Genomic, transcriptional and biochemical analyses of endophyte Burkholderia phytofirmans: Evaluating its effects on enhancing iron uptake in host plants and downstream plant biomass deconstruction

Plant growth promoting bacteria (PGPB) elicit positive effects on plant growth and biomass yield. However, the actual mechanism behind plant-PGPB interaction is poorly understood, and the literature is limited regarding the thermochemical pretreatability and enzymatic deconstruction of biomass derived from PGPB-inoculated plants. To fill this knowledge gap, we first conducted a genome analysis of PGPB strain Burkholderia phytofirmans PsJN, and identified a set of genes that are involved in the synthesis and excretion of siderophores (i.e. molecules with high binding affinity for iron); as well as in the uptake of iron. The existence of such genes prompted us to propose that PsJN-inoculation can improve the host plant’s iron uptake and accumulation, which facilitates downstream plant biomass pretreatment and conversion to simple sugars. To test this proposal, we employed B. phytofirmans PsJN to inoculate Arabidopsis thaliana plants, and then conducted transcriptional analysis of the above identified genes associated with the iron binding and uptake processes. We also investigated the effects of this bacterial inoculation of plants on plant biomass yield, the anatomical organization of stems, iron accumulation in plant tissues, and the pretreatability and enzymatic hydrolysis conversion yields of harvested biomass. The results show that B. phytofirmans PsJN stimulated plant growth in the earlier stage plant development, and indeed enhanced essential metal uptake and accumulation in host plants.  Moreover, the resultant plant biomass released more glucose and xylose after hot water pretreatment and subsequent enzymatic co-saccharification.  These data reveal novel components of -endophyte interactions that can benefit downstream biomass deconstruction.