Establishing self-sustainable colonies on another stellar object demands implementing space farming. Yet, the lower gravity and the availability of nutrients necessary for crop growth make the production of an adequate yield a challenge. A solution to this issue is to use the symbiosis between nitrogen-fixing bacteria (rhizobia) and legumes. Rhizobia play a key role in the nitrogen cycle on Earth and are responsible for about 60% of the total global nitrogen fixation. Hence, they could be used to improve the growth of crops in space. Yet, little is known about the impact of microgravity on mutualistic systems. Thus, we have been studying the effects of simulated microgravity (s0-g) on the growth and symbiotic performance in two rhizobia: Rhizobium tropici and Paraburkholderia phymatum. We have phenotypically characterized both rhizobia in s0-g using a random positioning machine (RPM) to induce simulated microgravity. Neither of the bacteria showed differences in resistance to antibiotic or oxidative stress. Yet, both rhizobia showed higher levels of vesicle formation and root attachment to the common bean root in s0-g compared to 1g. Also, differential RNA sequencing analysis performed on P. phymatum free-living cells showed that key genes for osmolarity maintenance, stress resistance and nitrogen fixation are upregulated in s0-g compared to 1g, hinting that rhizobia can survive and establish a successful symbiosis with legumes in s0-g. Next, we will use a transposon sequencing library of P. phymatum to determine the subset of genes that are important for thriving in s0-g. We plan to complement this genotypic analysis with metabolomic and proteomic analyses in cells growing in s0-g and 1g to study the molecular changes occurring in rhizobial cells incubated s0-g. Also, we want to analyze P. phymatum cells grown in s0-g and in 1g over an extended time frame to illuminate which genetic and epigenetic adaptations facilitate bacterial cell growth in s0-g.
