Diversity of endemic rhizobia on Christmas Island: Implications for agriculture following phosphate mining

• Published in: Systematic and applied microbiology Vol. 41; no. 6; pp. 641 - 649
• Main Authors: De Meyer, Sofie E., Ruthrof, Katinka X., Edwards, Tom, Hopkins, Anna J.M., Hardy, Giles, O’Hara, Graham, Howieson, John
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 01.11.2018
• Subjects: Agriculture; Australia; Bradyrhizobiaceae - classification; Bradyrhizobiaceae - genetics; Bradyrhizobiaceae - isolation & purification; Christmas Island; DNA, Bacterial - genetics; Fabaceae - microbiology; Genes, Bacterial; Mining; Phosphates; Phylogeny; Restoration; Rhizobia; Rhizobiaceae - classification; Rhizobiaceae - genetics; Rhizobiaceae - isolation & purification; RNA, Ribosomal, 16S - genetics; Root nodule bacteria; Root Nodules, Plant - microbiology; Symbiosis; Australia; Mining; BOM; Rhizobia; Restoration; CI; Christmas Island; Agriculture; Root nodule bacteria; ML
• ISSN: 0723-2020; 1618-0984
• DOI: 10.1016/j.syapm.2018.07.004

•First study to show that there is a large diversity of Bradyrhizobium species associated with legumes on Christmas Island.•Naturalised rhizobia are present for the crop legumes cowpea, mungbean, peanut and lablab.•No nodules were detected on common bean, chickpea, and soybean, and hence inoculation is required for these crops.•Mimosa species are nodulated by C. alkaliphilus-like strains and C. taiwanensis.•Vertical transmission of symbiosis genes in the alpha-rhizobia but horizontal transmission within the beta-rhizobia. Given that phosphate supplies may diminish and become uneconomic to mine after 2020, there is a compelling need to develop alternative industries to support the population on Christmas Island. Former mine sites could be turned into productive agricultural land, however, large-scale commercial agriculture has never been attempted, and, given the uniqueness of the island, the diversity of rhizobia prior to introducing legumes needed evaluation. Therefore, 84 rhizobia isolates were obtained from nine different hosts, both crop and introduced legumes, located at seven sites across the island. Based on 16S rRNA and recA gene sequence analysis, the isolates grouped into 13 clades clustering within the genus Bradyrhizobium, Ensifer, Cupriavidus and Rhizobium. According to the sequences of their symbiosis genes nodC and nifH, the isolates were classified into 12 and 11 clades, respectively, and clustered closest to tropical or crop legume isolates. Moreover, the symbiosis gene phylogeny and Multi Locus Sequence Analysis gene phylogeny suggested vertical transmission in the Alpha-rhizobia but horizontal transmission within the Beta-rhizobia. Furthermore, this study provides evidence of a large diversity of endemic rhizobia associated with both crop and introduced legumes, and highlights the necessity of inoculation for common bean, chickpea and soybean on the Island.