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1.
Isolates of Colletotrichum gloeosporioides obtained from yam‐based cropping systems in Nigeria, previously characterized on the basis of morphology, virulence and rDNA internal transcribed spacer (ITS) sequence variation were further compared for vegetative compatibility (VC). Chlorate‐resistant nitrate non‐utilizing (nit) mutants were generated from the isolates and used in complementation (heterokaryon) tests. Tests of VC between complementary mutants from different isolates indicated the presence of several genotypes within a single field, suggesting limited clonal spread. In some cases, isolates obtained from the same lesion were observed to belong to different vegetative compatibility groups (VCGs). No compatibility was observed between isolates of the highly virulent slow‐growing grey (SGG), the moderately virulent fast‐growing salmon (FGS) and the avirulent/weakly virulent fast‐growing grey (FGG) strains. Forty‐one C. gloeosporioides isolates belonged to 28 VCGs, giving a genotype diversity estimate of 0.68. This diversity confirmed the high variability of the pathogen population as revealed by previous characterization studies, however, a correlation between VCGs and isolate groupings based on morphology and virulence was not found. The finding that an isolate from weed was compatible with yam isolates indicated that transfer of important traits, such as virulence, may take place between isolates from yam and non‐yam hosts. The VCG diversity revealed by this study suggests that in addition to asexual reproduction, sexual reproduction may play an important role in the epidemiology of anthracnose on yam.  相似文献   

2.
Variation within Colletotrichum gloeosporioides, the causal agent of yam anthracnose disease, is still poorly defined and this hinders breeding for resistance. Two morphotypes of C. gloeosporioides, designated slow‐growing grey (SGG) and fast‐growing salmon (FGS), are associated with anthracnose disease of yam in Nigeria. The morphotypes are distinguishable based on colony and conidial morphology, growth rate, virulence, as well as vegetative compatibility, but molecular differentiation of SGG and FGS strains is needed to facilitate epidemiological studies. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)‐amplified small subunit (18S) rDNA fragments, and microsatellite‐primed PCR (MP‐PCR) genomic fingerprinting were employed to provide a basis for molecular differentiation of the morphotypes. DGGE analysis revealed patterns that clearly differentiated isolates of the aggressive defoliating SGG from the moderately virulent non‐defoliating FGS strains. Genetic analysis based on 52 MP‐PCR markers revealed highly significant differentiation between the SGG and FGS populations on yam (GST = 0.22; Nei's genetic identity = 0.85; θ = 0.28, P < 0.001), indicating that the SGG and FGS morphotypes represent genetically differentiated populations. The results of the molecular typing using DGGE and MP‐PCR analyses were consistent with the disease phenotype caused by the two morphotypes. Consequently, these molecular techniques might be used, at least partly, to replace time‐consuming virulence studies on yam.  相似文献   

3.
Several bacterial isolates were recovered from surface-sterilized root nodules of Arachis hypogaea L. (peanut) plants growing in soils from Córdoba, Argentina. The 16S rDNA sequences of seven fast-growing strains were obtained and the phylogenetic analysis showed that these isolates belonged to the Phylum Proteobacteria, Class Gammaproteobacteria, and included Pseudomonas spp., Enterobacter spp., and Klebsiella spp. After storage, these strains became unable to induce nodule formation in Arachis hypogaea L. plants, but they enhanced plant yield. When the isolates were co-inoculated with an infective Bradyrhizobium strain, they were even found colonizing pre-formed nodules. Analysis of symbiotic genes showed that the nifH gene was only detected for the Klebsiella-like isolates and the nodC gene could not be amplified by PCR or be detected by Southern blotting in any of the isolates. The results obtained support the idea that these isolates are opportunistic bacteria able to colonize nodules induced by rhizobia.  相似文献   

4.
Colletotrichum gloeosporioides causes anthracnose, the most severe foliar disease of field-grown water yam (Dioscorea alata). The inheritance of resistance to a moderately virulent (FGS) strain of the pathogen was investigated in crosses between tetraploid D. alata genotypes: TDa 95/00328 (resistant)×TDa 95–310 (susceptible) (cross A), and TDa 85/00257 (resistant)×TDa 92–2 (susceptible) (cross B). Segregation of F1 progeny fitted genetic ratios of 3:1, 5:1 (crosses A and B) and 7:1 (cross A) resistant:susceptible when inoculated with the FGS strain, indicating that resistance is dominantly inherited and suggesting that more than one gene controls the inheritance of resistance to this strain in the accessions studied. When parental and progeny lines of cross A were inoculated with an aggressive (SGG) strain of the pathogen, all plants expressed a susceptible phenotype, indicating strain-specific resistance in TDa 95/00328. Screening of 20 cultivars/landraces confirmed the high susceptibility of D. alata accessions to the SGG strain and revealed the presence of apparent strain non-specific resistance in TDa 85/00257. TDa 85/00257 and TDa 87/01091 which were resistant to the SGG strain, will be useful both as sources of resistance and in the development of a host differential series for D. alata. Received: 15 May 2000 / Accepted: 18 October 2000  相似文献   

5.
The aim of this study was to collect preliminary data on the carriage of pathogenic Yersinia enterocolitica in slaughtered pigs in France and to test a simplified method for detecting these strains from tonsils. From January to March 2009, 900 tonsil swabs were taken from pigs at one slaughterhouse in Brittany, France. The swabs were vortexed in 10 ml PSB broth, then 1 ml was added to 9 ml ITC broth. The media were incubated for 48 h at 25 °C. The PSB enrichment broth was streaked on CIN plates and the ITC enrichment broth on SSDC plates. In addition to the ISO 10273 method, we also streaked ITC enrichment broth on CIN plates. The plates were incubated for 24 h at 30 °C, and we then streaked a maximum of four typical colonies per plate onto a plate containing chromogenic medium (YeCM), for the isolation of pathogenic Y. enterocolitica isolates. In parallel, biochemical assays were carried out to confirm the identification of the isolates as Yersinia and to determine biotype.After passage on a YeCM plate and biochemical tests, 380 strains were confirmed to be pathogenic Y. enterocolitica. Finally, with the ISO 10273 method, 9.1% (CI95% [5.8-12.4]) of tonsil swabs and 60% (CI95% [45.4-74.6]) of the batches were positive. With the ITC-CIN method, 14.0% (CI95% [10.7-17.3]) of the tonsil swabs and 68.9% (CI95% [54.3-83.5]) of the batches were positive. Identification as pathogenic Y. enterocolitica was confirmed for 97.0% of the typical colonies obtained on the chromogenic medium, YeCM. The most prevalent biotype was biotype 4 (80.5% of the isolates), followed by biotype 3.This study demonstrates that the ITC-CIN method, followed by streaking on YeCM, may be an effective approach to the isolation of pathogenic Y. enterocolitica from tonsil swabs and the recovery of positive samples. This method is less time-consuming than the ISO 10273 method and reduces the number of biochemical tests required for the confirmation of Yersinia identification, through the use of YeCM.  相似文献   

6.
Termites encounter a diverse array of potentially useful and harmful fungi in their subterranean habitats. These vary from symbiotic to harmful species with varying levels of virulence. How these hemiedaphic insects survive in habitats with infective fungi is not well understood. Possible mediation of olfactory signals in avoiding contact with entomopathogenic fungi has been explored by a number of workers. In the present study, we initially found that Macrotermes michaelseni detected a virulent isolate of Metarhizium anisopliae from some distance and avoided direct physical contact. We hypothesized that there may be a relationship between virulence and repellency of different isolates of M. anisopliae and Beauveria bassiana to the termite. We compared these for selected isolates of the two fungi. Positive correlations between the two parameters for both sets of isolates of the fungi were obtained. The results show an interesting co-evolutionary phenomenon in which the termite's response to either M. anisopliae or B. bassiana is directly related to potential harm these fungi can inflict on the insect and that the virulent strains are more likely to be recognized from some distance and avoided.  相似文献   

7.
In a previous report (Luyo-Acero et al., 2004), we demonstrated that cytochrome b (Cyt b) gene analysis is an effective method for classifying several isolates of the genus Leishmania; hence, we have further applied this method to other Leishmania species in an effort to enhance the accuracy of the procedure and to construct a new phylogenic tree. In this study, a total of 30 Leishmania and Endotrypanum WHO reference strains, clinical isolates from our patients assigned to 28 strains (human and non-human pathogenic species) and two species of the genus Endotrypanum were analyzed. The Cyt b gene in each sample was amplified by PCR, and was then sequenced by several primers, as reported previously. The phylogenic tree was constructed based on the results obtained by the computer software MEGA v3.1 and PAUP* v4.0 Beta. The present phylogenic tree was almost identical to the traditional method of classification proposed by Lainson and Shaw (1987). However, it produces the following suggestions: (1) exclusion of L. (Leishmania) major from the L. (L.) tropica complex; (2) placement of L.tarentolae in the genus Sauroleishmania; (3) L. (L.) hertigi complex and L. (V.) equatorensis close to the genus Endotrypanum; (4) L. (L.) enrietti, defined as L. (L.) mexicana complex, placed in another position; and (5) L. (L.) turanica and L. (L.) arabica are located in an area far from human pathogenic Leishmania strains. Cyt b gene analysis is thus applicable to the analyzing phylogeny of the genus Leishmania and may be useful for separating non-human pathogenic species from human pathogenic species.  相似文献   

8.
赵建  黄建国  袁玲  时安东  杜如万  刑小军 《生态学报》2014,34(23):7093-7100
为了研发对番茄灰霉病高效、稳定、安全的生物农药,试验利用自主分离获得的寡雄腐霉菌株制备发酵液,采用盆栽试验研究寡雄腐霉发酵液对番茄生长的影响和对灰霉病的防治效果及机制,并在大田生产中验证其生防效果。结果表明,盆栽试验中,寡雄腐霉发酵液促进健康番茄植株生长,植株总生物量和根系生物量分别增加9.5%和15.4%,提高了植株叶绿素含量、根系活力及氮、磷、钾吸收量,并使带病番茄植株的发病率和病情指数分别降低57.2%和60.3%,相对防治效果达60.3%,施用寡雄腐霉发酵液对番茄叶片细胞膜具有保护性,降低丙二醛含量,提高病原性相关酶""超氧化物歧化酶、多酚氧化酶和苯丙氨酸解氨酶活性。后续田间试验中寡雄腐霉发酵液对番茄灰霉病的防治效果达71.2%。说明寡雄腐霉发酵液能有效防治番茄灰霉病,还具有促进番茄生长的作用,并且可诱导番茄植株对病原菌的防御作用,应用前景广泛。  相似文献   

9.
Virulence of Trypanosoma cruzi depends on a variety of genetic and biochemical factors. It has been proposed that components of the parasites’ antioxidant system may play a key part in this process by pre-adapting the pathogen to the oxidative environment encountered during host cell invasion. Using several isolates (10 strains) belonging to the two major phylogenetic lineages (T. cruzi-I and T. cruzi-II), we investigated whether there was an association between virulence (ranging from highly aggressive to attenuated isolates at the parasitemia and histopathological level) and the antioxidant enzyme content. Antibodies raised against trypanothione synthetase (TcTS), ascorbate peroxidase (TcAPX), mitochondrial and cytosolic tryparedoxin peroxidases (TcMPX and TcCPX) and trypanothione reductase (TcTR) were used to evaluate the antioxidant enzyme levels in epimastigote and metacyclic trypomastigote forms in the T. cruzi strains. Levels of TcCPX, TcMPX and TcTS were shown to increase during differentiation from the non-infective epimastigote to the infective metacyclic trypomastigote stage in all parasite strains examined. Peroxiredoxins were found to be present at higher levels in the metacyclic infective forms of the virulent isolates compared with the attenuated strains. Additionally, an increased resistance of epimastigotes from virulent T. cruzi populations to hydrogen peroxide and peroxynitrite challenge was observed. In mouse infection models, a direct correlation was found between protein levels of TcCPX, TcMPX and TcTS, and the parasitemia elicited by the different isolates studied (Pearson’s coefficient: 0.617, 0.771, 0.499; respectively, < 0.01). No correlation with parasitemia was found for TcAPX and TcTR proteins in any of the strains analyzed. Our data support that enzymes of the parasite antioxidant armamentarium at the onset of infection represent new virulence factors involved in the establishment of disease.  相似文献   

10.
The new bacterial strain with antimycobacterial activity has been isolated from the midgut of Dendrobaena veneta (Annelida). Biochemical and molecular characterization of isolates from 18 individuals identified all as Raoultella ornithinolytica genus with 99% similarity. The bacterium is a possible symbiont of the earthworm D. veneta. The isolated microorganism has shown the activity against four strains of fast-growing mycobacteria: Mycobacterium butiricum, Mycobacterium jucho, Mycobacterium smegmatis and Mycobacterium phlei. The multiplication of the gut bacterium on plates with Sauton medium containing mycobacteria has caused a lytic effect. After the incubation of the cell free extract prepared from the gut bacterium with four strains of mycobacteria in liquid Sauton medium, the cells of all tested strains were deformed and divided to small oval forms and sometimes created long filaments. The effect was observed by the use of light, transmission and scanning microscopy. Viability of all examined species of mycobacteria was significantly decreased. The antimycobacterial effect was probably the result of the antibiotic action produced by the gut bacterium of the earthworm. The application of ultrafiltration procedure allowed to demonstrate that antimicrobial substance with strong antimycobacterial activity from bacterial culture supernatant, is a protein with the molecular mass above 100 kDa.  相似文献   

11.
Inter-simple sequence repeat (ISSR) analysis was used to investigate the genetic diversity of 87 Cylindrocarpon liriodendri and C. macrodidymum isolates, the causal agents of black foot disease of grapevine. The four ISSR primers (GT)7, (CCA)5, (CGA)5 and (TCG)5, were able to provide reproducible and polymorphic DNA fingerprint patterns and detected relevant genetic diversity in C. macrodidymum. The cluster analysis of ISSR data showed 21 different genotypes that were grouped in seven ISSR groups, from which two corresponded to C. liriodendri (G1 and G2) and five to C. macrodidymum (G3-G7). Nineteen isolates selected from the seven ISSR groups were inoculated in grapevine seedlings obtained from cv. ‘Tempranillo’. The pathogenicity tests detected virulence diversity in C. macrodidymum. The isolates belonging to ISSR groups G6 and G7 were significantly more virulent than the other C. macrodidymum and C. liriodendri isolates.  相似文献   

12.
The entomopathogen Bacillus sphaericus is one of the most effective biolarvicides used to control the Culex species of mosquito. The appearance of resistance in mosquitoes to this bacterium, however, remains a threat to its continuous use in integrated mosquito control programs. Previous work showed that the resistance to B. sphaericus in Culex colonies was associated with the absence of the 60-kDa binary toxin receptor (Cpm1/Cqm1), an alpha-glucosidase present in the larval midgut microvilli. In this work, we studied the molecular basis of the resistance developed by Culex quinquefasciatus to B. sphaericus C3-41. The cqm1 genes were cloned from susceptible (CqSL) and resistant (CqRL/C3-41) colonies, respectively. The sequence of the cDNA and genomic DNA derived from CqRL/C3-41 colony differed from that of CqSL one by a one-nucleotide deletion which resulted in a premature stop codon, leading to production of a truncated protein. Recombinant Cqm1S from the CqSL colony expressed in Escherichia coli specifically bound to the Bin toxin and had α-glucosidase activity, whereas the Cqm1R from the CqRL/C3-41 colony, with a deletion of three quarters of the receptor’s C-terminal lost its α-glucosidase activity and could not bind to the binary toxin. Immunoblotting experiments showed that Cqm1 was undetectable in CqRL/C3-41 larvae, although the gene was correctly transcribed. Thus, the cqm1R represents a new allele in C. quinquefasciatus that confers resistance to B. sphaericus.  相似文献   

13.
Infection of Galleria mellonella by feeding a mixture of Bacillus thuringiensis spores or vegetative bacteria in association with the toxin Cry1C results in high levels of larval mortality. Under these conditions the toxin or bacteria have minimal effects on the larva when inoculated separately. In order to evaluate whether G. mellonella can function as an oral infection model for human and entomo-bacterial pathogens, we tested strains of Bacillus cereus, Bacillus anthracis, Enterococcus faecalis, Listeria monocytogenes, Pseudomonas aeruginosa and a Drosophila targeting Pseudomonas entomophila strain. Six B. cereus strains (5 diarrheal, 1 environmental isolate) were first screened in 2nd instar G. mellonella larvae by free ingestion and four of them were analyzed by force-feeding 5th instar larvae. The virulence of these B. cereus strains did not differ from the B. thuringiensis virulent reference strain 407Cry with the exception of strain D19 (NVH391/98) that showed a lower virulence. Following force-feeding, 5th instar G. mellonella larvae survived infection with B. anthracis, L. monocytogenes, E. faecalis and P. aeruginosa strains in contrast to the P. entomophila strain which led to high mortality even without Cry1C toxin co-ingestion. Thus, specific virulence factors adapted to the insect intestine might exist in B. thuringiensis/B. cereus and P. entomophila. This suggests a co-evolution between host and pathogens and supports the close links between B. thuringiensis and B. cereus and more distant links to their relative B. anthracis.  相似文献   

14.
15.
Two Saprolegnia isolates, JY isolated from silver crucian carp (Carassius auratus gibelio Bloch) and BMY isolated from zebra fish (Brachydanio rerio Hamilton) came from infections occurring concurrently in different locations in China. To confirm whether the two isolates were from the same Saprolegnia clone, comparative studies have been carried out based on their morphological, physiological and molecular characteristics. Observations showed that morphologically (both asexual and sexual organs) the two isolates were broadly similar and both isolates underwent repeated zoospore emergence. Comparing 704 base pairs of internal transcribed spacer (ITS) region and the 5.8S rDNA, we found isolates JY and BMY shared an identical ITS sequence with a minor variation (99.6 % similarity). Forty available sequences for representatives Saprolegnia spp. belonged to four phylogenetically separate clades. The two studied isolates fell within clade I that comprised a group of isolates which showed almost an identical ITS sequence but had been identified as a number of different morphological species. Our findings suggest that isolates JY and BMY appear to belong to the S. ferax clade and this clade (I) contains a number of closely related phylogenetic species. This is distinct from the more common fish pathogenic isolates, which belong to the Sparasitica clade (III) and are characterized by having cysts decorated by bundles of long hooked hairs and two further clades (II and IV) containing largely saprotrophic or soil born species.  相似文献   

16.
The activity of the White Line Inducing Principle (WLIP) and tolaasin I, produced by virulent strains of Pseudomonas reactans and Pseudomonas tolaasii, respectively, was comparatively evaluated on lipid membranes. Both lipodepsipeptides were able to induce the release of calcein from large unilamellar vesicles. Their activity was dependent on the toxin concentration and liposome composition and in particular it increased with the sphingomyelin content of the membrane. Studies of dynamic light scattering suggested a detergent-like activity for WLIP at high concentration (> 27 μM). This effect was not detected for tolaasin I at the concentrations tested (< 28 μM). Differences were also observed in lipodepsipeptides secondary structure. In particular, the conformation of the smaller WLIP changed slightly when it passed from the buffer solution to the lipid environment. On the contrary, we observed a valuable increment in the helical content of tolaasin I which was inserted in the membrane core and oriented parallel to the lipid acyl chains.  相似文献   

17.
Aiming at learning the microsymbionts of Arachis duranensis, a diploid ancestor of cultivated peanut, genetic and symbiotic characterization of 32 isolates from root nodules of this plant grown in its new habitat Guangzhou was performed. Based upon the phylogeny of 16S rRNA, atpD and recA genes, diverse bacteria belonging to Bradyrhizobium yuanmingense, Bradyrhizobium elkanii, Bradyrhizobium iriomotense and four new lineages of Bradyrhizobium (19 isolates), Rhizobium/Agrobacterium (9 isolates), Herbaspirillum (2 isolates) and Burkholderia (2 isolates) were defined. In the nodulation test on peanut, only the bradyrhizobial strains were able to induce effective nodules. Phylogeny of nodC divided the Bradyrhizobium isolates into four lineages corresponding to the grouping results in phylogenetic analysis of housekeeping genes, suggesting that this symbiosis gene was mainly maintained by vertical gene transfer. These results demonstrate that A. duranensis is a promiscuous host preferred the Bradyrhizobium species with different symbiotic gene background as microsymbionts, and that it might have selected some native rhizobia, especially the novel lineages Bradyrhizobium sp. I and sp. II, in its new habitat Guangzhou. These findings formed a basis for further study on adaptation and evolution of symbiosis between the introduced legumes and the indigenous rhizobia.  相似文献   

18.
The ovicidal activity of the nematophagous fungi Pochonia chlamydosporia (isolates VC1 and VC4), Duddingtonia flagrans (isolate AC001) and Monacrosporium thaumasium (isolate NF34) on Taenia saginata eggs was evaluated under laboratory conditions. T. saginata eggs were plated on 2% water-agar with fungal isolates and controls without fungus and examined after 5, 10 and 15 days. At the end of the experiment P. chlamydosporia showed ovicidal activity against T. saginata eggs (p < 0.05), mainly for internal egg colonization with results of 12.8% (VC1) and 2.2% (VC4); 18.1% (VC1) and 7.0% (VC4); 9.76% (VC1) and 8.0% (VC4) at 5, 10 and 15 days, respectively. The other fungi showed only lytic effect without morphological damage to the eggshell. Results demonstrated that P. chlamydosporia was effective in vitro against T. saginata eggs unlike the other fungi.  相似文献   

19.
Here we present the crystal structure of the Methanococcus jannaschii RelE-RelB (RelBE) toxin-antitoxin (TA) protein complex determined by the MIRAS (multiple isomorphous replacement with anomalous signal) method. The genes encoding this TA system are located in the chromosome of this archaeon and involved in stress response. RelE acts as an endoribonuclease that cleaves mRNA on the ribosome, and we compare the RelBE complex to the known structures of other TA systems belonging to this group and to endoribonucleases. M. jannaschii RelBE forms a heterotetramer with the antitoxin in the centre of the complex, a configuration that differs vastly from the heterotetramer structure of the previously published RelBE from another archaeon, Pyrococcus horikoshii. The long N-terminal α-helix of the tightly bound M. jannaschii antitoxin RelB covers the presumed active site of the toxin RelE that is formed by a central β-sheet, a loop on one side and a C-terminal α-helix on the other side. The active site of the M. jannaschii toxin RelE harbours positive charges that are thought to neutralize the negative charges of the substrate mRNA, including Arg62 that was changed to Ser62 by the Escherichia coli expression system, thereby leading to inactive toxin RelE. Comparative studies suggest that Asp43 and His79 are also involved in the activity of the toxin.  相似文献   

20.
This article summarizes the most effective protocols to isolate Campylobacter spp. (mainly Campylobacter jejuni and Campylobacter coli) from food, primarily poultry products, and includes a summary of the current methods recommended by the Food and Drug Administration and the U.S. Department of Agriculture in the USA, and ISO in Europe. The recommended temperature for incubation of the samples throughout the isolation procedure is 42 °C. The enrichment of the samples for 48 h, which can be performed under aerobic conditions, is recommended to achieve a detectable number of Campylobacter cells. Bolton broth or buffered peptone water supplemented with cefoperazone and amphotericin B is commonly used enrichment broths. The transfer of the enriched samples to plate media using membrane filters helps to obtain pure Campylobacter colonies. Charcoal cefoperazone deoxycholate (CCDA) is the best choice among all plate media. There is no need to add oxygen quenching substances or blood to enrichment broth for the isolation of Campylobacter spp. However, the addition of blood to plate media aids in differential identification of presumptive colonies. Phase contrast microscopy and latex agglutination tests are confirmatory tests for presumptive Campylobacter isolates. The use of multiplex polymerase chain reaction (mPCR) assays is the simplest and most rapid method to identify isolates to the species level. mPCR assays, or other methods assessing DNA sequence variations, will probably become the confirmation procedure of choice in the future. Recent work with retail broiler meat has revealed that the rinsing of meat is more sensitive for the recovery of naturally contaminated retail broiler meat than current reference methods and requires less time for preparation and processing of the samples. This protocol could be coupled with DNA-based methods for a fast screening of positive samples.  相似文献   

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