Plant growth promoting bacteria: a sustainable tool to minimize water footprint in agriculture in arid and semi-arid zones

Impact of climate change in arid and semi-arid zones is leading us to deliver innovative strategies in agriculture to increase safe food production and at the same time minimizing water footprint. Desert farming, combined with an improved wastewater recycling, might represent a smart solution to guarantee food access in water stressed countries to an increasing population. Plant Growth Promoting (PGP) microorganisms, recruited as components of the plant microbiome, exert several mechanisms to improve plant growth and health and could therefore be exploited to improve plant productivity and services. We aimed at the study of PGP bacteria associated to plants growing in Mediterranean African Countries (MACs): plants of interest for desert farming and/or adapted to arid/saline soils (Sorghum sp., Argania spinosa, Salicornia sp.) and plants cultivated in constructed wetland facilities having phytodepuration activity. A large collection of rhizosphere and endosphere bacterial isolates was established, dereplicated and identified. The phylogenetic and phenotypic characterization led to select strains for the in vivo assessment of PGP activity: i) classifiable as GRAS (Generally Regarded As Safe), basing on the literature screening about their species, ii) resistant to osmotic and saline stresses and iii) sensitive to different classes of antibiotics. The in vivo PGP assays were performed on potted tomato plants under greenhouse conditions, artificially inducing water stress. Several bacterial strains, including isolates belonging to the Bacillus and Pseudomonas genera, demonstrated to significantly increase plant growth compared with non-inoculated controls. Besides corroborating previous findings on the potential of extremophilic plants as source of PGP bacterial strains exploitable under adverse condition, we identified promising candidates for the future development of biofertilizers tailored on the need of MACs, exploitable to sustainably improve desert farming and phytodepuration.