title: Symbiotic and saprophytic survival of three unmarked Rhizobium leguminosarum biovar trifolii strains introduced into the field.
abstract: The symbiotic and saprophytic persistence of three unmarked Rhizobium leguminosarum biovar trifolii (Rlt) strains introduced into a field site in Iceland were followed. This site was free of clover cultivation and initially devoid of clover-nodulating rhizobia as tested by nodulation studies. Nodule occupancy by strains was identified based on their distinct ERIC-polymerase chain reaction (PCR) DNA fingerprint patterns. The survival and persistence of the individual strains in soil were monitored by the quantitative real-time PCR (qRT-PCR) assay, targeting the host-specific nodE gene. The most dominant strain in the nodule population, Rlt 20-15, showed relatively less saprophytic survival ability and maintained high numbers only in the presence of the appropriate host plant. Conversely, the minor nodule occupant, Rlt 32-28, persisted in soil at a relatively higher abundance both in the presence of its host legumes and in the presence of a non-host grass. The qRT-PCR assay was successfully applied to quantify rhizobial strains directly in soil without culturing or nodulation. However, the assay demonstrated less sensitivity compared with the plant infection most-probable-number (MPN) method for estimating the population size of rhizobia in soil. The quantitative detection limit of our qRT-PCR assays was 1 x 10(3) cells per gram of soil, as opposed to the MPN test which has a detection limit of 10 cells per gram of soil.
authors.affiliation: Department of Biology, Faculty of Science, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Samuel
authors.initials: S
authors.lastname: Duodu
authors.forename: T V
authors.initials: TV
authors.lastname: Bhuvaneswari
authors.forename: J
authors.initials: J
authors.lastname: Gudmundsson
authors.forename: Mette M
authors.initials: MM
authors.lastname: Svenning
mesh_terms: D000217:Acyltransferases / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D029902:Medicago / Q000382:microbiology*; D008565:Membrane Proteins / Q000235:genetics*; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000382:microbiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016961:Rhizobium leguminosarum / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D012988:Soil Microbiology; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins; C061842:NodE protein, Rhizobium; D000217:Acyltransferases