designated TolCV1 and TolCV2. Here, we show that both TolCV1 and TolCV2 partially complement the E. coli TolC function and physically interact with the membrane fusion protein AcrA, a component of the E. coli AcrAB-TolC efflux pump. Using site-directed mutational analyses and an in vivo cross-linking assay, we demonstrated that the α-barrel tip region of TolC homologs plays a critical role in the formation of functional AcrAB-TolC efflux pumps. Our findings suggest the adapter bridging model as a general assembly mechanism for tripartite drug efflux pumps in Gram-negative bacteria.

The PseEF Efflux System Is a Virulence Factor of Pseudomonas syringae pv. syringae: Hyosun Cho , Hyojeung Kang; J. Microbiol. 2012;50(1):79-90. Published online February 27, 2012; DOI: https://doi.org/10.1007/s12275-012-1353-9

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17 Citations

Abstract: An ATP-binding cassette (ABC) transporter, called the PseEF efflux system, was identified at the left border of the syr-syp genomic island of Pseudomonas syringae pv. syringae strain B301D. The PseEF efflux system was located within a 3.3-kb operon that encodes a periplasmic membrane fusion protein (PseE), and an ABC-type cytoplasmic membrane protein (PseF). The PseEF efflux system exhibited amino acid homology to a putative ABC efflux system (MacAB) of E. coli W3104 with identities of 47.2% (i.e., PseE to MacA) and 57.6% (i.e., PseF to MacB). A nonpolar mutation within the pseF gene was generated by nptII insertional mutagenesis. The resultant mutant strain showed significant reduction in secretion of syringomycin (74%) and syringopeptin (71%), as compared to parental strain B301D. Quantitative real-time RT-PCR was used to determine transcript levels of the syringomycin (syrB1) and syringopeptin (sypA) synthetase genes in strain B301D-HK7 (a pseF mutant). Expression of the sypA gene by mutant strain B301D-HK7 was approximately 6.9% as compared to that of parental strain B301D, while the syrB1 gene expression by mutant strain B301D-HK7 was nearly 14.6%. In addition, mutant strain B301D-HK7 was less virulent by approximately 67% than parental strain B301D in immature cherry fruits. Mutant strain B301D-HK7 was not reduced in resistance to any antibiotics used in this study as compared to parental strain B301D. Expression (transcript levels) of the pseF gene was induced approximately six times by strain B301D grown on syringomycin minimum medium (SRM) supplemented with the plant signal molecules arbutin and D-fructose (SRMAF), as compared to that of strain B301D grown on SRM (in the absence of plant signal molecules). In addition, during infection of bean plants by P. syringae pv. syringae strain B728a, expression of the pseF gene increased at 3 days after inoculation (dai). More than 180-fold induction was observed in transcript levels of the pseF gene by parental strain B728a as compared to strain B728a-SL7 (a salA mutant). Thus, the PseEF efflux system, an ABC-type efflux system, has an important role in secretion of syringomycin and syringopeptin, and is required for full virulence in P. syringae pv. syringae.

Functional Definition of LuxS, an Autoinducer-2 (AI-2) Synthase and Its Role in Full Virulence of Streptococcus suis Serotype 2: Min Cao , Youjun Feng , Changjun Wang , Feng Zheng , Ming Li , Hui Liao , Yinghua Mao , Xiuzhen Pan , Jing Wang , Dan Hu , Fuquan Hu , Jiaqi Tang; J. Microbiol. 2011;49(6):1000-1011. Published online December 28, 2011; DOI: https://doi.org/10.1007/s12275-011-1523-1

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38 Citations

Abstract: Quorum sensing is a widespread chemical communication in response to fluctuation of bacterial population density, and has been implicated into bacterial biofilm formation and regulation of expression of virulence factors. The luxS gene product, S-ribosylhomocysteinase, catalizes the last committed step in biosynthetic pathway of autoinducer 2 (AI-2), a signaling molecule for inter-species quorum sensing. We found a luxS homologue in 05ZYH33, an epidemic strain of Streptococcus suis serotype 2 (SS2) in China. A luxS null mutant (ΔluxS) of 05ZYH33 strain was obtained using an approach of homologous recombination. LuxS was determined to be required for AI-2 production in 05ZYH33 strain of S. suis 2. Inactivation of luxS gene led to a wide range of phenotypic changes including thinner capsular walls, increased tolerance to H2O2, reduced adherence capacity to epithelial cells, etc. In particular, loss of LuxS impaired dramatically its full virulence of SS2 in experimental model of piglets, and functional complementation restored it nearly to the level of parent strain. Genome-wide transcriptome analyses suggested that some known virulence factors such as CPS are down-regulated in the ΔluxS mutant, which might in part explain virulence attenuation by luxS deletion. Similarly, 29 of 71 genes with different expression level were proposed to be targets candidate regulated by LuxS/AI-2-dependent quorum sensing.

Periplasmic Domain of CusA in an Escherichia coli Cu+/Ag+ Transporter Has Metal Binding Sites: Bo-Young Yun , Yongbin Xu , Shunfu Piao , Nahee Kim , Jeong-Hyun Yoon , Hyun-Soo Cho , Kangseok Lee , Nam-Chul Ha; J. Microbiol. 2010;48(6):829-835. Published online January 9, 2011; DOI: https://doi.org/10.1007/s12275-010-0339-8

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6 Citations

Abstract: The resistance nodulation division (RND)-type efflux systems are utilized in Gram-negative bacteria to export a variety of substrates. The CusCFBA system is the Cu+ and Ag+ efflux system in Escherichia coli, conferring resistance to lethal concentrations of Cu+ and Ag+. The periplasmic component, CusB, which is essential for the assembly of the protein complex, has Cu+ or Ag+ binding sites. The twelve-span membrane protein CusA is a homotrimeric transporter, and has a relatively large periplasmic domain. Here, we constructed the periplasmic domain of CusA by joining two DNA segments and then successfully expressed and purified the protein. Isothermal titration calorimetry experiments revealed Ag+ binding sites with Kds of 10-6-10-5 M. Our findings suggest that the metal binding in the periplasmic domain of CusA might play an important role in the function of the efflux pump.

Identification of Vibrio natriegens uvrA and uvrB Genes and Analysis of Gene Regulation Using Transcriptional Reporter Plasmids: Keryn L. Simons , Susan M. Thomas , Peter A. Anderson; J. Microbiol. 2010;48(5):644-656. Published online November 3, 2010; DOI: https://doi.org/10.1007/s12275-010-9370-z

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6 Citations

Abstract: Nucleotide excision repair (NER) rectifies a variety of chemically and structurally distinct DNA lesions. The current model of NER is based upon the enteric bacterium Escherichia coli and there is scarce information about how other bacterial species respond to, and correct, DNA damage. Here we report the isolation and functional analysis of the uvrA and uvrB genes from Vibrio natriegens, a naturally occurring marine bacterium. Genetic studies were completed to assess the repair capabilities of V. natriegens uvrA and uvrB in E. coli uvrA and uvrB mutants. In addition to the genetic studies, transcriptional fusions between the luciferase gene and the 5′ regulatory regions of uvrA and uvrB gene of V. natriegens and E. coli were constructed. Luminescent measurements from E. coli transformed with these constructs showed that whilst the response to UV irradiation of either E. coli or V. natriegens uvrA regulatory sequences was similar, both the rate and induction of luminescence detected from the uvrB regulatory regions differed.

Journal Article

Molecular Characteristics and Resistant Mechanisms of Imipenem-Resistant Acinetobacter baumannii Isolates in Shenyang, China: Jing Ping Zhang , Wan Zhu , Su Fei Tian , Yun Zhuo Chu , Bai Yi Chen; J. Microbiol. 2010;48(5):689-694. Published online November 3, 2010; DOI: https://doi.org/10.1007/s12275-010-0137-3

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24 Citations

Abstract: The investigation was carried out to elucidate the molecular characteristics and resistant mechanisms of imipenem-resistant Acinetobacter baumannii. Thirty-seven isolates were collected from January 2007 to December 2007. The homology of the isolates was analyzed by both pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The genes of β-lactamases, adeB, and class 1 integron were polymerase chain reaction amplified. Genotype analysis of the 37 A. baumannii isolates by PFGE revealed the circulation of four PFGE types (A-D) ; the A- and B-type accounted for 48.6% and 40.5%, respectively. MLST showed the existence of three allelic profiles. The agar dilution method was carried out to determine the MIC of imipenem, in the absence or presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP, 10 μg/ml). The MICs of the strains to imipenem were between 16 μg/ml and 128 μg/ml. When CCCP was added, a MIC decrease of at least four-fold was observed in 20 isolates, which belonged to the A- or C-type. AdeB and blaPER-1 genes were each detected in 35 isolates, blaOXA-23 gene in 34 isolates and blaOXA-58-like gene in 24 isolates. All isolates harbored blaOXA-51-like genes. No isolates carried the blaIMP-1 gene. Integron was detected in 25 isolates, which mediated the resistance to aminoglycosides and rifampin. The epidemiologic data suggested that the increasing infection of A. baumannii in our hospital was mainly caused by the inter-hospital spread of two epidemic clones. The AdeABC efflux system may be the important factor that leads to the high level of imipenem-resistance in PFGE A-type.

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