Analysis of bacterial volatiles that promote plant growth

Despite advances in agricultural practices, it is necessary to increase the global production of food and energy from biomass by adopting environmentally sustainable approaches. Several bacteria that promote plant growth (PGPB) can significantly increase the yield of agricultural crops through a variety of mechanisms. Recently, many studies are being carried out with volatile organic compounds (VOCs), which are small lipophilic-looking molecules derived from a wide range of biosynthetic pathways. These metabolites are able to promote plant growth and their use in crops is promising, since they do not depend on direct contact and roots or shoots colonization, making them ideal molecules to mediate interactions between organisms at short and long distance. To date, many studies have shown the positive effect of VOCs on model plants, such as Arabidopsis thaliana. However, there are few studies showing their impact on C4 plants and crops, opening up prospects for new discoveries. Therefore, the main purposes of this project were: (i) to evaluate the potential of different bacterial genera from our collection in promoting growth of model plants C3 A. thaliana and C4 Setaria viridis mediated by VOCs; (ii) to test the effectiveness of the selected isolates after minimizing the carbon dioxide (CO2) effect; (iii) to establish a robust metabolomics pipeline based on HS-SPME/GC-MS for VOCs identification; (iv) to identify the VOCs produced by the selected isolates using HS-SPME/GC-MS; (v) to analyse and select the identified VOCs for functional evaluation in both model plants. 7 out of 14 isolates tested were identified as they efficiently increased the growth of model plants, being: MTS P6A5 and CRD P6B3 for promoting in A. thaliana; AI2.2-A and CTB P6B8 in S. viridis; IAT P3B1, IAT P6F4 and FBJ P1E2 for promoting the growth of both. The growth promotion in shoot and total root length of A. thaliana ranged between 190-320 % and 40-110 %, respectively, while in S. viridis we observed an increase between 190 and 350 % in shoot biomass and about 100 % in root length. In addition, we identified two isolates (MTS P5D6 and ITA P2F2) that had an antagonistic effect in promoting plant growth. The best isolates, even under an environment that minimizes the CO2 effect, were also efficient in increasing the seedlings total biomass in different ranges. From the analysis of the volatilome emitted by selected isolates through the pipeline developed by the group, it was possible to identify 105 VOCs candidates for plant growth-inducing molecules. 10 VOCs were selected for functional validation, and the results demonstrated that the synthetic compounds acetoin, 2,3-butanediol, 2-heptanone and phenethyl alcohol were responsible for increasing between 14 and 24 % the S. viridis growth, evidencing the efficiency of these compounds as plant growth modulators. This is the first report showing the growth promotion of S. viridis model plant mediated by bacterial VOCs, which will certainly generate insights for the development of innovative technologies to promote sustainable agriculture in important Brazilian agribusiness (AU)