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1.
S. MARIN, V. SANCHIS, I. VINAS, R. CANELA AND N. MAGAN. 1995. The effect of different water activities ( a w, 0.968, 0.956, 0.944, 0.925) and temperature (25°C and 30°C) on colonization and production of fumonisin B1 (FB1) and B2 (FB2) on sterile layers of maize by Fusarium proliferatum and F. moniliforme isolates was determined over periods of 6 weeks. Generally, both F. moniliforme and F. proliferatum grew faster with increasing a w and best at 30°C. All three isolates produced more FB 1 than FB2 regardless of a w or temperature. Very little FB1 and FB2 were produced at 0.925 a w, with maximum produced at 0.956 and 0.968 a w at both temperatures tested. Most FB1 and FB2 were produced by F. moniliforme (25N), followed by F. proliferatum isolates (73N and 131N). At all a w levels and both temperatures there was an increase in FB1 and FB2 concentration with time. Statistical analyses of a w, temperature, time, two- and three-way interactions showed some significant differences between isolates and FB1 and FB2 production.  相似文献   

2.
The natural occurrence of fumonisin B1 (FB1) in Indian maize and its impact on the viability and phagocytosis of chicken peritoneal macrophages in vitro were investigated. FB1 was found to be present at the levels of 300–366 ppm in Fusarium moniliforme -infected maize grains. The infected kernels in a population of 100 ears showed normal (Gaussian) frequency distribution. FB1, extracted from the contaminated kernels, reduced the viability and phagocytic activity of macrophages. These findings imply that FB1 exposure may become a potential problem in India and may lead to decreased immune responses with consequent susceptibility of a host to infection.  相似文献   

3.
Chlamydiae are obligate intracellular bacteria that are dependent on eukaryotic host cells for ribonucleoside triphosphates. The purpose of the present study was to determine whether Chlamydia trachomatis obtains deoxyribonucleotides from the host cell. The study was aided by the finding that host and parasite DNA synthesis activity could be distinguished by their differing sensitivities to aphidicolin and norfloxacin. Results from isotope incorporation experiments indicated that any nucleobase or ribonucleoside that could serve as a precursor for host DNA synthesis could also be utilized by C. trachomatis for DNA replication. C. trachomatis utilized only those precursors which the host cell converted to the nucleotide level. Pyrimidine deoxyribonucleotides were efficient precursors for host DNA synthesis; however, they were not used by C. trachomatis. On the other hand, purine deoxyribonucleosides are rapidly catabolized by host cells, it is necessary to regulate their metabolism to determine whether they serve as direct precursors for C. trachomatis DNA synthesis. This was partially achieved by using a hypoxanthine-guanine phosphoribosyltransferase-negative cell line and using deoxycoformycin and 8-aminoguanosine as inhibitors of (deoxy)adenosine deaminase and purine nucleoside phosphorylase, respectively. The results indicated that purine deoxyribonucleosides are efficiently utilized for host cell DNA synthesis even if degradation pathways are inhibited and salvage to ribonucleotides is minimized. In sharp contrast, the purine deoxyribonucleosides were utilized by C. trachomatis as precursors for DNA synthesis only when host catabolic pathways and salvage reactions were intact. High-pressure liquid chromatographic analysis of nucleotide pools extracted from host cells pulsed with radiolabeled precursors suggests that infected cells transport and phosphorylate all deoxynucleosides as effectively as mock-infected control cultures. In aggregate, these results show that chlamydiae do not take up deoxyribonucleotides from the host cells.  相似文献   

4.
Some rumen ciliates have endosymbiotic methanogens   总被引:16,自引:0,他引:16  
Abstract Most of the small ciliate protozoa, including Dasytricha ruminantium and Entodinium spp. living in the rumen of sheep, were found to have intracellular bacteria. These bacteria were not present in digestive vacuoles. They showed characteristic coenzyme F420 autofluorescence and they were detected with a rhodamine-labelled Archaea-specific oligonucleotide probe. The measured volume percent of autofluorescing bacteria (1%) was close to the total volume of intracellular bacteria estimated from TEM stereology. Thus it is likely that all of the bacteria living in the cytoplasm of these ciliates were endosymbiotic methanogens, using H2 evolved by the host ciliate to form methane. Intracellular methanogens appear to be much more numerous than those attached to the external cell surface of ciliates.  相似文献   

5.
There is little information on the trafficking of eukaryotic lipids from a host cell to either the cytoplasmic membrane of or the vacuolar membrane surrounding intracellular pathogens. Purified Chlamydia trachomatis, an obligate intracellular bacterial parasite, contains several eukaryotic glycerophospholipids, yet attempts to demonstrate transfer of these lipids to the chlamydial cell membrane have not been successful. In this report, we demonstrate that eukaryotic glycerophospholipids are trafficked from the host cell to C. trachomatis. Phospholipid trafficking was assessed by monitoring the incorporation of radiolabelled isoleucine, a precursor of C. trachomatis specific branched-chain fatty acids, into host-derived glycerophospholipids and by monitoring the transfer of host phosphatidylserine to chlamydiae and its subsequent decarboxylation to form phosphatidylethanolamine. Phospholipid trafficking to chlamydiae was unaffected by brefeldin A, an inhibitor of Golgi function. Furthermore, no changes in trafficking were observed when C. trachomatis was grown in a mutant cell line with a nonfunctional, nonspecific phospholipid transfer protein. Host glycerophospholipids are modified by C. trachomatis, such that a host-synthesized straight-chain fatty acid is replaced with a chlamydia-synthesized branched-chain fatty acid. We also demonstrate that despite the acquisition of host-derived phospholipids, C. trachomatis is capable of de novo synthesis of phospholipids typically synthesized by prokaryotic cells. Our results provide novel information on chlamydial phospholipid metabolism and eukaryotic cell lipid trafficking, and they increase our understanding of the evolutionary steps leading to the establishment of an intimate metabolic association between an obligate intracellular bacterial parasite and a eukaryotic host cell.  相似文献   

6.
One hypothesis for the mechanism of chlamydial interaction with its eukaryotic host cell invokes a trimolecular mechanism, whereby a Chlamydia -derived glycosaminoglycan bridges a chlamydial acceptor molecule and a host receptor enabling attachment and invasion. We show that a heparan sulphate-specific monoclonal antibody specifically binds a glycosaminoglycan localized to the surface of the chlamydial organism and effectively neutralizes infectivity of both C. trachomatis and C. pneumoniae . In addition to the ability of this antibody to neutralize infectivity, direct visualization using immunofluorescence demonstrated staining of chlamydial organisms localized to the intracellular vacuole. The chlamydial-associated glycosaminoglycan was specifically labelled with [14C]-glucosamine, and the labelled compound was immunoprecipitated and resolved by gel electrophoresis. The chlamydial-associated glycosaminoglycan is a high-molecular-weight compound similar in size to heparin or heparan sulphate and was sensitive to cleavage by heparan sulphate lyase. These data demonstrate that a glucosamine-containing sulphated polysaccharide is produced within the intracellular vacuole containing chlamydiae and is a target for antibody-mediated neutralization of infectivity.  相似文献   

7.
Autophagy, a eukaryotic cellular activity leading to the degradation of cellular components, serves as a defense mechanism against facultative intracellular bacteria as well as a growth niche for the obligate intracellular bacterium Coxiella burnetii . We here demonstrate that the obligate intracellular bacterial pathogen Chlamydia trachomatis lymphogranuloma venereum strongly induced autophagy in the middle of the chlamydial developmental cycle (24 h after infection), a time point with maximal level of chlamydial replication, but not during the early stages with low overall chlamydial metabolism (before 8 h). No autophagy induction was evident in cells exposed to heat- and UV-inactivated elementary bodies (EBs, the infectious form of Chlamydia ) or to inocula from which EBs had been removed before inoculation. Blocking chlamydial development with chloramphenicol also prevented autophagy induction in cells infected with infectious EBs. It appears that autophagy is activated primarily in response to the metabolic stress consequent to chlamydial replication. However, autophagy-defective ATG5−/− cells supported chlamydial development as efficiently as autophagy-proficient ATG5+/+ cells.  相似文献   

8.
The mechanism by which the intracellular bacterial pathogen Chlamydia trachomatis enters eukaryotic cells is poorly understood. There are conflicting reports of entry occurring by clathrin-dependent and clathrin-independent processes. We report here that C. trachomatis serovar K enters HEp-2 and HeLa 229 epithelial cells and J-774A.1 mouse macrophage/monocyte cells via caveolin-containing sphingolipid and cholesterol-enriched raft microdomains in the host cell plasma membranes. First, filipin and nystatin, drugs that specifically disrupt raft function by cholesterol chelation, each impaired entry of C. trachomatis serovar K. In control experiments, filipin did not impair entry of the same organism by an antibody-mediated opsonic process, nor did it impair entry of BSA-coated microspheres. Second, the chlamydia-containing endocytic vesicles specifically reacted with antisera against the caveolae marker protein caveolin. These vesicles are known to become the inclusions in which parasite replication occurs. They avoid fusion with lysosomes and instead traffic to the Golgi region, where they intercept Golgi-derived vesicles that recycle sphingolipids and cholesterol to the plasma membrane. We also report that late-stage C. trachomatis inclusions continue to display high levels of caveolin, which they likely acquire from the exocytic Golgi vesicles. We suggest that the atypical raft-mediated entry process may have important consequences for the host-pathogen interaction well after entry has occurred. These consequences include enabling the chlamydial vesicle to avoid acidification and fusion with lysosomes, to traffic to the Golgi region, and to intercept sphingolipid-containing vesicles from the Golgi.  相似文献   

9.
10.
Chlamydia trachomatis is an obligate intracellular bacterium that causes a variety of diseases in humans. C. trachomatis has a complex developmental cycle that depends on host cells for replication, during which gene expression is tightly regulated. Here we identify two C. trachomatis proteases that possess deubiquitinating and deneddylating activities. We have designated these proteins ChlaDub1 and ChlaDub2. The genes encoding ChlaDub1 and ChlaDub2 are present in all Chlamydia species except for Chlamydia pneumoniae, and their catalytic domains bear similarity to the catalytic domains of other eukaryotic ubiquitin-like proteases (Ulp). The C. trachomatis DUBs react with activity-based probes and hydrolyse ubiquitinated and neddylated substrates. ChlaDub1 and ChlaDub2 represent the first known bacterial DUBs that possess both deubiquitinating and deneddylating activities.  相似文献   

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