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Growing Cells (growing + cell)
Selected AbstractsFactors controlling the carbon isotope fractionation of tetra- and trichloroethene during reductive dechlorination by Sulfurospirillum ssp. and Desulfitobacterium sp. strain PCE-SFEMS MICROBIOLOGY ECOLOGY, Issue 1 2007Danuta Cichocka Abstract Carbon stable isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE) was investigated during reductive dechlorination. Growing cells of Sulfurospirillum multivorans, Sulfurospirillum halorespirans, or Desulfitobacterium sp. strain PCE-S, the respective crude extracts and the abiotic reaction with cyanocobalamin (vitamin B12) were used. Fractionation of TCE (,C=1.0132,1.0187) by S. multivorans was more than one order of magnitude higher than values previously observed for tetrachloroethene (PCE) (,C=1.00042,1.0017). Similar differences in fractionation were observed during reductive dehalogenation by the close relative S. halorespirans with ,C=1.0046,1.032 and ,C=1.0187,1.0229 for PCE and TCE respectively. TCE carbon isotope fractionation (,C=1.0150) by the purified PCE-reductive dehalogenase from S. multivorans was more than one order of magnitude higher than fractionation of PCE (,C=1.0017). Carbon isotope fractionation of TCE by Desulfitobacterium sp. strain PCE-S (,C=1.0109,1.0122) as well as during the abiotic reaction with cyanocobalamin (,C=1.0154) was in a similar range to previously reported values for fractionation by mixed microbial cultures. In contrast with previous results with PCE, no effects due to rate limitations, uptake or transport of the substrate to the reactive site could be observed during TCE dechlorination. Our results show that prior to a mechanistic interpretation of stable isotope fractionation factors it has to be carefully verified how other factors such as uptake or transport affect the isotope fractionation during degradation experiments with microbial cultures. [source] Hexavalent uranium supports growth of Anaeromyxobacter dehalogenans and Geobacter spp. with lower than predicted biomass yieldsENVIRONMENTAL MICROBIOLOGY, Issue 11 2007Robert A. Sanford Summary The stimulation of bacteria capable of reducing soluble U(VI) to sparingly soluble U(IV) is a promising approach for containing U(VI) plumes. Anaeromyxobacter dehalogenans is capable of mediating this activity; however, its ability to couple U(VI) reduction to growth has not been established. Monitoring the increase in 16S rRNA gene copy numbers using quantitative real-time PCR (qPCR) in cultures provided with U(VI) as an electron acceptor demonstrated growth, and 7.7,8.6 × 106 cells were produced per ,mole of U(VI) reduced. This biomass yield was lower than predicted based on the theoretical free energy changes associated with U(VI)-to-U(IV) reduction. Lower than predicted growth yields with U(VI) as electron acceptor were also determined in cultures of Geobacter lovleyi and Geobacter sulfurreducens suggesting that U(VI) reduction is inefficient or imposes an additional cost to growing cells. These findings have implications for U(VI) bioremediation because Anaeromyxobacter spp. and Geobacter spp. contribute to radionuclide immobilization in contaminated subsurface environments. [source] Bile salts and cholesterol induce changes in the lipid cell membrane of Lactobacillus reuteriJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2003M.P. Taranto Abstract Aims: The objective of this study was to evaluate the effect of bile salts and cholesterol in the lipid profile of Lactobacillus reuteri CRL 1098 and to determine the relationship existing between these changes: the in vitro removal of cholesterol and the tolerance of the cells to acid and cold stress. Methods and Results:Lactobacillus reuteri CRL 1098 was grown in the following media: MRS (deMan Rogosa Sharpe; MC, control medium), MB (MC with bile salts), MCH (MC with sterile cholesterol) and MBCH (MC with bile salts and cholesterol). Fatty acids were determined by analytical gas,liquid chromatography, and phospholipids and glycolipids by colorimetric techniques. The cells from different culture media were subjected to cold and acid stress. The MB cultures displayed a decrease in phospholipids and a low ratio of saturated : unsaturated fatty acids. The presence of the unusual C18 : 0,10-OH and C18 : 0,10-oxo fatty acids was the prominent characteristic of the bile salts growing cells. The relative increase in glycolipids and the changes in the fatty acids profiles of the MB cells would be responsible for the cholesterol remotion. The changes induced by bile salts in the lipid profile did not improve the tolerance of L. reuteri CRL 1098 to freezing and acid stress. Conclusions: The changes in lipid profiles reported in this study would play a key role in the response of Lactobacilli to environmental stress. Significance and Impact of the Study: This work provides useful information about the effect of bile salts on the cell membrane of L. reuteri, a probiotic enterolactobacillus. The steady-state response of the cells subjected to bile stress seems to be the appropriate model for evaluating the bacterial behaviour in detergent-containing gastrointestinal tracts, where the bile salts stress would presumably be continuous. [source] pH-controlled cell release and biomass distribution of alginate-immobilized Lactococcus lactis subsp. lactisJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2001G. Klinkenberg Aims:,To investigate the growth and release of Lactococcus lactis subsp. lactis in gel beads and to affect rates of cell release by changing the growth conditions. Methods and Results:,The rate of release and the distribution of immobilized L. lactis subsp. lactis in alginate beads were studied in continuous fermentations for 48 h. A change in operating pH from 6·5 to 9·25 initially reduced the ratio of the rates of cell release to lactate production by almost a factor of 105. Compared with fermentations at pH 6·5, growth at pH 9·25 also increased the final internal bead biomass concentration by a factor of 5 and increased the final rate of lactate production by 25%. After 48 h, the ratio of the rates of cell release to lactate production was still 10 times lower than in fermentations at pH 6·5. Conclusions:,A change in the operating pH from 6·5 to 9·25 reduced rates of cell release throughout 48 h of fermentation and increased the final rates of lactate production and internal bead biomass concentration. Significance and Impact of the Study:,These data illustrate that diffusional limitations and corresponding pH gradients can be exploited in affecting the distribution of immobilized growing cells and their concomitant release. [source] Biodesulfurization of dibenzothiophene using recombinant Pseudomonas strainJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2008Lavanya Meesala Abstract BACKGROUND: The sulfur content in crude oil available from various sources ranges from 0.03 to values as high as 8.0 wt%. These high quantities of sulfur must be removed before the crude oil is processed because combustion of this oil would result in severe environmental pollution, such as acid rain. Due to high utility and operating costs, the conventional hydrodesulfurization process (HDS) is considered to be uneconomic. The biotechnological option, biodesulfurization (BDS) seems an attractive low cost, environmentally benign technology. RESULTS: This paper reports the development of a recombinant strain of bacteria designed by introducing desulfurizing, dsz genes containing plasmid pSAD 225-32, which was isolated from Rhodococcus erythropolis IGTS8 into a gram negative solvent-tolerant bacterium, Pseudomonas putida (MTCC 1194). This recombinant bacterium can desulfurize the dibenzothiophene (DBT) in the sulfur selective 4S-pathway. It has been observed that for the same concentration of DBT, the recombinant strain's growth rate is greater than that of the parent strain. Increasing the concentration of DBT resulted in an increase of lag phase as well as decreased growth rate, which shows that the bacteria is following substrate inhibition type kinetics. This genetically modified bacterium can desulfurize 73.1% of 1.2 mmol L,1 DBT (dissolved in ethanol) in 67 h of cultivation time using growing cells. CONCLUSIONS: It is concluded that further research in this area of biodesulfurization using genetically modified organisms may remove the bottlenecks presently in the way of commercialization of the BDS process. Copyright © 2007 Society of Chemical Industry [source] Pressureless Sintering and Mechanical and Biological Properties of Fluor-hydroxyapatite Composites with ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Hae-Won Kim Fluor-hydroxyapatite (FHA) fabricated by a reaction between fluorapatite (FA) and hydroxyapatite (HA) was mixed with ZrO2 to produce FHA,ZrO2 composites. When the relative amount of FA to HA increased, the decomposition of the composite was decreased gradually because of the formation of thermally stable FHA solid solutions. With such suppression of decomposition, the FHA,ZrO2 composites retained fully densified bodies. As a result, significant enhancements in mechanical properties, such as hardness, flexural strength, and fracture toughness, were achieved as the relative amount of FA to HA increased. The highest values in strength and toughness were 220 MPa and 2.5 MPa·m1/2, respectively, with FHA,40 vol% ZrO2 composites. In vitro proliferation of osteoblast-like cells (MG63) on the composites showed behavior similar to that observed on pure HA and FHA. Alkaline phosphatase (ALP) activity of the growing cells (HOS) on the composites was slightly down-regulated compared with that on pure HA and FHA at prolonged periods. [source] The CBS subdomain of inosine 5,-monophosphate dehydrogenase regulates purine nucleotide turnoverMOLECULAR MICROBIOLOGY, Issue 2 2008Maxim Pimkin Summary Inosine 5,-monophosphate dehydrogenase (IMPDH) catalyses the rate-limiting step in guanine nucleotide biosynthesis. IMPDH has an evolutionary conserved CBS subdomain of unknown function. The subdomain can be deleted without impairing the in vitro IMPDH catalytic activity and is the site for mutations associated with human retinitis pigmentosa. A guanine-prototrophic Escherichia coli strain, MP101, was constructed with the subdomain sequence deleted from the chromosomal gene for IMPDH. The ATP content was substantially elevated in MP101 whereas the GTP content was slighty reduced. The activities of IMPDH, adenylosuccinate synthetase and GMP reductase were two to threefold lower in MP101 crude extracts compared with the BW25113 wild-type strain. Guanine induced a threefold reduction in the MP101 ATP pool and a fourfold increase in the GTP pool within 10 min of addition to growing cells; this response does not result from the reduced IMPDH activity or starvation for guanylates. In vivo kinetic analysis using 14-C tracers and 33-P pulse-chasing revealed mutation-associated changes in purine nucleotide fluxes and turnover rates. We conclude that the CBS subdomain of IMPDH may coordinate the activities of the enzymes of purine nucleotide metabolism and is essential for maintaining the normal ATP and GTP pool sizes in E. coli. [source] Swimming characteristics of magnetic bacterium, Magnetospirillum sp.BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2001AMB-, implications as toxicity measurement Abstract To develop a novel toxicity measurement system using the persistent swimming property of magnetic bacteria along an externally applied magnetic field, certain characteristics of Magnetospirillum sp. AMB-1 cells were examined, including their growth pattern, motility, magnetosensitivity, swimming speed, and cell length distribution. In addition, the effect of toxic compounds on the swimming speed was assessed relative to application as a toxicity sensor. With an inoculum of 1.0 × 108 cells/mL, the cells reached the stationary phase with a concentration of about 5 × 108 cells/mL after 20 h, under both aerobic and anaerobic conditions. The distribution of the cell length did not vary significantly during the growth period, and both aerobically and anaerobically growing cells showed a similar cell length distribution. Although the cells showed similar growth patterns under both conditions, the anaerobically grown cells exhibited higher motility and magnetosensitivity. Actively growing cells under anaerobic conditions had an average swimming speed of 49 ,m/s with a standard deviation of 20 ,m/s. When the anaerobically growing cells were exposed to various concentrations of toxic compounds, such as 1-propanol and acetone, the swimming speed decreased with an increased concentration of the toxic compound. Accordingly, the relationship between swimming speed and toxicity can be used as an effective quantitative toxicity measurement; furthermore, the relative sensitivity of the proposed system was comparable to Microtox, which is commercially available. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 11,16, 2001. [source] A multiparallel bioreactor for the cultivation of mammalian cells in a 3D-ceramic matrixBIOTECHNOLOGY PROGRESS, Issue 2 2010Vicky Goralczyk Abstract For adherently growing cells, cultivation is limited by the provided growth surface. Excellent surface-to-volume ratios are found in highly porous matrices, which have to face the challenge of nutrient supply inside the matrices' caverns. Therefore, perfusion strategies are recommended which often have to deal with the need of developing an encompassing bioreactor periphery. We present a modular bioreactor system based on a porous ceramic matrix that enables the supply of cells with oxygen and nutrients by perfusion. The present version of the reactor system focuses on simple testing of various inoculation and operation modes. Moreover, it can be used to efficiently test different foam structures. Protocols are given to set-up the system together with handling procedures for long-time cultivation of a CHO cell line. Experimental results confirm vital growth of cells inside the matrices' caverns. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Understanding and Improving NADPH-Dependent Reactions by Nongrowing Escherichia coli CellsBIOTECHNOLOGY PROGRESS, Issue 2 2004Adam Z. Walton We have shown that whole Escherichia coli cells overexpressing NADPH-dependent cyclohexanone monooxygenase carry out a model Baeyer-Villiger oxidation with high volumetric productivity (0.79 g ,-caprolactone/L·h ) under nongrowing conditions (Walton, A. Z.; Stewart, J. D. Biotechnol. Prog.2002, 18, 262,268). This is approximately 20-fold higher than the space-time yield for reactions that used growing cells of the same strain. Here, we show that the intracellular stability of cyclohexanone monooxygenase and the rate of substrate transport across the cell membrane were the key limitations on the overall reaction duration and rate, respectively. Directly measuring the levels of intracellular nicotinamide cofactors under bioprocess conditions suggested that E. coli cells could support even more efficient NADPH-dependent bioconversions if a more suitable enzyme-substrate pair were identified. This was demonstrated by reducing ethyl acetoacetate with whole cells of an E. coli strain that overexpressed an NADPH-dependent, short-chain dehydrogenase from bakerapos;s yeast ( Saccharomyces cerevisiae). Under glucose-fed, nongrowing conditions, this reduction proceeded with a space-time yield of 2.0 g/L·h and a final product titer of 15.8 g/L using a biocatalyst:substrate ratio (g/g) of only 0.37. These values are significantly higher than those obtained previously. Moreover, the stoichiometry linking ketone reduction and glucose consumption (2.3 ± 0.1) suggested that the citric acid cycle supplied the bulk of the intracellular NADPH under our process conditions. This information can be used to improve the efficiency of glucose utilization even further by metabolic engineering strategies that increase carbon flux through the pentose phosphate pathway. [source] | ||||||||||||||||||||||