IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Tuesday 29 November 2011
Concurrent Session 9 – Native Legume RNB
1600 - 1720
Authors: Robert Walker 1,2 , Graham O‟Hara 2 , Lesley Mutch 1 , Lambert Bräu 2 & Elizabeth Watkin 1
1 School of Biomedical Sciences, Curtin University, Bentley, 6845, Western Australia.
2 Centre for Rhizobium Studies, Murdoch University, Murdoch, 6150, Western Australia.
Presentation Title: The phylogenetic diversity of australian Burkholderia root nodule bacteria
Presentation Time: 1620 – 1640
Recently, members of the beta-proteobacteria were described as novel root nodule bacteria (coined betarhizobia)
with many species represented by the genus Burkholderia and some Cupriavidus. Endosymbionts
isolated from nodules of Mimosa spp. are predominantly Burkholderia spp. and this appears to be a preferential
association however, Burkholderia spp. have also been isolated from Papillionoideae and other members of the
Mimosoideae subfamily of legumes. Beta-rhizobia from Australia have been isolated from Acacia spp. and from
members of the tribes Kennediinae and the endemic Mirbeliaea, however in glasshouse trials these isolates form
ineffective nodules on many other Australian legume species. This study examined twelve authenticated
Burkholderia sp. isolated from both native and invasive legumes from New South Wales, Western Australia, the
Northern Territory, and two South African isolates from Rhynchosia ferulifolia. The type strains Burkholderia
phymatum STM815 and Cupriavidus taiwanensis LMG19424 were also included. The phylogenetic diversity of
these isolates was explored by examining the partial sequences from coding regions of the 16S rRNA, recA,
dnaK and atpD genes. To determine the phylogenetic distribution within Australian isolates only, a concatenated
neighbour-joining tree was constructed and most isolates fell into geographical clades. When including non-
Australian isolates, Australian Burkholderia root nodule bacteria appear to form a distinct monophyletic group,
separate to the Burkholderia cepacia complex (BCC) and from non-Australian isolates. Nodulation and nitrogen
fixation genes were also partially sequenced and strongly align to nod and nif genes from Australian
Bradyrhizobium spp. however, very few sequence data exist for the nodulation and nitrogen fixation genes of
Australian Burkholderia root nodule bacteria. Australian root nodule Burkholderia may have evolved from a
distinct monophyletic lineage from other beta-rhizobia allowing them to nodulate Australian legumes with varying
effectiveness providing a competitive advantage over other soil saprophytes however, Australian beta-rhizobia
may not be useful as effective nitrogen fixing endosymbionts.
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