Phymabactin Facilitates the Growth of the Legume Symbiont <em>Paraburkholderia phymatum</em> in Aluminium‐Rich Martian Soil and Acts as a Bioremediation Agent

Beneficial interactions between nitrogen-fixing soil bacteria and legumes offer a solution to increase crop yield on Earth and potentially in future Martian colonies. In this study, we assessed the growth of the beta rhizobium Paraburkholderia phymatum in Martian simulant soil using Enhanced Mojave Mars Simulant 2 (MMS-2) that contains a high amount of iron (18.37 percent by weight) and aluminium (13.07 percent by weight). We observed that while P. phymatum wild-type’s growth was not affected by exposure to MMS-2, a mutant strain impaired in siderophore biosynthesis (ΔphmJK) grew less than P. phymatum wild-type on gradient plates prepared with increasing proportions of MMS-2 or aluminium concentration. This result suggests that the P. phymatum siderophore phymabactin alleviates aluminium-induced heavy metal stress. Using Ultra-high performance liquid chromatography-mass spectrometry (UHPLC MS), we showed that phymabactin can bind to aluminium more efficiently than iron. These results not only deepen our understanding of the behaviour of rhizobia in simulated extraterrestrial environments but also provide new insights into the potential use of P. phymatum for bioremediation and the multiple roles of the siderophore phymabactin.