| Two strains of filamentous fungi N3 and N9 were isolated from one yoghurt sample. By morphological observation, RAPD typing, nucleotide sequence analysis of their internal transcribed spacer regions and 5.8SrDNA as well as cultivating experiment, the taxonomy position of strains N3, N9 and biosystematics of them and their close relative species were identified.The colony and mycelial microscopic characters of N3, N9 on potato dextrose agar (PDA) medium were observed respectively. Colonial growth for 7d at 25 °C was characterized by the radial extension of mycelia on the surface of medium, creating a circular and smooth fungal colony. Their hyphae were dense, thick and aerial, and had distinct clamp connections structure, which was unique to basidiomycetes. Based on the characters above, strains N3 and N9 were primarily identified as basidiomycetes.Three kinds of methods (i. e. benzyl choeide, CTAB and SDS-CTAB method) were used to extract DNA from eight strains of basidiomycetes. The results showed that the benzyl choeide method was able to be used to extract the DNA of these basidiomycetes, and bands resulting from gel electrophoretic separations were very clear. However, both the CTAB and SDS-CTAB methods were only adequate to be used to extract DNA from some strains of basidiomycetes and the DNA bands of some strains were clear, but others were not obvious. The effects of both the pH values of extracts and the grinding to mycelia in liquid nitrogen on the result of extracting DNA were also discussed.Eight strains of basidiomycetes, i.e. N3, N9 and 6 standard strains, had been analyzed for their RAPD genotype. Among 40 arbitrary primers, 18 primers could get enough amplified bands for all strains. The genetic relationship had been evaluated by similarity cofficient obtained from these profiles. The cluster showed that all strains could be divided into two parts. The first part consisted of strains N3 and N9, all strains of Pleurotus and Coprinus comatus. The second part was Lentinus edodes and Flammulinavelutipes. N3, N9 and P. ostreatus were closely related. According the result, strains N3 and N9 were identified to the genus Pleurotus.RAPD was again employed to study the genetic variation of strains N3, N9 and 7 standard strains of Pleurotus. Twenty-one random primers selected from 40 ones were used for DNA amplification. Specific characteristic bands were produced by most of the 21 primers. The dendrogram resulated from hierarchical cluster analysis based on all bands amplified by the 21 primers showed that the isolates were distinctly classified into two large categories. The first group was composed of the strains N3, N9 and 4 isolates of Pleurotus (i.e. bai, aohei, hebei 33, heipingl). Furthermore, the strains N3, N9 and P. ostreatus had a close relationship. The second group was consisted of P. abalones, P. citrinopileatus and P. ferulae.The internal transcribed spacer regions and 5.8S of the ribosomal RNA gene from strains N3, N9 were amplified using the polymerase chain reaction and sequenced. Sequences from the above isolates were compared with published sequences of P. ostreatus, P. columbinus, P. spodoleucus and so on in Genbank database and phylogenetic trees were produced based on ITS sequence data by "Neighbour-joining" methods of the software Bioedit. The sequence analysis showed that the strain N3 and P. spodoleucus had the most close relationship with a bootstrap value of 100%. This suggested that they were probably conspecific. The strain N9 and P. floridanus were closely related with 99% bootstrap value, it indicated that N9 might belong to P. floridanus.The strains N3, N9 were cultivated for the formation of fruitbodies. The result showed that strains N3, N9 had the capability forming fruitbody and they were identified to the genus Pleurotus by the morphological character observation to their fruitbodies.
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