假丝酵母属疑难菌株大亚基rDNA D1/D2区域序列分析及其分类学意义

对根据常规形态和生理生化性状难以确定分类学地位的8株假丝酵母菌,进行了以大亚基(26S) rDNA中D1/D2区域(约500～600 bp)的碱基序列分析为依据的分子分类学研究.根据系统树上所显示的供试菌株与假丝酵母属及相关子囊菌酵母已知种的亲缘关系,以及与最近缘种模式菌株D1/D2区域序列的相似性比较,确定了各个菌株的归属.本研究也显示了DNA序列分析在假丝酵母菌快速鉴定中的优越性.

MOLECULAR TAXONOMIC STUDY ON THE PROBLEMATIC CANDIDA STRAINS BASED ON 26S rDNA D1/D2 DOMAIN SEQUENCE COMPARISON

Eight anamorphic ascomycetous yeast strains isolated from natural sources in China, which were unable to be identified to species level by conventional methods, were selected for molecular taxonomic study. The large-subunit (26S) rRNA gene D1/D2 domain sequences (approximately 500~600 nucleotides) of these strains were determined by direct sequencing method. The taxonomic relationships of these strains with the described anamorphic or teleomorphic ascomycetous yeast species were indicated by sequence comparison in the D1/D2 domain through BLAST search in GenBank/EMBL/DDBJ nucleotide sequence databases, and by the phylogentic tree drawn from neighbor-joining analysis based on the D1/D2 domain sequence alignment. AS 2.1695 and AS 2.1700 were identified as Candida membranifaciens because of their identical D1/D2 domain sequences and similar phenotypical characters with the type strains of this species. AS 2.1679, AS 2.1777 and AS 2.1981 were found to have identical sequences in this domain with those of the type strains of C. melibiosica, Pichia holstii (anamorph: C. silvicola) and C. ethanolica, respectively, and were likewise identified. AS 2.2220 and AS 2.2221 were similar with C. pseudolambica in D1/D2 domain sequences (only 1~2 base divergences) and in phenotypic characters, indicating they are conspecific. AS 2.1651 was most closely related to C. cacaoi and P. farinose, only 2 base differences were found between the former and the type strains of the latter two species.