核酸碱基组分与毛霉目的分类

本文对毛霉目中6科16属40个种共60株真菌DNA的G+C含量与分布作了系统的研究。在提取DNA时选用了Storck等人在Marmur提取细菌DNA方法基础上发展起来的真菌DNA提取法,经过一些修改后成功地提取了毛霉目真菌的DNA。经该法提取的DNA片段长、纯度高,在热变性时DNA的增色效应一般都大于35%。各个种的GC含量大致有一固定值。根据所测毛霉目16属各属真菌的平均GC含量,可将它们分为明显的三组:Gongronella, Haplosporangium, Mortierella及Syncephalastrum为一组,GC含量最高为46.0-49.8%; Cunninghamella单独成一组,GC含量最低只有28.8%;其他各属包括Absidia, Mucor, Rhizopus等GC含量介乎这两组之间,分布于34.9-41.9%。这一次序除Helicostylum与Circinella的数值低于他人的报道外,其余和文献报道值一致。一般属内GC含量变化小于10%,种内变化小于2%。所测得的G+C mol%对分Syncephalastrum monosporum Zheng et al.和Mortierella ramanniana (Moeller) Linneman的合理归属提供了佐证。对某些所测结果与文献报道值有出入的原因作了讨论和分析。对采用Mandel等1970年建议的公式GC=(Tm 0.1×SSC/50.2)-0.990来计算GC含量的依据也作了讨论。

BASE COMPOSITION OF DNA AND CLASSIFICATION OF THE MUCORALES

GC contents of the DNA of 60 isolates belonging to 40 species, 16 genera, 6 families of the Mucorales were investigated systematically. DNA extraction gave highly polymeric DNAs of good quality. After heat denaturation, a hyperchromicity of more than 35% was obtained. The GC content of different species was relatively constant. According to their average GC contents, the 16 genera of the Mucorales fell into 3 distinct groups: Gongronella, Haplosporangium, Mortierella, and Syncephalastrum belonging to the group with highest value, Cunninghamella belonging to the one with lowest value, while the other genera including Absidia, Mucor, Rhizopus, etc. gave GC values in between. The GC contents of these three groups range from 46.0 to 49.8%, 28.8%, and 34.9 to 41.9%, respectively. This agrees with the literature except that the GC contents of Helicostylum and Circinella are lower than reported. The differences of GC values within a single genus and a single species were generally less than 10% and 2% respectively. The GC values furnish more evidences to confirm the taxonomic position of Syncephalastrum monosporum Zheng et al. and Mortierella ramanniana (Moeller) Linnemann. Possible causes for the inconsistencies of some of the GC contents found in the present work and other works are discussed.