Species of Microvirga are novel alpha-proteobacterial root nodule bacteria that specifically nodulate Lotononis angolensis and Lupinus texensis.
Ardley, J.K., Parker, M.A., De Meyer, S., O'Hara, G.W., Reeve, W.G., Yates, R.J., Dilworth, M.J., Willems, A. and Howieson, J.G. (2010) Species of Microvirga are novel alpha-proteobacterial root nodule bacteria that specifically nodulate Lotononis angolensis and Lupinus texensis. In: 9th European Nitrogen Fixation Conference, 6 - 10 September, Geneva, Switzerland.
Root nodule bacteria isolated from Zambian Lotononis angolensis (1) and southern USA Lupinus texensis (2) form a group that is distinct from other named and described legume root nodule bacteria. A phylogenetic tree based on the sequence of nearly full-length portions of the 16S rRNA gene indicates these isolates are affiliated to the α-proteobacterial genus Microvirga. Microvirga spp isolated from soil, air and thermal waters or hot springs have previously been formally described but none has been reported as capable of symbiotic nitrogen fixation. These isolates therefore represent a new lineage of nitrogen-fixing legume symbionts. We present here a polyphasic description of these novel species. A phylogenetic tree based on rpoB sequences supports the topography of the 16S rRNA tree in affiliating these isolates with Microvirga. Sequences of nifD and nifH are closely related in the L. angolensis and L. texensis strains, and there is no indication of horizontal gene transfer. In contrast, the nodA sequence of a L. angolensis strain grouped with Burkholderia tuberum and Methylobacterium nodulans nodA sequences, while that of a L. texensis strain was placed within a different group of rhizobia. The 16S rRNA phylogenetic tree indicates that L. texensis strains do not form a single lineage that is phylogenetically divergent from the African L. angolensis strains; rather, multiple lineages of these root nodule bacteria seem to be distributed across both geographic regions. DNA:DNA hybridization, fatty acid composition and % G+C data are consistent with these isolates forming several novel species. This study presents additional characterisation of these isolates, such as morphology, physiology, substrate utilisation, antibiotic resistance and legume host range that differentiates them from other Microvirga spp. These novel root nodule bacteria tolerate comparatively high temperatures and may have potential as inoculants in hot climates.
|Publication Type:||Conference Item|
|Murdoch Affiliation:||Centre for Rhizobium Studies|
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