Abstract

Ericaceous plants (Ericaceae, the heath family) establish complex symbioses with soil-borne microorganisms that facilitate their survival in challenging environments such as nutrient-impoverished heathlands, heavy metal-polluted soils, and inert volcanic rock substrates. While the symbiosis with the ericoid mycorrhizal (ErM) fungi has attracted significant attention, little is known about the endophytic bacteria and how they affect fitness of their ericaceous hosts. In this study, we isolated and identified endophytic bacteria from hair roots of Gaultheria poeppigii colonizing volcanic deposits at a site in the Chilean southern Andes. In addition, their in vitro capacity to solubilize phosphate, produce exopolysaccharides, siderophores, ammonia, indole acetic acid (IAA), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity was evaluated. In total, 74 isolates were obtained, belonging to the phyla Proteobacteria, Firmicutes, and Actinobacteria and the genera Paraburkholderia, Paenibacillus, Variovorax, Bacillus, Leifsonia, and Arthrobacter. Only two Paraburkholderia sp. isolates showed phosphate solubilization. Siderophore production was detected in six isolates, with the highest production detected in the Variovorax paradoxus. All strains produced ammonia and IAA in different amounts and six displayed ACC deaminase activity, the highest being detected in V. paradoxus GC55. The results of our biocontrol assay showed that V. paradoxus GC51 had the highest percentages of inhibition of common phytopathogens with values ranging from 65 to 100%. To our best knowledge, this is the first report on the cultivable bacteria colonizing the hair roots of ericaceous plants growing in volcanic deposits and our results suggest that at least some of them might promote the host growth and confer protection against pathogens. We suggest that not only the ErM fungi but also the root-symbiotic bacteria contribute to the remarkable resilience of ericaceous plants in challenging environments such as volcanic deposits.