Transgenic plants for tropical regions: some considerations about their development and their transfer to the small farmer.
(9/2707)
Biotechnological applications, especially transgenic plants, probably hold the most promise in augmenting agricultural production in the first decades of the next millennium. However, the application of these technologies to the agriculture of tropical regions where the largest areas of low productivity are located, and where they are most needed, remains a major challenge. In this paper, some of the important issues that need to be considered to ensure that plant biotechnology is effectively transferred to the developing world are discussed. (+info)
Use of a field portable X-Ray fluorescence analyzer to determine the concentration of lead and other metals in soil samples.
(10/2707)
Field portable methods are often needed in risk characterization, assessment and management to rapidly determine metal concentrations in environmental samples. Examples are for determining: "hot spots" of soil contamination, whether dust wipe lead levels meet housing occupancy standards, and worker respiratory protection levels. For over 30 years portable X-Ray Fluorescence (XRF) analyzers have been available for the in situ, non-destructive, measurement of lead in paint. Recent advances made possible their use for analysis of airborne dust filter samples, soil, and dust wipes. Research at the University of Cincinnati with the NITON 700 Series XRF instrument (40 millicurie Cadmium 109 source, L X-Rays) demonstrated its proficiency on air sample filters (NIOSH Method No. 7702, "Lead by Field Portable XRF; limit of detection 6 microg per sample; working range 17-1,500 microg/m3 air). Research with lead dust wipe samples from housing has also shown promising results. This XRF instrument was used in 1997 in Poland on copper smelter area soil samples with the cooperation of the Wroclaw Medical Academy and the Foundation for the Children from the Copper Basin (Legnica). Geometric mean soil lead concentrations were 200 ppm with the portable XRF, 201 ppm with laboratory-based XRF (Kevex) and 190 ppm using atomic absorption (AA). Correlations of field portable XRF and AA results were excellent for samples sieved to less than 125 micrometers with R-squared values of 0.997, 0.957, and 0.976 for lead, copper and zinc respectively. Similarly, correlations were excellent for soil sieved to less than 250 micrometers, where R-squared values were 0. 924, 0.973, and 0.937 for lead, copper and zinc, respectively. The field portable XRF instrument appears to be useful for the determination of soil pollution by these metals in industrial regions. (+info)
Method for detection and enumeration of Cryptosporidium parvum oocysts in feces, manures, and soils.
(11/2707)
Eight concentration and purification methods were evaluated to determine percentages of recovery of Cryptosporidium parvum oocysts from calf feces. The NaCl flotation method generally resulted in the highest percentages of recovery. Based on the percentages of recovery, the amounts of fecal debris in the final oocyst preparations, the relatively short processing time (<3 h), and the low expense, the NaCl flotation method was chosen for further evaluation. Extraction efficiency was evaluated by using oocyst concentrations of 25, 50, 10(2), 10(3), 10(4), and 10(5) oocysts g of bovine feces-1. The percentages of recovery ranged from 10.8% (25 oocysts g-1) to 17.0% (10(4) oocysts g-1) (r2 = 0.996). A conservative estimate of the detection limit for bovine feces is ca. 30 oocysts g of feces-1. Percentages of recovery were determined for six different types of animal feces (cow, horse, pig, sheep, deer, and chicken feces) at a single oocyst concentration (10(4) oocysts g-1). The percentages of recovery were highest for bovine feces (17. 0%) and lowest for chicken feces (3.2%). Percentages of recovery were determined for bovine manure after 3 to 7 days of storage. The percentages of recovery ranged from 1.9 to 3.5% depending on the oocyst concentration, the time of storage, and the dispersing solution. The percentages of oocyst recovery from soils were evaluated by using different flotation solutions (NaCl, cold sucrose, ZnSO4), different dispersing solutions (Triton X-100, Tween 80, Tris plus Tween 80), different dispersion techniques (magnetic stirring, sonication, blending), and different dispersion times (5, 15, and 30 min). Twenty-five-gram soil samples were used to reduce the spatial variability. The highest percentages of recovery were obtained when we used 50 mM Tris-0.5% Tween 80 as the dispersing solution, dispersion for 15 min by stirring, and saturated NaCl as the flotation solution. The percentages of oocyst recovery from freshly spiked sandy loam, silty clay loam, and clay loam soils were ca. 12 to 18, 8, and 6%, respectively. The theoretical detection limits were ca. 1 to 2 oocysts g of soil-1 depending on the soil type. The percentages of recovery without dispersant (distilled H2O or phosphate-buffered saline) were less than 0.1%, which indicated that oocysts adhere to soil particles. The percentages of recovery decreased with storage time, although the addition of dispersant (Tris-Tween 80) before storage appeared to partially prevent adhesion. These data indicate that the NaCl flotation method is suitable for routine detection and enumeration of oocysts from feces, manures, soils, or soil-manure mixtures. (+info)
Chloramphenicol inhibition of denitrifying enzyme activity in two agricultural soils.
(12/2707)
Chloramphenicol, at concentrations greater than 0.1 g/liter (0.3 mM), inhibited the denitrifying enzyme activity (DEA) of slurries of humisol and sandy loam soils by disrupting the activity of existing nitrate reductase enzymes. When the concentration of chloramphenicol was increased from 0.1 to 2.0 g/liter (6.0 mM), the rate of nitrite production from nitrate decreased by 25 to 46%. The rate of NO production from nitrate decreased by 20 to 39%, and the rate of N(2)O production from nitrate, in the presence of acetylene (DEA), decreased by 21 to 61%. The predicted values of DEA at 0 g of chloramphenicol/liter computed from linear regressions of DEA versus chloramphenicol concentration were 18 to 43% lower than DEA measurements made in the absence of chloramphenicol and within a few per cent of DEA rates measured in the presence of 0.1 g of chloramphenicol/liter. We conclude that DEA assays should be carried out with a single (0.1-g/liter) chloramphenicol concentration. Chloramphenicol at concentrations greater than 0.1 g/liter inhibits the activity of existing denitrifying enzymes and should not be used in DEA assays. (+info)
Evidence for involvement of gut-associated denitrifying bacteria in emission of nitrous oxide (N(2)O) by earthworms obtained from garden and forest soils.
(13/2707)
Earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion lacteum) obtained from nitrous oxide (N(2)O)-emitting garden soils emitted 0.14 to 0.87 nmol of N(2)O h(-1) g (fresh weight)(-1) under in vivo conditions. L. rubellus obtained from N(2)O-emitting forest soil also emitted N(2)O, which confirmed previous observations (G. R. Karsten and H. L. Drake, Appl. Environ. Microbiol. 63:1878-1882, 1997). In contrast, commercially obtained Lumbricus terrestris did not emit N(2)O; however, such worms emitted N(2)O when they were fed (i.e., preincubated in) garden soils. A. caliginosa, L. rubellus, and O. lacteum substantially increased the rates of N(2)O emission of garden soil columns and microcosms. Extrapolation of the data to in situ conditions indicated that N(2)O emission by earthworms accounted for approximately 33% of the N(2)O emitted by garden soils. In vivo emission of N(2)O by earthworms obtained from both garden and forest soils was greatly stimulated when worms were moistened with sterile solutions of nitrate or nitrite; in contrast, ammonium did not stimulate in vivo emission of N(2)O. In the presence of nitrate, acetylene increased the N(2)O emission rates of earthworms; in contrast, in the presence of nitrite, acetylene had little or no effect on emission of N(2)O. In vivo emission of N(2)O decreased by 80% when earthworms were preincubated in soil supplemented with streptomycin and tetracycline. On a fresh weight basis, the rates of N(2)O emission of dissected earthworm gut sections were substantially higher than the rates of N(2)O emission of dissected worms lacking gut sections, indicating that N(2)O production occurred in the gut rather than on the worm surface. In contrast to living earthworms and gut sections that produced N(2)O under oxic conditions (i.e., in the presence of air), fresh casts (feces) from N(2)O-emitting earthworms produced N(2)O only under anoxic conditions. Collectively, these results indicate that gut-associated denitrifying bacteria are responsible for the in vivo emission of N(2)O by earthworms and contribute to the N(2)O that is emitted from certain terrestrial ecosystems. (+info)
Oxygen-sensing reporter strain of Pseudomonas fluorescens for monitoring the distribution of low-oxygen habitats in soil.
(14/2707)
The root-colonizing bacterium Pseudomonas fluorescens CHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomal attTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 x 10(2) Pa to 2 x 10(2) Pa of O(2) by a nearly 100-fold increase in beta-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 x 10(2) Pa. This dose response closely resembles that found for E. coli promoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats. (+info)
Hydrogen profiles and localization of methanogenic activities in the highly compartmentalized hindgut of soil-feeding higher termites (Cubitermes spp.).
(15/2707)
It has been shown that the coexistence of methanogenesis and reductive acetogenesis in the hindgut of the wood-feeding termite Reticulitermes flavipes is based largely on the radial distribution of the respective microbial populations and relatively high hydrogen partial pressures in the gut lumen. Using Clark-type microelectrodes, we showed that the situation in Cubitermes orthognathus and other soil-feeding members of the subfamily Termitinae is different and much more complex. All major compartments of agarose-embedded hindguts were anoxic at the gut center, and high H(2) partial pressures (1 to 10 kPa) in the alkaline anterior region rendered the mixed segment and the third proctodeal segment (P3) significant sources of H(2). Posterior to the P3 segment, however, H(2) concentrations were generally below the detection limit (<100 Pa). All hindgut compartments turned into efficient hydrogen sinks when external H(2) was supplied, but methane was formed mainly in the P3/4a and P4b compartments, and in the latter only when H(2) or formate was added. Addition of H(2) to the gas headspace stimulated CH(4) emission of living termites, indicating that endogenous H(2) production limits methanogenesis also in vivo. At the low H(2) partial pressures in the posterior hindgut, methanogens would most likely outcompete homoacetogens for this electron donor. This might explain the apparent predominance of methanogenesis over reductive acetogenesis in the hindgut of soil-feeding termites, although the presence of homoacetogens in the anterior, highly alkaline region cannot yet be excluded. In addition, the direct contact of anterior and posterior hindgut compartments in situ permits a cross-epithelial transfer of H(2) or formate, which would not only fuel methanogenesis in these compartments, but would also create favorable microniches for reductive acetogenesis. In situ rates and spatial distribution of H(2)-dependent acetogenic activities are addressed in a companion paper (A. Tholen and A. Brune, Appl. Environ. Microbiol. 65:4497-4505, 1999). (+info)
Regulative development in a nematode embryo: a hierarchy of cell fate transformations.
(16/2707)
Cell specification during embryogenesis of the model system Caenorhabditis elegans involves a combination of inductive and autonomous mechanisms. We have begun to study the development of other nematodes to investigate how well cell-specification mechanisms are preserved among closely related species. Here we report that the embryo of the soil nematode Acrobeloides nanus expresses a so far undescribed regulative potential. When, for instance, the first somatic founder cell AB is eliminated it is replaced by its posterior neighbor EMS, which in turn is replaced by the C cell. This allows-different from C. elegans-the development of partial embryos up to hatching and sometimes to fertile adults. Thus, early somatic blastomeres in A. nanus are multipotent, each being capable of giving rise to more than one somatic founder cell. Lost germ-line cells, however, are not replaced. A model is presented, according to which in A. nanus cellular identities are assigned by specific reciprocal inhibitory cell-cell interactions absent in C. elegans. Differences and similarities in cell specification between the two species are discussed and related to different developmental strategies. (+info)