Changes in the population of seed bacteria of transgenerationally Cd-exposed Arabidopsis thaliana

Plant-associated bacteria can have beneficial effects on the growth and health of their host. Nevertheless, the role of endophytic bacteria present in seeds has not been investigated in depth. In this study, the cultivable endophytic population of seeds from Arabidopsis thaliana exposed to 2m cadmium for several generations (Cd seeds) was compared with a population isolated from seeds of plants that were never exposed to Cd (control seeds). We observed obvious differences between the two types of seed concerning genera present and phenotypic characteristics of the different isolates. Sinorhizobium sp. and Micrococcus sp. were only found in control seeds, while Pseudomonas sp., Bosea sp. and Paenibacillus sp. were only found in Cd seeds. Sphingomonas sp., Rhizobium sp., Acidovorax sp., Variovorax sp., Methylobacterium sp., Bacillus sp. and Staphylococcus sp. occurred in varying numbers in both types of seed. Metal tolerance and 1-aminocyclopropane-1-carboxylate deaminase activity were predominantly found in strains isolated from Cd seeds, while the production of siderophores, indole-3-acetic acid and organic acids was more prevalent in endophytes isolated from control seeds. These data support the hypothesis that certain endophytes are selected for transfer to the next generation and that their presence might be important for subsequent germination and early seedling development.