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Molecular Microbiology

Tue, 03/06/2018 - 10:55
Summary Enteropathogenic Escherichia coli (EPEC) use a type 3 secretion system (T3SS) for injection of effectors into host cells and intestinal colonization. Here, we demonstrate that the multicargo chaperone CesT has two strictly conserved tyrosine phosphosites, Y152 and Y153, that regulate differential effector secretion in EPEC. Conservative substitution of both tyrosine residues to...
Sat, 02/17/2018 - 05:30
Summary Transcriptional silencing and anti-silencing mechanisms modulate bacterial physiology and virulence in many human pathogens. In Shigella species, many virulence plasmid genes are silenced by the histone-like nucleoid structuring protein H-NS and anti-silenced by the virulence gene regulator VirB. Despite the key role that these regulatory proteins play in Shigella virulence, their...
Mon, 02/05/2018 - 10:12
Summary Endolysins are bacteriophage-encoded peptidoglycan hydrolases that specifically degrade the bacterial cell wall at the end of the phage lytic cycle. They feature a distinct modular architecture, consisting of enzymatically active domains (EADs) and cell wall binding domains (CBDs). Structural analysis of the complete enzymes or individual domains is required for better understanding the...
Thu, 02/01/2018 - 04:45
Summary Integration of horizontally acquired genes into transcriptional networks is essential for the regulated expression of virulence in bacterial pathogens. In Salmonella enterica, expression of such genes is repressed by the nucleoid-associated protein H-NS, which recognizes and binds to AT-rich DNA. H-NS-mediated silencing must be countered by other DNA-binding proteins to allow expression...
Sat, 01/20/2018 - 05:14
Summary DNA in intracellular Salmonella enterica serovar Typhimurium relaxes during growth in the acidified (pH 4 to 5) macrophage vacuole and DNA relaxation correlates with upregulation of Salmonella genes involved in adaptation to the macrophage environment. Bacterial ATP levels did not increase during adaptation to acid pH unless the bacterium was deficient in MgtC, a cytoplasmic-membrane-...
Thu, 12/14/2017 - 09:01
Summary Genes required for fungal secondary metabolite production are usually clustered, co-regulated and expressed in stationary growth phase. Chromatin modification has an important role in co-regulation of secondary metabolite genes. The virulence factor dothistromin, a relative of aflatoxin, provided a unique opportunity to study chromatin level regulation in a highly fragmented gene cluster...
Thu, 12/07/2017 - 08:03
Abstract Listeria monocytogenes and other pathogenic bacteria modify their peptidoglycan to protect it against enzymatic attack through the host innate immune system, such as the cell wall hydrolase lysozyme. During our studies on GpsB, a late cell division protein that controls activity of the bi-functional penicillin binding protein PBP A1, we discovered that GpsB influences lysozyme resistance...
Mon, 11/20/2017 - 04:26
Abstract VieA is a cyclic diguanylate phosphodiesterase that modulates biofilm development and motility in Vibrio cholerae O1 of the classical biotype. vieA is part of an operon encoding the VieSAB signal transduction pathway that is nearly silent in V. cholerae of the El Tor biotype. A DNA pull-down assay for proteins interacting with the vieSAB promoter identified the LysR-type regulator LeuO....
Fri, 10/27/2017 - 08:20
Summary The AbcR small RNAs (sRNAs) are a fascinating example of two highly conserved sRNAs that differ tremendously at the functional level amongst organisms. From their transcriptional activation to their regulatory capabilities, the AbcR sRNAs exhibit varying characteristics in three well-studied bacteria belonging to the Rhizobiales order: the plant symbiont Sinorhizobium meliloti, the plant...
Tue, 09/19/2017 - 06:40
Summary The proton-driven flagellar motor of Salmonella enterica can accommodate a dozen MotA/B stators in a load-dependent manner. The C-terminal periplasmic domain of MotB acts as a structural switch to regulate the number of active stators in the motor in response to load change. The cytoplasmic loop termed MotAC is responsible for the interaction with a rotor protein, FliG. Here, to test if...
Thu, 09/14/2017 - 08:10
Summary In the environment and during infection, the human intestinal pathogen Vibrio cholerae must overcome noxious compounds that damage the bacterial outer membrane. The El Tor and classical biotypes of O1 V. cholerae show striking differences in their resistance to membrane disrupting cationic antimicrobial peptides (CAMPs), such as polymyxins. The classical biotype is susceptible to CAMPs,...
Fri, 09/01/2017 - 03:35
Abstract Microbial expression of genes for resistance to heavy metals and metalloids is usually transcriptionally regulated by the toxic ions themselves. Arsenic is a ubiquitous, naturally occurring toxic metalloid widely distributed in soil and groundwater. Microbes biotransform both arsenate (As(V)) and arsenite (As(III)) into more toxic methylated metabolites methylarsenite (MAs(III)) and...
Wed, 06/14/2017 - 05:45
Summary Anti-virulence (AV) compounds are a promising alternative to traditional antibiotics for fighting bacterial infections. The Type Three Secretion System (T3SS) is a well-studied and attractive AV target, given that it is widespread in more than 25 species of Gram-negative bacteria, including enterohemorrhagic E. coli (EHEC), and as it is essential for host colonization by many pathogens....
Tue, 06/06/2017 - 12:15
Summary The generation of a membrane potential (Δψ), the major constituent of the proton motive force (pmf), is crucial for ATP synthesis, transport of nutrients and flagellar rotation. Campylobacter jejuni harbors a branched electron transport chain, enabling respiration with different electron donors and acceptors. Here, we demonstrate that a relatively high Δψ is only generated in the presence...
Tue, 05/16/2017 - 06:20
Summary Through Minos transposon mutagenesis we obtained A. nidulans mutants resistant to 5-fluorouracil due to insertions into the upstream region of the uncharacterized gene nmeA, encoding a Major Facilitator Superfamily (MFS) transporter. Minos transpositions increased nmeA transcription, which is otherwise extremely low under all conditions tested. To dissect the function of NmeA we used...
Tue, 05/16/2017 - 00:10
Abstract To enable specific and tightly controlled gene expression both in-vitro and during the intracellular lifecycle of the pathogen Listeria monocytogenes, a TetR-dependent genetic induction system was developed. Highest concentration of cytoplasmic TetR and best repression of tetO-controlled genes was obtained by tetR expression from the synthetic promoter Pt17. Anhydrotetracycline (ATc) as...
Tue, 05/02/2017 - 11:59
Abstract ToxR is a transmembrane transcription factor that is essential for virulence gene expression and human colonization by Vibrio cholerae. ToxR requires its operon partner ToxS, a periplasmic integral membrane protein, for full activity. These two proteins are thought to interact through their respective periplasmic domains, ToxRp and ToxSp. In addition, ToxR is thought to be responsive to...
Fri, 04/07/2017 - 19:30
Summary Members of the multihaem cytochrome c (MCC) family such as pentahaem cytochrome c nitrite reductase (NrfA) or octahaem hydroxylamine oxidoreductase (Hao) are involved in various microbial respiratory electron transport chains. Some members of the Hao subfamily, here called εHao proteins, have been predicted from the genomes of nitrate/nitrite-ammonifying bacteria that usually lack NrfA....
Thu, 03/30/2017 - 04:45
Abstract Small RNAs (sRNAs), particularly those that act by limited base pairing with mRNAs, are part of most regulatory networks in bacteria. In many cases, the base-pairing interaction is facilitated by the RNA chaperone Hfq. However, not all bacteria encode Hfq and some base-pairing sRNAs do not require Hfq raising the possibility of other RNA chaperones. Candidates are proteins with homology...
Sat, 03/18/2017 - 11:55
SUMMARY Campylobacter jejuni helical shape is important for colonization and host interactions with straight mutants having altered biological properties. Passage on calcofluor white (CFW) resulted in C. jejuni 81-176 isolates with morphology changes: either a straight morphology from frameshift mutations and single nucleotide polymorphisms in peptidoglycan hydrolase genes pgp1 or pgp2 or a...
Thu, 03/02/2017 - 11:30
Summary LeuO is a conserved LysR-type transcription factor of pleiotropic function in Enterobacteria. Regulation of the leuO gene has been best studied in Escherichia coli and Salmonella enterica. Its expression is silenced by the nucleoid-associated proteins H-NS and StpA, autoregulated by LeuO, and in E. coli activated by the transcription regulator BglJ-RcsB. However, signals which induce leuO...
Sat, 02/18/2017 - 10:55
Summary Bacteria of the genera Bacillus and Clostridium form highly resistant spores, which in the case of some pathogens act as the infectious agents. An exosporium forms the outermost layer of some spores; it plays roles in protection, adhesion, dissemination, host targeting in pathogens, and germination control. The exosporium of the Bacillus cereus group, including the anthrax pathogen,...
Fri, 02/17/2017 - 03:20
Abstract The Escherichia coli K-12 nrf operon encodes a periplasmic nitrite reductase, the expression of which is driven from a single promoter, pnrf. Expression from pnrf is activated by the FNR transcription factor in response to anaerobiosis and further increased in response to nitrite by the response regulator proteins, NarL and NarP. FNR-dependent transcription is suppressed by the binding...
Tue, 02/14/2017 - 17:45
A common mechanism for high affinity carbohydrate uptake in microbial species is the phosphoenolpyruvate-dependent phosphotransferase system (PTS). This system consists of a shared component, EI, which is required for all PTS transport, and numerous carbohydrate uptake transporters. In V. cholerae, there are 13 distinct PTS transporters. Due to genetic redundancy within this system, the...
Fri, 01/27/2017 - 03:26
Abstract Methylation of inorganic arsenic is a central process in the organoarsenical biogeochemical cycle. Members of every kingdom have ArsM As(III) S-adenosylmethionine (SAM) methyltransferases that methylates inorganic As(III) into mono- (MAs(III)), di- (DMAs(III)) and tri- (TMAs(III)) methylarsenicals. Every characterized ArsM to date has four conserved cysteine residues. All four cysteines...
Wed, 01/18/2017 - 04:10
Summary Cyclic di-adenosine monophosphate (c-di-AMP) is a conserved nucleotide second messenger critical for bacterial growth and resistance to cell wall-active antibiotics. In Listeria monocytogenes, the sole diadenylate cyclase, DacA, is essential in rich, but not synthetic media and ΔdacA mutants are highly sensitive to the β-lactam antibiotic cefuroxime. In this study, loss of function...
Mon, 12/26/2016 - 05:31
Abstract Invasion of intestinal epithelial cells by Campylobacter jejuni is a critical step during infection of the intestine by this important human pathogen. In this study we investigated the role played by DNA supercoiling in the regulation of invasion of epithelial cells and the mechanism by which this could be mediated. A significant correlation between more relaxed DNA supercoiling and an...
Fri, 12/23/2016 - 18:48
Summary In bacteria, the RNA chaperone Hfq enables pairing of small regulatory RNAs with their target mRNAs and therefore is a key player of post-transcriptional regulation network. As a global regulator, Hfq is engaged in the adaptation to external environment, regulation of metabolism and bacterial virulence. In this study we used RNA-sequencing and quantitative proteomics (LC-MS/MS) to...
Tue, 12/20/2016 - 13:25
Abstract Type III Secretion Systems (T3SSs) are structurally conserved nanomachines that span the inner and outer bacterial membranes, and via a protruding needle complex contact host cell membranes and deliver type III effector proteins. T3SS are phylogenetically divided into several families based on structural basal body components. Here we have studied the evolutionary and functional...
Mon, 11/28/2016 - 09:40
Abstract Brucella abortus is a pathogen infecting cattle, able to survive, traffic and proliferate inside host cells. It belongs to the Alphaproteobacteria, a phylogenetic group comprising bacteria with free living, symbiotic and pathogenic lifestyles. An essential regulator of cell cycle progression named CtrA was described in the model bacterium Caulobacter crescentus. This regulator is...
Sat, 11/12/2016 - 03:30
Abstract Regulatory network plasticity is a key attribute underlying changes in bacterial gene expression and a source of phenotypic diversity to interact with the surrounding environment. Here, we sought to study the transcriptional circuit of HutC, a regulator of both metabolic and virulence genes of the facultative intracellular pathogen Brucella. Using in silico and biochemical approaches, we...
Mon, 10/17/2016 - 11:30
Abstract 5,6-Dimethylbenzimidazolyl-(DMB)-α-ribotide, [α-ribazole-5'-phosphate (α-RP)] is an intermediate in the biosynthesis of adenosylcobalamin (AdoCbl) in many prokaryotes. In such microbes, α-RP is synthesized by nicotinate mononucleotide (NaMN):DMB phosphoribosyltransferases (CobT in S. enterica), in a reaction that is considered to be the canonical step for the activation of the base of...
Wed, 09/14/2016 - 10:45
Abstract The assembly of the class 5 CFA/I fimbriae of enterotoxigenic E. coli was proposed to proceed via the alternate chaperone-usher pathway. Here, we show that in the absence of the chaperone CfaA, CfaB, the major pilin subunit of CFA/I fimbriae, is able to spontaneously refold and polymerize into cyclic trimers. CfaA kinetically traps CfaB to form a metastable complex that can be stabilized...
Wed, 09/14/2016 - 04:47
Abstract Bacterial pathogens display versatile gene expression to adapt to changing surroundings. For example, Vibrio cholerae, the causative agent of cholera, utilizes distinct genetic programs to combat reactive oxygen species (ROS) in aquatic environments or during host infection. We previously reported that the virulence activator AphB in V. cholerae is involved in ROS resistance. Here by...
Fri, 09/09/2016 - 11:21
Abstract Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, has evolved signal transduction systems to control coordinately the expression of virulence determinants. We previously showed that the presence of the bile salts glycocholate and taurocholate in the small intestine causes dimerization of the transmembrane transcription factor TcpP by inducing intermolecular...
Thu, 08/04/2016 - 18:45
Summary AtxA is a critical transcriptional regulator of plasmid-encoded virulence genes in Bacillus anthracis. Bacillus cereus G9241, which caused an anthrax-like infection, has two virulence plasmids, pBCXO1 and pBC210, that each harbor toxin genes and a capsule locus. G9241 also produces two orthologs of AtxA: AtxA1, encoded on pBCXO1, and AtxA2, encoded on pBC210. The amino acid sequence of...
Wed, 07/06/2016 - 04:25
Abstract Heteroresistance, a phenomenon where subpopulations of a bacterial isolate exhibit different susceptibilities to an antibiotic, is a growing clinical problem where the underlying genetic mechanisms in most cases remain unknown. We isolated colistin resistant mutants in Escherichia coli and Salmonella enterica serovar Typhimurium at different concentrations of colistin. Genetic analysis...
Tue, 07/05/2016 - 05:20
SUMMARY Cellular turgor is of fundamental importance to bacterial growth and survival. Changes in external osmolarity as a consequence of fluctuating environmental conditions and colonization of diverse environments can significantly impact cytoplasmic water content, resulting in cellular lysis or plasmolysis. To ensure maintenance of appropriate cellular turgor, bacteria import ions and small...
Wed, 06/29/2016 - 04:50
Abstract Bacterial flagella assembly is tightly regulated to ensure a timely and sequential production of the various flagellum constituents. In the pathogen Campylobacter jejuni the hierarchy in flagella biosynthesis is largely determined at the transcriptional level through the activity of the alternative sigma factors sigma54 and sigma28. Here we report that C. jejuni flagellin levels are also...
Tue, 06/28/2016 - 04:31
Abstract Bacterial ribosome requires elongation factor P to translate fragments harboring consecutive proline codons. Given the abundance of ORFs with potential EF-P regulated sites, EF-P was assumed to be constitutively expressed. Here, we report that the intracellular pathogen Salmonella enterica serovar Typhimurium decreases efp mRNA levels during course of infection. We determined that the...
Mon, 06/13/2016 - 07:20
Abstract Toxin-antitoxin (TA) systems are widely distributed in bacteria and play an important role in maintaining plasmid stability. The leading foodborne pathogen, Campylobacter jejuni, can carry multiple plasmids associated with antibiotic resistance or virulence. Previously a virulence plasmid named pVir was identified in C. jejuni 81-176 and IA3902, but determining the role of pVir in...
Fri, 06/10/2016 - 04:41
Summary pH regulates gene expression, biochemical activities and cellular behaviors. A mildly acidic pH activates the master virulence regulatory system PhoP/PhoQ in the facultative intracellular pathogen Salmonella enterica serovar Typhimurium. The sensor PhoQ harbors an extracytoplasmic domain implicated in signal sensing, and a cytoplasmic domain controlling activation of the regulator PhoP....
Tue, 05/24/2016 - 03:20
Summary To survive in a continuously changing environment, bacteria sense concentration gradients of attractants or repellents, and purposefully migrate until a more favorable habitat is encountered. While glucose is known as the most effective attractant, the flagellar biosynthesis and hence chemotactic motility has been known to be repressed by glucose in some bacteria. To date, the only known...
Fri, 05/20/2016 - 10:06
Abstract The bacterial flagellum enables directed movement of Salmonella enterica towards favorable conditions in liquid environments. Regulation of flagellar synthesis is tightly controlled by various environmental signals at transcriptional and post-transcriptional levels. The flagellar master regulator FlhD4C2 resides on top of the flagellar transcriptional hierarchy and is under autogenous...
Sat, 05/07/2016 - 00:41
Summary Unchecked amino acid accumulation in living cells has the potential to cause stress by disrupting normal metabolic processes. Thus, many organisms have evolved degradation strategies that prevent endogenous accumulation of amino acids. L-2,3-diaminopropionate (Dap) is a non-protein amino acid produced in nature where it serves as a precursor to siderophores, neurotoxins and antibiotics....
Tue, 05/03/2016 - 10:46
Abstract Campylobacter jejuni and Campylobacter coli are zoonotic pathogens once considered asaccharolytic, but are now known to encode pathways for glucose and fucose uptake/metabolism. For C. jejuni, strains with the fuc locus possess a competitive advantage in animal colonization models. We demonstrate that this locus is present in >50% of genome-sequenced strains and is prevalent in...
Thu, 04/28/2016 - 05:35
SUMMARY The natural resistance of Mycobacterium abscessus to most commonly available antibiotics seriously limits chemotherapeutic treatment options, which is particularly challenging for treating cytic fibrosis patients infected with this rapid-growing mycobacterium. New drugs with novel molecular targets are urgently needed against this emerging pathogen. However, the discovery of such new...
Tue, 04/26/2016 - 11:10
Abstract Biofilm formation can be considered a bacterial virulence mechanism. In a range of Gram-negatives, increased levels of the second messenger cyclic diguanylate (c-di-GMP) promotes biofilm formation and reduces motility. Other bacterial processes known to be regulated by c-di-GMP include cell division, differentiation and virulence. Among Gram-positive bacteria, where the function of c-di-...
Sat, 04/02/2016 - 14:39
Summary AraC Negative Regulators (ANR) suppress virulence genes by directly down-regulating AraC/XylS members in Gram-negative bacteria. In this study we sought to investigate the distribution and molecular mechanisms of regulatory function for ANRs among different bacterial pathogens. We identified more than 200 ANRs distributed in diverse clinically important gram negative pathogens, including...
Wed, 03/23/2016 - 15:50
Summary Listeria monocytogenes is a Gram-positive environmental bacterium that lives within soil but transitions into a pathogen upon contact with a mammalian host. The transition of L. monocytogenes from soil dweller to cytosolic pathogen is dependent upon secreted virulence factors that mediate cell invasion and intracellular growth. PrsA1 and PrsA2 are secreted bacterial lipoprotein chaperones...

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