High-Resolution Denitrification Kinetics in Pasture Soils Link N2O Emissions to pH,and Denitrification to C Mineralization

Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N₂O and N₂. It is known that N₂O reduction to N₂ is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N₂O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N₂O production index (IN₂O) and N₂O/(N₂O+N₂) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N₂O+N₂ μmol N/h/vial) were significantly associated with C mineralization (CO₂ μmol/h/vial) measured both under oxic (r² = 0.62, p = 0.0015) and anoxic (r² = 0.89, p<0.0001) conditions.     

Genetic Analysis of Diaminopimelic Acid- and Lysine-Requiring Mutants of Escherichia coli

Several diaminopimelic acid (DAP)- and lysine-requiring mutants of Escherichia coli were isolated and studied by genetic, physiological, and biochemical means. The genes concerned with DAP-lysine synthesis map at several different sites on the E. coli chromosome and, therefore, do not constitute a single operon. Three separate loci affecting DAP synthesis are located in the 0 to 2.5 min region of the genetic map. The order of the loci in this region is thr-dapB-pyrA-ara-leu-pan-dapC-tonA-dapD. Two additional DAP genes map in the region between min 47 and 48, with the gene order being gua-dapA-dapE-ctr. The lys locus at min 55 determines the synthesis of the enzyme DAP decarboxylase, which catalyzes the conversion of DAP into lysine. The order of the genes in this region is serA-lysA-thyA.     

Factors affecting acceptability of long-acting contraceptive injections in a rural Egyptian community

This study was carried out in 4 adjacent villages in Lower Eghypt with a combined population of 24,000. A team of social workers and physicians worked together to introduce the injectable contraceptive depomedroxyprogesterone acetate as a post-partum long-acting contraceptive to the community leaders and the villagers at several meetings and individual home visits. Post-partum women who agreed to use the drug were defined as acceptors (591) and those who did not were defined as rejectors (715). The incidence of polygamy was higher among the rejectors, and rejectors' husbands had more children from their other wives. Acceptors had more previous pregnancies and children of both sexes than rejectors. The interval between the last 2 pregnancies was shorter among the rejectors. A greater % of acceptors had previously used another contraceptive. The commonest reasons for rejection were desire for further pregnancy (69%), health problems (11%), and desire for another method of contraception (8%). Religious factors figured in only 3% of cases.     

Transposition studies of mini-Mu plasmids constructed from the chemically synthesized ends of bacteriophage Mu

We describe below the chemical synthesis of the right and left ends of bacteriophage Mu and characterize the activity of these synthetic ends in mini-Mu transposition. Mini-Mu plasmids were constructed which carry the synthetic Mu ends together with the Mu A and B genes under control of the bacteriophage λ p_L promoter. Derepression of p_L leads to a high frequency of mini-Mu transposition (5.6 × 10⁻²) which is dependent on the presence of the Mu ends and the Mu A and B proteins. Five deletion mutants in the Mu ends were tested in the mini-Mu transposition system and their effects on transposition are described.     

Predominant end-products of prophage Mu DNA transposition during the lytic cycle are replicon fusions

The structure of l-arabinose-binding protein (M_r 33, 100), an essential component of the osmotic shock-sensitive, high-affinity l-arabinose transport system in Escherichia coli, has been determined at 2.4 Å resolution. The phases were solved by the method of multiple isomorphous replacement, using four derivatives, p-chloromercuribenzenesulfonate and CdI₂ (data to 2.4 Å resolution), and p-chloromercurinitrophenol and (NH₄)₂PtCl₄ to 3.5 Å resolution. A final mean figure of merit of 0.65 was obtained for 9628 reflections.With the aid of the amino acid sequence determined by Hogg &; Hermodson (1977), a complete model of the protein molecule has been determined using initially an optical comparator. The entire model was subsequently examined in detail using a computer graphic system.The protein molecule is ellipsoidal (axial ratio of 2:1), and consists of two globular domains (designated P and Q). Each domain is made from two separate polypeptide chain segments. Despite the discontinuity in the folding, the arrangements of the secondary structure in the two domains are very similar. Both domains contain a six-stranded parallel β-sheet (with the exception of the sixth anti-parallel strand in the Q domain) flanked by two α-helices on either side. The packing topology is α/β. A C-terminal helix is shared by both domains.The two domains show significant conformational similarity but lack sequence homology. A comparison of the two domains revealed that of the 139 α-carbons in the P domain and 152 in the Q domain, 92 were found to be equivalent with a root-mean-square distance of 2.6 Å.The cleft formed by the packing of the two domains is predominantly lined with hydrophilic residues. The sugar-binding site is located in this cleft.     

Hormone mediated changes in monoamine stores and regulation of enzymes of biosynthesis and metabolism in the rat adrenal gland. Influence of progesterone, estradiol, ACTH and testosterone administration

The influence of daily injections, for 7 days, of 17-hydroxyprogesterone caproate (8 mg/100 g body weight pro die), of estradiol-17 beta 17-undecylate (1.2 mg/100 g body weight pro die) of testosterone enanthate (2 mg/100 g body weight pro die) and of ACTH (4 IU/100 g body weight pro die) to male Wistar rats, weighing 200 g, were investigated. Monamine storage and regulation of enzymes phenylethanolamine N-methyl transferase (PNMT), monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) were studied in the adrenal glands. Results from testosterone treated rats were especially significant : the hormone administration decreased the stores of dopamine and norepinephrine (epinephrine precursors), stimulated PNMT and decreased metabolism of epinephrine by MAO and COMT. However, the adrenal content of epinephrine remained in the normal range. These findings suggest that uptake of epinephrine is accelerated in peripheral tissues by testosterone.     

Effects of estrogens and progesterone on the catecholaminergic activity of the adrenal medulla in female rats

Some reports in the literature allow to suspect the existence of an effect of sexual steroids on the adrenal catecholamines. To test this possibility, we have examined the catecholaminergic activity in the adrenal medulla of normal cycling rats in three phases of estrous cycle and of ovariectomized (OVX) rats injected with pharmacological doses of estradiol (ES), 2-hydroxyestradiol (HE) and/or progesterone (P). Adrenomedullary content of norepinephrine (NE) was similar during the estrous cycle, while epinephrine (E) content was increased during diestrous. This increase was concomitant with an increased phenylethanolamine-N-methyltransferase (PNMT) activity. Moreover, the monoamine oxidase (MAO) activity was significantly increased during proestrous, while the catechol-O-methyltransferase (COMT) activity was significantly decreased during estrous. In addition to these observations, ovariectomy caused a significant reduction of the E/NE ratio and of COMT and MAO activities. Administration of ES to OVX rats increased the E content, the E/NE ratio and the COMT activity as compared to vehicle-treated OVX rats. Administration of P to OVX animals led also to a significant increase of the E/NE ratio and of the COMT activity but not of the E content, while the administration of this steroid to OVX rats previously treated with ES only increased the COMT activity. Finally, administration of HE caused non-significant changes in NE and E contents and in MAO, COMT and PNMT activities. We can conclude that sexual steroids seem to be able to modify the catecholamine metabolism in the adrenal medulla and, hence, they could alter the ability of this gland to store and release these amines.     

Likelihood based population viability analysis in the presence of observation error

Population viability analysis (PVA) entails calculation of extinction risk, as defined by various extinction metrics, for a study population. These calculations strongly depend on the form of the population growth model and inclusion of demographic and/or environmental stochasticity. Form of the model and its parameters are determined based on observed population time series data. A typical population time series, consisting of estimated population sizes, inevitably has some observation error and likely has missing observations. In this paper, we present a likelihood based PVA in the presence of observation error and missing data. We illustrate the importance of incorporation of observation error in PVA by reanalyzing the population time series of song sparrow Melospiza melodia on Mandarte Island, British Columbia, Canada from 1975–1998. Using Akaike information criterion we show that model with observation error fits the data better than the one without observation error. The extinction risks predicted by with and without observation error models are quite different. Further analysis of possible causes for observation error revealed that some component of the observation error might be due to unreported dispersal. A complete analysis of such data, thus, would require explicit spatial models and data on dispersal along with observation error. Our conclusions are, therefore, two‐fold: 1) observation errors in PVA matter and 2) integrating these errors in PVA is not always enough and can still lead to important biases in parameter estimates if other processes such as dispersal are ignored.