Beneficial soil bacteria enhancing the functional value of fruits and vegetables

Fruits and vegetables have been largely investigated for their content in health-promoting secondary metabolites, that can be constitutively expressed and/or elicited by beneficial soil microorganisms colonizing plant rhizosphere, mycorrhizosphere and endosphere. Beyond arbuscular mycorrhizal fungi, which represent the most studied group, several bacterial taxa can improve the nutritional and nutraceutical content of food crops. Some Bacillus strains were shown to promote the activity of antioxidant enzymes, such as polyphenol oxidase, ascorbate peroxidase, catalase and superoxidase dismutase, in different plant species, while Pseudomonas spp. inoculated in strawberry plants stimulated the production of anthocyanins, well known for their antioxidant, antiangiogenic and antiproliferative properties. Only a few works investigated the mechanistic basis of the enhanced production of bioactive compounds. Indeed, metabolomics and transcriptomics studies could reveal the correlation between the expression levels of modulated genes and the functions leading to the synthesis of the relevant plant secondary metabolites. In the years to come, the effectiveness of different microbial combinations, designed considering their additional or synergistic effects, should be evaluated also in the field, in order to select the best individual strains and consortia to be used as innovative plant inocula able to boost the production of fruits and vegetables with high functional value.