Mixture Of Carbon Sources Research Articles

Diamonds from the iridium-rich K-T boundary layer at Arroyo el Mimbral, Tamaulipas, Mexico

Research Article| November 01, 1997 Diamonds from the iridium-rich K-T boundary layer at Arroyo el Mimbral, Tamaulipas, Mexico R. M. Hough; R. M. Hough 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom Search for other works by this author on: GSW Google Scholar I. Gilmour; I. Gilmour 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom Search for other works by this author on: GSW Google Scholar C. T. Pillinger; C. T. Pillinger 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom Search for other works by this author on: GSW Google Scholar F. Langenhorst; F. Langenhorst 2Institut für Mineralogie, Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany Search for other works by this author on: GSW Google Scholar A. Montanari A. Montanari 3Osservatorio Geologico di Coldigioco, I-62020, Frontale di Apiro (MC), Italy4École des Mines de Paris, Boulevard Saint-Michel, 75272, Paris Cedex 06, France Search for other works by this author on: GSW Google Scholar Author and Article Information R. M. Hough 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom I. Gilmour 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom C. T. Pillinger 1Planetary Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, United Kingdom F. Langenhorst 2Institut für Mineralogie, Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany A. Montanari 3Osservatorio Geologico di Coldigioco, I-62020, Frontale di Apiro (MC), Italy4École des Mines de Paris, Boulevard Saint-Michel, 75272, Paris Cedex 06, France Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1997) 25 (11): 1019–1022. https://doi.org/10.1130/0091-7613(1997)025<1019:DFTIRK>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. M. Hough, I. Gilmour, C. T. Pillinger, F. Langenhorst, A. Montanari; Diamonds from the iridium-rich K-T boundary layer at Arroyo el Mimbral, Tamaulipas, Mexico. Geology 1997;; 25 (11): 1019–1022. doi: https://doi.org/10.1130/0091-7613(1997)025<1019:DFTIRK>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Diamonds, up to 30 µm in size, were found in the iridium-rich layer from the K-T boundary site at Arroyo El Mimbral and the spherule bed from Arroyo El Peñon, northeastern Mexico. Stepped heating experiments indicate two or more isotopically distinct diamond components with carbon isotopic compositions characteristic of a mixture of carbon sources. The diamonds' crystal form is cubic—not the hexagonal polymorph of diamond, lonsdaleite, which has been used previously to infer formation due to shock transformation of graphite. The size, crystallography, and mineralogic associations of K-T diamonds are similar to those of impact-produced diamonds from the Ries crater in Germany where both shock transformation of graphite and a mode of formation by condensation from a vapor plume have been inferred. The discovery of impact-produced diamonds in association with high Ir contents for these sediments supports their impact origin, K-T age, and the inference that their source was from the buried impact crater of Chicxulub on the Yucatan peninsula, Mexico. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Kinetics of the simultaneous utilization of sugar mixtures by Escherichia coli in continuous culture

In natural environments heterotrophic microorganisms encounter complex mixtures of carbon sources, each of which is present at a concentration of a few micrograms per liter or even less. Under such conditions no significant growth would be expected if cells utilized only one of the available carbon compounds, as suggested by the principle of diauxic growth. Indeed, there is much evidence that microbial cells utilize many carbon compounds simultaneously. Whereas the kinetics of single-substrate and diauxic growth are well understood, little is known about how microbial growth rates depend on the concentrations of several simultaneously utilized carbon sources. In this study this question was answered for carbon-limited chemostat growth of Escherichia coli fed with mixtures of up to six sugars; the sugars used were glucose, galactose, maltose, ribose, arabinose, and fructose. Independent of the mixture composition and dilution rate tested, E. coli utilized all sugars simultaneously. Compared with growth with a single sugar at a particular growth rate, the steady-state concentrations were consistently lower during simultaneous utilization of mixtures of sugars. The steady-state concentrations of particular sugars depended approximately linearly on their contributions to the total carbon consumption rate of the culture. Our experimental data demonstrate that the simultaneous utilization of mixtures of carbon sources enables heterotrophic microbes to grow relatively fast even in the presence of low environmental substrate concentrations. We propose that the observed reductions in the steady-state concentrations of individual carbon sources during simultaneous utilization of mixtures of carbon sources by heterotrophic microorganisms reflect a general kinetic principle.

AMS radiocarbon analyses from Lake Baikal, Siberia: Challanges of dating sediments from a large, oligotrophic lake

A suite of 146 new accelerator-mass spectrometer (AMS) radiocarbon ages provides the first reliable chronology for late Quaternary sediments in Lake Baikal. In this large, highly oligotrophic lake, biogenic and authigenic carbonate are absent, and plant macrofossils are extremely rare. Total organic carbon is therefore the primary material available for dating. Several problems are associated with the TOC ages. One is the mixture of carbon sources in TOC, not all of which are syndepositional in age. This problem manifests itself in apparent ages for the sediment surface that are greater than zero. However, because most of the organic carbon in Lake Baikal sediments is algal (autochthonous) in origin, this effect is limited to about 1000±500 years, which can be corrected, at least for young deposits. The other major problem with dating Lake Baikal sediments is the very low carbon contents of glacial-age deposits, which makes them extremely susceptible to contamination with modern carbon. This problem can be minimized by careful sampling and handling procedures. The ages show almost an order of magnitude difference in sediment-accumulation rates among different sedimentary environments in Lake Baikal, from about 0.04 mm/year on isolated banks such as Academician Ridge, to nearly 0.3 mm/year in the turbidite depositional areas beneath the deep basin floors, such as the Central Basin. The new AMS ages clearly indicate that the dramatic increase in diatom productivity in the lake, as evidenced by increases in biogenic silica and organic carbon, began about 13 ka, in contrast to previous estimates of 7 ka for the age of this transition. Holocene net sedimentation rates may be less than, equal to, or greater than those in the late Pleistocene, depending on the site. This variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations. The ages reported here, and the temporal and spatial variation in sedimentation rates that they imply, provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions.

Bioengineering of poly(β-hydroxyalkanoates) for advanced material applications: incorporation of cyano and nitrophenoxy side chain substituents

Novel functional poly(β-hydroxyalkanoates), PHAs, with hyperpolarizable side groups were prepared. Pseudomonas oleovorans ATCC 29347 and Pseudomonas putida KT 2442 were selected as biocatalysts. These organisms were first grown on citrate (40 mM) before polymer formation was studied in a second stage. The carbon sources in second-stage cultivations were mixtures (total of 15 mM) of octanoate (OA) with either 7.5 or 10 mM para-cyanophenoxyhexanoate (CPH), para-cyanophenoxyvalerate (CPV), para-cyanophenoxybutyrate (CPB), or para-nitrophenoxyhexanoate (NPH). For both organisms, only small deviations in the number of colony-forming units per millilitre were observed when second-stage cultivations containing only 15 mM octanoate were compared with those using mixtures of OA with either CPB, CPV, CPH, or NPH. PHA volumetric yields as a function of organism, carbon source mixture, and culture time are reported. The percent incorporations of substituted phenoxy side groups in the polymer products were determined by1H NMR spectroscopy. Pseudomonas putida formed PHAs with up to 24.2% 3-hydroxy-6-(para-cyanophenoxy)hexanoate side groups when 5 mM OA and 10 mM CPH were used. A dramatic decrease in the percent incorporation of para-cyanophenoxy (CP) by P. putida was observed when the relatively shorter CP-substituted n-alkanoate chain CPV and CPB cosubstrates were used. Use of NPH in place of CPH had deleterious effects on both polymer formation and percent incorporation of substituted phenoxy side groups in P. putida. Pseudomonas oleovorans formed PHAs with only up to ~2% CP side chains when a combination of OA and CPH was used and little to no CP side groups when a combination of OA and CPV or CPB was used. Substitution of NPH in place of CPH led to a modest increase (up to ~5%) in substituted phenoxy side groups. Thus, a new route to first-generation chiral polymer structures for nonlinear optical applications was demonstrated.Key words: Pseudomonas oleovorans, Pseudomonas putida, poly(β-hydroxyalkanoate), poly(3-hydroxy-6-para-cyanophenoxyhexanoate), poly(3-hydroxy-6-para-nitrophenoxyhexanoate), poly(β-hydroxy-para-cyanophenoxyvalerate).

Kinetics of microbial growth with mixtures of carbon sources

Several investigations have shown that during growth in carbon-limited chemostats the simultaneous utilisation of carbon substrates which usually provoke diauxie under batch conditions, i.e., 'mixed substrate growth,' is probably the rule under ecologically relevant growth conditions. In contrast, the models presently available for the description of the kinetics of microbial growth are all based on the use of single substrates. Systematic studies in chemostat culture have shown that steady-state residual concentrations of individual compounds were consistently lower during mixed substrate growth than during growth with the single substrates. This effect is clearly demonstrated for the case of Escherichia coli growing with mixtures of glucose plus galactose. The data presented indicate that the extent of reduction of steady-state residual substrate concentration is dependent on the proportions of the substrates in the mixture, the nature of substrates mixed and the regulation pattern of enzymes involved in their breakdown. If this behaviour can be shown to be typical for growth under environmental conditions, it may provide an explanation why microbes still grow relatively fast at the low substrate concentrations encountered in nature.

Comparative study on the production of guar alpha-galactosidase by Saccharomyces cerevisiae SU50B and Hansenula polymorpha 8/2 in continuous cultures

Saccharomyces cerevisiae SU50B and Hansenula polymorpha 8/2, both carrying a multicopy integrated guar alpha-galactosidase, have been cultivated in continuous cultures, using various mixtures of carbon sources and cultivation conditions. Both S. cerevisiae SU50B and H. polymorpha 8/2 are stable and produce high levels of extracellular alpha-galactosidase in continuous cultures for more than 500 h. For these expression systems the strong inducible promoter systems GAL7 and methanol oxidase, respectively, were used. The induction of alpha-galactosidase synthesis by galactose in SU50B is limited by the low galactose uptake. Apart from that, at high dilution rates, the glucose repression is substantial, and a maximal expression level of 28.6 mg of extracellular alpha-galactosidase.g (dry weight) of biomass-1 could be obtained. In H. polymorpha, the induction of alpha-galactosidase synthesis, in addition to methanol oxidase synthesis using formaldehyde, is very effective up to 42 mg of extracellular alpha-galactosidase.g (dry weight) of biomass-1. Productivities in terms of specific production rate enable a good comparison with those of other heterologous expression systems in the literature. The productivities found with S. cerevisiae SU50B and H. polymorpha, 3.25 and 5.5 mg of alpha-galactosidase.g of biomass-1.liter-1.h-1, respectively, rank among the highest reported in the literature. Enzyme production and secretion in H. polymorpha are more complex. A two-peaked optimum is found in enzyme production. No clear explanation of this phenomenon can be given.

Influence of Medium Composition on Mycelial Growth and Oxalic Acid Production in Sclerotium Rolfsii

Several fungi produce oxalic acid (OA) during growth in liquid culture (2, 8, 9). In the plant pathogenic fungus Sclerotium rolfsii Sacc. [teleomorph: Athelia rolfsii (Curzi) Tu and Kimbrough] (13), OA is a product ofthe glyoxylate bypass ofthe tricarboxylic acid cycle (7). Production of OA in plant tissues was reported to facilitate infection by the fungus and enhance disease development (1, 3, 5). In a study by Higgins (3), some factors influencing OA production by S. rolfsii in culture media were described. Maxwell and Bateman (6) investigated the effect of selected carbon sources and pH on OA production. Although S. rolfsii can utilize numerous carbon sources for growth (4), abundant mycelial growth does not insure high OA production (1, 6). The standard liquid basal salts medium (LSM) for growth of S. rolfsii contains the following: K2HP04, 0.7 g; KC1, 0.15 g; MgS04-7H20, 0.4 g; ZnS04 7H20, 12 mg; MnS04H20, 14 mg; FeCl3H20, 14 mg; thiamine HC1, 1 mg; distilled water, 1 liter (6). Dextrose (19.8 g/1) and NH4N03 (1 g/1) are added to provide the carbon and nitrogen sources, respectively. While this complete medium (C-LSM) supports good mycelial growth, OA production is negligible (6). A defined medium that would support abundant OA production without affecting mycelial growth would greatly facilitate studies on factors regulating OA production in S. rolfsii. The objective of this study was to define the constituents of such a medium. The following additions to LSM were tested: a) carbon sources (with NH4N03 as the nitrogen source)?19.8 g/1 dextrose, potato starch, citrus pectin, carboxymethylcellulose (CMC), peptone, or Na salts of succinate, citrate, and acetate; b) mixtures of carbon sources?9.9 g/1 dextrose mixed with 9.9 g/1 pectin, CMC, yeast extract, peptone, or with 20 g/1 Na succinate (0.074 m), 16.2 g/1 Na citrate (0.055 m), or citric acid-tris buffer (0.1 m, pH 6); c) inorganic nitrogen sources (with dextrose as the carbon source)?NH4N03, NH4H2P04, Ca(N03)2, (NH4)2S04, NH4C1, NaN03, KN03, and urea, all tested at a nitrogen level equivalent to that in 1 g/1 NH4N03 (12.5 mM of N); d) organic nitrogen sources?DL-asparagine, L-arginine, DL-threonine, DL-tryptophan, DL-phenylalanine, DL-leucine, L-alanine, and L-histidine, all tested at a N level of 12.5 mM; or 0.1% yeast extract; e) buffersC-LSM was buffered at pH values ranging from 2.1 to 6.9 with 0.1 m citric acidtris or at pH 5 with 12.5 mM KH2P04. Isolate 1132-8 of S. rolfsii from bentgrass was used throughout this study. Six additional isolates (1094, 1126, 2672, 2394, 2823, 3078), described in detail elsewhere (13), were grown in C-LSM to compare differences among isolates in dry weight (DW) and OA production. Each carbon and nitrogen source (in distilled water) was sterilized separately by autoclaving at 121 C for 15 min or by passage through a 0.45 p,m Millipore filter before mixing aseptically with cooled, autoclaved, double-strength LSM. The pH was adjusted to 5.7-5.8 with sterile 1 n NaOH or HC1. The media were dispensed in 30 ml aliquots into 125 ml Erlenmeyer flasks. Each flask was in-

Catabolite Effects On Enzyme Induction And Substrate Utilization In Rhizobium leguminosarum

The catabolism of l-histidine and p-hydroxybenzoate in Rhizobium leguminosarum 3841 is inducible. Glucose or succinate have relatively little effect on the induction of histidase whereas they produce about 50% repression of the p-hydroxybenzoate catabolic system. When grown in the presence of a mixture of carbon sources, e.g. glucose plus histidine, or succinate plus p-hydroxybenzoate, the cells co-utilize both substrates. However, consumption of histidine and p-hydroxybenzoate (which support slower growth rates than glucose or succinate) is substantially reduced in comparison with that of glucose or succinate.