Ascaris lumbricoides: succinate and tiglate in hemolymph

When hemolymph is taken from Ascaris lumbricoides at the time the worm is collected from pigs, it contains acetic, propionic, 2-methylbutyric, n-valeric, 2-methylvaleric, and succinic acid radicals; tiglic acid is absent.     

实验小鼠种群管理（英文）

2009年11月份在西安举行由中国实验动物学会发起的实验动物医药技术培训研讨会上,本人做了关于实验小鼠种群管理的演讲。其主题涵盖了小鼠繁殖性能的维护和基因工程种群的管理。本篇文章的目的在于强调其所涵盖的材料并为进一步研究提供参考。如若对本文所讨论的内容希望有更深刻的理解,这篇文章所引用的参考资料值得进一步的阅读。另外本文未涉及远交系小鼠的繁殖培育和基因管理,但如有需要可以联系本文作者,可推荐需阅读的材料清单。     

Tree form in a mixed dipterocarp forest in Indonesian Borneo

The form of tropical trees was studied with reference to the production structure of the component individuals of a tropical rain forest stand in Sebulu, East Kalimantan in Indonesian Borneo, since the production structure as a physical or bio-economical basis of tree form still remains obscure in tropical rain forests. The pipe model theory successfully explained the crown shapes of different trees, and its parameter, designated as specific pipe length, suggested an increase in the cost of leaf mass growth with an increase in crown size. A mathematical model consisting of exponential functions of aboveground height was applied for describing stem form, and its properties were examined through changes in its coefficients and by adopting an assumption of the geometrical similarity of individual stem form as a criterion for comparing differences in stem form among individual trees. Furthermore, the cost of buttersses was discussed using the relation between bole- and buttress weight calculated from the mathematical model.     

Isolation and characterization of a thermophilic acetotrophic strain of Methanothrix

An enrichment culture which converted acetate to methane at 60°C was obtained from a thermophilic anaerobic bioreactor. The predominant morphotype in the enrichment was a sheathed gas-vacuolated rod with marked resemblence to the mesophile Methanothrix soehngenii. This organism was isolated using vancomycin treatments and serial dilutions and was named Methanothrix sp. strain CALS-1. Strain CALS-1 grew as filaments typically 2–5 cells long, and cultures showed opalescent turbidity rather than macroscopic clumps. The cells were enclosed in a striated subunit-type sheath and there were distinct cross-walls between the cells, similar to M. soehngenii. The gas vesicles in cells were typically 70 nm in diameter and up to 0.5 m long, and were collapsed by pressures over 3 atm (ca. 300 kPa). Stationary-phase cells tended to have a higher vesicle content than did growing cells, and occasionally bands of cells were seen floating at the top of the liquid in stationary-phase cultures. Acetate was the only substrate of those tested which was used for methanogenesis by strain CALS-1, and acetate was decarboxylated by the aceticlastic reaction. The optimum temperature for growth of strain CALS-1 was near 60°C (doubling time=24–26 h), with no growth occurring at 70°C and 37°C. The optimum pH value for growth was near 6.5 in bicarbonate/CO₂ buffered medium and no growth occurred at pH 5.5 or pH 8.4. No growth was obtained below pH 7 when the medium was buffered with 20 mM phosphate. Strain CALS-1 grew in a chemically defined medium and required biotin. Sulfide concentrations over 1 mM were inhibitory to the culture, and growth was more rapid with 1 mM 2-mercaptoethane sulfonate (coenzyme M) or 1 mM titanium citrate as an accessory reductant than with 1 mM cysteine. It is likely that strain CALS-1 represents a new species in the genus Methanothrix.     

Carbonic anhydrase activity in acetate grown Methanosarcina barkeri

Cell extracts (27000xg supernatant) of acetate grown Methanosarcina barkeri were found to have carbonic anhydrase activity (0.41 U/mg protein), which was lost upon heating or incubation with proteinase K. The activity was inhibited by Diamox (apparent K _i=0.5 mM), by azide (apparent K _i=1 mM), and by cyanide (apparent K _i=0.02 mM). These and other properties indicate that the archaebacterium contains the enzyme carbonic anhydrase (EC 4.2.1.1). Evidence is presented that the protein is probably located in the cytoplasm. Methanol or H₂/CO₂ grown cells of M. barkeri showed no or only very little carbonic anhydrase activity. After transfer of these cells to acetate medium the activity was induced suggesting a function of this enzyme in acetate fermentation to CO₂ and CH₄. Interestingly, Desulfobacter postgatei and Desulfotomaculum acetoxidans, which oxidize acetate to 2 CO₂ with sulfate as electron acceptor, were also found to exhibit carbonic anhydrase activity (0.2 U/mg protein).     

Oxidation of ethanol by methanogenic bacteria

Methanogenium organophilum, a non-autotrophic methanogen able to use primary and secondary alcohols as hydrogen donors, was grown on ethanol. Per mol of methane formed, 2 mol of ethanol were oxidized to acetate. In crude extract, an NADP⁺-dependent alcohol dehydrogenase (ADH) with a pH optimum of about 10.0 catalyzed a rapid (5 mol/min·mg protein; 22°C) oxidation of ethanol to acetaldehyde; after prolonged incubation also acetate was detectable. With NAD⁺ only 2% of the activity was observed. F₄₂₀ was not reduced. The crude extract also contained F₄₂₀: NADP⁺ oxidoreductase (0.45 mol/min·mg protein) that was not active at the pH optimum of ADH. With added acetaldehyde no net reduction of various electron acceptors was measured. However, the acetaldehyde was dismutated to ethanol and acetate by the crude extract. The dismutation was stimulated by NADP⁺. These findings suggested that not only the dehydrogenation of alcohol but also of aldehyde to acid was coupled to NADP⁺ reduction. If the reaction was started with acetaldehyde, formed NADPH probably reduced excess aldehyde immediately to ethanol and in this way gave rise to the observed dismutation. Acetate thiokinase activity (0.11 mol/min·mg) but no acetate kinase or phosphotransacetylase activity was observed. It is concluded that during growth on ethanol further oxidation of acetaldehyde does not occur via acetylCoA and acetyl phosphate and hence is not associated with substrate level phosphorylation. The possibility exists that oxidation of both ethanol and acetaldehyde is catalyzed by ADH. Isolation of a Methanobacterium-like strain with ethanol showed that the ability to use primary alcohols also occurs in genera other than Methanogenium.Non-standard abbreviations ADH alcohol dehydrogenase - Ap₅ALi₃ P¹,P⁵-Di(adenosine-5-)pentaphosphate - DTE dithioerythritol (2,3-dihydroxy-1,4-dithiolbutane) - F₄₂₀ N-(N-l-lactyl--l-glutamyl)-l-glutamic acid phosphodiester of 7,8-dimethyl-8-hydroxy-5-deazariboflavin-5-phosphate - Mg. Methanogenium - OD₅₇₈ optical density at 578 nm - PIPES 1,4-piperazine-diethanesulfonic acid - TRICINE N-(2-hydroxy-1,1-bis[hydroxymethyl]methyl)-glycine - Tris 2-amino-2-hydroxy-methylpropane-1,3-diol - U unit (mol substrate/min)     

Fermentation parameters of Peptostreptococcus productus on gaseous substrates (CO,H2/CO2)

Intrinsic growth and substrate uptake parameters were obtained for Peptostreptococcus productus, strain U-1, using carbon monoxide as the limiting substrate. A modified Monod model with substrate inhibition was used for modeling. In addition, a product yield of 0.25 mol acetate/mol CO and a cell yield of 0.034 g cells/g CO were obtained. While CO was found to be the primary substrate, P. productus is able to produce acetate from CO₂ and H₂, although this substrate could not sustain growth. Yeast extract was found to also be a growth substrate. A yield of 0.017 g cell/g yeast extract and a product yield of 0.14 g acetate/g yeast extract were obtained. In the presence of acetate, the maximum specific CO uptake rate was increased by 40% compared to the maximum without acetate present. Cell replication was inhibited at acetate concentrations of 30 g/l. Methionine was found to be an essential nutrient for growth and CO uptake by P. productus. A minimum amount of a complex medium such as yeast extract (0.01%) is, however, required.     

Production and purification of Escherichia coli fimbrial antigen F165

Abstract The production of fimbrial antigen F165 by Escherichia coli strains was found to be dependent on the composition of the culture medium and was repressed in the presence of alanine or high levels of glucose, in anaerobic conditions or at growth temperatures of lower than 37°C. Optimal F165 production was found on a minimal medium containing 1% (w/v) casamino acids (MD-1). F165 antigen was isolated from bacteria by mechanical shearing, precipitated with ammonium sulfate, and purified by deoxycholate treatment and gel filtration on Superose 12. The purified fimbriae retained their native morphology as observed by electron microscopy and consisted of two separate protein subunits with apparent molecular weights of 17 500 and 19 000 on sodium dodecyl sulfate-polyacrylamide gels.     

Acetate as the main energy substrate for the sulfate-reducing bacteria in Lake Eliza (South Australia) hypersaline sediments

Abstract Simultaneous measurements of sulfate reduction and acetate oxidation using ³⁵S and ¹⁴C tracers showed that acetate was the main energy substrate for the sulfate-reducing bacteria in Lake Eliza sediments. Sulfate reduction rates calculated from acid-volatile sulfide data only, correlated with acetate oxidation at around 0.5:1. However, the rates calculated from acid-volatile plus pyrite sulfur data correlated with acetate oxidation at a ratio of around 1:1. Molybdate completely inhibited sulfate reduction but acetate oxidation was not totally inhibited. From 10 to 15% of acetate oxidation was not attributable to the sulfate-reducing bacteria. There was rapid accumulation of acetate, within the first 12 h of incubation. Acetate, propionate and butyrate accumulated in the presence of molybdate.