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At least 343 records · Page 19Linked to original sources
PubMed2004

Diel changes in bacteriochlorophyll a concentration suggest rapid bacterioplankton cycling in the Baltic Sea.

Aerobic anoxygenic phototrophs were recently found to constitute a significant portion of the marine microbial community. These bacteria use bacteriochlorophyll-containing reaction centers to perform photoheterotrophic metabolism. A new instrument for routine measurements of both chlorophyll a and bacteriochlorophyll a was used for monitoring anoxygenic phototrophs in the Baltic Sea in late summer 2003. Bacteriochlorophyll a concentration ranged from 8 to 50 ngl(-1), with an average bacteriochlorophyll/chlorophyll ratio of 4.2 x 10(-3). Moreover, diel trends in bacteriochlorophyll a signals were observed, with a distinct decline occurring during daylight hours. Based on laboratory measurements this phenomenon was ascribed to the complete inhibition of bacteriochlorophyll synthesis by light, which, in combination with a concurrent turnover of the cells, resulted in a pigment decline. Following this explanation, we postulate that bacteriochlorophyll a can serve as a natural 'pulse-and-chase' marker, allowing estimation of the mortality rates of anoxygenic phototrophs from the rates of pigment decline. Based on this assumption, we suggest that the Baltic photoheterotrophic community was characterized by high turnover rates, in a range of 0.7-2 d(-1).

Aerobiosis↗
PubMed1985

Kinetic studies of bacterial sulfate reduction in freshwater sediments by high-pressure liquid chromatography and microdistillation.

Indirect photometric chromatography and microdistillation enabled a simultaneous measurement of sulfate depletion and sulfide production in the top 3 cm of freshwater sediments to be made. The simultaneous measurement of sulfate depletion and sulfide production rates provided added insight into microbial sulfur metabolism. The lower sulfate reduction rates, as derived from the production of acid-volatile S only, were explained by a conversion of this pool to an undistillable fraction under acidic conditions during incubation. A mathematical model was applied to calculate sulfate reduction from sulfate gradients at the sediment-water interface. To avoid disturbance of these gradients, the sample volume was reduced to 0.2 g (wet weight) of sediment. Sulfate diffusion coefficients in the model were determined (D(s) = 0.3 x 10 cm s at 6 degrees C). The results of the model were compared with those of radioactive sulfate turnover experiments by assessing the actual turnover rate constants (2 to 5 day) and pool sizes of sulfate at different sediment depths.

Journal Article↗
PubMed1988

Biomass of the cryptoendolithic microbiota from the Antarctic desert.

Extractable lipid phosphate was used to determine the biomass of the cryptoendolithic microbiota that colonizes sandstone rocks in the Ross Desert region of Antarctica. The mean amount of lipid phosphate was 0.053 micromole/cm2 (n = 9), which equals 2.54 g of C per m2 (range, 1.92 to 3.26 g of C per m2) of biomass in the biotic zone of these rocks. The turnover of phospholipids was comparable to that of temperate sediments and soils (t1/2, 6 to 9 days) at 0 degrees C and a light intensity of 305 micromoles of photons per m2 per s, indicating that this was a good method to measure viable biomass. The biomass was 0.3 to 9.6% of the total carbon content of the biotic zone and was about 2 orders of magnitude smaller than the epilithic lichen dry weight at a location some 7 degrees north in latitude. The cryptoendolithic microbiota had a uniform density throughout the biotic zone under the rock surface. The results indicate that the cryptoendolithic microbial biomass is small but viable in this unique, extreme ecosystem.

Adenosine Triphosphate↗
PubMed1988

Restoration of colony-forming activity in osmotically stressed Escherichia coli by betaine.

Exposure of Escherichia coli to 0.8 M NaCl caused a rapid and large decrease in colony-forming activity. When such osmotically upshocked cells were exposed to betaine, colony-forming activity was restored. Betaine was able to restore colony-forming activity even when chloramphenicol inhibited protein synthesis. Thus, restoration was not the result of cell turnover. The cells were not killed by exposure to 0.8 M NaCl, because during exposure they accumulated ATP intracellularly. Betaine treatment caused this cellular ATP to decrease to a lower level. This work may provide the foundation for a simple plating procedure to quantitatively detect nonculturable E. coli in ocean beach recreational waters.

Adenosine Triphosphate↗
PubMed2003

A plasma membrane syntaxin is phosphorylated in response to the bacterial elicitor flagellin.

In vivo pulse labeling of suspension-cultured Arabidopsis cells with [32P]orthophosphate allows a systematic analysis of dynamic changes in protein phosphorylation. Here, we use this technique to investigate signal transduction events at the plant plasma membrane triggered upon perception of microbial elicitors of defense responses, using as a model elicitor flg22, a peptide corresponding to the most conserved domain of bacterial flagellin. We demonstrate that two-dimensional gel electrophoresis in conjunction with mass spectrometry is a suitable tool for the identification of intrinsic membrane proteins, and we show that among them a syntaxin, AtSyp122, is phosphorylated rapidly in response to flg22. Although incorporation of radioactive phosphate into the protein only occurs significantly after elicitation, immunoblot analysis after two-dimensional gel separation indicates that the protein is also phosphorylated prior to elicitation. These results indicate that flg22 elicits either an increase in the rate of turnover of phosphate or an additional de novo phosphorylation event. In vitro, phosphorylation of AtSyp122 is calcium-dependent. In vitro phosphorylated peptides separated by two-dimensional thin layer chromatography comigrate with two of the three in vivo phosphopeptides, indicating that this calcium-dependent phosphorylation is biologically relevant. These results indicate a regulatory link between elicitor-induced calcium fluxes and the rapid phosphorylation of a syntaxin. Because syntaxins are known to be important in membrane fusion and exocytosis, we hypothesize that one of the functions of the calcium signal is to stimulate exocytosis of defense-related proteins and compounds.

Amino Acid Sequence↗
PubMed2005

C-di-GMP: the dawning of a novel bacterial signalling system.

Bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) has come to the limelight as a result of the recent advances in microbial genomics and increased interest in multicellular microbial behaviour. Known for more than 15 years as an activator of cellulose synthase in Gluconacetobacter xylinus, c-di-GMP is emerging as a novel global second messenger in bacteria. The GGDEF and EAL domain proteins involved in c-di-GMP synthesis and degradation, respectively, are (almost) ubiquitous in bacterial genomes. These proteins affect cell differentiation and multicellular behaviour as well as interactions between the microorganisms and their eukaryotic hosts and other phenotypes. While the role of GGDEF and EAL domain proteins in bacterial physiology and behaviour has gained appreciation, and significant progress has been achieved in understanding the enzymology of c-di-GMP turnover, many questions regarding c-di-GMP-dependent signalling remain unanswered. Among these, the key questions are the identity of targets of c-di-GMP action and mechanisms of c-di-GMP-dependent regulation. This review discusses phylogenetic distribution of the c-di-GMP signalling pathway in bacteria, recent developments in biochemical and structural characterization of proteins involved in its metabolism, and biological processes affected by c-di-GMP. The accumulated data clearly indicate that a novel ubiquitous signalling system in bacteria has been discovered.

Bacteria↗
PubMed2002

Hindgut fermentation in three species of marine herbivorous fish.

Symbioses with gut microorganisms provides a means by which terrestrial herbivores are able to obtain energy. These microorganisms ferment cell wall materials of plants to short-chain fatty acids (SCFA), which are then absorbed and used by the host animal. Many marine herbivorous fishes contain SCFA (predominantly acetate) in their hindgut, indicative of gut microbial activity, but rates of SCFA production have not been measured. Such information is an important prerequisite to understanding the contribution that gut microorganisms make in satisfying the energy needs of the fish. We have estimated the rates of acetate production in the gut of three species of temperate marine herbivorous fish from northeastern New Zealand: Kyphosus sydneyanus (family Kyphosidae), Odax pullus (family Odacidae), and Aplodactylus arctidens (family Aplodactylidae). Ex vivo preparations of freshly caught fish were maintained with their respiratory and circulatory systems intact, radiolabeled acetate was injected into ligated hindgut sections, and gut fluid was sampled at 20-min intervals for 2 h. Ranges for acetate turnover in the hindguts of the studied species were determined from the slope of plots as the log of the specific radioactivity of acetate versus time and pool size, expressed on a nanomole per milliliter per minute basis. Values were 450 to 570 (K. sydneyanus), 373 to 551 (O. pullus), and 130 to 312 (A. arctidens). These rates are comparable to those found in the guts of herbivorous reptiles and mammals. To determine the contribution of metabolic pathways to the fate of acetate, rates of sulfate reduction and methanogenesis were measured in the fore-, mid-, and hindgut sections of the three fish species. Both rates increased from the distal to proximal end of the hindgut, where sulfate reduction accounted for only a small proportion (<5%) of acetate methyl group transformed to CO(2), and exceeded methanogenesis from acetate by >50-fold. When gut size was taken into account, acetate uptake from the hindgut of the fish species, determined on a millimole per day per kilogram of body weight basis, was 70 (K. sydneyanus), 18 (O. pullus), and 10 (A. arctidens).

Acetates↗
PubMed1971

Promoter-like mutant with increased expression of the glycerol kinase operon of Escherichia coli.

A glycerol-specific phenotypic revertant isolated from a mutant of Escherichia coli missing enzyme I of the phosphoenolpyruvate phosphotransferase system was studied. This revertant is capable of producing higher levels of glycerol kinase and the protein mediating the facilitated diffusion of glycerol (facilitator) than wild-type cells. The kinase of the revertant is indistinguishable from the wild-type enzyme with respect to its sensitivity to feedback inhibition by fructose-1,6-diphosphate, its pH optimum, and its turnover number. The synthesis of glycerol kinase in strains bearing the suppressor locus is resistant to catabolite repression. The suppressor mutation mapped at the known glpK locus. Thus, it is suggested that the mutation occurred in the promoter of the operon specifying the kinase and the facilitator.

Arabinose↗
PubMed1984

Heterogeneity of uridine incorporation along the rabbit nephron. I. Autoradiographic study.

We present here an autoradiographic study of uridine labeling in tubular segments micro-dissected from the rabbit kidney. Kidney pyramids were incubated for 60 min with low (66 nM) and high (66 microM) [3H]-uridine concentration. At the two concentrations studied the labeling was almost exclusively nuclear in all segments studied. At the low concentration, labeling predominated in the macula densa (MD = 63.88 +/- 6.15 silver grains/100 micron2, n = 11), cortical ascending limb (CAL = 19.65 +/- 1.65, n = 15), and initial distal tubule (DCTa = 24.31 +/- 2.70, n = 6). It was minimal in the proximal tubule (PCT2 = 9.14 +/- 1.61, n = 16) and in the cortical (CCT = 5.23 +/- 0.75, n = 18) and medullary (MCT = 5.52 +/- 1.10, n = 12) collecting ducts. At a high concentration, the profile of labeling was roughly similar except for a relative increase in labeling much more pronounced in collecting ducts (CCT = +373, MCT = +323%) than in the other structures (MD = -14, CAL = +66, DCTa = +49, PCT = +9%). Pulse-chase experiments do not show evidence for differences in turnover or degradation rates of RNA between segments, at least in the PCT and the connecting part of the CCT. Analysis of the results at low and high concentration suggests that the observed heterogeneity in uridine labeling depends on both variable endogenous nucleoside pools and different rates of uridine incorporation into RNA from one segment to another.

Animals↗
PubMed1987

Collagen in abdominal aortic aneurysm: typing, content, and degradation.

The collagen content of the media of infrarenal aorta has been compared in age- and sex-matched normal aorta and dilated and nondilated atherosclerotic aorta. The proportion of collagen was increased in aneurysmal aorta from 62% to 84% and appears to be the result of preferential elastin degradation. The ratio of type I to type III collagen, estimated from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of specific cyanogenbromide peptides, did not vary significantly from 2:1 in any of the three groups of aortas. There was no evidence of increased collagenase activity in unruptured aneurysmal aorta. Collagenase activity was increased in ruptured aneurysmal aorta but could only be satisfactorily measured after resolution from the endogenous tissue inhibitor of metalloproteinases. We suggest that only limited collagen turnover occurs in the media of abdominal aortic aneurysms before rupture. A subgroup of three patients with a significant family history of aneurysm had lower amounts of type III collagen in the aortic media, suggesting that abnormalities in type III collagen may be one of the genetic factors contributing to familial clustering of aneurysms.

Aorta, Abdominal↗
PubMed1995

HIV population dynamics in vivo: implications for genetic variation, pathogenesis, and therapy.

Several recent reports indicate that the long, clinically latent phase that characterizes human immunodeficiency virus (HIV) infection of humans is not a period of viral inactivity, but an active process in which cells are being infected and dying at a high rate and in large numbers. These results lead to a simple steady-state model in which infection, cell death, and cell replacement are in balance, and imply that the unique feature of HIV is the extraordinarily large number of replication cycles that occur during infection of a single individual. This turnover drives both the pathogenic process and (even more than mutation rate) the development of genetic variation. This variation includes the inevitable and, in principle, predictable accumulation of mutations such as those conferring resistance to antiviral drugs whose presence before therapy must be considered in the design of therapeutic strategies.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Microsensor measurements of sulfate reduction and sulfide oxidation in compact microbial communities of aerobic biofilms.

The microzonation of O(2) respiration, H(2)S oxidation, and SO(4) reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 mum) with microsensors for O(2), S, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H(2)S produced from sulfate reduction was reoxidized by O(2) in a narrow reaction zone, and no H(2)S escaped to the overlying water. Turnover times of H(2)S and O(2) in the reaction zone were only a few seconds owing to rapid bacterial H(2)S oxidation. Anaerobic H(2)S oxidation with NO(3) could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO(4) or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively.

Journal Article↗
PubMed1993

Thioltransferases.

A family of small molecular weight proteins with thiol-disulfide exchange activity have been discovered, widely distributed from E. coli to mammalian systems, called thioltransferases or glutaredoxins. There are no substantiated reports of thioltransferases-glutaredoxins in plants; however, partially purified dehydroascorbate reductase from peas had thiol-disulfide exchange catalytic activity using glutathione as reductant and S-sulfocysteine as thiosulfate cosubstrate (unpublished data). Thus, this class of proteins is universally distributed. Based on mutagenesis studies, a sequence of Cys-Pro-Tyr(Phe)-Cys- followed by Arg-Lys- or Lys alone is critical for both the thiol-disulfide exchange reaction and the dehydroascorbate reductase activity. The dithiol-disulfide loop represented by this structure is unique since the cystine closer to the N-terminus has a highly acidic thiol pKa (3.8 as determined for the pig liver enzyme) that contributes to the protein's high S- nucleophilicity. Compared with the microbial enzyme, the mammalian thioltransferases (glutaredoxins) are extended at both N and C termini by 10-12 amino acid residues, including a second pair of cysteines toward the C-terminus with no known special function. Yeast thioltransferase is more like mammalian enzymes in length (106 amino acids) but more like E. coli glutaredoxin in being unblocked at the N-terminus and having only one set of cysteines; that is, at the active center. The three mammalian enzymes, for which sequences are available, are blocked at the N-terminus by an acetyl group linked to alanine with no known special function other than possibly to impart greater cellular turnover stability. A report of carbohydrate (8.6%) content in rat liver thioltransferase has not been verified by more sensitive methods of carbohydrate analysis, nor has carbohydrate been identified in samples of purified glutaredoxin from any source. Thiol transferase and glutaredoxin are two names for the same protein based on similarity of amino acid sequence, immunochemical cross-reactivity, and other enzyme properties. The inability of thioltransferase from some mammalian sources to act as an electron carrier in ribonucleotide reductase systems, whether homologous or heterologous in origin, remains to be explained in future studies.

Amino Acid Sequence↗
PubMed1996

Forage source alters nutrient supply to the intestine without influencing milk yield.

Eight Holstein cows in early lactation and fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design experiment to determine the influence of forage source on microbial digestion in the rumen and nutrient supply to the intestine and to determine relationships between DMI, ruminal fill, and NDF content of silage. Cows were fed a TMR formulated to contain a 50:50 concentrate:forage ratio. A significant negative correlation was found between dietary NDF concentration (range 32.2 to 37.9%) and DMI (16.7 to 19.6 kg/d). In addition to forage NDF concentration, the lower DMI of cows fed oat or triticale silage (16.7 and 17.2 kg/d, respectively) relative to that of cows fed barley or alfalfa silage (18.6 and 19.6 kg/d, respectively) might reflect a lower true rate of NDF digestion (range 2.39 to 4.09%/h), higher ruminal turnover time (12.9 to 17.1 h), and lower rate of NDF intake (3.31 to 3.96%/h). However, differences in ruminal bacterial yield, ruminal metabolites, and nutrient supply to the intestine associated with different silages had no major effect on dairy cow performance. We concluded that the dairy cow can maintain similar milk yield despite marked differences in the type of end products arising from carbohydrate and protein digestion.

Animal Feed↗
PubMed1982

Effects of cold exposure on feed protein degradation, microbial protein synthesis and transfer of plasma urea to the rumen of sheep.

1. Three diets of barley-canola-seed (Brassica campestris), lucerne (Medicago sativa) or chopped brome-grass (Bromus inermis) were given at intervals of 3 h to closely-shorn Suffolk wethers held at a temperature of 1-5 degree (cold) or 22-24 degree (warm). Apparent digestibility of organic matter (OM) and nitrogen was reduced by 0.08-0.05 and 0.04 units respectively for lucerne and brome-grass diets given to cold-exposed sheep, but no treatment effects on digestibility were observed for the barley-CSM diet. Measurements achieved using infusion of the digesta markers 58Co-EDTA and 103Ru-phenanthroline (103Ru-P) showed that cold exposure depressed apparent OM digestion in the stomach and intestines by 33 and 42 g/d for the lucerne diet, and 13 and 35 g/d for the brome-grass diet respectively. 2. The turnover time (h) of the 103Ru-P marker in the rumen of warm sheep was 38.9 for barley-CSM, 18.4 for lucerne, and 15.6 for brome-grass. In cold-exposed sheep, 103Ru-P turnover time (h) tended to be reduced to 32.3, 12.3 and 15.3 for the three diets, respectively. OM fermentation in the stomach was highly related to 103RU-P turnover time for lucerne and brome-grass diets. 3. Cold exposure increased the escape of dietary N from the abomasum by 0.04 and 0.09 of dietary N intake for sheep given lucerne and brome-grass diets respectively. Dietary N degradation was closely related to 103Ru-P turnover time for lucerne, and to the proportion of large particles in rumen digesta for the brome-grass diet. Estimates of feed N degradation made by use of information on the rate of fermentation of the diet in nylon bags and 103Ru-P turnover time were consistently lower than those observed in vivo for barley-CSM and lucerne diets. Intestinal digestibility of non-ammonia N was not significantly changed by cold exposure. 4. Transfer of urea from plasma to the rumen was 1.4-2.5 g N/d for the barley-CSM and lucerne diets, but the value for brome-grass was 4.5-4.9 g N/d. Cold exposure did not affect urea transfer. The production of ammonia from feed and endogenous protein was approximately 0.66 and 0.47 g N/g N intake of barley-CSM and lucerne diets, with no effect of cold exposure. Cold exposure reduced the value from 0.57 to 0.38 for brome-grass. 5. The results are compared with those obtained previously with pelleted hay, and the importance of large particle breakdown in the prediction of OM and N fermentation using nylon bags is discussed.

Animal Feed↗
PubMed1981

The role of intracellular lysosomal enzymes in the autocellular-surveillance of unhydroxylated collagens in dermal and gingival fibroblasts.

The turnover of unhydroxylated collagen was investigated in dermal and gingival fibroblasts derived from C57Bl/6J mice. Unhydroxylated collagen molecules were fostered by the inhibition of prolyl- and lysyl-hydroxylase by the addition of alpha, alpha' dipyridyl. Turnover of collagens was determined by single isotope continuous labeling, double-isotopic labeling, the use of lysosomal pH modulators, and proteinase inhibitors. These studies reveal that the turnover of unhydroxylated collagen is an extracellular event, in spite of the susceptibility of these abnormal structural and conformational proteins to proteolysis; the synthesizing cell does not utilize intracellular lysosomal enzymes as a means of modulating the quantities of non-helical unhydroxylated collagen as an intolerable post-translational error of protein processing.

Animals↗
PubMed1998

Extracellular Enzyme Activities in Relation to Hydrodynamics in the Pomeranian Bight (Southern Baltic Sea).

Abstract The Pomeranian Bight in the southern Baltic Sea is characterized by a huge input of nutrients from the Oder river. This input shows seasonal variation. In winter, the nutrients are introduced in inorganic form. Particulate organic material is dominant in the growth season (summer/autumn). From 1993 to 1996, extracellular enzyme activities (alkaline phosphatase, peptidase, alpha-, beta-glucosidase, and chitinase) were investigated to describe microbial reaction to the input of organic material and the modification of introduced material. The distribution patterns of extracellular enzyme activities in salinity gradients were studied, in response to the nutrient load. These activities were distinctly lower in winter than in summer and autumn. A close relationship to other biological parameters (Chl a, POC, PON) was observed during the growth season, but not in winter. Changes in peptidase and phosphatase activities between summer and autumn were also observed. The peptidase activity was 9 to 72 times higher in autumn than in summer. In contrast, the alkaline phosphatase activity was 5 to 30 times higher in summer than in autumn. The organic compound turnover rate/hydrolysis rate (To/Hr) ratio is a relative index which describes the coupling of enzymatic hydrolysis and utilization of monomers from investigated substrates (carbohydrates and proteins). In summer, after dilution, the raised To/Hr quotients of glucose indicated limited importance for hydrolysis products in bacterial turnover. The increased demand for glucose resulted in a parallel decrease in monosaccharides. In autumn, the relationship between the turnover of glucose and amino acids and the supply of these substances by enzymatic degradation remained at the same level.

Journal Article↗
PubMed2002

Modelling of activated sludge processes with structured biomass.

Bacterial communities when subjected to feast-famine conditions as occurring in many wastewater treatment systems store substrates as reserve polymers. Including storage polymers in a description of microbial growth processes makes important the choice of kinetic relations. Presently there is no sound description for the diversion of substrate towards biomass growth or substrate storage. Based on observations with pure cultures and mixed cultures growing under dynamic conditions a model is proposed to describe such behaviour. This description is based on the observation that bacteria in order to grow fast have to induce a high level of RNA and proteins in order to allow fast growth. We assume that this protein synthesising system is only induced in the presence of external substrates. Based on this assumption a model structure is proposed and evaluated. It seems that this model can predict the turnover of PHA in the cells correctly, and describes well the overall behaviour mixed culture SBR systems. However especially the growth rate in the famine phase seems to be overestimated. The model defined here is a contribution to a further development of mechanistically based models for activated sludge processes.

Biomass↗