Production of the postharvest biocontrol agent Bacillus subtilis CPA-8 using low cost commercial products and by-products

The aim of this research was to identify a low cost medium based on commercial products and by-products that provided maximum Bacillus subtilis CPA-8 growth and maintained biocontrol efficacy. Low cost media combining economical nitrogen and carbon sources such as yeast extract, peptone, soy products, sucrose, maltose and molasses were tested. Tests were carried out in 250-ml flasks containing 50 ml of each tested medium. Maximum cell growth (>3 × 109 CFU ml−1) was obtained in defatted soy flour 44% combined with sucrose or molasses media. Second, CPA-8 production was scaled up in a 5-l fermenter and CPA-8 population dynamics, pH and oxygen consumption in the optimized medium (defatted soy flour 44% – molasses) was recorded. In these tests, there was a 5-h lag phase before growth, after which exponential growth occurred and maximum production was 3 × 109 CFU ml−1 after 20 h. Fruit trials with cells and cell free supernatants from CPA-8 grown in optimized medium maintained biocontrol efficacy against Monilinia fructicola on peaches, resulting in disease reductions up to 95%. CPA-8 populations survived in wounds on inoculated peaches, regardless of the culture media used. The results show that B. subtilis CPA-8 can be produced in a low cost medium combining inexpensive nitrogen and carbon sources (40 g l−1 defatted soy flour 44%, 5 g l−1 molasses plus mineral trace supplements) in shake flasks and a laboratory fermenter (5 l). The results could be used to provide a reliable basis for scaling up the fermentation process to an industrial level.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► CPA-8 is an effective biocontrol agent of postharvest pathogens on stone fruit. ► Mass production of CPA-8 is an essential step for its commercial use. ► Low cost medium defatted soy flour and molasses provided a high CPA-8 production. ► CPA-8 grown in this cheap medium maintained its biocontrol efficacy against peach brown rot.