The effects of plant-growth promoting actinobacteria on Origanum vulgare growth and bioactive molecule production

Plant growth promoting (PGP) bacteria are naturally occurring in plant crop soil and rhizosphere. They are increasing attention for their possible use as biofertilizers, since PGP bacteria exert beneficial effects on plant growth and development by improving, as examples, nutrition uptake, abiotic and biotic stress tolerance in plants1. Among the PGP bacteria, the actinobacteria are considered very promising due to their metabolic versatility, bioactive metabolites production and drought resistance. Sicily, like most semi-arid Southern European regions, hosts drought-resistant plants such as aromatics, with a diversified microbiota and high nutritional value, due to the production of valuable bioactive molecules. In this context, the two PGP actinobacteria Kocuria rhizophila and Streptomyces violaceoruber have been investigated for their possible effects on Origanum vulgare growth and bioactive molecule production. In particular, O. vulgare cultures were grown in pots and, subsequently, inoculated with actinobacterial cultures or mixtures thereof, using water, bacterial growth medium and a commercial microbial mix biofertilizer as control conditions, respectively. In this regard, the inoculum contribution on the composition of the soil microbiota has been also investigated by mean of culture-dependent approaches to reveal the presence of actinobacteria. The plants were then transplanted into an open field and grown until flowering. Preliminary results showed that PGP bacterial treatments exerted significant effects on selected morpho-physiological parameters like plant height. In addition, leaves and flowers were sampled to perform solid phase microextraction (SPME) analyses to reveal possible qualitative and quantitative changes on plant volatile organic compounds that could be ascribed to plant-actinobacteria interaction.