SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
FrzS protein is important for normal social motility in myxobacteria, which includes periodic reversals in the direction of cell motion. Recent results show that cell reversal correlates with the migration of FrzS from the old leading pole of the cell to the new leading pole.
Myxobacteria colonies during their aggregation phase propagate complex waves over their surface. These waves are fundamentally different from the analogous phenomenon in diffusion-reaction systems or in populations of Dictyostelium discoideum where colliding waves annhilate. Myxobacterial waves appear to pass through one another, analogous to solitons. Moreover, individual bacteria oscillate back and forth, exhibiting no net mass transfer. A mathematical model can explain virtually all of the experimentally observed properties of these waves and draw several conclusions about the properties of the intercelular signaling system.
The potential benefits of cooperation in microorganisms can be undermined by genetic conflict within social groups, which can take the form of 'cheating'. For cooperation to succeed as an evolutionary strategy, the negative effects of such conflict must somehow be either prevented or mitigated. To generate an interpretive framework for future research in microbial behavioural ecology, here we outline a wide range of hypothetical mechanisms by which cheaters might be constrained.
A short, efficient route has been developed to analogues of myxovirescin using ring-closing metathesis whereby the antibacterial activity has been retained.
Factors that are simultaneously secreted and sensed are used by cells to monitor local cell density; a recently discovered factor of this type controls the transformation-competence of Bacillus subtilis.
Many bacteria glide over surfaces without the aid of flagella. Gliding is still somewhat mysterious, but recent studies show that it involves specialized secretory systems that assemble membrane-associated filaments, and the recognition of extracellular components that trigger movement via transmembrane transducers.
Explore the source record for details and available documents.
Silicified flake conglomerates and in situ stratiform stromatolites of the Upper Proterozoic (c. 700-800 Ma) Limestone-Dolomite 'Series', central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages is Siphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder, Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively by Siphonophycus kestron. Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new: Myxococcoides stragulescens n.sp. and Scissilisphaera gradata n. sp.
A sensor for purine nucleoside diphosphates in solution based on nucleoside diphosphate kinase (NDPK) has been developed. A single cysteine was introduced into the protein and labeled with the environmentally sensitive fluorophore, N-[2-(iodoacetamido)ethyl]-7-diethylaminocoumarin-3-carboxamide. The resultant molecule shows a 4-fold fluorescence increase when phosphorylated on His117; this phosphorylation is on the normal reaction pathway of the enzyme. The emission maximum of the phosphoenzyme is at 475 nm, with maximum excitation at 430 nm. The fluorescent phosphorylated NDPK is used to measure the amount of ADP and the unphosphorylated to measure ATP. The labeled protein is phosphorylated to > 90%, and the resultant molecule is stable on ice or can be stored at -80 degrees C. The fluorescence responds to the fraction of protein phosphorylated and so to the equilibrium between ADP plus NDPK approximately P and ATP plus NDPK. In effect, the sensor measures the ADP/ATP concentration ratio. The enzyme has a broad specificity for the purine of the nucleotides, so the sensor also can measure GDP/GTP ratios. The fluorescence and kinetic properties of the labeled protein are described. The binding rate constants of nucleotides are approximately 10(5) M(-1) s(-1), and the fluorescence change is at >200 s(-1) when the ADP concentration is >1 mM. Results are presented with two well-defined systems, namely, the kinetics of ADP release from myosin subfragment 1 and GDP release from the small G protein, human rho. The results obtained with this novel sensor agree with those from alternate methods and demonstrate the applicability for following micromolar changes in nucleoside diphosphate in real time.
Many secondary metabolites, including various polyketides, require complex enzymatic pathways for modification into their final biologically active forms. Limitation of the dissolved oxygen supplied during cultivation of various microbial strains can decrease the activity of cytochrome P-450 monooxygenases required for the processing of pathway intermediates into their final forms, resulting in the accumulation of these intermediates as the primary products. Here, a generalized oxygen-limited cultivation strategy is specifically demonstrated with a myxobacterial strain engineered to heterologously express the epothilone polyketide synthase (PKS) gene cluster under either an excess (the dissolved oxygen tension is maintained at 50% of saturation) or a depleted (no residual dissolved oxygen detected) level of oxygenation during cultivation. Cultivation of this myxobacterial strain with excess oxygenation resulted in the production of epothilones A and B as the primary products, while cultivation of this same strain under depleted oxygenation resulted in the production of epothilones C and D as the primary products. Additionally, the peak cell density in the oxygen-depleted cultivations was 60% higher than that observed in oxygen-excess cultivations. Finally, an active EpoK epoxidase was found to catalyze the production of a novel epothilone (Epo506) with an unexpected structure during the cultivation of another myxobacterial strain expressing a genetically modified epothilone PKS under excess oxygenation. The structure of Epo506 was determined by high-resolution mass spectrometry and one- and two-dimensional NMR.
Epothilone D is a member of a class of potent antineoplastic natural products produced by myxobacteria. Previously, we have described a fed-batch epothilone D production process in which an adsorber resin is incorporated into the bioreactor setup to capture and stabilize the product in situ, preventing its degradation within the bioreactor. The capture of epothilone D by these relatively large resin beads enables the development of continuous and semicontinuous culturing systems incorporating bead retention mechanisms to completely retain the product within the bioreactor, increasing the epothilone D product titer by almost 3-fold in both cases over a baseline fed-batch system. These product retention strategies, described here for production of the epothilones, are generally applicable to any system using adsorber resins as a method to capture product during a microbial cultivation.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The myxobacteria are Gram-negative organisms that are capable of multicellular, social behaviour. In the presence of nutrients, swarms of myxobacteria feed cooperatively by sharing extracellular digestive enzymes, and can prey on other bacteria. When the food supply runs low, they initiate a complex developmental programme that culminates in the production of a fruiting body. Myxobacteria move by gliding and have two, polarly positioned engines to control their motility. The two engines undergo coordinated reversals, and changes in the reversal frequency and speed are responsible for the different patterns of movement that are seen during development. The myxobacteria communicate with each other and coordinate their movements through a cell-contact-dependent signal. Here, the cell movements that culminate in the development of the multicellular fruiting body are reviewed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Recently, the epothilone polyketide synthase (PKS) was successfully introduced into a heterologous production host for the large-scale production of epothilone D. We have found that at least three other epothilones can also be produced as the major fermentation product of this recombinant strain by supplementation of specific substrates to the production media. Addition of acetate or propionate to the media results in modulation of the epothilone D:C ratio, whereas addition of L-serine with either acetate or propionate yields epothilone H(1) or H(2) as the major product. This strategy permits production of at least four novel epothilones by culturing a single host with a genetically modified epothilone PKS in various media.