Identifying functional multi-host shuttle plasmids to advance synthetic biology applications in Mesorhizobium and Bradyrhizobium

Ammonia availability has a crucial role in agriculture as it ensures healthy plant growth and increased crop yields. Since diazotrophs are the only organisms capable of reducing dinitrogen to ammonium, they have a great ecological importance and potential to mitigate the environmental and economic costs of synthetic fertilizer use. Rhizobia are especially valuable being that they can engage in nitrogen-fixing symbiotic relationships with legumes, and they demonstrate great diversity and plasticity in genomic and phenotypic traits. However, few rhizobial species have improved genetic tractability for synthetic biology applications. This study established a basic genetic toolbox with antibiotic resistance markers, multi-host shuttle plasmids and a streamlined protocol for biparental conjugation with Mesorhizobium and Bradyrhizobium species. We identified two repABC origins of replication from Sinorhizobium meliloti (pSymB) and Rhizobium etli (p42d) that were stable across all three strains of interest. Furthermore, the NZP2235 genome was sequenced and phylogenetic analysis determined its reclassification to Mesorhizobium huakuii. These tools will enable the use of plasmid-based strategies for more advanced genetic engineering projects and ultimately contribute towards the development of more sustainable agriculture practices by means of novel nitrogen-fixing organelles, elite bioinoculants or symbiotic association with non-legumes. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=94 SRC="FIGDIR/small/572671v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@70e377org.highwire.dtl.DTLVardef@165b06corg.highwire.dtl.DTLVardef@12196a9org.highwire.dtl.DTLVardef@2a33e0_HPS_FORMAT_FIGEXP M_FIG C_FIG