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

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Wednesday 30 November 2011
Concurrent Session 10 – Ecology of RNB
1100 – 1230
Authors: Tomasz Stępkowski 1 , Alison McInnes 2 , Elizabeth Watkin 3 , Dorota Narożna 4 , Magdalena
Mantaj 1 , Justyna Rudnicka 1 , Graham O‟Hara 5 , Emma T. Steenkamp 6
1 Institute of Bioorganic Chemistry Polish Academy of Sciences, Poznań , Poland;
2 Centre for Plant and Food Science, University of Western Sydney, Penrith South DC,
Australia;
3 School of Biomedical Sciences, Curtin University, Perth, Australia
; 4 Department of Biochemistry and Biotechnology, Poznan University of Life Sciences,
Poznan , Poland;
5 Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
; 6 Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria,
South Africa
Presentation Title: Diverse origin of Bradyrhizobium strains nodulating legumes native to the tropicalmonsoon
part of Australia
Presentation Time: 1200 – 1220
The geographical isolation of Australia, together with the formation of an arid climate in its central regions and a
tropical-monsoon climate in its northern part impacted significantly on the evolution of legumes native to the
continent. Additionally, the northward drift of the Australian plate and its collision with the Euroasian plate
facilitated the colonization of Australia by many alien legume taxa during the last ten million years. Conceivably,
these factors also shaped the evolution of root-nodule bacteria associated with these legumes, and contributed
to the high diversity of indigenous rhizobium communities and the presence of many groups unique to Australia.
By making use of multilocus sequence analysis we investigated 132 strains of Bradyrhizobium, which originated
from the tropical-monsoon part of the Northern Territory. All strains were obtained from root nodules of legumes
belonging to endemic or native Australian tribes, genera or species. Phylogenetic analyses based on six
housekeeping genes (atpD, dnaK, glnII, gyrB, recA and rpoB) separated the strains into 16 lineages, of which
most were different from the known species of Bradyrhizobium. Phylogenies based on the symbiotic nodA and
nifD genes separated the strains into six clades (i.e., Clade I (subgroup I.2), III (subgroup III.3), IV, V, VII and
VIII), out of the eight clades that have been described thus far for Bradyrhizobium. Legumes with centers of
diversification located outside Australia were nodulated predominantly by strains belonging to Clade III, which is
regarded as a cosmopolitan, pantropical group. Surprisingly, this was also true for all strains from Clade IV,
which suggests that this apparently Australian clade may have originally diversified outside this continent.
Conversely, the legumes with Australian centers of diversity (e.g. phylodinous Acacia spp.) were nodulated by
strains representing the Australian Clade I and Clade VIII, but also by Clade V, which also occurs in South
America.
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