The in vitro excystation of Sarcocystis gigantea sporocysts     

P B McKenna  W A Charleston 《Veterinary parasitology》1990,37(3-4):207-221

Studies on the in vitro excystation of Sarcocystis gigantea sporocysts revealed that pretreatment before exposure to trypsin and bile was an essential prerequisite. However, in contrast to Sarcocystis tenella and Sarcocystis capracanis, incubation in cysteine hydrochloride under CO2 was largely unsuccessful for excysting Sarcocystis gigantea: of the pretreatments tested, only exposure to sodium hypochlorite proved effective. Excystation from sodium hypochlorite-pretreated S. gigantea sporocysts took place in trypsin and bile between temperatures of 30 and 43 degrees C and occurred rapidly at 39 degrees C. While the presence of bile or bile salts was essential for this process, that of trypsin was not, although more sporocysts excysted in its presence than in its absence. Excystation occurred in the presence of all bile types tested but not when Tween 80 was substituted for bile. The highest levels of excystation were recorded when cattle or sheep bile or sodium taurocholate were used and the lowest when chicken or pig bile were employed. Neither the concentration of sheep bile above 2.5%, nor hydrogen ion concentration (pH range 5.0-10.0) appeared to have any marked effect on the level of excystation obtained.  相似文献   

Pyruvate dehydrogenase activity is important for colonization of seeds and roots by Enterobacter cloacae     

Daniel P. Roberts  Laurie F. McKenna  Stephen Rehner 《Soil biology & biochemistry》2007,39(8):2150-2159

Enterobacter cloacae is a plant-beneficial bacterium that shows promise for suppression of damping-off of cucumber and other crops caused by Pythium ultimum. We have been using a mutational approach to determine the E. cloacae genes important in bacterial-plant and bacterial-pathogen interactions in the spermosphere and rhizosphere. E. cloacae M43 is a transposon mutant of E. cloacae 501R3 that was significantly impaired in colonization of seeds and roots of diverse crop plants. Strain M43 did not increase in population on cucumber, sunflower, and wheat seeds and was significantly reduced in growth on pea seeds relative to strain 501R3. Populations of M43 were also dramatically lower than those of strain 501R3 in cucumber, pea, sunflower, and wheat rhizosphere in 42 d experiments. Molecular characterization of M43 demonstrated that there was a single transposon insertion in the genome of this strain and that this insertion was in a region of the E. cloacae genome with a high degree of DNA sequence identity with aceF. aceF encodes the dihydrolipoamide acetyltransferase subunit of the pyruvate dehydrogenase complex (PDHC). Cell lysates from strain 501R3 grown on minimal medium plus 50 mM glycerol and 2 mM acetate contained 0.011±0.0036 U pyruvate dehydrogenase activity while cell lysates from M43 grown under identical conditions contained no detectable pyruvate dehydrogenase activity. Additionally, the nutritional use profile of M43 under aerobic and anaerobic conditions was as expected for an ace mutant. Experiments reported here strongly suggest a role for aceF and the PDHC in colonization of seeds and roots of diverse crop plants by E. cloacae.  相似文献   

A theropod dinosaur embryo and the affinities of the flaming cliffs dinosaur eggs     

Norell MA  Clark JM  Demberelyin D  Rhinchen B  Chiappe LM  Davidson AR  McKenna MC  Altangerel P  Novacek MJ 《Science (New York, N.Y.)》1994,266(5186):779-782

An embryonic skeleton of a nonavian theropod dinosaur was found preserved in an egg from Upper Cretaceous rocks in the Gobi Desert of Mongolia. Cranial features identify the embryo as a member of Oviraptoridae. Two embryo-sized skulls of dromaeosaurids, similar to that of Velociraptor, were also recovered in the nest. The eggshell microstructure is similar to that of ratite birds and is of a type common in the Djadokhta Formation at the Flaming Cliffs (Bayn Dzak). Discovery of a nest of such eggs at the Flaming Cliffs in 1923, beneath the Oviraptor philoceratops holotype, suggests that this dinosaur may have been a brooding adult.  相似文献   

Princeton's Intellectual Trust     

Jenkins FA  Simons EL  McKenna MC  Gingerich PD 《Science (New York, N.Y.)》1985,229(4711):330

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A critical role for eosinophils in allergic airways remodeling     

Humbles AA  Lloyd CM  McMillan SJ  Friend DS  Xanthou G  McKenna EE  Ghiran S  Gerard NP  Yu C  Orkin SH  Gerard C 《Science (New York, N.Y.)》2004,305(5691):1776-1779

Features of chronic asthma include airway hyperresponsiveness, inflammatory infiltrates, and structural changes in the airways, termed remodeling. The contribution of eosinophils, cells associated with asthma and allergy, remains to be established. We show that in mice with a total ablation of the eosinophil lineage, increases in airway hyperresponsiveness and mucus secretion were similar to those observed in wild-type mice, but eosinophil-deficient mice were significantly protected from peribronchiolar collagen deposition and increases in airway smooth muscle. These data suggest that eosinophils contribute substantially to airway remodeling but are not obligatory for allergen-induced lung dysfunction, and support an important role for eosinophil-targeted therapies in chronic asthma.  相似文献   

Mutation of a degS homologue in Enterobacter cloacae decreases colonization and biological control of damping-off on cucumber     

Roberts DP  Lohrke SM  McKenna L  Lakshman DK  Kong H  Lydon J 《Phytopathology》2011,101(2):271-280

We have been using mutagenesis to determine how biocontrol bacteria such as Enterobacter cloacae 501R3 deal with complex nutritional environments found in association with plants. E. cloacae C10, a mutant of 501R3 with a transposon insertion in degS, was diminished in growth on synthetic cucumber root exudate (SRE), colonization of cucumber seed and roots, and control of damping-off of cucumber caused by Pythium ultimum. DegS, a periplasmic serine protease in the closely related bacterium Escherichia coli K12, is required for the RpoE-mediated stress response. C10 containing wild-type degS from 501R3 or from E. coli K12 on pBeloBAC11 was significantly increased in growth on SRE, colonization of cucumber roots, and control of P. ultimum relative to C10 containing pBeloBAC11 alone. C10 and 501R3 were similar in sensitivity to acidic conditions, plant-derived phenolic compounds, oxidative stress caused by hydrogen peroxide, dessication, and high osmoticum; stress conditions potentially associated with plants. This study demonstrates a role for degS in the spermosphere and rhizosphere during colonization and disease control by Enterobacter cloacae. This study implicates, for the first time, the involvement of DegS and, by extension, the RpoE-mediated stress response, in reducing stress on E. cloacae resulting from the complex nutritional environments in the spermosphere and rhizosphere.  相似文献   

Influence of lipid extraction process on the rheological characteristics, swelling power, and granule size of rice starches in excess water     

Kar A  Jacquier JC  Morgan DJ  Lyng JG  McKenna BM 《Journal of agricultural and food chemistry》2005,53(21):8259-8264

The influence of the lipid extraction process on both macroscopic and microscopic characteristics of nonwaxy rice starch gelatinization in excess water was examined. Surface lipids extraction did not change the thermodynamics of starch gelatinization but lead to a significant reduction (33%) in the enthalpy of starch-lipid complex melting at high temperature, resulting in less viscous dispersions. Internal lipid extraction using hot aqueous alcoholic solutions resulted in an irreversible increase in starch granule diameter (50% increase in D[4,3]) and a dramatic change in cooking characteristics of the starch. Instead of the bimodal swelling observed for native nonwaxy rice starch, only one broad transition in swelling, solubility, granule size, and viscosity was observed in the case of the totally defatted starch. While the total removal of lipids resulted in a slight increase in starch swelling at intermediate temperatures, the harshness of the process caused irreparable changes leading to notably lower swelling at high temperatures.  相似文献   

The survival of Sarcocystis gigantea sporocysts following exposure to various chemical and physical agents.     

P B McKenna  W A Charleston 《Veterinary parasitology》1992,45(1-2):1-16

Using in vitro excystation as a measure of viability, it was found that at 4 degrees C Sarcocystis gigantea sporocysts survived considerably better in tap water (85% excystation after 174 days) than in either 2.5% potassium dichromate (15% excystation after 174 days) or 2% sulphuric acid (0% excystation after 5 days). Although they were able to resist 48 h suspension at room temperature in most laboratory reagents and disinfectants tested, six (sulphuric acid, ammonia, methanol, ethanol, potassium hydroxide, sodium hydroxide, Medol) had substantial sporocysticidal properties. Further investigation with three of these showed that sporocyst excystation was reduced from 65% to less than 10% following contact with 2.5% sulphuric acid for 1 h or with 2% ammonia or 4% Medol for 4 h. Sporocysts were either killed or had their ability to excyst severely impaired by heating to 60 degrees C and 55 degrees C for 5 and 60 min, respectively, by exposure to ultraviolet radiation at a dose of 4000 ET, or by prolonged storage in water at 24 degrees C. Sporocysts exposed to either constant or intermittent freezing at -18 degrees C suffered a comparatively slow decline in excystation rate with time, as did those subjected to desiccation. The duration of survival of desiccated sporocysts was inversely related to relative humidity and after 245 days at 33% relative humidity and temperatures of 15 degrees C or 24 degrees C, 60% of such sporocysts excysted.  相似文献   

The seasonal occurrence of inhibited abomasal nematodes in young sheep     

P B McKenna 《New Zealand veterinary journal》1974,22(11):214-217

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The occurrence of Ostertagia crimensis and O. pinnata in New Zealand sheep     

P B McKenna  U Ozkoc 《New Zealand veterinary journal》1971,19(4):80-82

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