Nodulation of Mimosa spp. by the beta-proteobacterium Ralstonia taiwanensis.
Several beta-proteobacteria have been isolated from legume root nodules and some of these are thought to be capable of nodulating and fixing N2. However, in no case has there been detailed studies confirming that they are the active symbionts. Here, Ralstonia taiwanensis LMG19424, which was originally isolated from Mimosa pudica nodules, was transformed to carry the green fluorescent protein (gfp) reporter gene before being used to inoculate axenically-grown seedlings of M. pudica and M. diplotricha. Plants were harvested at various intervals for 56 days after inoculation, then examined for evidence of infection and nodule formation. Nodulation of both Mimosa spp. was abundant, and acetylene reduction assays confirmed that nodules had nitrogenase activity. Confocal laser scanning microscopy (CLSM) showed that fresh M. pudica nodules with nitrogenase activity had infected cells containing bacteroids expressing gfp. In parallel, fixed and embedded nodules from both Mimosa spp. were sectioned for light and electron microscopy, followed by immunogold labeling with antibodies raised against gfp and nitrogenase Fe (nifH) protein. Significant immunolabeling with these antibodies confirmed that R. taiwanensis LMG19424 is an effective N2-fixing symbiont of Mimosa spp. Both species were infected via root hairs and, in all respects, the nodule ontogeny and development was similar to that described for other mimosoid legumes. The nodules were indeterminate with a persistent meristem, an invasion zone containing host cells being invaded via prominent infection threads, and an N2-fixing zone with infected cells containing membrane-bound symbiosomes.
Chen
Wen-Ming
WM
Laboratory of Microbiology, Department of Seafood Science, National Kaohsiung Institute of Marine Technology, Kaohsiung City 811, Taiwan.
James
Euan K
EK
Prescott
Alan R
AR
Kierans
Martin
M
Sprent
Janet I
JI
D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D008854:Microscopy, Electron; D031298:Mimosa / Q000382:microbiology / Q000502:physiology* / Q000648:ultrastructure; D009586:Nitrogen Fixation; D043367:Ralstonia / Q000235:genetics / Q000502:physiology*; D014170:Transformation, Genetic
D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins