Endophytic bacteria of Brassicaceae seeds depend on the plant species

Seeds harbor diverse endophytic microbes that can be transmitted to offspring through parental plants. However, studies on the seed microbiomes of metal hyperaccumulators—plants capable of accumulating high levels of specific metals in their tissues—are scarce. This study aimed to characterize the diversity of endophytic bacterial communities in seeds from the Brassicaceae family, which contains the highest number of hyperaccumulating species. The seed collection analyzed included 65 accessions from 53 hyperaccumulating and 12 non- hyperaccumulating Brassicaceae species, spanning five genera and 24 species. These seeds were collected from various countries (Albania, Austria, France, Greece, Italy, Slovakia, Spain, and Romania) between 2010 and 2021. Using 16S rRNA metabarcoding, we characterized seed endophytic bacterial communities and investigated potential correlations between bacterial diversity and nickel concentrations in seeds through ICP-MS and µXRF analyses. Our findings indicate that plant host taxonomy is the primary determinant of endophytic bacterial community diversity in Brassicaceae seeds. Non-hyperaccumulating plants harbored significantly more diverse bacterial communities than hyperaccumulators. Certain bacterial families, such as Pseudomonadaceae and Nocardiaceae, were more abundant in non-hyperaccumulating Brassicaceae seeds, whereas Stenotrophomonas was more prevalent in nickel-rich seeds of hyperaccumulators. These differences suggest that metal accumulation in hyperaccumulator seeds imposes selective pressures, leading to shifts in bacterial community composition. This work confirms that plant host taxonomy is the primary driver of the seed endophytic bacterial com munity. However, in hyperaccumulating plants, the high metal concentrations that may occurred in seeds also influence bacterial diversity in this plant organ.