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COMPARISON OF TWO METHODS FOR EXTRACTION OF ATP FROM SOIL
No full textThe main aim of this work was to investigate previously published reports that an acidic mixture
of 0.67 M phosphoric acid, 20% dimethyl sulphoxide, 2 M urea, 20 mM EDTA, 0.75 mM adenosine and
32.5 mM Zwittergent (termed the PA reagent) extracted up to 7 times more adenosine S-triphosphate (ATP)
from soil than a reagent consisting of 0.5 M trichloroacetic acid (TCA), 0.25 M phosphate and 0.10 M
paraquat (termed the TCA reagent). Several extraction tests were performed using both fresh and air-dried
soils at different soil-to-extractant ratios. The ATP concentrations in the soil extracts were determined by
the fire-fly hlciferin-luciferase system. In 5 fresh U.K. arable soils the amounts of ATP extracted, corrected
for incomplete extraction by measurement of the recovery of an internal standard of added ATP (the spike),
ranged from 1.29 to 7.80 and from 1.01 to 5.24 nmol ATP g-’ soil, for the TCA and PA reagent,
respectively. In air-dried soils the range was from 0.35 to 1.11 and from 0.35 to 1.24 nmol ATP g-’ soil,
respectively, for the TCA and PA reagent. Except for an acid soil, the amount of native ATP extracted from
the soils by the two reagents and uncorrected for incomplete extraction was not significantly different within
soils when a 1:5 soil-to-extractant ratio was used. However, the percentage recovery of added ATP as a spike
was larger at higher soil-to-solution ratios with the TCA reagent but not with the PA reagent. The recoveries
of the spike with the TCA reagent were always lower than with PA reagent. However, soil ATP, corrected
for incomplete extraction, was always greater with the TCA reagent than with PA. The use of [14C]ATP as
a spike showed that no appreciable dephosphorylation of ATP added as the spike occurred with either
reagents. The main difference between PA and TCA reagents was that with PA a constant and high recovery
of spike ATP (ca. 90%) was obtained at all soil-to-solution ratios tested, while TCA gave higher recoveries
of spike ATP at higher soil-to-solution ratios. Paradoxically, the amounts of native ATP extracted at each
soil-to-solution ratio were generally similar between PA and TCA, although increasing with increasing
soil-to-solufon ratio. Correction for incomplete extraction of the spike with the TCA reagent gave very
similar soil ATP concentrations while this was not the case with the PA reagent. We suggest that this is the
main difference between the two reagents. We can find no evidence to support other work which suggested
that the PA reagent extracts more ATP from soil than the TCA reagent
Soil microbial biomass is triggered into activity by trace amounts of substrate
No full textThe microbial biomass in moist aerobic soils has an adenosine 5′-triphosphate (ATP) concentration of around 8-12 μmol ATP g-1 biomass C and an adenylate energy charge (AEC) of between about 0.8-0.95, both typical of micro-organisms undergoing exponential growth in vitro. In fact, only a very small fraction of the biomass can be in this condition at any time due to substrate limitations. Our hypothesis is that the microbial biomass expends energy to maintain a large ATP concentration and high AEC despite the expenditure of valuable energy reserves because this strategy offers an evolutionary advantage over one based on resting spores. Thus, by the time a spore becomes active in response to the presence of a suitable substrate, a more speculative organism may have captured it. We found that trace concentrations (i.e. μg g-1 quantities) of appropriate 'trigger solutions' of glucose, amino acids and root exudates can cause the biomass to evolve about 2- to 5-times more C as CO2 than was contained in the original 'trigger solution'. The effect (essentially a "priming effect") was mainly over with a single addition after 200 h, but the biomass could be reactivated with further additions. Addition of 'trigger solutions' to soils recently amended with cellulose produced an accelerated rate of mineralization of the cellulose until the experiment was terminated. We consider that our results describe a previously unreported response of the microbial biomass which equips it for survival in the generally substrate-poor soil environment. © 2001 Elsevier Science Ltd. All rights reserved
Epoxide rearrangements using dilithiated aminoalcohols as chiral bases
No full textDilithiated norephedrine and ephedrine have been utilised in the enantioselective rearrangement of cyclic epoxides to allylic alcohols, with dilithiated norephedrine generally giving the best enantioselectivity. Dilithiated ephedrine offered better levels of substrate conversion, but with lower enantioselectivity
The exploitation of soil organic matter reserves as an energy source by the soil microbial biomass.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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