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11.
Methane monooxygenase mutants of Methylosinus trichosporium constructed by marker-exchange mutagenesis 总被引:1,自引:0,他引:1
Abstract Methylosinus trichosporium OB3b synthesizes a soluble cytoplasmic methane monooxygenase when grown in copper-depleted medium and a membrane-bound particulate methane monooxygenase under copper-replete conditions. The genes encoding the hydroxylase component of soluble methane monooxygenase, carried on a plasmid in Escherichia coli , were insertionally inactivated using a kanamycin cassette and transferred back into M. trichosporium by conjugation. Marker-exchange mutagenesis, via a double homologous recombination event, yielded a soluble methane monooxygenase-negative mutant which grew only on methane using the particulate methane monooxygenase during copper-replete growth conditions, thus proving that the two methane oxidation systems in this methanotroph are genetically distinct. 相似文献
12.
Radiolabeled surface proteins of adult Schistosoma mansoni were prepared by in vitro labeling of whole worms, and by labeling freeze-thaw surface membrane extracts. Incorporation of 125I into surface proteins was attempted using the lactoperoxidase, chloramine-T, iodosulfanilic acid, and Bolton-Hunter methods. Radiolabeling of whole worms with lactoperoxidase, chloramine-T and iodosulfanilic acid yielded a single protein peak (mol wt greater than 100,000) on SDS-PAGE, and showed considerable incorporation of label in the lipid fraction. Bolton-Hunter labeling of whole worms yielded four major peaks with molecular weights of 100,000, 60,000, 30,000 and 21,000, and minor peaks with molecular weights of 26,000, 36,000, 43,000, 68,000 and 78,000; three of the four major peaks corresponded to prominent bands in Coomassie blue-stained gels. Although carbohydrate-labeling techniques were not successful, a single carbohydrate band, molecular weight greater than 100,000, was detected was PAS staining. Radiolabeling of freeze-thaw extracts yielded results similar to those obtained with whole worms. Electron microscopy revealed the tegument to be left intact and undamaged after labeling with the Bolton-Hunter reagent. 相似文献
13.
Biological characterization of Trichinella isolates from various host species and geographical regions. 总被引:4,自引:0,他引:4
Forty isolates of Trichinella collected from 5 continents were compared for 7 biological characters: newborn larvae produced per female worm cultured in vitro at the seventh, eighth, and ninth day postinfection, host muscle nurse cell development time, reproductive capacity index in rats and chickens, and resistance of muscle larvae to freezing. The isolates also were compared by analyses of an environmental character of the location from which they were isolated: the isotherms for January and July. By factorial analysis of correspondence of the biological and environmental data, the 40 isolates were grouped into 8 gene pools (T1-T8). The environmental temperature-related distribution was more evident for the sylvatic isolates (T2, T3, T5, T6, T7, T8), than for T1, which was isolated from domestic pigs, and for T4, a bird-adapted, nonencapsulating genetic type. The 8 biological groups correlated closely with the 8 gene pools previously identified on the basis of allozyme analysis. These results support the concept that the genus Trichinella is composed of at least 5 distinct gene pools or sibling species: Trichinella spiralis sensu stricto (T1), Trichinella nativa (T2), Trichinella sp. (T3), Trichinella pseudospiralis (T4), and Trichinella nelsoni (T7), and 3 other groups of uncertain taxonomic status (i.e., T5, T6, and T8). 相似文献
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A radiometric method for the detection of Salmonella in foods has been developed which is based on Salmonella poly H agglutinating serum preventing Salmonella from producing 14CO2 from [14C]dulcitol. The method will detect the presence or absence of Salmonella in a product within 30 h compared to 4 to 5 days by routine culture methods. The method has been evaluated against a routine culture method using 58 samples of food. The overall agreement was 91%. Five samples negative for Salmonella by the routine method were positive by the radiometric method. These may have been false positives. However, the routine method may have failed to detect Salmonella due to the presence of large numbers of lactose-fermenting bacteria which hindered isolation of Salmonella colonies on the selective agar plates. 相似文献
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Joanna L Dixon Stephanie Sargeant Philip D Nightingale J Colin Murrell 《The ISME journal》2013,7(3):568-580
Methanol biogeochemistry and its importance as a carbon source in seawater is relatively unexplored. We report the first microbial methanol carbon assimilation rates (k) in productive coastal upwelling waters of up to 0.117±0.002 d−1 (∼10 nmol l−1 d−1). On average, coastal upwelling waters were 11 times greater than open ocean northern temperate (NT) waters, eight times greater than gyre waters and four times greater than equatorial upwelling (EU) waters; suggesting that all upwelling waters upon reaching the surface (⩽20 m), contain a microbial population that uses a relatively high amount of carbon (0.3–10 nmol l−1 d−1), derived from methanol, to support their growth. In open ocean Atlantic regions, microbial uptake of methanol into biomass was significantly lower, ranging between 0.04–0.68 nmol l−1 d−1. Microbes in the Mauritanian coastal upwelling used up to 57% of the total methanol for assimilation of the carbon into cells, compared with an average of 12% in the EU, and 1% in NT and gyre waters. Several methylotrophic bacterial species were identified from open ocean Atlantic waters using PCR amplification of mxaF encoding methanol dehydrogenase, the key enzyme in bacterial methanol oxidation. These included Methylophaga sp., Burkholderiales sp., Methylococcaceae sp., Ancylobacter aquaticus, Paracoccus denitrificans, Methylophilus methylotrophus, Methylobacterium oryzae, Hyphomicrobium sp. and Methylosulfonomonas methylovora. Statistically significant correlations for upwelling waters between methanol uptake into cells and both chlorophyll a concentrations and methanol oxidation rates suggest that remotely sensed chlorophyll a images, in these productive areas, could be used to derive total methanol biological loss rates, a useful tool for atmospheric and marine climatically active gas modellers, and air–sea exchange scientists. 相似文献
18.
Philip N Ainslie Alice Barach Kevin J Cummings Carissa Murrell Mike Hamlin John Hellemans 《Journal of applied physiology》2007,102(5):1953-1961
We tested the hypothesis that intermittent hypoxia (IH) and/or continuous hypoxia (CH) would enhance the ventilatory response to acute hypoxia (HVR), thereby altering blood pressure (BP) and cerebral perfusion. Seven healthy volunteers were randomly selected to complete 10-12 days of IH (5-min hypoxia to 5-min normoxia repeated for 90 min) before ascending to mild CH (1,560 m) for 12 days. Seven other volunteers did not receive any IH before ascending to CH for the same 12 days. Before the IH and CH, following 12 days of CH and 12-13 days post-CH exposure, all subjects underwent a 20-min acute exposure to poikilocapnic hypoxia (inspired fraction of O(2), 0.12) in which ventilation, end-tidal gases, arterial O(2) saturation, BP, and middle cerebral artery blood flow velocity (MCAV) were measured continuously. Following the IH and CH exposures, the peak HVR was elevated and was related to the increase in BP (r = 0.66 to r = 0.88, respectively; P < 0.05) and to a reciprocal decrease in MCAV (r = 0.73 to r = 0.80 vs. preexposures; P < 0.05) during the hypoxic test. Following both IH and CH exposures, HVR, BP, and MCAV sensitivity to hypoxia were elevated compared with preexposure, with no between-group differences following the IH and/or CH conditions, or persistent effects following 12 days of sea level exposure. Our findings indicate that IH and/or mild CH can equally enhance the HVR, which, by either direct or indirect mechanisms, facilitates alterations in BP and MCAV. 相似文献
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Economic losses caused by foodborne parasitic diseases 总被引:3,自引:0,他引:3
Fragmentary data indicate that zoonotic parasites cause human illnesses with medical costs and productivity and disability losses totalling billions of dollars annually. Food is an important vehicle for some of these parasitic diseases. The cost to public health is not reflected in the priorities given to these parasitic diseases in either research or public health planning. In this article, Tanya Roberts, Darwin Murrell and Suzanne Marks discuss the cost of toxoplasmosis, taeniasis, cysticercosis, trichinellosis and other foodborne parasitic diseases. 相似文献