Rhizobia with 16S rRNA and nifH Similar to Mesorhizobium huakuii but Novel recA, glnII, nodA and nodC Genes Are Symbionts of New Zealand Carmichaelinae

Heng Wee Tan,Janet I Sprent,J Peter W Young,Euan K James,Peter B Heenan,Mitchell Andrews,Bevan S Weir,Noel Carter,Hayley J Ridgway,Vishal Shah

doi:10.1371/journal.pone.0047677

Abstract

New Zealand became geographically isolated about 80 million years ago and this separation gave rise to a unique native flora including four genera of legume, Carmichaelia, Clianthus and Montigena in the Carmichaelinae clade, tribe Galegeae, and Sophora, tribe Sophoreae, sub-family Papilionoideae. Ten bacterial strains isolated from NZ Carmichaelinae growing in natural ecosystems grouped close to the Mesorhizobium huakuii type strain in relation to their 16S rRNA and nifH gene sequences. However, the ten strains separated into four groups on the basis of their recA and glnII sequences: all groups were clearly distinct from all Mesorhizobium type strains. The ten strains separated into two groups on the basis of their nodA sequences but grouped closely together in relation to nodC sequences; all nodA and nodC sequences were novel. Seven strains selected and the M. huakuii type strain (isolated from Astragalus sinicus) produced functional nodules on Carmichaelia spp., Clianthus puniceus and A. sinicus but did not nodulate two Sophora species. We conclude that rhizobia closely related to M. huakuii on the basis of 16S rRNA and nifH gene sequences, but with variable recA and glnII genes and novel nodA and nodC genes, are common symbionts of NZ Carmichaelinae.

Highlights

IntroductionMembers of the Fabaceae (the legume family) are components of most of the world’s vegetation types [1]
Members of the Fabaceae are components of most of the world’s vegetation types [1]
All ten bacterial strains isolated from Carmichaelia, Clianthus or Montigena studied here clustered closely with the M. huakuii type strain and five other strains previously isolated from Carmichaelia or Clianthus spp. (ICMP 11708, International Collection of Microorganisms from Plants (ICMP) 14319, ICMP 12680, ICMP 11722 and ICMP 12635) [16,32], on the basis of their 16S rRNA sequences (Fig. 1)

Summary

Introduction

Members of the Fabaceae (the legume family) are components of most of the world’s vegetation types [1]. Many legume species have the capacity to fix atmospheric nitrogen (N2) via symbiotic bacteria (generally termed ‘rhizobia’) in root nodules and this can give them an advantage under low soil N conditions if other factors are suitable for growth [2,3,4]. New Zealand (NZ) became geographically isolated about 80 million years ago [5,6] and this separation gave rise to a unique native flora [7] that is considered to have evolved during the late Cenozoic [8,9]. There are four genera of legume, of the sub-family Papilionoideae on the main New Zealand islands, plus the strand species Canavalia rosea which occurs in the Kermadec Islands [10]. All species in all four genera are capable of nodulation, but genotypic data on the rhizobia which induce nodules on these plants are limited [4,16]

Methods

Results

Conclusion