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Molecular Microbiology

Susanne Brenzinger, Anna Pecina, Devid Mrusek, Petra Mann, Kerstin Völse, Stephan Wimmi, Ulrike Ruppert, Anke Becker, Simon Ringgaard, Gert Bange, Kai M Thormann
The ability of most bacterial flagellar motors to reverse the direction of rotation is crucial for efficient chemotaxis. In Escherichia coli, motor reversals are mediated by binding of phosphorylated chemotaxis protein CheY to components of the flagellar rotor, FliM and FliN, which induces a conformational switch of the flagellar C-ring. Here we show that for Shewanella putrefaciens, Vibrio parahaemolyticus and likely a number of other species an additional transmembrane protein, ZomB, is critically required for motor reversals as mutants lacking ZomB exclusively exhibit straight forward swimming also upon full phosphorylation or overproduction of CheY...
July 11, 2018: Molecular Microbiology
Alexander Strecker, Christopher Schubert, Sandra Zedler, Philipp Steinmetz, Gottfried Unden
DcuA of Escherichia coli is known as an alternative C4 -dicarboxylate transporter for the main anaerobic C4 -dicarboxylate transporter DcuB. Since dcuA is expressed constitutively under aerobic and anaerobic conditions, DcuA was suggested to serve aerobically as a back-up of the aerobic (DctA) transporter, or for the anabolic uptake of C4 -dicarboxylates. In this work, it is shown that DcuA is required for aerobic growth with L-aspartate as a nitrogen source, whereas for growth with L-aspartate as a carbon source, DctA was needed...
July 11, 2018: Molecular Microbiology
Mizuki Tanaka, Sakurako Ichinose, Takahiro Shintani, Katsuya Gomi
Carbon catabolite repression is regulated by the C2 H2 -type transcription factor CreA/Cre1 in filamentous fungi including Aspergillus oryzae. We investigated the stability and subcellular localization of CreA in A. oryzae. The abundance of FLAG-tagged CreA (FLAG-CreA) was dramatically reduced after incubation in maltose and xylose, which stimulated the export of CreA from the nucleus to the cytoplasm. Mutation of a putative nuclear export signal resulted in nuclear retention and significant stabilization of CreA...
July 11, 2018: Molecular Microbiology
Kara M Schoenemann, Marcin Krupka, Veronica W Rowlett, Steven L Distelhorst, Bo Hu, William Margolin
Escherichia coli requires FtsZ, FtsA and ZipA proteins for early stages of cell division, the latter two tethering FtsZ polymers to the cytoplasmic membrane. Hypermorphic mutants of FtsA such as FtsA* (R286W) map to the FtsA self-interaction interface and can bypass the need for ZipA. Purified FtsA forms closed minirings on lipid monolayers that antagonize bundling of FtsZ protofilaments, whereas FtsA* forms smaller oligomeric arcs that enable bundling. Here, we examined three additional FtsA*-like mutant proteins for their ability to form oligomers on lipid monolayers and bundle FtsZ...
July 11, 2018: Molecular Microbiology
Miguel Hernández-González, Areti Pantazopoulou, Dimitris Spanoudakis, Christel L C Seegers, Miguel A Peñalva
Hyphal tip cells of Aspergillus nidulans are > 100 μm-long, which challenges intracellular traffic. In spite of the basic and applied interest of the secretory pathway of filamentous fungi, only recently has it been investigated in detail. We used InuA, an inducible and highly glycosylated inulinase, and mutations affecting different intracellular membranous compartments, to investigate the route by which the enzyme traffics to the extracellular medium. InuA is core-N-glycosylated in the ER and hyperglycosylated during transit across the Golgi...
July 11, 2018: Molecular Microbiology
Mildred Castellanos, Theodore B Verhey, George Chaconas
Borrelia burgdorferi evades the host immune system by switching the surface antigen VlsE, in a process known as antigenic variation. The DNA mechanisms and genetic elements present on the vls locus that participate in the switching process remain to be elucidated. Manipulating the vls locus has been difficult due to its instability on E. coli plasmids. In this study, we generated for the first time a mini-vls system composed of a single silent vlsE variable region (silent cassette 2) through the vlsE gene by performing some cloning steps directly in a highly transformable B...
July 11, 2018: Molecular Microbiology
Jade M Noble, Johann Lubieniecki, Benjamin H Savitzky, Jürgen Plitzko, Harald Engelhardt, Wolfgang Baumeister, Lena F Kourkoutis
The size of whole Rhodobacter sphaeroides prevents 3D visualization of centermost chromatophores in their native environment. This study combines cryo-focused ion beam milling with cryo-electron tomography to probe vesicle architecture both in situ and in 3D. Developing chromatophores are membrane-bound buds that remain in topological continuity with the cytoplasmic membrane and detach into vesicles when mature. Mature chromatophores closest to the cell wall are typically isolated vesicles, whereas centermost chromatophores are either linked to neighboring chromatophores or contain smaller, budding structures...
July 11, 2018: Molecular Microbiology
Kelsey W Riley, Alfonso Gonzalez, Douglas D Risser
Filamentous cyanobacteria exhibit developmental complexity, including the transient differentiation of motile hormogonia in many species. Using a forward genetic approach, a trio of genes unique to filamentous cyanobacteria encoding a putative Rsb-like partner-switching regulatory system (PSRS) were implicated in regulating hormogonium development in the model filamentous cyanobacterium Nostoc punctiforme. Analysis of in-frame deletion strains indicated that HmpU (putative serine phosphatase) and HmpV (STAS domain) enhance, while HmpW (putative serine kinase) represses motility and persistence of the hormogonium state...
July 11, 2018: Molecular Microbiology
Heng Zhao, Daniel M Roistacher, John D Helmann
Peptidoglycan synthesis is an important target for antibiotics and relies on intermediates derived from central metabolism. As a result, alterations of metabolism may affect antibiotic sensitivity. An aspB mutant is auxotrophic for aspartate (Asp) and asparagine (Asn) and lyses when grown in Difco sporulation medium (DSM), but not in LB medium. Genetic and physiological studies, supported by amino acid analysis, reveal that cell lysis in DSM results from Asp limitation due to a relatively low Asp and high glutamate (Glu) concentrations, with Glu functioning as a competitive inhibitor of Asp uptake by the major Glu/Asp transporter GltT...
July 11, 2018: Molecular Microbiology
Wenhui Wei, Yifei Zhang, Rongsui Gao, Jun Li, Yongchang Xu, Shihua Wang, Quanjiang Ji, Youjun Feng
Biotin (vitamin B7), a sulfur-containing fatty acid derivative, is a nutritional virulence factor in certain mycobacterial species. Tight regulation of biotin biosynthesis is important because production of biotin is an energetically-expensive process requiring 15-20 equivalents of ATP. The Escherichia coli bi-functional BirA is a prototypical biotin regulatory system. In contrast, mycobacterial BirA is an unusual biotin protein ligase (BPL) without DNA-binding domain. Recently, we established a novel two-protein paradigm of BioQ-BirA...
July 11, 2018: Molecular Microbiology
Calum Johnston, Isabelle Mortier-Barriere, Vanessa Khemici, Patrice Polard
Natural genetic transformation is a widespread mechanism of horizontal gene transfer. It involves the internalization of exogenous DNA as single strands and chromosomal integration via homologous recombination, promoting acquisition of new genetic traits. Transformation occurs during a distinct physiological state called competence. In Streptococcus pneumoniae, competence is controlled by ComDE, a two-component system induced by an exported peptide pheromone. DprA is universal among transformable species, strongly induced during pneumococcal competence, and crucial for pneumococcal transformation...
July 11, 2018: Molecular Microbiology
Xue-Qiang Cao, Jia-Yuan Wang, Lian Zhou, Bo Chen, Yu Jin, Ya-Wen He
Xanthomonadins are yellow pigments that are produced by the phytopathogen Xanthomonas campestris pv. campestris (Xcc). A pig cluster is responsible for xanthomonadin biosynthesis. Previously, Xcc4014 of the cluster was characterized as a bifunctional chorismatase that produces 3-hydroxybenzoic acid (3-HBA) and 4-HBA. In this study, genetic analysis identified 11 genes within the pig cluster to be essential for xanthomonadin biosynthesis. Biochemical and bioinformatics analysis suggest that xanthomonadins are synthesized via an unusual type II polyketide synthase pathway...
July 11, 2018: Molecular Microbiology
E M Ostrem Loss, J H Yu
The growing release of organic contaminants into the environment due to industrial processes has inevitably increased the incidence of their exposure to humans which often results in negative health effects. Microorganisms are also increasingly exposed to the pollutants, yet their diverse metabolic capabilities enable them to survive toxic exposure making these degradation mechanisms important to understand. Fungi are the most abundant microorganisms in the environment, yet less has been studied to understand their ability to degrade contaminants than in bacteria...
July 11, 2018: Molecular Microbiology
Sebastian Beblawy, Thea Bursac, Catarina Paquete, Ricardo Louro, Thomas A Clarke, Johannes Gescher
Shewanella oneidensis is the best understood model organism for the study of dissimilatory iron reduction. This review focuses on the current state of our knowledge regarding this extracellular respiratory process and highlights its physiologic, regulatory and biochemical requirements. It seems that we have widely understood how respiratory electrons can reach the cell surface and what the minimal set of electron transport proteins to the cell surface is. Nevertheless, even after decades of work in different research groups around the globe there are still several important questions that were not answered yet...
July 11, 2018: Molecular Microbiology
Blake R Bertani, Rebecca J Taylor, Emma Nagy, Daniel Kahne, Natividad Ruiz
Most Gram-negative bacteria assemble lipopolysaccharides (LPS) on their surface to form a permeability barrier against many antimicrobials. LPS is synthesized at the inner membrane and then transported to the outer leaflet of the outer membrane. Although the overall LPS structure is conserved, LPS molecules can differ in composition at the species and strain level. Some bacteria also regulate when to modify phosphates on LPS at the inner membrane in order to become resistant to cationic antimicrobial peptides...
July 11, 2018: Molecular Microbiology
Thomas Franke, Uwe Deppenmeier
The human gut microbiota is a crucial factor for the host's physiology with respect to health and disease. Metagenomic shotgun sequencing of microbial gut communities revealed that Prevotella copri is one of the most important players in the gastrointestinal tract of many individuals. Because of the importance of this bacterium we analyzed the growth behavior and the central metabolic pathways of P. copri. Bioinformatic data, transcriptome profiling and enzyme activity measurements indicated that the major pathways are based on glycolysis and succinate production from fumarate...
July 11, 2018: Molecular Microbiology
Fanny Coppens, Gaetano Castaldo, Ayla Debraekeleer, Suresh Subedi, Kristof Moonens, Alvin Lo, Han Remaut
The human stomach pathogen Helicobacter pylori attaches to healthy and inflamed gastric tissue through members of a paralogous family of "Helicobacter outer membrane proteins" (Hops), including adhesins BabA, SabA, HopQ, LabA and HopZ. Hops share a conserved 25 kDa C-terminal region that is thought to form an autotransporter-like transmembrane domain. Instead, our results show that Hops contain a non-continuous transmembrane domain, composed of seven predicted β-strands at the C-terminus and one at the N-terminus...
July 11, 2018: Molecular Microbiology
Annabelle Mouammine, Justine Collier
Alphaproteobacteria include bacteria with very different modes of life, from free-living to host-associated and pathogenic bacteria. Their genomes vary in size and organization from single circular chromosomes to multipartite genomes and are often methylated by one or more adenine or cytosine methyltransferases (MTases). These include MTases that are part of restriction/modification systems and so-called orphan MTases. The development of novel technologies accelerated the analysis of methylomes and revealed the existence of epigenetic patterns in several Alphaproteobacteria...
July 11, 2018: Molecular Microbiology
Telma S Martins, Vítor Costa, Clara Pereira
Iron is an essential element for eukaryotes as it participates as a redox-active co-factor in many biological processes. Since iron is also potentially toxic, iron levels are carefully regulated. In the yeast Saccharomyces cerevisiae, iron homeostasis is maintained by the transcriptional control of the iron acquisition systems (iron regulon), mainly by the iron-responsive transcriptional factors Aft1p and Yap5p. Intracellular iron is stored in the vacuole, mobilized for other locations when necessary, particularly for the mitochondria, the major site of iron-utilizing pathways...
July 11, 2018: Molecular Microbiology
Katrin Eisenhardt, Carina Reuscher, Gabriele Klug
Facultative phototrophic bacteria like Rhodobacter sphaeroides can produce ATP by anoxygenic photosynthesis, which is of advantage under conditions with limiting oxygen. However, the simultaneous presence of pigments, light and oxygen leads to the generation of harmful singlet oxygen. In order to avoid this stress situation, the formation of photosynthetic complexes is tightly regulated by light and oxygen signals. In a complex regulatory network several regulatory proteins and the small non-coding RNA PcrZ contribute to the balanced expression of photosynthesis genes...
July 11, 2018: Molecular Microbiology
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