scholarly journals The LetE Protein Enhances Expression of Multiple LetA/LetS-Dependent Transmission Traits by Legionella pneumophila

2004 ◽  
Vol 72 (6) ◽  
pp. 3284-3293 ◽  
Author(s):  
Michael A. Bachman ◽  
Michele S. Swanson
Keyword(s):  
Stationary Phase ◽  
Legionella Pneumophila ◽  
Molecular Genetic ◽  
Nutrient Supply ◽  
Sigma Factors ◽  
Exponential Phase ◽  
Regulatory Rna ◽  
Flagellin Gene ◽  
Insight Into ◽  
Novel Protein

ABSTRACT Legionella pneumophila colonizes freshwater amoebae and can also replicate within alveolar macrophages. When their nutrient supply is exhausted, replicating bacteria become cytotoxic, motile, and infectious, which is thought to promote transmission to a new amoeba. The differentiation of L. pneumophila is coordinated by the sigma factors RpoS and FliA and the two-component regulator LetA/LetS and is enhanced by the letE locus. Here we demonstrate that letE promotes motility by increasing expression of the flagellin gene flaA but has little impact on the transcription of fliA, the flagellar sigma factor gene. In addition to promoting motility, letE induces the characteristic shape, pigment, and heat resistance of stationary-phase L. pneumophila. To gain insight into how letE promotes the expression of the transmission phenotype, we designed molecular genetic experiments to discriminate between the following three models: letE mutations are polar on milX; letE encodes a small novel protein; or, by analogy to csrB, letE encodes a regulatory RNA that sequesters CsrA to relieve repression. We report that letE encodes an activator protein, as it does not complement an Escherichia coli csrB mutant, it directs the synthesis of an ∼12-kDa polypeptide, and a letE nonsense mutation eliminates function. A monocistronic letE RNA is abundant during the exponential phase, and its decay during the stationary phase requires RpoS and LetA/LetS. We also discuss how the LetE protein may interact with LetA/LetS and CsrA to enhance L. pneumophila differentiation to a transmissible form.

scholarly journals Genetic Evidence that Legionella pneumophila RpoS Modulates Expression of the Transmission Phenotype in Both the Exponential Phase and the Stationary Phase

2004 ◽  
Vol 72 (5) ◽  
pp. 2468-2476 ◽  
Author(s):  
Michael A. Bachman ◽  
Michele S. Swanson
Keyword(s):  
Life Cycle ◽  
Rna Polymerase ◽  
Stationary Phase ◽  
Growth Phase ◽  
Legionella Pneumophila ◽  
Opportunistic Pathogen ◽  
Sigma Factors ◽  
Exponential Phase ◽  
Posttranscriptional Control ◽  
Multiple Copies

ABSTRACT The opportunistic pathogen Legionella pneumophila alternates between two states: replication within phagocytes and transmission between host amoebae or macrophages. In broth cultures that model this life cycle, during the replication period, CsrA inhibits expression of transmission traits. When nutrients become limiting, the alarmone (p)ppGpp accumulates and the sigma factors RpoS and FliA and the positive activators LetA/S and LetE promote differentiation to the transmissible form. Here we show that when cells enter the postexponential growth phase, RpoS increases expression of the transmission genes fliA, flaA, and mip, factors L. pneumophila needs to establish a new replication niche. In contrast, in exponential (E)-phase cells whose (p)ppGpp levels are low, rpoS inhibits expression of transmission traits, on the basis of three separate observations. First, rpoS RNA levels peak in the E phase, suggestive of a role for RpoS during replication. Second, in multiple copies, rpoS decreases the amounts of csrA, letE, fliA, and flaA transcripts and inhibits the transmission traits of motility, infectivity, and cytotoxicity. Third, rpoS blocks expression of cytotoxicity and motility by E-phase bacteria that have been induced to express the LetA activator ectopically. The data are discussed in the context of a model in which the alarmone (p)ppGpp enables RpoS to outcompete other sigma factors for binding to RNA polymerase to promote transcription of transmission genes, while LetA/S acts in parallel to relieve CsrA posttranscriptional repression of the transmission regulon. By coupling transcriptional and posttranscriptional control pathways, intracellular L. pneumophila could respond to stress by rapidly differentiating to a transmissible form.

scholarly journals Survival of virulentLegionella pneumophilain aerosols

1983 ◽  
Vol 90 (3) ◽  
pp. 451-460 ◽  
Author(s):  
P. Hambleton ◽  
M. G. Broster ◽  
P. J. Dennis ◽  
R. Henstridge ◽  
R. Fitzgeorge ◽  
...  
Keyword(s):  
Stationary Phase ◽  
Respiratory Disease ◽  
Legionella Pneumophila ◽  
Solid Medium ◽  
Exponential Phase ◽  
Metabolic Status ◽  
Aqueous Suspensions

SUMMARYAqueous suspensions of virulentLegionellapneumophilagrown on solid medium retained virulence and aerosol survival characteristics for several months. Significant numbers of viable organisms were recovered from aerosols held at various relative humidities (r.h.) for up to 2 h. The organisms survived best at 65% r.h. and were least stable at 55% r.h.Exponential phase broth-grown organisms survived poorly in aerosols in comparison with stationary phase broth cultures or organisms grown on solid medium, suggesting that the metabolic status ofLegionella pneumophilaorganisms may be an important factor affecting their ability to survive in aerosols and cause respiratory disease.

scholarly journals Rab1-AMPylation by Legionella DrrA is allosterically activated by Rab1

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jiqing Du ◽  
Marie-Kristin von Wrisberg ◽  
Burak Gulen ◽  
Matthias Stahl ◽  
Christian Pett ◽  
...  
Keyword(s):  
Legionella Pneumophila ◽  
Adenosine Monophosphate ◽  
Vesicular Trafficking ◽  
Bacterial Protein ◽  
Post Translational Modification ◽  
Allosteric Control ◽  
Rab Protein ◽  
Biochemical Characterisation ◽  
A Site ◽  
Insight Into

AbstractLegionella pneumophila infects eukaryotic cells by forming a replicative organelle – the Legionella containing vacuole. During this process, the bacterial protein DrrA/SidM is secreted and manipulates the activity and post-translational modification (PTM) states of the vesicular trafficking regulator Rab1. As a result, Rab1 is modified with an adenosine monophosphate (AMP), and this process is referred to as AMPylation. Here, we use a chemical approach to stabilise low-affinity Rab:DrrA complexes in a site-specific manner to gain insight into the molecular basis of the interaction between the Rab protein and the AMPylation domain of DrrA. The crystal structure of the Rab:DrrA complex reveals a previously unknown non-conventional Rab-binding site (NC-RBS). Biochemical characterisation demonstrates allosteric stimulation of the AMPylation activity of DrrA via Rab binding to the NC-RBS. We speculate that allosteric control of DrrA could in principle prevent random and potentially cytotoxic AMPylation in the host, thereby perhaps ensuring efficient infection by Legionella.

scholarly journals Metabolic, Physiological, and Transcriptomics Analysis of Batch Cultures of the Green Microalga Chlamydomonas Grown on Different Acetate Concentrations

Cells ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1367 ◽  
Author(s):  
Bogaert ◽  
Perez ◽  
Rumin ◽  
Giltay ◽  
Carone ◽  
...  
Keyword(s):  
Stationary Phase ◽  
Biomass Yield ◽  
Fatty Acid Content ◽  
Biological Significance ◽  
Exponential Phase ◽  
Low Light ◽  
Batch Mode ◽  
Batch Cultures ◽  
Green Microalga ◽  
Transcriptomics Data

Acetate can be efficiently metabolized by the green microalga Chlamydomonas reinhardtii. The regular concentration is 17 mM, although higher concentrations are reported to increase starch and fatty acid content. To understand the responses to higher acetate concentrations, Chlamydomonas cells were cultivated in batch mode in the light at 17, 31, 44, and 57 mM acetate. Metabolic analyses show that cells grown at 57 mM acetate possess increased contents of all components analyzed (starch, chlorophylls, fatty acids, and proteins), with a three-fold increased volumetric biomass yield compared to cells cultivated at 17 mM acetate at the entry of stationary phase. Physiological analyses highlight the importance of photosynthesis for the low-acetate and exponential-phase samples. The stationary phase is reached when acetate is depleted, except for the cells grown at 57 mM acetate, which still divide until ammonium exhaustion. Surprisal analysis of the transcriptomics data supports the biological significance of our experiments. This allows the establishment of a model for acetate assimilation, its transcriptional regulation and the identification of candidates for genetic engineering of this metabolic pathway. Altogether, our analyses suggest that growing at high-acetate concentrations could increase biomass productivities in low-light and CO2-limiting air-bubbled medium for biotechnology.

scholarly journals The distribution of myosin II in Dictyostelium discoideum slug cells.

1991 ◽  
Vol 115 (5) ◽  
pp. 1267-1274 ◽  
Author(s):  
S Eliott ◽  
P H Vardy ◽  
K L Williams
Keyword(s):  
Cell Motility ◽  
Dictyostelium Discoideum ◽  
Immunofluorescence Microscopy ◽  
Molecular Genetic ◽  
Myosin Ii ◽  
Three Dimensional ◽  
Homogeneous Distribution ◽  
Multicellular Development ◽  
Insight Into

While the role of myosin II in muscle contraction has been well characterized, less is known about the role of myosin II in non-muscle cells. Recent molecular genetic experiments on Dictyostelium discoideum show that myosin II is necessary for cytokinesis and multicellular development. Here we use immunofluorescence microscopy with monoclonal and polyclonal antimyosin antibodies to visualize myosin II in cells of the multicellular D. discoideum slug. A subpopulation of peripheral and anterior cells label brightly with antimyosin II antibodies, and many of these cells display a polarized intracellular distribution of myosin II. Other cells in the slug label less brightly and their cytoplasm displays a more homogeneous distribution of myosin II. These results provide insight into cell motility within a three-dimensional tissue and they are discussed in relation to the possible roles of myosin II in multicellular development.

scholarly journals Effects of Combination of Different −10 Hexamers and Downstream Sequences on Stationary-Phase-Specific Sigma Factor ςS-Dependent Transcription in Pseudomonas putida

2000 ◽  
Vol 182 (23) ◽  
pp. 6707-6713 ◽  
Author(s):  
Eve-Ly Ojangu ◽  
Andres Tover ◽  
Riho Teras ◽  
Maia Kivisaar
Keyword(s):  
Stationary Phase ◽  
Pseudomonas Putida ◽  
Sigma Factor ◽  
Sigma Factors ◽  
Deficient Mutant ◽  
Wild Type ◽  
In Vivo Experiments ◽  
Silent Genes ◽  
Rna Polymerase Holoenzyme

ABSTRACT The main sigma factor activating gene expression, necessary in stationary phase and under stress conditions, is ςS. In contrast to other minor sigma factors, RNA polymerase holoenzyme containing ςS (EςS) recognizes a number of promoters which are also recognized by that containing ς70 (Eς70). We have previously shown that transposon Tn4652 can activate silent genes in starvingPseudomonas putida cells by creating fusion promoters during transposition. The sequence of the fusion promoters is similar to the ς70-specific promoter consensus. The −10 hexameric sequence and the sequence downstream from the −10 element differ among these promoters. We found that transcription from the fusion promoters is stationary phase specific. Based on in vivo experiments carried out with wild-type and rpoS-deficient mutant P. putida, the effect of ςS on transcription from the fusion promoters was established only in some of these promoters. The importance of the sequence of the −10 hexamer has been pointed out in several published papers, but there is no information about whether the sequences downstream from the −10 element can affect ςS-dependent transcription. Combination of the −10 hexameric sequences and downstream sequences of different fusion promoters revealed that ςS-specific transcription from these promoters is not determined by the −10 hexameric sequence only. The results obtained in this study indicate that the sequence of the −10 element influences ςS-specific transcription in concert with the sequence downstream from the −10 box.

Structural and Molecular Genetic Insight into a Widespread Sulfur Oxidation Pathway

2008 ◽  
Vol 384 (5) ◽  
pp. 1287-1300 ◽  
Author(s):  
Christiane Dahl ◽  
Andrea Schulte ◽  
Yvonne Stockdreher ◽  
Connie Hong ◽  
Frauke Grimm ◽  
...  
Keyword(s):  
Molecular Genetic ◽  
Sulfur Oxidation ◽  
Oxidation Pathway ◽  
Insight Into

Susceptibility of the Heat-, Acid-, and Bile-Adapted Vibrio vulnificus to Lethal Low-Salinity Stress

2006 ◽  
Vol 69 (12) ◽  
pp. 2924-2928 ◽  
Author(s):  
HIN-CHUNG WONG ◽  
SHU-HUI LIU
Keyword(s):  
Stationary Phase ◽  
Salinity Stress ◽  
Natural Environment ◽  
Food Processing ◽  
Vibrio Vulnificus ◽  
Pathogenic Bacterium ◽  
Protective Response ◽  
Low Salinity ◽  
Salinity Challenge ◽  
Insight Into

As a marine pathogenic bacterium that inhabits seawater or seafood, Vibrio vulnificus encounters low salinity and other stresses in the natural environment and during food processing. This investigation explores the cross-protective response of sublethal heat-, acid-, or bile-adapted V. vulnificus YJ03 against lethal low-salinity stress. Experimental results reveal that the acid (pH 4.4)– and heat (41°C)–adapted V. vulnificus were not cross-protected against the lethal low-salinity challenge (0.04% NaCl). The bile (0.05%)–adapted exponential- and stationary-phase cells were cross-protected against low salinity, whereas low-salinity (0.12% NaCl)–adapted stationary cells were sensitized against 12% bile stress. Results of this study provide further insight into the interaction between low salinity and other common stresses in V. vulnificus.

Mannose-Binding Activity of Escherichia coli: a Determinant of Attachment and Ingestion of the Bacteria by Macrophages

1980 ◽  
Vol 29 (2) ◽  
pp. 417-424
Author(s):  
Zvi Bar-Shavit ◽  
Rachel Goldman ◽  
Itzhak Ofek ◽  
Nathan Sharon ◽  
David Mirelman
Keyword(s):  
Escherichia Coli ◽  
Stationary Phase ◽  
Pathogenic Bacteria ◽  
Binding Activity ◽  
Exponential Phase ◽  
Restrictive Temperature ◽  
Filamentous Bacteria ◽  
Phagocytic Cells ◽  
E Coli ◽  
Mannose Binding

Recently, it was suggested that a mannose-specific lectin on the bacterial cell surface is responsible for the recognition by phagocytic cells of certain nonopsonized Escherichia coli strains. In this study we assessed the interaction of two strains of E. coli at different phases of growth with a monolayer of mouse peritoneal macrophages and developed a direct method with [ 14 C]mannan to quantitate the bacterial mannose-binding activity. Normal-sized bacteria were obtained from logarithmic and stationary phases of growth. Nonseptated filamentous cells were formed by growing the organisms in the presence of cephalexin or at a restrictive temperature. Attachment to macrophages of all bacterial forms was inhibited by methyl α- d -mannoside and mannan but not by other sugars tested. The attachment of stationary phase and filamentous bacteria to macrophages, as well as their mannose-binding activity, was similar, whereas in the exponential-phase bacteria they were markedly reduced. The results show a linear relation between the two parameters ( R = 0.98, P < 0.001). The internalization of the filamentous cells attached to macrophages during 45 min of incubation was much less efficient (20%) compared to that of exponential-phase, stationary-phase, or antibody-coated filamentous bacteria (90%). The results indicate that the mannose-binding activity of E. coli determines the recognition of the organisms by phagocytes. They further suggest that administration of β-lactam antibiotics may impair elimination of certain pathogenic bacteria by inducing the formation of filaments which are inefficiently internalized by the host's phagocytic cells.

Sign in / Sign up

Export Citation Format

Share Document