Horn M, Fritsche T R, Gautom R K, Schleifer K H, Wagner M
Lehrstuhl für Mikrobiologie, Technische Universität München, Germany.
Environ Microbiol. 1999 Aug;1(4):357-67. doi: 10.1046/j.1462-2920.1999.00045.x.
Acanthamoebae are increasingly being recognized as hosts for obligate bacterial endosymbionts, most of which are presently uncharacterized. In this study, the phylogeny of three Gram-negative, rod-shaped endosymbionts and their Acanthamoeba host cells was analysed by the rRNA approach. Comparative analyses of 16S rDNA sequences retrieved from amoebic cell lysates revealed that the endosymbionts of Acanthamoeba polyphaga HN-3, Acanthamoeba sp. UWC9 and Acanthamoeba sp. UWE39 are related to the Paramecium caudatum endosymbionts Caedibacter caryophilus, Holospora elegans and Holospora obtusa. With overall 16S rRNA sequence similarities to their closest relative, C. caryophilus, of between 87% and 93%, these endosymbionts represent three distinct new species. In situ hybridization with fluorescently labelled endosymbiont-specific 16S rRNA-targeted probes demonstrated that the retrieved 16S rDNA sequences originated from the endosymbionts and confirmed their intracellular localization. We propose to classify provisionally the endosymbiont of Acanthamoeba polyphaga HN-3 as 'Candidatus Caedibacter acanthamoebae', the endosymbiont of Acanthamoeba sp. strain UWC9 as 'Candidatus Paracaedibacter acanthamoebae' and the endosymbiont of Acanthamoeba sp. strain UWE39 as 'Candidatus Paracaedibacter symbiosus'. The phylogeny of the Acanthamoeba host cells was analysed by comparative sequence analyses of their 18S rRNA. Although Acanthamoeba polyphaga HN-3 clearly groups together with most of the known Acanthamoeba isolates (18S rRNA sequence type 4), Acanthamoeba sp. UWC9 and UWE39 exhibit <92% 18S rRNA sequence similarity to each other and to other Acanthamoeba isolates. Therefore, we propose two new sequence types (T13 and T14) within the genus Acanthamoeba containing, respectively, Acanthamoeba sp. UWC9 and Acanthamoeba sp. UWE39.
棘阿米巴越来越被认为是专性细菌内共生体的宿主，其中大多数目前尚未得到鉴定。在本研究中，采用rRNA方法分析了三种革兰氏阴性杆状内共生体及其棘阿米巴宿主细胞的系统发育。对从阿米巴细胞裂解物中检索到的16S rDNA序列进行比较分析，结果显示多食棘阿米巴HN-3、棘阿米巴属UWC9菌株和棘阿米巴属UWE39菌株的内共生体与尾草履虫内共生体嗜核凯氏杆菌、秀丽霍氏孢菌和钝霍氏孢菌相关。这些内共生体与它们最接近的亲缘种嗜核凯氏杆菌的16S rRNA序列总体相似性在87%至93%之间，代表三个不同的新物种。用荧光标记的内共生体特异性16S rRNA靶向探针进行原位杂交，结果表明检索到的16S rDNA序列源自内共生体，并证实了它们的细胞内定位。我们建议将多食棘阿米巴HN-3的内共生体暂定为“嗜核棘阿米巴凯氏杆菌候选种”，棘阿米巴属UWC9菌株的内共生体暂定为“棘阿米巴副凯氏杆菌候选种”，棘阿米巴属UWE39菌株的内共生体暂定为“共生副凯氏杆菌候选种”。通过对棘阿米巴宿主细胞的18S rRNA进行比较序列分析，分析了其系统发育。尽管多食棘阿米巴HN-3与大多数已知的棘阿米巴分离株（18S rRNA序列类型4）明显聚在一起，但棘阿米巴属UWC9菌株和UWE39菌株彼此之间以及与其他棘阿米巴分离株的18S rRNA序列相似性均小于92%。因此，我们在棘阿米巴属内提出了两个新的序列类型（T13和T14），分别包含棘阿米巴属UWC9菌株和棘阿米巴属UWE39菌株。
