Enhanced biomass production of a novel Acetobacter strain isolated from Moroccan biotopes using response surface methodology approach

The objective of this work was first the isolation of novel acetic acid bacteria strains from natural Moroccan habitats, and then, the evaluation of their ability to produce microbial starters for vinegar production in large-scale. The isolation was made from figs, dates, cactus, and traditional fruit vinegars. Four strains, selected from a total of 63 isolates were confirmed to be belonged to Acetobacter species according to biochemical tests and molecular study based on 16s rDNA sequence analysis. Acetic acid fermentation tests, performed on date and apple fermented juices by the selected Acetobacter strains, showed high capacity of acidification. The most efficient strain, isolated from cactus vinegar, yielded an acidity of about 42.5 g/L on apple juice. A cell growth optimization was carried out on the most efficient strain using the response surface methodology (RSM). The linear, quadratic and interaction effects of four factors; ethanol, acetic acid, glucose and pH were studied by the application of a central composite design. 30 experiments were designed to predict the maximum concentration of cell biomass. The optimal calculated values of ethanol, acetic acid, glucose and pH allowing the prediction of the maximum biomass production (2.2 g/L) were 28.18 g/L, 10.12 g/L, 15.15 g/L and 5.33, respectively. Subsequently, further batch fermentations were carried out in a 6 L lab-bioreactor using the optimased culture medium. The results were in line with the predict values. It was concluded that the studied strain is well suited to be used as parental strain to prepare a starter for vinegar fruit production.