Phenanthrene contamination and ploidy level influence the rhizosphere microbiome of Spartina

Spartina spp. are widely distributed salt marsh plants that have a recent history of hybridization and polyploidization. These evolutionary events have resulted in species with a heightened resilience to hydrocarbon contamination, which could make them an ideal model plant for the phytoremediation/reclamation of contaminated coastal ecosystems. However, it is still unknown if allopolyploidization events also resulted in differences in the plant rhizosphere-associated microbial communities, and if this could improve the plant phytoremediation potential. Here, we grew two parental Spartina species, their hybrid and the resulting allopolyploid in salt marsh sediments that were contaminated or not with phenanthrene, a model tricyclic PAH. The DNA from the rhizosphere soil was extracted and the bacterial 16S rRNA gene and ITS region were amplified and sequenced. Generally, both the presence of phenanthrene and the identity of the plant species had significant influences on the bacterial and fungal community structure, composition and diversity. In particular, the allopolyploid S. anglica, harbored a more diverse bacterial community in its rhizosphere, and relatively higher abundance of various bacterial and fungal taxa. Putative hydrocarbon degraders were significantly more abundant in the rhizosphere soil contaminated with phenanthrene, with the Nocardia genus being significantly more abundant in the rhizosphere of S. anglica. Overall our results are showing that the recent polyploidization events in the Spartina did influence the rhizosphere microbiome, both under normal and contaminated conditions, but more work will be necessary to confirm if these differences result in a higher phytoremediation potential.