Growth of Lactobacillus plantarum BF001 and production of plantaricin F, an antimicrobial substance, in batch and continuous cultures

Lactobacillus plantarum BF00 1 growth and production of plantaricin F, an antimicrobial activity previously believed to be possibly a bacteriocin, were studied in batch and continuous cultures. Evidence was obtained that supported plantaricin F being lactic acid and not a bacteriocin. Lactobacillus plantarum BF001 was grown in static, aerobic batch cultures, using MRS medium containing various initial glucose concentrations. At initial glucose concentrations below 2.5% glucose, growth and fermentation proceeded until glucose was depleted. At initial glucose concentrations of 2.5% and above, growth ceased at ca pH 3.6, but resting cells continued to ferment residual glucose uncoupled from growth. Growth yield increases in three successive batch experiments could not be explained. Molar growth yields varied considerably dependent upon growth phase and initial glucose concentration in the MRS medium. Fermentation product analysis in the third batch experiment revealed that lactic acid and acetic acid were produced (2.2n:1, respectively) at 0.21% initial glucose and (6.3:1, respectively) at 0.44% initial glucose. While cultures having these low initial concentrations of glucose had heterolactic: fermentation, initial glucose concentrations of 0.85% and higher had strictly homolactic fermentation. Y_ATP was found to be variable and not a constant value of 10.5 g dry weight of cells mole-1 ATP. Y_ATP values for log/limited growth phase were 10.8, 16.2 and 19.8 g dry weight cells mole-1 ATP, respectively. In continuous cultures, Y_ATP increased with growth rate. Y_ATP values increased from 7.1 to 15.9 g dry weight of cells mole-1 ATP at dilution rates of 0.025 to 0.5 h-1. In continuous cultures, using 2% glucose MRS medium, glucose was never limiting at any dilution rate. At the lowest dilution rate (0.025 h-1), ca 25% of glucose in the medium was not utilized. Molar growth yields increased with dilution rate, indicating more efficient utilization of glucose to produce biomass at higher growth rates. Growth rate was probably limited by the inhibitory action of low pH and/or lactic acid concentration.