title: Earthworm ecology affects the population structure of their Verminephrobacter symbionts.
abstract: Earthworms carry species-specific Verminephrobacter symbionts in their nephridia (excretory organs). The symbionts are vertically transmitted via the cocoon, can only colonize the host during early embryonic development, and have co-speciated with their host for about 100 million years. Although several studies have addressed Verminephrobacter diversity between worm species, the intra-species diversity of the symbiont population has never been investigated. In this study, symbiont population structure was examined by using a multi-locus sequence typing (MLST) approach on Verminephrobacter isolated from two contrasting ecological types of earthworm hosts: the high population density, fast reproducing compost worms, Eisenia andrei and Eisenia fetida, and the low-density, slow reproducing Aporrectodea tuberculata, commonly found in garden soils. Three distinct populations were investigated for both types and, according to MLST analysis of 193 Verminephrobacter isolates, the symbiont community in each worm individual was very homogeneous. The more solitary A. tuberculata carried unique symbiont populations in 9 out of 10 host individuals, whereas the symbiont populations in the social compost worms were homogeneous across host individuals from the same population. These data suggested that host ecology shaped the population structure of Verminephrobacter symbionts. The homogeneous symbiont populations in the compost worms led to the hypothesis that Verminephrobacter could be transferred bi-parentally or via leaky horizontal transmission in high-density, frequently mating worm populations.
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Building 1540, 8000 Aarhus, Denmark. Electronic address: f.d.m.viana@gmail.com.
authors.forename: Flávia
authors.initials: F
authors.lastname: Viana
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Building 1540, 8000 Aarhus, Denmark. Electronic address: cej_91@hotmail.com.
authors.forename: Christopher Erik
authors.initials: CE
authors.lastname: Jensen
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Building 1540, 8000 Aarhus, Denmark. Electronic address: Michael_macey@hotmail.co.uk.
authors.forename: Michael
authors.initials: M
authors.lastname: Macey
authors.affiliation: Section for Microbiology, Department of Bioscience, Aarhus University, Ny Munkegade 116, Building 1540, 8000 Aarhus, Denmark. Electronic address: andreas.schramm@bios.au.dk.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schramm
authors.affiliation: Aarhus Institute of Advanced Studies, Aarhus University, Høegh-Guldbergs Gade 6B, 8000 Aarhus, Denmark. Electronic address: mblu@aias.au.dk.
authors.forename: Marie Braad
authors.initials: MB
authors.lastname: Lund
mesh_terms: D000262:Adenylyl Cyclases / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D042621:Comamonadaceae / Q000145:classification* / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D018445:Infectious Disease Transmission, Vertical; D058885:Multilocus Sequence Typing; D009245:NADH Dehydrogenase / Q000235:genetics; D009835:Oligochaeta / Q000145:classification / Q000382:microbiology*; D011157:Population Dynamics; D011938:Rec A Recombinases / Q000235:genetics; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D011938:Rec A Recombinases; D012321:DNA-Directed RNA Polymerases; D000262:Adenylyl Cyclases
keywords: Earthworm; Nephridia; Population structure; Symbiont transmission; Symbiosis; Verminephrobacter