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At least 685 records · Page 38Linked to original sources
PubMed2005

Identification of a protein Ser/Thr kinase cascade that regulates essential transcriptional activators in Myxococcus xanthus development.

Pkn8 is a membrane-associated protein Ser/Thr kinase (PSTK) of Myxoccocus xanthus that was previously found to associate with a novel cytoplasmic kinase, Pkn14. In the present study, MrpC, an essential transcription factor for fruA expression during fruiting body development, was identified using a genomic yeast two-hybrid screen with Pkn14 as bait. Our biochemical studies demonstrated that purified Pkn8 and Pkn14 are active kinases and that Pkn8 is able to phosphorylate Pkn14 that forms a tetramer via its C-terminal 41 residues. Moreover, Pkn14 phosphorylated purified MrpC, indicating that Pkn8 is a Pkn14 kinase and Pkn14 is an MrpC kinase. The pkn8 and pkn14 deletion strains (Deltapkn8 and Deltapkn14) developed into fruiting bodies significantly faster than that of the parent strain, DZF1. While mrpC expression was at a low level in DZF1 during vegetative growth, it was highly elevated in Deltapkn8 and Deltapkn14 during vegetative growth and development. Furthermore, FruA, usually induced at 6 h of development, was instead detected at the early stationary phase and accumulated faster during development in Deltapkn8 and Deltapkn14. Therefore, the developmental phenotype of Deltapkn8 and Deltapkn14 seems to be due to untimely FruA production mediated by elevated levels of MrpC in Deltapkn8 and Deltapkn14 during vegetative growth. As pkn14 expression was increased at the mid- and late-log. phases in DZF1 but decreased during development, the Pkn8-Pkn14 kinase cascade appears to negatively regulate mrpC expression by phosphorylating MrpC during vegetative growth. This is the first demonstration of a functional PSTK cascade in prokaryotes. mrpC expression has been proposed to be activated by MrpA and MrpB which belong to a two-component His-Asp phosphorelay signal transduction system and that MrpC autoregulate its own expression (Sun H. and Shi W., 2001 J Bacteriol 183: 4786-4795). Therefore, M. xanthus seems to utilize both eukaryotic PSTK cascade and prokaryotic His-Asp phosphorelay system to precisely regulate mrpC expression with specific timing during development.

Amino Acid Sequence↗
PubMed2006

Mutations of the act promoter in Myxococcus xanthus.

Mutations within the -12 and -24 elements provide evidence that the act promoter is recognized by sigma-54 RNA polymerase. Deletion of the -20 base pair, which lies between the two conserved elements of sigma-54 promoters, decreased expression by 90%. In addition, mutation of a potential enhancer sequence, around -120, led to an 80% reduction in act gene expression. actB, the second gene in the act operon, encodes a sigma-54 activator protein that is proposed to be an enhancer-binding protein for the act operon. All act genes, actA to actE, are expressed together and constitute an operon, because an in-frame deletion of actB decreased expression of actA and actE to the same extent. After an initially slow phase of act operon expression, which depends on FruA, there is a rapid phase. The rapid phase is shown to be due to the activation of the operon expression by ActB, which completes a positive feedback loop. That loop appears to be nested within a larger positive loop in which ActB is activated by the C signal via ActA, and the act operon activates transcription of the csgA gene. We propose that, as cells engage in more C signaling, positive feedback raises the number of C-signal molecules per cell and drives the process of fruiting body development forward.

Amino Acid Sequence↗
PubMed1991

Effects of glucosamine on lysis, glycerol formation, and sporulation in Myxococcus xanthus.

Glucosamine (GlcN), which has previously been shown to rescue fruiting body formation, lysis, and sporulation in a developmental mutant (G. Janssen and M. Dworkin, Dev. Biol. 112:194-202, 1985), induced lysis in vegetative and developing wild-type cells and inhibited fruiting body formation. It also resulted in a transient, intracellular increase in the concentration of glycerol, a known sporulation inducer, and sporulation of the surviving cells. Phospholipase activity, which was shown to be normally developmentally regulated, increased 7.6-fold after treatment of vegetative cells with 50 mM GlcN. Likewise, autocidal activity, which normally increased 18 to 24 h after the initiation of development, increased 20% when vegetative or developing cells were exposed to GlcN. Two mutants resistant to GlcN-induced lysis (MD1021 and MD1022) were isolated and showed neither an increase in autocide production nor an increase in phospholipase activity in response to added GlcN. MD1021 was developmentally deficient, and GlcN rescued fruiting body formation as well as phospholipase activity and autocide production. We propose that GlcN exerts its lytic effect by regulating the activity of phospholipase enzymes that release autocides, compounds that are believed to be responsible for developmental autolysis. GlcN-induced sporulation was found to depend on several factors: the initial cell density, the amount of lysis induced by GlcN, and the presence of tan-phase variants. An initial cell density of greater than 2 x 10(5) cells per ml was required to support GlcN-induced sporulation, and sporulation did not occur unless 50 to 75% of these cells had lysed. Mutants that were resistant to GlcN-induced lysis also did not sporulate in the presence of GlcN. The effects of GlcN on developing cells depended on the concentration of GlcN added; the addition of low concentrations of GlcN resulted in enhancement of sporulation, while higher concentrations resulted in the inhibition of sporulation. The ultrastructure of GlcN-induced spores resembled that of spores induced by the exogenous addition of glycerol, in contrast to spores isolated from mature fruiting bodies. A model by which GlcN may regulate both lysis and sporulation is presented.

Drug Resistance, Microbial↗
PubMed1991

Upstream gene of the mgl operon controls the level of MglA protein in Myxococcus xanthus.

The mgl operon contains two open reading frames (ORFs) which are transcribed together. A collection of nonmotile mutants helped to define the downstream ORF as the mglA gene. Single mutations at the mglA locus completely abolish motility. A series of deletion mutations was constructed to determine the role of the upstream ORF (now called mglB). A strain carrying a deletion in mglB and with an intact mglA produces small colonies. The cells are motile, but their rate of swarm spreading is reduced. Measurements of cell movement showed that mglB mutant cells advanced, on average, less than 0.1 cell length in 5 min. The mglB+ cells advanced an average of 1.3 cell lengths in the same time. Extracts of delta mglB cells contain 15 to 20% as much of the 22-kDa MglA protein as do mglB+ cells, as measured in Western immunoblots and enzyme-linked immunosorbent assays. However, the amount of mgl transcript is the same in the delta mglB mutants as in the mglB+ strain. Heterozygous partial diploids mglB/mglA with the wild-type alleles in trans have normal motility, demonstrating that the largest of the mglB deletions is not polar on mglA. Like other motility defects, a delta mglB mutation alters fruiting body development and sporulation. The mglB mutants delayed aggregation, produced small immature fruiting bodies, and sporulated at 45 to 50% wild-type levels. All aspects of the mglB mutant phenotype are explained by the reduced levels of mglA protein and the assumption that it limits the amount of gliding.

Bacterial Proteins↗
PubMed2002

act operon control of developmental gene expression in Myxococcus xanthus.

Cell-bound C-signal guides the building of a fruiting body and triggers the differentiation of myxospores. Earlier work has shown that transcription of the csgA gene, which encodes the C-signal, is directed by four genes of the act operon. To see how expression of the genes encoding components of the aggregation and sporulation processes depends on C-signaling, mutants with loss-of-function mutations in each of the act genes were investigated. These mutations were found to have no effect on genes that are normally expressed up to 3 h into development and are C-signal independent. Neither the time of first expression nor the rate of expression increase was changed in actA, actB, actC, or actD mutant strains. Also, there was no effect on A-signal production, which normally starts before 3 h. By contrast, the null act mutants have striking defects in C-signal production. These mutations changed the expression of four gene reporters that are related to aggregation and sporulation and are expressed at 6 h or later in development. The actA and actB null mutations substantially decreased the expression of all these reporters. The other act null mutations caused either premature expression to wild-type levels (actC) or delayed expression (actD), which ultimately rose to wild-type levels. The pattern of effects on these reporters shows how the C-signal differentially regulates the steps that together build a fruiting body and differentiate spores within it.

Bacterial Proteins↗
PubMed2005

PhoR1-PhoP1, a third two-component system of the family PhoRP from Myxococcus xanthus: role in development.

The pair PhoR1-PhoP1 is the third two-component system of the family PhoRP reported in M. xanthus. PhoR1 is a histidine kinase anchored to the membrane through a transmembrane domain located in the amino-terminal portion of the protein. As a result, 93% of the protein is located in the cytoplasm. This topology is unusual in the PhoR-type histidine kinases. PhoP1 is a response regulator with a helix-loop-helix motif typical of the DNA-binding proteins. Although the operon phoPR1 is expressed during vegetative growth, it peaks during development. The expression levels of this operon are higher in phosphate-containing media than in those in which the nutrient is absent. A deletion mutant in this system exhibits a delay in aggregation and the formation of fruiting bodies larger than those of the wild-type strain. The expression of the operon is autoregulated. This system is also partially responsible for the expression of Mg-independent acid and neutral phosphatases, but it is not required for the expression of alkaline phosphatases.

Amino Acid Sequence↗
PubMedDate not supplied

[Induction of Bacillus anthracis hemolytic activity with the use of Myxococcus xanthus].

The development of a new method for the induction of the B. anthracis hemolytic activity with the use of M. xanthus and the differentiation of pure cultures of the causative agent of anthrax from those contaminated with myxobacteria is presented. To demonstrate the induction of the hemolytic acivity of B. anthracis with the use of M. xanthus, conditions for the symbiosis of B. anthracis cells STI, exhibiting no hemolytic activity, with M. xanthus non-hemolytic cells were created by mixing them and inoculating the symbiotic biomass on the surface of blood agar.

Agar↗
PubMed1990

Modification of immune response by coats of Myxococcus xanthus myxospores.

Treatment with coats of M. xanthus myxospores produced a marked modificatory effect on humoral response, depending on the inoculation model. Also we observed that the percentage of adherent phagocytes and phagocytic index were enhanced after treatment. These results were similar to the effect obtained by M. xanthus myxospores. Data showed that the immune response modifier properties of M. xanthus myxospores are principally present in the coats.

Animals↗
PubMed1978

Site of ATPase activity in Myxococcus xanthus: lipid requirement for enzyme activity. Dedicated to Professor Dr. W. Schwartz on his 80th birthday.

Treatment of cells with lysophosphatidylcholine, lysozyme, and phospholipase D removed most of their phospholipids and reduced ATPase activity to near zero. Addition of a microdispersion of phospholipids restored enzyme activity to various degrees. Phosphatidylcholine was most effective in reconstitution experiments, less effective were phosphatidylethanolamine and phosphatidylserine. Lipid analyses of cell fractions were possible through separation of cell wall and cell membrane in a sucrose gradient after differentiated treatment of glutaraldehyde fixed cells with lysophosphatidylcholine, lysozyme, and pronase. Phosphatidylcholine was almost exclusively a component of the cell membrane, whereas phosphatidylethanolamine was that of the wall. It is concluded that lipids are necessary for in vivo function of a Mg-dependent ATPase, and that membrane-associated phosphatidylcholine may serve as a matrix for the enzyme. Lipid extracts made from cells or cell fractions contained plasmologens, not previously reported to occur in Gram-negative, aerobic bacteria.

Adenosine Triphosphatases↗