Effect of phenolic acids from banana root exudates on root colonization and pathogen suppressive properties of Bacillus amyloliquefaciens NJN-6

Bacillus amyloliquefaciens NJN-6, a plant growth promoting bacterium can act as an efficient antagonist against F. oxysporum f. sp. cubense (FOC). This study tests the response of antibiotic producing genes (ituA and bamD) and biofilm formation related genes (epsD and yqxM) in strain NJN-6 to phenolic acids in banana root exudates. Phenolic acid in banana root exudates (infected or non-infected by FOC) were identified by HPLC. Transcription analysis of genes involved in biofilm formation and antibiotic synthesis in strain NJN-6 were investigated with quantitative reverse transcription PCR (RT-qPCR). We found that the transcription levels of two antibiotic producing genes and two biofilm formation related genes in strain NJN-6 were upregulated in the banana seedling roots. Root secretion of phthalic acid, salicylic acid and cinnamic acid were enhanced in FOC infected banana seedlings. Further additional experiments demonstrated that the transcription level of ituA, bamD and epsD increased linearly to the concentration of phthalic acid. Results from antibiotic production and biofilm formation assays demonstrated a similar trend to gene transcription analysis. The results in this study indicated that the phenolic acids in root exudates of banana can potentially enhance root colonization and pathogen suppression abilities of Bacillus amyloliquefaciens NJN-6.