共查询到20条相似文献,搜索用时 15 毫秒
1.
Paul A. Hamblin Bruce A. Maguire Ruslan N. Grishanin & Judith P. Armitage 《Molecular microbiology》1997,26(5):1083-1096
In contrast to enteric bacteria, chemotaxis in Rhodobacter sphaeroides requires transport and partial metabolism of chemoattractants. Although a chemotaxis operon has been identified containing homologues of the enteric cheA, cheW, cheR genes and two homologues of the cheY gene, deletion of the entire chemotaxis operon had only minor effects on chemotactic behaviour under the conditions tested. Responses to sugars were enhanced in tethered cells but in all other chemotaxis assays behaviour of the operon deletion mutant was wild type. The mutant also showed wild-type responses to weak organic acids such as acetate and propionate, the dominant chemoattractants for this organism, under all conditions. This is in direct contrast to the enterics in which CheA, CheW and CheY are absolutely essential for taxis to PTS sugars, oxygen and MCP-dependent chemoeffectors. The operon deletion mutant was subjected to Tn5 transposon mutagenesis and new mutants selected using a chemotaxis and phototaxis screen. One mutant, JPA203, was non-chemotactic on swarm plates and showed inverted responses when tethered or subjected to changes in light intensity. Characterization of the Tn5 insertion in JPA203 identified a second chemotaxis operon in R. sphaeroides that contains homologues of cheY, cheA and cheR, the first homologue of cheB and two homologues of cheW. The new genes were labelled orf10, cheYIII, cheAII, cheWII, cheWIII, cheRII, cheB and tlpC. When introduced into a wild-type background, deletion of cheAII produced a chemotaxis minus phenotype in R. sphaeroides, suggesting that cheAII forms part of a dominant chemotactic pathway, whereas the earlier identified operon plays only a minor role under laboratory conditions. The data presented here support the existence of two chemosensory pathways in R. sphaeroides, a feature that so far is unique in bacterial chemotaxis. 相似文献
2.
In the model organism Escherichia coli, the coupling protein CheW, which bridges the chemoreceptors and histidine kinase CheA, is essential for chemotaxis. Unlike the situation in E. coli, Borrelia burgdorferi, the causative agent of Lyme disease, has three cheW homologues (cheW1, cheW2 and cheW3). Here, a comprehensive approach is utilized to investigate the roles of the three cheWs in chemotaxis of B. burgdorferi. First, genetic studies indicated that both the cheW1 and cheW3 genes are essential for chemotaxis, as the mutants had altered swimming behaviours and were non‐chemotactic. Second, immunofluorescence and cryo‐electron tomography studies suggested that both CheW1 and CheW3 are involved in the assembly of chemoreceptor arrays at the cell poles. In contrast to cheW1 and cheW3, cheW2 is dispensable for chemotaxis and assembly of the chemoreceptor arrays. Finally, immunoprecipitation studies demonstrated that the three CheWs interact with different CheAs: CheW1 and CheW3 interact with CheA2 whereas CheW2 binds to CheA1. Collectively, our results indicate that CheW1 and CheW3 are incorporated into one chemosensory pathway that is essential for B. burgdorferi chemotaxis. Although many bacteria have more than one homologue of CheW, to our knowledge, this report provides the first experimental evidence that two CheW proteins coexist in one chemosensory pathway and that both are essential for chemotaxis. 相似文献
3.
Sheng‐Wen Chiu Mark A. J. Roberts Mark C. Leake Judith P. Armitage 《Molecular microbiology》2013,90(2):322-337
Bacterial chemotaxis depends on signalling through large protein complexes. Each cell must inherit a complex on division, suggesting some co‐ordination with cell division. In Escherichia coli the membrane‐spanning chemosensory complexes are polar and new static complexes form at pre‐cytokinetic sites, ensuring positioning at the new pole after division and suggesting a role for the bacterial cytoskeleton. Rhodobacter sphaeroides has both membrane‐associated and cytoplasmic, chromosome‐associated chemosensory complexes. We followed the relative positions of the two chemosensory complexes, FtsZ and MreB in aerobic and in photoheterotrophic R. sphaeroides cells using fluorescence microscopy. FtsZ forms polar spots after cytokinesis, which redistribute to the midcell forming nodes from which FtsZ extends circumferentially to form the Z‐ring. Membrane‐associated chemosensory proteins form a number of dynamic unit‐clusters with mature clusters containing about 1000 CheW3 proteins. Individual clusters diffuse randomly within the membrane, accumulating at new poles after division but not colocalizing with either FtsZ or MreB. The cytoplasmic complex colocalizes with FtsZ at midcells in new‐born cells. Before cytokinesis one complex moves to a daughter cell, followed by the second moving to the other cell. These data indicate that two homologous complexes use different mechanisms to ensure partitioning, and neither complex utilizes FtsZ or MreB for positioning. 相似文献
4.
Marcus J. Tindall Steven L. Porter Philip K. Maini Judith P. Armitage 《PLoS computational biology》2010,6(8)
Understanding how multiple signals are integrated in living cells to produce a balanced response is a major challenge in biology. Two-component signal transduction pathways, such as bacterial chemotaxis, comprise histidine protein kinases (HPKs) and response regulators (RRs). These are used to sense and respond to changes in the environment. Rhodobacter sphaeroides has a complex chemosensory network with two signaling clusters, each containing a HPK, CheA. Here we demonstrate, using a mathematical model, how the outputs of the two signaling clusters may be integrated. We use our mathematical model supported by experimental data to predict that: (1) the main RR controlling flagellar rotation, CheY6, aided by its specific phosphatase, the bifunctional kinase CheA3, acts as a phosphate sink for the other RRs; and (2) a phosphorelay pathway involving CheB2 connects the cytoplasmic cluster kinase CheA3 with the polar localised kinase CheA2, and allows CheA3-P to phosphorylate non-cognate chemotaxis RRs. These two mechanisms enable the bifunctional kinase/phosphatase activity of CheA3 to integrate and tune the sensory output of each signaling cluster to produce a balanced response. The signal integration mechanisms identified here may be widely used by other bacteria, since like R. sphaeroides, over 50% of chemotactic bacteria have multiple cheA homologues and need to integrate signals from different sources. 相似文献
5.
David J. Castillo Teresa Ballado Laura Camarena Georges Dreyfus 《Antonie van Leeuwenhoek》2009,95(1):77-90
The single subpolar flagellum of Rhodobacter sphaeroides shows an enlarged hook-filament junction. One of the two proteins that compose this section of the filament is HAP1
Rs
(FlgK
Rs
) it contains a central non-conserved region of 860 amino acids that makes this protein about three times larger than its
homologue in Salmonella enterica serovar Typhimurium. We investigated the role of this central portion of the unusually large HAP1 protein of R. sphaeroides by monitoring the effects of serial deletions in flgK
Rs
, the gene encoding HAP1
Rs
, on swimming and swarming. Two deletion mutants did not assemble functional flagella, two were paralyzed and five exhibited
reduced free-swimming speeds. Some mutants produced unusual swarming patterns on soft agar without or with Ficoll 400. A segment
of approximately 200-aa of the central region of HAP1
Rs
that aligns with the variable region of the flagellin sequence from other γ- and β-proteobacteria was also found. Therefore,
it is possible that the origin of this large central domain of HAP1
Rs
could be associated with an event of horizontal transfer and subsequent duplications and/or insertions. 相似文献
6.
Photosynthetic organisms need defense systems against photooxidative stress caused by the generation of highly reactive singlet oxygen (1O2). Here we show that the alternative sigma factor RpoHII is required for the expression of important defense factors and that deletion of rpoHII leads to increased sensitivity against exposure to 1O2 and methylglyoxal in Rhodobacter sphaeroides. The gene encoding RpoHII is controlled by RpoE, and thereby a sigma factor cascade is constituted. We provide the first in vivo study that identifies genes controlled by an RpoHII-type sigma factor, which is widely distributed in the Alphaproteobacteria. RpoHII-dependent genes encode oxidative-stress defense systems, including proteins for the degradation of methylglyoxal, detoxification of peroxides, 1O2 scavenging, and redox and iron homeostasis. Our experiments indicate that glutathione (GSH)-dependent mechanisms are involved in the defense against photooxidative stress in photosynthetic bacteria. Therefore, we conclude that systems pivotal for the organism's defense against photooxidative stress are strongly dependent on GSH and are specifically recognized by RpoHII in R. sphaeroides. 相似文献
7.
Role of CheY1 and CheY2 in the Chemotaxis of <Emphasis Type="Italic">A. tumefaciens</Emphasis> Toward Acetosyringone 总被引:1,自引:0,他引:1
Harighi B 《Current microbiology》2008,56(6):547-552
Agrobacterium tumefaciens has a chemtaxis operon, which includes orf1, orf2, cheY1, cheA, cheR, cheB, cheY2, orf9, and orf10. In-frame deletions of cheY1 and cheY2 were constructed and the chemosensory behavior of the mutants was examined on swarm plates and in a chemotaxis assay toward
acetosyringone. The cheY2 mutant (C1/delY2) showed impaired chemotactic capabilities in both swarming and chemotaxis assays. The effect of lacking
CheY1 on chemotaxis is less severe than that of CheY2, under the conditions studied. 相似文献
8.
Lydia M. Bogomolnaya Lindsay Aldrich Yuri Ragoza Marissa Talamantes Katharine D. Andrews Michael McClelland Helene L. Andrews-Polymenis 《PloS one》2014,9(11)
Salmonella enterica serotype Typhimurium can move through liquid using swimming motility, and across a surface by swarming motility. We generated a library of targeted deletion mutants in Salmonella Typhimurium strain ATCC14028, primarily in genes specific to Salmonella, that we have previously described. In the work presented here, we screened each individual mutant from this library for the ability to move away from the site of inoculation on swimming and swarming motility agar. Mutants in genes previously described as important for motility, such as flgF, motA, cheY are do not move away from the site of inoculation on plates in our screens, validating our approach. Mutants in 130 genes, not previously known to be involved in motility, had altered movement of at least one type, 9 mutants were severely impaired for both types of motility, while 33 mutants appeared defective on swimming motility plates but not swarming motility plates, and 49 mutants had reduced ability to move on swarming agar but not swimming agar. Finally, 39 mutants were determined to be hypermotile in at least one of the types of motility tested. Both mutants that appeared non-motile and hypermotile on plates were assayed for expression levels of FliC and FljB on the bacterial surface and many of them had altered levels of these proteins. The phenotypes we report are the first phenotypes ever assigned to 74 of these open reading frames, as they are annotated as ‘hypothetical genes’ in the Typhimurium genome. 相似文献
9.
Kathryn A. Scott Steven L. Porter Eleanor A. L. Bagg Rebecca Hamer Jennifer L. Hill David A. Wilkinson Judith P. Armitage 《Molecular microbiology》2010,76(2):318-330
Specificity of protein–protein interactions plays a vital role in signal transduction. The chemosensory pathway of Rhodobacter sphaeroides comprises multiple homologues of chemotaxis proteins characterized in organisms such as Escherichia coli. Three CheA homologues are essential for chemotaxis in R. sphaeroides under laboratory conditions. These CheAs are differentially localized to two chemosensory clusters, one at the cell pole and one in the cytoplasm. The polar CheA, CheA2, has the same domain structure as E. coli CheA and can phosphorylate all R. sphaeroides chemotaxis response regulators. CheA3 and CheA4 independently localize to the cytoplasmic cluster; each protein has a subset of the CheA domains, with CheA3 phosphorylating CheA4 together making a functional CheA protein. Interestingly, CheA3‐P can only phosphorylate two response regulators, CheY6 and CheB2. R. sphaeroides CheAs exhibit two interesting differences in specificity: (i) the response regulators that they phosphorylate and (ii) the chemosensory cluster to which they localize. Using a domain‐swapping approach we investigated the role of the P1 and P5 CheA domains in determining these specificities. We show that the P1 domain is sufficient to determine which response regulators will be phosphorylated in vitro while the P5 domain is sufficient to localize the CheAs to a specific chemosensory cluster. 相似文献
10.
Dietmar Meletzus Paul Rudnick Natalie Doetsch Andrew Green Christina Kennedy 《Journal of bacteriology》1998,180(12):3260-3264
To determine whether in Azotobacter vinelandii the PII protein influences the regulation of nif gene expression in response to fluxes in the ammonium supply, the gene encoding PII was isolated and characterized. Its deduced translation product was highly similar to PII proteins from other organisms, with the greatest degree of relatedness being exhibited to the Escherichia coli glnK gene product. A gene designated amtB was found downstream of and was cotranscribed with glnK as in E. coli. The AmtB protein is similar to functionally characterized ammonium transport proteins from a few other eukaryotes and one other prokaryote. glnK and amtB comprise an operon. Attempts to isolate a stable glnK mutant strain were unsuccessful, suggesting that glnK, like glnA, is an essential gene in A. vinelandii. amtB mutants were isolated, and although growth on limiting amounts of ammonium was similar in the mutant and wild-type strains, the mutants were unable to transport [14C]methylammonium. 相似文献
11.
Behavioral Mutants in PARAMECIUM CAUDATUM 总被引:4,自引:0,他引:4
Takahashi M 《Genetics》1979,91(3):393-408
Mutants of Paramecium caudatum with abnormal swimming behavior or responses to cations were obtained by mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Some of the mutants, like pawn in P. tetraurelia, cannot swim backward and are called CNR. Seven independently obtained CNR mutants belonged to three complementation groups, designated as cnrA, cnrB and cnrC. Some characteristics of double homo- and heterozygotes were compared with single homo- and heterozygotes. Other behavioral mutants shown to have a genic basis included K+-sensitive, temperature-shock behavioral and slow swimmer. All those mutants except for slow swimmer had lesions in the membrane because Triton-extracted models of them show almost the same swimming behavior as wild type. 相似文献
12.
A new iso-accepting tRNAphe from extracts of chemoheterotrophic and photoheterotrophic cells of Rhodopseudomonas sphaeroides has been identified by both BDEAE cellulose and RPC-5 chromatography. Rechromatography of each of the tRNAphe species in either the acylated or deacylated state shows that they migrate as single homogeneous peaks.In steady-state chemoheterotrophic cultures of R. sphaeroides tRNA
I–II
phe
account for 25–30% of the total phenylalanine accepting activity while in steadystate photoheterotrophic cultures tRNA
I–II
phe
account for no more than 10% of the total phenylalanine accepting activity.During the transition from chemoheterotrophic to photoheterotrophic growth conditions the levels of tRNA
I–II
phe
fall in an exponential manner during the first half of the intracytoplasmic membrane induction period. tRNA
I
phe
then remains at a level 10% that of its steady-state chemoheterotrophic level as long as photoheterotrophic growth conditions remain. tRNA
II
phe
, after dropping to 10% of its former chemoheterotrophic level then returns to a level 50% that of its chemoheterotrophic level as long as photoheterotrophic growth conditions remain.Abbreviations BDEAE
benzoylated diethyl amino ethyl
- RPC
reversed phase chromatography
- TCA
tricholroacetic acid
- ICM
intracytoplasmic membrane
Submitted by WDS in partial fullfilment of requirements for the M.S. degree 相似文献
13.
Putative role of the malate valve enzyme NADP–malate dehydrogenase in H2O2 signalling in Arabidopsis
Eiri Heyno Gilles Innocenti Stéphane D. Lemaire Emmanuelle Issakidis-Bourguet Anja Krieger-Liszkay 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2014,369(1640)
In photosynthetic organisms, sudden changes in light intensity perturb the photosynthetic electron flow and lead to an increased production of reactive oxygen species. At the same time, thioredoxins can sense the redox state of the chloroplast. According to our hypothesis, thioredoxins and related thiol reactive molecules downregulate the activity of H2O2-detoxifying enzymes, and thereby allow a transient oxidative burst that triggers the expression of H2O2 responsive genes. It has been shown recently that upon light stress, catalase activity was reversibly inhibited in Chlamydomonas reinhardtii in correlation with a transient increase in the level of H2O2. Here, it is shown that Arabidopsis thaliana mutants lacking the NADP–malate dehydrogenase have lost the reversible inactivation of catalase activity and the increase in H2O2 levels when exposed to high light. The mutants were slightly affected in growth and accumulated higher levels of NADPH in the chloroplast than the wild-type. We propose that the malate valve plays an essential role in the regulation of catalase activity and the accumulation of a H2O2 signal by transmitting the redox state of the chloroplast to other cell compartments. 相似文献
14.
15.
Lee Hyun Jeong Park Ju-Yong Han Chul-Hee Chang Suk-Tai Kim Yang-Hoon Min Jiho 《World journal of microbiology & biotechnology》2011,27(1):189-192
Rhodobacter sphaeroides is a purple non-sulfur photosynthetic bacteria that participates in the anoxic cycling of carbon both as the primary producer
and as the light-stimulated consumers of the reduced organic compounds. In this study, six different organic acids, i.e. acetate,
lactate, oxaloacetate, malate, succinate, and citrate, were selected and used to analyze the relationships between the organic
acid source and the cell growth. The C4 compound exhibited an enhanced cell growth compared to the other organic acids, and the growth rate of R. sphaeroides that was grown with 0.03 M succinic acid was significantly 3.2-fold faster than the C6 compound of 0.03 M citrate. Additionally, the cell growth of R. sphaeroides was enhanced with increasing light intensity, and the growth rate and the dry cell weight of R.
sphaeroides that were grown under the light conditions of 15 W/m2 were 2.0- and 1.2-fold higher than R. sphaeroides at 3 W/m2. Therefore, the high light intensity probably affected the growth of R. sphaeroides. Moreover, the blue-colored light emitting diode (LED) exhibited a highest growth rate and cell concentration of R. sphaeroides among the various types of LEDs, and the enhanced cell growth phenomenon under the blue LED conditions was dramatically stimulated
at low concentrations of succinic acid, which was compensatory for succinic acid. Therefore, a high light intensity and a
blue LED as the light source were necessary for the enhanced cell growth for the C4 organic acid, i.e. succinic acid. 相似文献
16.
With the help of an automated tracking system we have studied the characteristics of the transient light growth response of Phycomyces. The response shows a sharply defined latency. The Q10 of the reciprocal latency is 2.4. Response patterns at different peaks of the action spectrum are the same. The gradual variation of response magnitude over a wide range of adapted intensifies parallels that of phototropism. The responses to saturating stimuli exhibit a strong oscillation with a constant period of 1.6 min and variable damping. The growth responses to sinusoidally varying light intensities show a system bandwidth of 2.5 x 10-3 Hz. The linear dependence of phase shift on frequency is largely attributable to the latency observed with pulse stimuli. In the high intensity range a previously suspected increase of the steady-state growth rate with intensity has been confirmed. The light growth responses of mutants selected for diminished phototropism have been investigated. Many of these mutants have sizable but grossly distorted growth responses. 相似文献
17.
Responses of Paramecium bursaria to light intensity changes were investigated. The resting paramecia show a direction changing response (photophobic response) to a sudden decrease of light intensity, whereas no response was shown to an increase in intensity. The critical intensity decrease dIc necessary to show the response was measured at various values of initial light intensity, and the ratio dIc/I was found to be equal to ~0.15. The swimming paramecia show different behavior depending on their swimming direction in the spatial gradient of light intensity. Paramecia show direction change more frequently when they are swimming down the gradient than in the opposite direction. This difference in the rate of direction changing is 13–17%. These results may offer an explanation for the mechanism of photoaccumulation. 相似文献
18.
H. -H. Sommer 《Helgoland Marine Research》1977,29(4):493-502
Shadow responses, including reactions to both increase (on) and decrease (off) in light intensity have been hitherto described in the adults of various bottom-dwelling marine invertebrates. These reactions as expressed by decrease in activity are assumed to be protective (withdrawal responses, kinetic rigidity after v. Buddenbrock, 1952). By contrast, the free-swimming larvae of these species normally show increase in activity to both increase and decrease in light intensity as expressed by negative or positive photoresponses. In the sessile barnacleBalanus balanus L. reactions to increase in light intensity are demonstrated which, contrary to the withdrawal responses or kinetic rigidity, result in an increase of cirral activity. The shadow responses of the barnacles (off responses) are described as withdrawal responses. The light responses are expressed by two different modes of behaviour: (a) If an active barnacle is stimulated by increase in light intensity, the frequency of cirral activity increases; (b) if an inactive barnacle is stimulated by increase in light intensity, the cirral activity arises a short time later. The light responses observed are interpreted as a metamorphosis of larval swimming activity.
Gefördert von der Deutschen Forschungsgemeinschaft 相似文献
Gefördert von der Deutschen Forschungsgemeinschaft 相似文献
19.