Synthetic communities of maize root bacteria interact and redirect benzoxazinoid metabolisation

Plant roots are colonised by diverse microbial communities. These communities are shaped by root exudates including plant-specialized metabolites. Benzoxazinoids are such secreted compounds of maize. Individual microbes differ in their ability to tolerate and metabolise antimicrobial benzoxazinoids. To investigate how these traits combine in a community, we designed two synthetic communities of maize root bacteria that share six common strains and differ in their ability to metabolise benzoxazinoids based on the seventh strain. We exposed both communities to the benzoxazinoid MBOA (6-methoxybenzoxazolin-2(3H)-one) and found that MBOA shaped the composition of both communities and increased the fraction of MBOA-tolerant strains. The benzoxazinoid metabolising community showed a higher tolerance to MBOA and was able to utilize MBOA as their sole carbon source for growth. Unexpectedly, we found that the metabolising community did not degrade MBOA to its aminophenoxazinone, as observed for individual strains, but as a community they formed the corresponding acetamide. Hence, bacterial interaction results in alternative benzoxazinoid metabolisation. Future work is needed to uncover the genetics of this metabolic interaction and ecological consequences for the bacterial community and the host plant.