Graduate Student North Carolina State University Hillsborough, North Carolina
Body of Abstract: Plants will be an essential part of biological life support systems to recycle waste, supplement nutrition, and bring psychological benefits for crews on long duration space missions. Beneficial microbes, such as plant growth-promoting rhizobacteria (PGPR), could help reduce plant stress and improve nutrient extraction from extraterrestrial substrates, such as lunar regolith. I evaluated plant growth promotion effects of six strains of bacteria isolated by Khodadad et al. (2020) from plant roots and substrate of plants grown in the Veggie system on the International Space Station. Five of these six strains had been previously characterized by Handy et al. (2021) as being able to solubilize phosphorus in vitro. For one series of experiments, I grew Arabidopsis plants in agar media with replete, low, and insoluble phosphorus with and without each microbe. For a second series of experiments, I grew axenic Arabidopsis plants with and without microbes in lunar regolith simulant fertilized with either replete or no-phosphorus fertilizer. Despite previous characterization as phosphorus solubilizing, no bacteria promoted plant growth under low phosphorus conditions. Significant plant growth promotion was observed for several strains of bacteria in replete fertilizer agar media and in lunar regolith simulant with complete fertilizer added. These results suggest that beneficial microbe properties tested in vitro may not be a good predictor of growth promotion under low phosphorus conditions in planta. Strains that promoted plant growth under replete phosphorus still have the potential to improve horticulture in spaceflight and on earth.