scholarly journals Molecular Basis and Ecological Relevance of Caulobacter Cell Filamentation in Freshwater Habitats

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Kristina Heinrich ◽  
David J. Leslie ◽  
Michaela Morlock ◽  
Stefan Bertilsson ◽  
Kristina Jonas
Keyword(s):  
Stationary Phase ◽  
Cell Biology ◽  
Algal Blooms ◽  
Caulobacter Crescentus ◽  
Natural Habitat ◽  
Growth Conditions ◽  
Microbial Composition ◽  
Content Type ◽  
Ecological Relevance ◽  
Cell Shapes

ABSTRACT All living cells are characterized by certain cell shapes and sizes. Many bacteria can change these properties depending on the growth conditions. The underlying mechanisms and the ecological relevance of changing cell shape and size remain unclear in most cases. One bacterium that undergoes extensive shape-shifting in response to changing growth conditions is the freshwater bacterium Caulobacter crescentus. When incubated for an extended time in stationary phase, a subpopulation of C. crescentus forms viable filamentous cells with a helical shape. Here, we demonstrated that this stationary-phase-induced filamentation results from downregulation of most critical cell cycle regulators and a consequent block of DNA replication and cell division while cell growth and metabolism continue. Our data indicate that this response is triggered by a combination of three stresses caused by prolonged growth in complex medium, namely, the depletion of phosphate, alkaline pH, and an excess of ammonium. We found that these conditions are experienced in the summer months during algal blooms near the surface in freshwater lakes, a natural habitat of C. crescentus, suggesting that filamentous growth is a common response of C. crescentus to its environment. Finally, we demonstrate that when grown in a biofilm, the filamentous cells can reach beyond the surface of the biofilm and potentially access nutrients or release progeny. Altogether, our work highlights the ability of bacteria to alter their morphology and suggests how this behavior might enable adaptation to changing environments. IMPORTANCE Many bacteria drastically change their cell size and morphology in response to changing environmental conditions. Here, we demonstrate that the freshwater bacterium Caulobacter crescentus and related species transform into filamentous cells in response to conditions that commonly occur in their natural habitat as a result of algal blooms during the warm summer months. These filamentous cells may be better able to scavenge nutrients when they grow in biofilms and to escape from protist predation during planktonic growth. Our findings suggest that seasonal changes and variations in the microbial composition of the natural habitat can have profound impact on the cell biology of individual organisms. Furthermore, our work highlights that bacteria exist in morphological and physiological states in nature that can strongly differ from those commonly studied in the laboratory.

scholarly journals Sugar-Phosphate Metabolism Regulates Stationary-Phase Entry and Stalk Elongation in Caulobacter crescentus

2019 ◽  
Vol 202 (4) ◽  
Author(s):  
Kevin D. de Young ◽  
Gabriele Stankeviciute ◽  
Eric A. Klein
Keyword(s):  
Stationary Phase ◽  
Cell Shape ◽  
Caulobacter Crescentus ◽  
Phosphate Starvation ◽  
Phosphomannose Isomerase ◽  
Sugar Phosphate ◽  
Content Type ◽  
Environmental Perturbations ◽  
Bacterial Cell Shape ◽  
Phase Entry

ABSTRACT Bacteria have a variety of mechanisms for adapting to environmental perturbations. Changes in oxygen availability result in a switch between aerobic and anaerobic respiration, whereas iron limitation may lead to siderophore secretion. In addition to metabolic adaptations, many organisms respond by altering their cell shape. Caulobacter crescentus, when grown under phosphate-limiting conditions, dramatically elongates its polar stalk appendage. The stalk is hypothesized to facilitate phosphate uptake; however, the mechanistic details of stalk synthesis are not well characterized. We used a chemical mutagenesis approach to isolate and characterize stalk-deficient mutants, one of which had two mutations in the phosphomannose isomerase gene (manA) that were necessary and sufficient to inhibit stalk elongation. Transcription of the pho regulon was unaffected in the manA mutant; therefore, ManA plays a unique regulatory role in stalk synthesis. The mutant ManA had reduced enzymatic activity, resulting in a 5-fold increase in the intracellular fructose 6-phosphate/mannose 6-phosphate ratio. This metabolic imbalance impaired the synthesis of cellular envelope components derived from mannose 6-phosphate, namely, lipopolysaccharide O-antigen and exopolysaccharide. Furthermore, the manA mutations prevented C. crescentus cells from efficiently entering stationary phase. Deletion of the stationary-phase response regulator gene spdR inhibited stalk elongation in wild-type cells, while overproduction of the alarmone ppGpp, which triggers growth arrest and stationary-phase entry, increased stalk length in the manA mutant strain. These results demonstrate that sugar-phosphate metabolism regulates stalk elongation independently of phosphate starvation. IMPORTANCE Metabolic control of bacterial cell shape is an important mechanism for adapting to environmental perturbations. Caulobacter crescentus dramatically elongates its polar stalk appendage in response to phosphate starvation. To investigate the mechanism of this morphological adaptation, we isolated stalk-deficient mutants, one of which had mutations in the phosphomannose isomerase gene (manA) that blocked stalk elongation, despite normal activation of the phosphate starvation response. The mutant ManA resulted in an imbalance in sugar-phosphate concentrations, which had effects on the synthesis of cellular envelope components and entry into stationary phase. Due to the interconnectivity of metabolic pathways, our findings may suggest more generally that the modulation of bacterial cell shape involves the regulation of growth phase and the synthesis of cellular building blocks.

scholarly journals Chronological Aging Is Associated with Biophysical and Chemical Changes in the Capsule of Cryptococcus neoformans

2011 ◽  
Vol 79 (12) ◽  
pp. 4990-5000 ◽  
Author(s):  
Radames J. B. Cordero ◽  
Bruno Pontes ◽  
Allan J. Guimarães ◽  
Luis R. Martinez ◽  
Johanna Rivera ◽  
...  
Keyword(s):  
Stationary Phase ◽  
Cryptococcus Neoformans ◽  
Pathogenic Fungus ◽  
Growth Conditions ◽  
Cellular Aging ◽  
Phase Growth ◽  
Chronic Infections ◽  
Content Type ◽  
Chronological Aging ◽  
Dynamic Structures

ABSTRACTDoes the age of a microbial cell affect its virulence factors? To our knowledge, this question has not been addressed previously, but the answer is of great relevance for chronic infections where microbial cells persist and age in hosts.Cryptococcus neoformansis an encapsulated human-pathogenic fungus notorious for causing chronic infections where cells of variable age persist in tissue. The major virulence factor forC. neoformansis a polysaccharide (PS) capsule. To understand how chronological age could impact the cryptococcal capsule properties, we compared the elastic properties, permeabilities, zeta potentials, and glycosidic compositions of capsules from young and old cells and found significant differences in all parameters measured. Changes in capsular properties were paralleled by changes in PS molecular mass and density, as well as modified antigenic density and antiphagocytic properties. Remarkably, chronological aging under stationary-phase growth conditions was associated with the expression of α-1,3-glucans in the capsule, indicating a new structural capsular component. Our results establish that cryptococcal capsules are highly dynamic structures that change dramatically with chronological aging under prolonged stationary-phase growth conditions. Changes associated with cellular aging in chronic infections could contribute to the remarkable capacity of this fungus to persist in tissues by generating phenotypically and antigenically different capsules.

scholarly journals Flagellar Mutants Have Reduced Pilus Synthesis in Caulobacter crescentus

2019 ◽  
Vol 201 (18) ◽  
Author(s):  
Courtney K. Ellison ◽  
Douglas B. Rusch ◽  
Yves V. Brun
Keyword(s):  
Cell Biology ◽  
Regulatory Networks ◽  
Caulobacter Crescentus ◽  
Single Cells ◽  
Bacterial Species ◽  
Type Iv Pili ◽  
Content Type ◽  
Transcription Profiles ◽  
Type Iv ◽  
Genes Encoding

ABSTRACT Surface appendages, such as flagella and type IV pili, mediate a broad range of bacterial behaviors, including motility, attachment, and surface sensing. While many species harbor both flagella and type IV pili, little is known about how or if their syntheses are coupled. Here, we show that deletions of genes encoding different flagellum machinery components result in a reduction of pilus synthesis in Caulobacter crescentus. First, we show that different flagellar mutants exhibit different levels of sensitivity to a pilus-dependent phage and that fewer cells within populations of flagellar mutants make pili. Furthermore, we find that single cells within flagellar mutant populations produce fewer pili per cell. We demonstrate that these gene deletions result in reduced transcription of pilus-associated genes and have a slight but significant effect on general transcription profiles. Finally, we show that the decrease in pilus production is due to a reduction in the pool of pilin subunits that are polymerized into pilus fibers. These data demonstrate that mutations in flagellar gene components not only affect motility but also can have considerable and unexpected consequences for other aspects of cell biology. IMPORTANCE Most bacterial species synthesize surface-exposed appendages that are important for environmental interactions and survival under diverse conditions. It is often assumed that these appendages act independently of each other and that mutations in either system can be used to assess functionality in specific processes. However, we show that mutations in flagellar genes can impact the production of type IV pili, as well as alter general RNA transcriptional profiles compared to a wild-type strain. These data demonstrate that seemingly simple mutations can broadly affect cell-regulatory networks.

scholarly journals Essential Genome of the Metabolically Versatile Alphaproteobacterium Rhodopseudomonas palustris

2015 ◽  
Vol 198 (5) ◽  
pp. 867-876 ◽  
Author(s):  
Kieran B. Pechter ◽  
Larry Gallagher ◽  
Harley Pyles ◽  
Colin S. Manoil ◽  
Caroline S. Harwood
Keyword(s):  
Nitrogen Fixation ◽  
Caulobacter Crescentus ◽  
Essential Gene ◽  
Rhodopseudomonas Palustris ◽  
Model Organism ◽  
Growth Conditions ◽  
Essential Genes ◽  
Content Type ◽  
E Coli ◽  
Production Of Hydrogen

ABSTRACTRhodopseudomonas palustrisis an alphaproteobacterium that has served as a model organism for studies of photophosphorylation, regulation of nitrogen fixation, production of hydrogen as a biofuel, and anaerobic degradation of aromatic compounds. This bacterium is able to transition between anaerobic photoautotrophic growth, anaerobic photoheterotrophic growth, and aerobic heterotrophic growth. As a starting point to explore the genetic basis for the metabolic versatility ofR. palustris, we used transposon mutagenesis and Tn-seq to identify 552 genes as essential for viability in cells growing aerobically on semirich medium. Of these, 323 have essential gene homologs in the alphaproteobacteriumCaulobacter crescentus, and 187 have essential gene homologs inEscherichia coli. There were 24R. palustrisgenes that were essential for viability under aerobic growth conditions that have low sequence identity but are likely to be functionally homologous to essentialE. coligenes. As expected, certain functional categories of essential genes were highly conserved among the three organisms, including translation, ribosome structure and biogenesis, secretion, and lipid metabolism.R. palustriscells divide by budding in which a sessile cell gives rise to a motile swarmer cell. Conserved cell cycle genes required for this developmental process were essential in bothC. crescentusandR. palustris. Our results suggest that despite vast differences in lifestyles, members of the alphaproteobacteria have a common set of essential genes that is specific to this group and distinct from that of gammaproteobacteria likeE. coli.IMPORTANCEEssential genes in bacteria and other organisms are those absolutely required for viability.Rhodopseudomonas palustrishas served as a model organism for studies of anaerobic aromatic compound degradation, hydrogen gas production, nitrogen fixation, and photosynthesis. We used the technique of Tn-seq to determine the essential genes ofR. palustrisgrown under heterotrophic aerobic conditions. The transposon library generated in this study will be useful for future studies to identifyR. palustrisgenes essential for viability under specialized growth conditions and also for survival under conditions of stress.

scholarly journals Convergence of Alarmone and Cell Cycle Signaling from Trans-Encoded Sensory Domains

mBio ◽  
2015 ◽  
Vol 6 (5) ◽  
Author(s):  
Stefano Sanselicio ◽  
Patrick H. Viollier
Keyword(s):  
Cell Cycle ◽  
Stationary Phase ◽  
Cell Cycle Progression ◽  
Caulobacter Crescentus ◽  
Control Cell ◽  
Phase Cell ◽  
Cycle Progression ◽  
Content Type ◽  
Cell Cycle Regulator ◽  
Domain Protein

ABSTRACT Despite the myriad of different sensory domains encoded in bacterial genomes, only a few are known to control the cell cycle. Here, suppressor genetics was used to unveil the regulatory interplay between the PAS (Per-Arnt-Sim) domain protein MopJ and the uncharacterized GAF (cyclic GMP-phosphodiesterase–adenylyl cyclase–FhlA) domain protein PtsP, which resembles an alternative component of the phosphoenolpyruvate (PEP) transferase system. Both of these systems indirectly target the Caulobacter crescentus cell cycle master regulator CtrA, but in different ways. While MopJ acts on CtrA via the cell cycle kinases DivJ and DivL, which control the removal of CtrA at the G1-S transition, our data show that PtsP signals through the conserved alarmone (p)ppGpp, which prevents CtrA cycling under nutritional stress and in stationary phase. We found that PtsP interacts genetically and physically with the (p)ppGpp synthase/hydrolase SpoT and that it modulates several promoters that are directly activated by the cell cycle transcriptional regulator GcrA. Thus, parallel systems integrate nutritional and systemic signals within the cell cycle transcriptional network, converging on the essential alphaproteobacterial regulator CtrA while also affecting global cell cycle transcription in other ways. IMPORTANCE Many alphaproteobacteria divide asymmetrically, and their cell cycle progression is carefully regulated. How these bacteria control the cell cycle in response to nutrient limitation is not well understood. Here, we identify a multicomponent signaling pathway that acts on the cell cycle when nutrients become scarce in stationary phase. We show that efficient accumulation of the master cell cycle regulator CtrA in stationary-phase Caulobacter crescentus cells requires the previously identified stationary-phase/cell cycle regulator MopJ as well as the phosphoenolpyruvate protein phosphotransferase PtsP, which acts via the conserved (p)ppGpp synthase SpoT. We identify cell cycle-regulated promoters that are affected by this pathway, providing an explanation of how (p)ppGpp-signaling might couple starvation to control cell cycle progression in Caulobacter spp. and likely other Alphaproteobacteria. This pathway has the potential to integrate carbon fluctuation into cell cycle control, since in phosphotransferase systems it is the glycolytic product phosphenolpyruvate (PEP) rather than ATP that is used as the phosphor donor for phosphorylation.

scholarly journals The Caulobacter crescentus Homolog of DnaA (HdaA) Also Regulates the Proteolysis of the Replication Initiator Protein DnaA

2015 ◽  
Vol 197 (22) ◽  
pp. 3521-3532 ◽  
Author(s):  
Richard Wargachuk ◽  
Gregory T. Marczynski
Keyword(s):  
Escherichia Coli ◽  
Stationary Phase ◽  
Caulobacter Crescentus ◽  
Extra Chromosome ◽  
Chromosome Replication ◽  
Wild Type ◽  
Content Type ◽  
Antibiotic Development ◽  
E Coli ◽  
Dnaa Protein

ABSTRACTIt is not known how diverse bacteria regulate chromosome replication. Based onEscherichia colistudies, DnaA initiates replication and the homolog of DnaA (Hda) inactivates DnaA using the RIDA (regulatoryinactivation ofDnaA) mechanism that thereby prevents extra chromosome replication cycles. RIDA may be widespread, because the distantly relatedCaulobacter crescentushomolog HdaA also prevents extra chromosome replication (J. Collier and L. Shapiro, J Bacteriol 191:5706–5715, 2009,http://dx.doi.org/10.1128/JB.00525-09). To further study the HdaA/RIDA mechanism, we created aC. crescentusstrain that shuts offhdaAtranscription and rapidly clears HdaA protein. We confirm that HdaA prevents extra replication, since cells lacking HdaA accumulate extra chromosome DNA. DnaA binds nucleotides ATP and ADP, and our results are consistent with the establishedE. colimechanism whereby Hda converts active DnaA-ATP to inactive DnaA-ADP. However, unlikeE. coliDnaA,C. crescentusDnaA is also regulated by selective proteolysis.C. crescentuscells lacking HdaA reduce DnaA proteolysis in logarithmically growing cells, thereby implicating HdaA in this selective DnaA turnover mechanism. Also, wild-typeC. crescentuscells remove all DnaA protein when they enter stationary phase. However, cells lacking HdaA retain stable DnaA protein even when they stop growing in nutrient-depleted medium that induces complete DnaA proteolysis in wild-type cells. Additional experiments argue for a distinct HdaA-dependent mechanism that selectively removes DnaA prior to stationary phase. Related freshwaterCaulobacterspecies also remove DnaA during entry to stationary phase, implying a wider role for HdaA as a novel component of programed proteolysis.IMPORTANCEBacteria must regulate chromosome replication, and yet the mechanisms are not completely understood and not fully exploited for antibiotic development. Based onEscherichia colistudies, DnaA initiates replication, and the homolog of DnaA (Hda) inactivates DnaA to prevent extra replication. The distantly relatedCaulobacter crescentushomolog HdaA also regulates chromosome replication. Here we unexpectedly discovered that unlike theE. coliHda, theC. crescentusHdaA also regulates DnaA proteolysis. Furthermore, this HdaA proteolysis acts in logarithmically growing and in stationary-phase cells and therefore in two very different physiological states. We argue that HdaA acts to help time chromosome replications in logarithmically growing cells and that it is an unexpected component of the programed entry into stationary phase.

scholarly journals Autophagy-Related Protein ATG8 Has a Noncanonical Function for Apicoplast Inheritance in Toxoplasma gondii

mBio ◽  
2015 ◽  
Vol 6 (6) ◽  
Author(s):  
Maude F. Lévêque ◽  
Laurence Berry ◽  
Michael J. Cipriano ◽  
Hoa-Mai Nguyen ◽  
Boris Striepen ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Growth Conditions ◽  
Model Organisms ◽  
Secondary Endosymbiosis ◽  
Related Protein ◽  
Content Type ◽  
Superresolution Microscopy ◽  
Animal Pathogens ◽  
Cellular Components ◽  
Catabolic Process

ABSTRACT Autophagy is a catabolic process widely conserved among eukaryotes that permits the rapid degradation of unwanted proteins and organelles through the lysosomal pathway. This mechanism involves the formation of a double-membrane structure called the autophagosome that sequesters cellular components to be degraded. To orchestrate this process, yeasts and animals rely on a conserved set of autophagy-related proteins (ATGs). Key among these factors is ATG8, a cytoplasmic protein that is recruited to nascent autophagosomal membranes upon the induction of autophagy. Toxoplasma gondii is a potentially harmful human pathogen in which only a subset of ATGs appears to be present. Although this eukaryotic parasite seems able to generate autophagosomes upon stresses such as nutrient starvation, the full functionality and biological relevance of a canonical autophagy pathway are as yet unclear. Intriguingly, in T. gondii, ATG8 localizes to the apicoplast under normal intracellular growth conditions. The apicoplast is a nonphotosynthetic plastid enclosed by four membranes resulting from a secondary endosymbiosis. Using superresolution microscopy and biochemical techniques, we show that TgATG8 localizes to the outermost membrane of this organelle. We investigated the unusual function of TgATG8 at the apicoplast by generating a conditional knockdown mutant. Depletion of TgATG8 led to rapid loss of the organelle and subsequent intracellular replication defects, indicating that the protein is essential for maintaining apicoplast homeostasis and thus for survival of the tachyzoite stage. More precisely, loss of TgATG8 led to abnormal segregation of the apicoplast into the progeny because of a loss of physical interactions of the organelle with the centrosomes. IMPORTANCE By definition, autophagy is a catabolic process that leads to the digestion and recycling of eukaryotic cellular components. The molecular machinery of autophagy was identified mainly in model organisms such as yeasts but remains poorly characterized in phylogenetically distant apicomplexan parasites. We have uncovered an unusual function for autophagy-related protein ATG8 in Toxoplasma gondii: TgATG8 is crucial for normal replication of the parasite inside its host cell. Seemingly unrelated to the catabolic autophagy process, TgATG8 associates with the outer membrane of the nonphotosynthetic plastid harbored by the parasite called the apicoplast, and there it plays an important role in the centrosome-driven inheritance of the organelle during cell division. This not only reveals an unexpected function for an autophagy-related protein but also sheds new light on the division process of an organelle that is vital to a group of important human and animal pathogens.

scholarly journals A Distinctive and Host-Restricted Gut Microbiota in Populations of a Cactophilic Drosophila Species

2017 ◽  
Vol 83 (23) ◽  
Author(s):  
Vincent G. Martinson ◽  
Javier Carpinteyro-Ponce ◽  
Nancy A. Moran ◽  
Therese A. Markow
Keyword(s):  
Sonoran Desert ◽  
Natural Habitat ◽  
Natural Food ◽  
Content Type ◽  
Columnar Cacti ◽  
Social Bees ◽  
Insect Gut ◽  
Almost All ◽  
Natural Settings ◽  
Bacterial Groups

ABSTRACT Almost all animals possess gut microbial communities, but the nature of these communities varies immensely. For example, in social bees and mammals, the composition is relatively constant within species and is dominated by specialist bacteria that do not live elsewhere; in laboratory studies and field surveys of Drosophila melanogaster, however, gut communities consist of bacteria that are ingested with food and that vary widely among individuals and localities. We addressed whether an ecological specialist in its natural habitat has a microbiota dominated by gut specialists or by environmental bacteria. Drosophila nigrospiracula is a species that is endemic to the Sonoran Desert and is restricted to decaying tissues of two giant columnar cacti, Pachycereus pringlei (cardón cactus) and Carnegiea gigantea (saguaro cactus). We found that the D. nigrospiracula microbiota differs strikingly from that of the cactus tissue on which the flies feed. The most abundant bacteria in the flies are rare or completely absent in the cactus tissue and are consistently abundant in flies from different cacti and localities. Several of these fly-associated bacterial groups, such as the bacterial order Orbales and the genera Serpens and Dysgonomonas, have been identified in prior surveys of insects from the orders Hymenoptera, Coleoptera, Lepidoptera, and Diptera, including several Drosophila species. Although the functions of these bacterial groups are mostly unexplored, Orbales species studied in bees are known to break down plant polysaccharides and use the resulting sugars. Thus, these bacterial groups appear to be specialized to the insect gut environment, where they may colonize through direct host-to-host transmission in natural settings. IMPORTANCE Flies in the genus Drosophila have become laboratory models for microbiota research, yet the bacteria commonly used in these experiments are rarely found in wild-caught flies and instead represent bacteria also present in the food. This study shows that an ecologically specialized Drosophila species possesses a distinctive microbiome, composed of bacterial types absent from the flies' natural food but widespread in other wild-caught insects. This study highlights the importance of fieldwork-informed microbiota research.

scholarly journals A Rhodobacter sphaeroides Protein Mechanistically Similar to Escherichia coli DksA Regulates Photosynthetic Growth

mBio ◽  
2014 ◽  
Vol 5 (3) ◽  
Author(s):  
Christopher W. Lennon ◽  
Kimberly C. Lemmer ◽  
Jessica L. Irons ◽  
Max I. Sellman ◽  
Timothy J. Donohue ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Structure Function ◽  
Rhodobacter Sphaeroides ◽  
Fatty Acid Content ◽  
Regulatory Protein ◽  
Growth Conditions ◽  
Globular Domain ◽  
Content Type ◽  
E Coli

ABSTRACTDksA is a global regulatory protein that, together with the alarmone ppGpp, is required for the “stringent response” to nutrient starvation in the gammaproteobacteriumEscherichia coliand for more moderate shifts between growth conditions. DksA modulates the expression of hundreds of genes, directly or indirectly. Mutants lacking a DksA homolog exhibit pleiotropic phenotypes in other gammaproteobacteria as well. Here we analyzed the DksA homolog RSP2654 in the more distantly relatedRhodobacter sphaeroides, an alphaproteobacterium. RSP2654 is 42% identical and similar in length toE. coliDksA but lacks the Zn finger motif of theE. coliDksA globular domain. Deletion of the RSP2654 gene results in defects in photosynthetic growth, impaired utilization of amino acids, and an increase in fatty acid content. RSP2654 complements the growth and regulatory defects of anE. colistrain lacking thedksAgene and modulates transcriptionin vitrowithE. coliRNA polymerase (RNAP) similarly toE. coliDksA. RSP2654 reduces RNAP-promoter complex stabilityin vitrowith RNAPs fromE. coliorR. sphaeroides, alone and synergistically with ppGpp, suggesting that even though it has limited sequence identity toE. coliDksA (DksAEc), it functions in a mechanistically similar manner. We therefore designate the RSP2654 protein DksARsp. Our work suggests that DksARsphas distinct and important physiological roles in alphaproteobacteria and will be useful for understanding structure-function relationships in DksA and the mechanism of synergy between DksA and ppGpp.IMPORTANCEThe role of DksA has been analyzed primarily in the gammaproteobacteria, in which it is best understood for its role in control of the synthesis of the translation apparatus and amino acid biosynthesis. Our work suggests that DksA plays distinct and important physiological roles in alphaproteobacteria, including the control of photosynthesis inRhodobacter sphaeroides. The study of DksARsp, should be useful for understanding structure-function relationships in the protein, including those that play a role in the little-understood synergy between DksA and ppGpp.

Integration host factor alleviates H-NS silencing of the Salmonella enterica serovar Typhimurium master regulator of SPI1, hilA

Microbiology ◽  
2011 ◽  
Vol 157 (9) ◽  
pp. 2504-2514 ◽  
Author(s):  
Mário H. Queiroz ◽  
Cristina Madrid ◽  
Sònia Paytubi ◽  
Carlos Balsalobre ◽  
Antonio Juárez
Keyword(s):  
Stationary Phase ◽  
Salmonella Enterica ◽  
Growth Conditions ◽  
Integration Host Factor ◽  
Band Shift ◽  
Global Regulators ◽  
Serovar Typhimurium ◽  
Associated Proteins ◽  
Transcription Data

Coordination of the expression of Salmonella enterica invasion genes on Salmonella pathogenicity island 1 (SPI1) depends on a complex circuit involving several regulators that converge on expression of the hilA gene, which encodes a transcriptional activator (HilA) that modulates expression of the SPI1 virulence genes. Two of the global regulators that influence hilA expression are the nucleoid-associated proteins Hha and H-NS. They interact and form a complex that modulates gene expression. A chromosomal transcriptional fusion was constructed to assess the effects of these modulators on hilA transcription under several environmental conditions as well as at different stages of growth. The results obtained showed that these proteins play a role in silencing hilA expression at both low temperature and low osmolarity, irrespective of the growth phase. H-NS accounts for the main repressor activity. At high temperature and osmolarity, H-NS-mediated silencing completely ceases when cells enter the stationary phase, and hilA expression is induced. Mutants lacking IHF did not induce hilA in cells entering the stationary phase, and this lack of induction was dependent on the presence of H-NS. Band-shift assays and in vitro transcription data showed that for hilA induction under certain growth conditions, IHF is required to alleviate H-NS-mediated silencing.

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