Optimal fermentation of <i>Pseudomonas synxantha</i> M1 and metabolomics analysis

The microbial agents based on plant growth promoting rhizobacteria (PGPR) have become a hot topic in agricultural research, while the optimization of fermentation conditions for PGPR-based microbial agents still lack systematic research. The single-factor and orthogonal experiments were conducted to determine the optimal fermentation conditions of <i>Pseudomonas synxantha</i> M1. The results indicated that the glycerol and shaker speed was the most significant factors that influence the number of bacteria of <i>P. synxantha</i> M1 fermentation liquid. The viable bacteria count of microbial agent reached 7.1 × 10¹² cfu/mL at 36 h, which OD₆₀₀ value increased by 116.40% compared to before optimization, and promote the growth of highland barley. Significant differences of metabolites of fermentation liquid was observed in different fermentation times, including organic acids, lipids, and organoheterocyclic compounds using liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, the fermentation liquid was found to contain indoleacetic acid, glutathione and xanthine at the end of fermentation, which might contribute for the growth of plants as bioactive substances.