title: Complex array of endobionts in Petalomonas sphagnophila, a large heterotrophic euglenid protist from Sphagnum-dominated peatlands.
abstract: Petalomonas sphagnophila is a poorly studied plastid-lacking euglenid flagellate living in Sphagnum-dominated peatlands. Here we present a broad-ranging microscopic, molecular and microspectrophotometric analysis of uncultured P. sphagnophila collected from four field locations in Nova Scotia, Canada. Consistent with its morphological characteristics, 18S ribosomal DNA (rDNA) phylogenies indicate that P. sphagnophila is specifically related to Petalomonas cantuscygni, the only other Petalomonas species sequenced to date. One of the peculiar characteristics of P. sphagnophila is the presence of several green-pigmented particles approximately 5 mum in diameter in its cytoplasm, which a previously published study suggested to be cyanobacterial endosymbionts. New data presented here, however, suggest that the green intracellular body may not be a cyanobacterium but rather an uncharacterized prokaryote yet to be identified by molecular sequencing. 16S rDNA library sequencing and fluorescence in situ hybridizations show that P. sphagnophila also harbors several other endobionts, including bacteria that represent five novel genus-level groups (one firmicute and four different proteobacteria). 16S rDNA phylogenies suggest that three of these endobionts are related to obligate intracellular bacteria such as Rickettsiales and Coxiella, while the others are related to the Daphnia pathogen Spirobacillus cienkowskii or belong to the Thermoactinomycetaceae. TEM, 16S rDNA library sequencing and a battery of PCR experiments show that the presence of the five P. sphagnophila endobionts varies markedly among the four geographic collections and even among individuals collected from the same location but at different time points. Our study adds significantly to the growing evidence for complex and dynamic protist-bacterial associations in nature.
authors.affiliation: Department of Biochemistry and Molecular Biology, Canadian Institute for Advanced Research, Program in Integrated Microbial Biodiversity, Dalhousie University, Halifax, Nova Scotia, Canada. eunsookim@dal.ca
authors.forename: Eunsoo
authors.initials: E
authors.lastname: Kim
authors.forename: Jong Soo
authors.initials: JS
authors.lastname: Park
authors.forename: Alastair G B
authors.initials: AG
authors.lastname: Simpson
authors.forename: Shigeru
authors.initials: S
authors.lastname: Matsunaga
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Watanabe
authors.forename: Akio
authors.initials: A
authors.lastname: Murakami
authors.forename: Katrin
authors.initials: K
authors.lastname: Sommerfeld
authors.forename: Naoko T
authors.initials: NT
authors.lastname: Onodera
authors.forename: John M
authors.initials: JM
authors.lastname: Archibald
mesh_terms: D001419:Bacteria / Q000145:classification* / Q000254:growth & development / Q000302:isolation & purification*; D016000:Cluster Analysis; D003593:Cytoplasm / Q000382:microbiology / Q000648:ultrastructure; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D016822:Euglenida / Q000166:cytology / Q000235:genetics / Q000382:microbiology* / Q000502:physiology*; D008853:Microscopy; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009674:Nova Scotia; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA; D012987:Soil; D012988:Soil Microbiology; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S; D012337:RNA, Ribosomal, 18S; D012987:Soil