Snel J, Heinen P P, Blok H J, Carman R J, Duncan A J, Allen P C, Collins M D
Central Animal Laboratory, University of Nijmegen, The Netherlands.
Int J Syst Bacteriol. 1995 Oct;45(4):780-2. doi: 10.1099/00207713-45-4-780.
Segmented filamentous bacteria (SFB) are nonpathogenic bacteria that are commonly found attached to the intestinal walls of many animals. Until now, these bacteria have not been cultured in vitro. Recently, a 16S rRNA sequence analysis revealed that SFB isolated from mice represent a distinct subline within the Clostridium subphylum of the gram-positive bacteria. Since SFB isolated from mice, rats, and chickens are known to be host specific, we investigated the phylogenetic relationships among SFB obtained from these three hosts. Total DNAs from the intestinal floras of chickens and rats were used as templates for PCR amplification of 16S rRNA genes. PCR products were cloned and screened by a dot blot hybridization procedure to identify homologous sequences that cross-reacted with mouse SFB-specific oligonucleotide probes. A phylogenetic analysis of these 16S ribosomal DNA sequences revealed that SFB isolated from these three hosts form a natural group, which is peripherally related to the genus Clostridium sensu stricto (group I Clostridium). The SFB obtained from chickens, rats, and mice had closely related, albeit different, 16S rRNA gene sequences. The observed levels of 16S rRNA sequence divergence, ca. 1.5 to 3%, together with host specificity, suggest that SFB isolated from mice, rats, and chickens represent different species and that coevolution of the SFB and their hosts occurred. "Candidatus Arthromitus" is proposed as the provisional generic name for this group of organisms.
分节丝状菌（SFB）是一种非致病性细菌，常见于许多动物的肠道壁上。到目前为止，这些细菌尚未在体外培养成功。最近，一项16S rRNA序列分析表明，从小鼠体内分离出的SFB属于革兰氏阳性菌梭菌亚门中的一个独特亚系。由于已知从小鼠、大鼠和鸡体内分离出的SFB具有宿主特异性，我们研究了从这三种宿主中获得的SFB之间的系统发育关系。以鸡和大鼠肠道菌群的总DNA为模板，对16S rRNA基因进行PCR扩增。PCR产物经克隆后，通过斑点杂交程序进行筛选，以鉴定与小鼠SFB特异性寡核苷酸探针发生交叉反应的同源序列。对这些16S核糖体DNA序列进行的系统发育分析表明，从这三种宿主中分离出的SFB形成了一个自然群体，该群体与狭义梭菌属（第一组梭菌）在亲缘关系上较为疏远。从鸡、大鼠和小鼠中获得的SFB虽然16S rRNA基因序列不同，但密切相关。观察到的16S rRNA序列差异水平约为1.5%至3%，再加上宿主特异性，表明从小鼠、大鼠和鸡中分离出的SFB代表不同的物种，且SFB与其宿主发生了共同进化。建议将“暂定节杆菌属（Candidatus Arthromitus）”作为这一组生物体的临时属名。
