Normand P, Orso S, Cournoyer B, Jeannin P, Chapelon C, Dawson J, Evtushenko L, Misra A K
Ecologie Microbienne du Sol, URA CNRS 1977, Université Claude-Bernard, Villeurbanne, France.
Int J Syst Bacteriol. 1996 Jan;46(1):1-9. doi: 10.1099/00207713-46-1-1.
The members of the actinomycete genus Frankia are nitrogen-fixing symbionts of may species of woody dicotyledonous plants belonging to eight families. Several strains isolated from diverse actinorhizal plants growing in different geographical areas were used in this study. The phylogenetic relationships of these organisms and uncharacterized microsymbionts that are recalcitrant to isolation in pure culture were determined by comparing complete 16S ribosomal DNA sequences. The resulting phylogenetic tree revealed that there was greater diversity among the Alnus-infective strains than among the strains that infect other host plants. The four main subdivisions of the genus Frankia revealed by this phylogenetic analysis are (i) a very large group comprising Frankia alni and related organisms (including Alnus rugosa Sp+ microsymbionts that are seldom isolated in pure culture), to which Casuarina-infective strains, a Myrica nagi microsymbiont, and other effective Alnus-infective strains are related; (ii) unisolated microsymbionts of Dryas, Coriaria, and Datisca species; (iii) Elaeagnus-infective strains; and (iv) "atypical" strains (a group which includes an Alnus-infective, non-nitrogen-fixing strain). Taxa that are related to this well-defined, coherent Frankia cluster are the genera Geodermatophilus, "Blastococcus," Sporichthya, Acidothermus, and Actinoplanes. However, the two genera whose members have multilocular sporangia (the genera Frankia and Geodermatophilus) did not form a coherent group. For this reason, we propose that the family Frankiaceae should be emended so that the genera Geodermatophilus and "Blastococcus" are excluded and only the genus Frankia is retained.
放线菌属的弗兰克氏菌成员是属于八个科的多种木本双子叶植物的固氮共生体。本研究使用了从生长在不同地理区域的多种放线菌根植物中分离出的几个菌株。通过比较完整的16S核糖体DNA序列，确定了这些生物体与在纯培养中难以分离的未鉴定微共生体之间的系统发育关系。所得的系统发育树显示，感染桤木的菌株之间的多样性比感染其他寄主植物的菌株之间的多样性更大。系统发育分析揭示的弗兰克氏菌属的四个主要亚群是：（i）一个非常大的群体，包括桤木弗兰克氏菌及相关生物体（包括很少在纯培养中分离到的皱叶桤木Sp+微共生体），感染木麻黄的菌株、一种杨梅微共生体和其他有效的感染桤木的菌株与该群体相关；（ii）仙女木属、马桑属和刺续断属物种的未分离微共生体；（iii）感染胡颓子属的菌株；（iv）“非典型”菌株（包括一种感染桤木的、不固氮的菌株）。与这个定义明确、连贯的弗兰克氏菌群相关的分类单元有地嗜皮菌属、“芽球菌属”、生孢嗜皮菌属、嗜酸热放线菌属和游动放线菌属。然而，其成员具有多室孢子囊的两个属（弗兰克氏菌属和地嗜皮菌属）并未形成一个连贯的类群。因此，我们建议修订弗兰克氏菌科，排除地嗜皮菌属和“芽球菌属”，仅保留弗兰克氏菌属。
