Diversity and potential plant growth promoting capacity of seed endophytic bacteria of the holoparasite Cistanche phelypaea (Orobanchaceae)

Salt marshes are highly dynamic, biologically diverse ecosystems with a broad range of ecological functions. We investigated the endophytic bacterial community of surface sterilized seeds of the holoparasitic Cistanche phelypaea growing in coastal salt marshes of the Iberian Peninsula in Portugal. C. phelypaea is the only representative of the genus Cistanche that was reported in such habitat. Using high-throughput sequencing methods, 23 bacterial phyla and 263 different OTUs on genus level were found. Bacterial strains belonging to phyla Proteobacteria and Actinobacteriota were dominating. Also some newly classified or undiscovered bacterial phyla, unclassified and unexplored taxonomic groups, symbiotic Archaea groups inhabited the C. phelypaea seeds. gamma-Proteobacteria was the most diverse phylogenetic group. Sixty-three bacterial strains belonging to Bacilli, Actinomycetes, alpha-, gamma- and beta-Proteobacteria and unclassified bacteria were isolated. We also investigated the in vitro PGP traits and salt tolerance of the isolates. Among the Actinobacteria, Micromonospora spp. showed the most promising endophytes in the seeds. Taken together, the results indicated that the seeds were inhabited by halotolerant bacterial strains that may play a role in mitigating the adverse effects of salt stress on the host plant. In future research, these bacteria should be assessed as potential sources of novel and unique bioactive compounds or as novel bacterial species.