Summary auto-generated
This study identifies six rod-shaped, Gram-negative bacterial endosymbionts from clinical and environmental isolates of Acanthamoeba amoebae collected in the USA and Malaysia. Using 16S and 23S rDNA sequence analysis, the researchers demonstrated that these obligate intracellular bacteria form a novel, monophyletic lineage within the β-Proteobacteria, showing less than 90% sequence similarity to all other recognized members of this bacterial group. The endosymbionts were visualized within host amoebae using electron microscopy and fluorescence in situ hybridization. Notably, the 23S rRNA genes contain rare 146-base intervening sequences at helix-25 that appear unique to these organisms and have no homology to known sequences. The host amoebae were identified as either Acanthamoeba lenticulata (sequence type T5) or sequence type T4, which comprises most clinical and environmental Acanthamoeba isolates. Based on these phylogenetic and molecular findings, the authors propose the provisional name 'Candidatus Procabacter acanthamoebae' for a representative of these novel β-proteobacterial symbionts. This represents the first documented β-proteobacterial endosymbionts of Acanthamoeba and expands the known diversity of bacterial-amoeba symbiotic relationships.
Key findings
- Six novel β-proteobacterial endosymbionts of Acanthamoeba form a distinct monophyletic lineage with less than 90% 16S rDNA similarity to other β-Proteobacteria
- The endosymbionts possess uncommon 146-base intervening sequences in their 23S rRNA genes with no sequence homology to other known bacterial rDNA
- Proposed classification as 'Candidatus Procabacter acanthamoebae' represents the first β-proteobacterial endosymbionts described in Acanthamoeba species
- Host amoebae were identified as Acanthamoeba lenticulata (T5) or sequence type T4, the most prevalent clinical and environmental Acanthamoeba types
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Abstract
M. Horn, T. R. Fritsche, T. Linner, R. K. Gautom, M. D. Harzenetter and M. Wagner
Lehrstuhl fur Mikrobiologie, Technische Universitat Munchen, Am Hochanger 4, D-85350 Freising, Germany
All obligate bacterial endosymbionts of free-living amoebae currently described are affiliated with the alpha-Proteobacteria, the Chlamydiales or the phylum Cytophaga--Flavobacterium--Bacteroides. Here, six rod-shaped Gram-negative obligate bacterial endosymbionts of clinical and environmental isolates of Acanthamoeba spp. from the USA and Malaysia are reported. Comparative 16S rDNA sequence analysis demonstrated that these endosymbionts form a novel, monophyletic lineage within the beta-Proteobacteria, showing less than 90% sequence similarity to all other recognized members of this subclass. 23S rDNA sequence analysis of two symbionts confirmed this affiliation and revealed the presence of uncommon putative intervening sequences of 146 bp within helix-25 that shared no sequence homology to any other bacterial rDNA. In addition, the 23S rRNA of these endosymbionts displayed one polymorphism at the target site of oligonucleotide probe BET42a that is conserved in all other sequenced beta-Proteobacteria. Intra-cytoplasmatic localization of the endosymbionts within the amoebal host cells was confirmed by electron microscopy and fluorescence in situ hybridization with a specific 16S rRNA-targeted oligonucleotide probe. Based on these findings, the provisional name 'Candidatus Procabacter acanthamoebae' is proposed for classification of a representative of the six endosymbionts of Acanthamoeba spp. studied in this report. Comparative 18S rDNA sequence analysis of the Acanthamoeba host cells revealed their membership with either Acanthamoeba 18S rDNA sequence type T5 (Acanthamoeba lenticulata) or sequence type T4, which comprises the majority of all Acanthamoeba isolates.