Effects of Bacillus amyloliquefaciens and organic and inorganic phosphate amendments on Maize plants as revealed by NMR and GC-MS based metabolomics

Aims: Plant growth-promoting bacteria of the genus Bacillus are known to solubilize phosphates and enhance plant growth in many plant species. We explored the effects of the inoculation with a commercial isolate Bacillus amyloliquefaciens on the growth and metabolic processes of maize plants in pot soils treated with triple superphosphate, rock phosphate, and either cow- or horse-manure composts, as P-fertilizers. Methods: The metabolic profiles of maize leaves in the different treatments were determined by both Gas Chromatography–Mass Spectrometry and Nuclear Magnetic Resonance spectroscopy. Principle Components Analysis (PCA) based on data matrix from both techniques revealed a relationship between treatments and specific plant metabolites. Results: Inoculated plants showed larger P and N contents and a more differentiated metabolome when treated with the two composts than with inorganic fertilizers. B. amyloliquefaciens in combination with composts significantly increased glucose, fructose, alanine and GABA metabolites in maize leaves, thus suggesting an improved photosynthetic activity due to enhanced P and N uptake. Both composts sustained plant growth and the phosphate solubilizing activity of B. amyloliquefaciens, while differences in P and N contents in plant leaves were attributed to the different content in compost of lignin residues and alkyl moieties, and consequent impact on microbial growth. Conclusions: The combination of B. amyloliquefaciens inoculation with composted organic P-fertilizers rich in available metabolic carbon appears as an efficient alternative to mineral fertilizers to enhance nutrients uptake and foster growth mechanisms in maize plants