Evaluation of mycobacillin and versicolin as agricultural fungicides. II. Stability in soil.
(1/2707)
The effect of paddy soils on mycobacillin and versicolin was investigated. Soil inactivated mycobacillin as determined by spectral analysis and microbiological assay. Soil can inactive mycobacillin only at or above the threshold concentration (125 approximately 130 mug per 10 mg of soil), the excess being unreacted. No new peak appears in the ultraviolet spectrum (240 approximately 300 nm) while mycobacillin is inactivated. Soil is without any effect on versicolin. (+info)
Metabolism of threo-beta-methylmalate by a soil bacterium.
(2/2707)
Studies on threo-beta-methylmalate metabolism in a soil bacterium of the genus Bacillus which can utilize threo-beta-methylmalate as a sole carbon source were carried out. When DL-threo-beta-methylmalate was incubated with a cell-free extract of the bacterium, citramalate was found to be formed. Similarly, formation of threo-beta-methylmalate from DL-citramalate was confirmed. These dicarbosylic acids were identified by gas chromatography-mass spectrometry. Examination of inducibility, substrate specificity, and cofactor requirement of the enzymes involved in the reactions showed the existence of two interconversion reactions between the threo-beta-methylmalate and citramalate. One was an interconversion reaction between L-threo-beta-methylmalate and L-citramalate via mesaconate and the other was an interconversion reaction between D-threo-beta-methylmalate and D-citramalate via citraconate. These reactions were both reversible and were catalyzed by distinct and inducible enzymes. It is suggested that the two reactions participate in the catabolism of threo-beta-methylmalate. (+info)
Nematode intestinal parasites of children in rural Guinea, Africa: prevalence and relationship to geophagia.
(3/2707)
BACKGROUND: Intestinal parasitism is common among children in developing countries, but the risk factors for infection are not well characterized. METHODS: A stool examination was performed on 286 randomly selected children aged 1-18 years from three rural villages in Guinea, Africa. Information collected by questionnaire was used to examine the relationship between geophagia and infection with intestinal nematodes acquired by ingestion versus skin penetration. RESULTS: Fifty-three per cent of children were infected by at least one type of soil-transmitted nematode. Geophagia was reported by parents to occur in 57%, 53%, and 43%, of children ages 1-5, 6-10, and 11-18 years, respectively. The pattern of geophagia by age and gender of the children more closely resembled the infection pattern for the two orally acquired and soil-transmitted nematodes (Ascaris lumbricoides, Trichuris trichiura) than it did the infection pattern for the two soil-transmitted nematodes that infect by skin penetration (hookworm, Strongyloides stercoralis). CONCLUSIONS: These findings demonstrate that geophagia is an important risk factor for orally acquired nematode infections in African children. Education regarding geophagia prevention should be an integral component of any soil-transmitted parasite control programme. (+info)
Towards a kala azar risk map for Sudan: mapping the potential distribution of Phlebotomus orientalis using digital data of environmental variables.
(4/2707)
The need to define the geographical distribution of Phlebotomus orientalis results from its importance as the dominant vector of kala azar (visceral Iceishmaniasis) in Sudan. Recent epidermics of this disease in southern and eastern Sudan caused an estimated 100000 deaths and have renewed the impetus for defining the ecological boundaries of the vector. This information is an essential prerequisite to the production of a risk map for kala azar. This study uses data on the presence and absence of P. orientalis from 44 collecting sites across the central belt of Sudan. A logistic regression model was used to estimate the probability of the presence of P. orientalis at each collecting site as a function of climatic and environmental variables (rainfall; temperature; altitude; soil type and the satellite-derived environmental proxies - Normalized Difference Vegetation Index and Land Surface Temperature). The logistic regression model indicates mean annual maximum daily temperature and soil type as the most important ecological determinants of P. orientalis distribution. An initial risk map was created in a raster-based geographical information system which delineates the area where P. orientalis may occur. This map was then refined using a mask layer indicating the known rainfall-based boundaries of the distribution of Acacia-Balanites woodland - a woodland type known to be associated with the distribution of this vector. The predictive performance of the risk map is discussed. (+info)
Use of a sentinel system for field measurements of Cryptosporidium parvum oocyst inactivation in soil and animal waste.
(5/2707)
A small-volume sentinel chamber was developed to assess the effects of environmental stresses on survival of sucrose-Percoll-purified Cryptosporidium parvum oocysts in soil and animal wastes. Chambers were tested for their ability to equilibrate with external chemical and moisture conditions. Sentinel oocysts were then exposed to stresses of the external environment that affected their viability (potential infectivity), as indicated by results of a dye permeability assay. Preliminary laboratory experiments indicated that temperatures between 35 and 50 degrees C and decreases in soil water potential (-0.003 to -3.20 MPa) increased oocyst inactivation rates. The effects of two common animal waste management practices on oocyst survival were investigated on three dairy farms in Delaware County, N.Y., within the New York City watershed: (i) piling wastes from dairy youngstock (including neonatal calves) and (ii) spreading wastes as a soil amendment on an agricultural field. Sentinel containers filled with air-dried and sieved (2-mm mesh) youngstock waste or field soil were wetted and inoculated with 2 million oocysts in an aqueous suspension and then placed in waste piles on two different farms and in soil within a cropped field on one farm. Controls consisted of purified oocysts in either phosphate-buffered saline or distilled water contained in sealed microcentrifuge tubes. Two microdata loggers recorded the ambient temperature at each field site. Sentinel experiments were conducted during the fall and winter (1996 to 1997) and winter (1998). Sentinel containers and controls were removed at 2- to 4-week intervals, and oocysts were extracted and tested by the dye permeability assay. The proportions of potentially infective oocysts exposed to the soil and waste pile material decreased more rapidly than their counterpart controls exposed to buffer or water, indicating that factors other than temperature affected oocyst inactivation in the waste piles and soil. The effect of soil freeze-thaw cycles was evident in the large proportion of empty sentinel oocysts. The potentially infective sentinel oocysts were reduced to <1% while the proportions in controls did not decrease below 50% potentially infective during the first field experiment. Microscopic observations of empty oocyst fragments indicated that abrasive effects of soil particles were a factor in oocyst inactivation. A similar pattern was observed in a second field experiment at the same site. (+info)
The growth of demand will limit output growth for food over the next quarter century.
(6/2707)
The rate of growth of world food demand will be much slower for 1990-2010 than it was for the prior three decades. The major factor determining the increase in food demand is population growth. Income growth has a much smaller effect. From 1960 to 1990, population growth accounted for approximately three fourths of the growth in demand or use of grain. For 1990-2010, it is anticipated that population growth will account for nearly all of the increase in world demand for grain. The rate of population growth from 1990 to 2020 is projected to be at an annual rate of 1.3% compared with 1.9% for 1960 to 1990-a decline of more than 30%. World per capita use of grain will increase very little-perhaps by 4%. The increase in grain use is projected to be 40% less than in 1960-1990. It is anticipated that real grain prices will decline during the period, although not nearly as much as the 40% decline in the previous three decades. Concern has been expressed concerning the deterioration of the quality and productivity of the world's farmland. A study for China and Indonesia indicates that there has been no significant change in the productive capacity of the land over the past 50 years. Contrary to numerous claims, the depth of the topsoil has not changed, indicating that erosion has had little or no impact. (+info)
Ecological intensification of cereal production systems: yield potential, soil quality, and precision agriculture.
(7/2707)
Wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) provide about two-thirds of all energy in human diets, and four major cropping systems in which these cereals are grown represent the foundation of human food supply. Yield per unit time and land has increased markedly during the past 30 years in these systems, a result of intensified crop management involving improved germplasm, greater inputs of fertilizer, production of two or more crops per year on the same piece of land, and irrigation. Meeting future food demand while minimizing expansion of cultivated area primarily will depend on continued intensification of these same four systems. The manner in which further intensification is achieved, however, will differ markedly from the past because the exploitable gap between average farm yields and genetic yield potential is closing. At present, the rate of increase in yield potential is much less than the expected increase in demand. Hence, average farm yields must reach 70-80% of the yield potential ceiling within 30 years in each of these major cereal systems. Achieving consistent production at these high levels without causing environmental damage requires improvements in soil quality and precise management of all production factors in time and space. The scope of the scientific challenge related to these objectives is discussed. It is concluded that major scientific breakthroughs must occur in basic plant physiology, ecophysiology, agroecology, and soil science to achieve the ecological intensification that is needed to meet the expected increase in food demand. (+info)
Use of plant roots for phytoremediation and molecular farming.
(8/2707)
Alternative agriculture, which expands the uses of plants well beyond food and fiber, is beginning to change plant biology. Two plant-based biotechnologies were recently developed that take advantage of the ability of plant roots to absorb or secrete various substances. They are (i) phytoextraction, the use of plants to remove pollutants from the environment and (ii) rhizosecretion, a subset of molecular farming, designed to produce and secrete valuable natural products and recombinant proteins from roots. Here we discuss recent advances in these technologies and assess their potential in soil remediation, drug discovery, and molecular farming. (+info)