Nodulation and effective nitrogen fixation of Macroptilium atropurpureum (siratro) by Burkholderia tuberum, a nodulating and plant growth promoting beta-proteobacterium, are influenced by environmental factors

Burkholderia tuberum STM678(T) was isolated from a South African legume, but did not renodulate this plant. Until a reliable host is found, studies on this and other interesting beta-rhizobia cannot advance. We investigated B. tuberum STM678(T)'s ability to induce Fix(+) nodules on a small-seeded, easy-to-propagate legume (Macroptilium atropurpureum). Previous studies demonstrated that B. tuberum elicited either Fix(-) or Fix(+) nodules on siratro, but the reasons for this difference were unexplored. Experiments to promote effective siratro nodule formation under different environmental conditions were performed. B. tuberum STM678(T)'s ability to withstand high temperatures and desiccation was checked as well as its potential for promoting plant growth via mechanisms in addition to nitrogen fixation, e.g., phosphate solubilization and siderophore production. Potential genes for these activities were found in the sequenced genomes. Higher temperatures and reduced watering resulted in reliable, effective nodulation on siratro. Burkholderia spp. solubilize phosphate and produce siderophores. Genes encoding proteins potentially involved in these growth-promoting activities were detected and are described. Siratro is an excellent model plant for B. tuberum STM678(T). We identified genes that might be involved in the ability of diazotrophic Burkholderia species to survive harsh conditions, solubilize phosphate, and produce siderophores.