A study was undertaken to determine the effects of a strain of Arthrobacter sp., a Plant Growth-Promoting Bacteria (PGPB), on plant phenology and qualitative composition of Opuntia ficus-indica (L.) Mill. fruits and cladodes. The strain was inocu- lated in soil, and its effects on cactus pear plants were detected and compared to nontreated plants. Compared to the latter, the treatment with bacteria promoted an earlier plant sprouting (2 months before the control) and fruitification, ameliorat- ing fruit quality (i.e., improved fresh and dry weight: + 24% and + 26%, respectively, increased total solid content by 30% and polyphenols concentrations by 22%). The quality and quantity of monosaccharides of cladodes were also increased by Arthrobacter sp. with a positive effect on their nutraceutical value. In summer, the mean values of xylose, arabinose, and mannose were significantly higher in treated compared to not treated plants (+ 3.54; + 7.04; + 4.76 mg/kg d.w. respectively). A similar trend was observed in autumn, when the cladodes of inoculated plants had higher contents, i.e., 33% xylose, 65% arabinose, and 40% mannose, respect to the controls. In conclusion, Arthrobacter sp. plays a role in the improvement of nutritional and nutraceutical properties of cactus pear plants due to its capabilities to promote plant growth. Therefore, these results open new perspectives in PGPB application in the agro-farming system as alternative strategy to improve cactus pear growth, yield, and cladodes quality, being the latter the main by-product to be utilized for additional industrial uses.
Due to its ‘multi-functionality,’ OFI is indicated as one of the species of the future, and our results may contribute to disclose its potentialities in the contest of bioeconomy and circular economy. Since natural resources and cultural prac- tices are crucial in defining the quality of cladodes when addressed to food/nutraceutical applications, the inoculation of OFI with Arthrobacter sp. may be foreseen to provide a better plant growth under environmental stress conditions, or as soil fertilizer, but also to improve the synthesis of natural products, used for therapeutic applications. Further studies would be aimed to better understand the connecting path- ways involved in OFI-Arthrobacter interaction in order to assess bacteria contribution to cactus pear metabolism and to bridge the gap in the use of Arthrobacter sp. from labora- tory to field scale.