Optimization of growth of Bacillus coagulans DSM 2314 for biomass harvesting and prove its effectiveness as microbial inoculant for lactic acid production

Weizmannia coagulans is a microorganism that is suitable to produce lactic acid via simultaneous saccharification and fermentation. However, previous studies mainly focused on fermentation process rather than achieving high-cell-density cultivation to maximize product yield. In order to obtain a strong inoculum that can resist inhibitors produced during pre-treatment of complex substrates like lignocellulosic materials, and subsequent fermentation, there is a need to find suitable conditions for growth and to prove lactic acid-forming ability of the microorganism at high titre. First, the strain DSM 2314 was screened in bench-scale cultivations, and then different glucose concentrations were tested in controlled reactors to enhance biomass accumulation. Furthermore, shake flask cultures were optimised to provide a strong and viable inoculum for batch fermentations at 500 mL scale. Lactic acid accumulation with CaCO3 as neutralizing agent was also investigated in shake flasks, and higher lactic acid production by W. coagulans was validated at 500 mL scale bioreactors. In summary, glucose depletion was achieved with low amount of added sugar in aerobic fermentations. In addition, precultivation was optimised thus enabling the cells to adapt quickly in subsequent fermentation. In anaerobic fermentation, glucose was completely consumed by the cells in both fermentations with 25 g L-1 and 50 g L-1. However, the lactic acid titre was low in the second case (0.66 g g-1 ) in contrast to other lactic acid bacteria. In addition, it was shown that addition of CaCO3 as a buffer had a beneficial effect on bacterial growth of W. coagulans DSM 2314, thus enhancing product formation of LA of more than 52.58% compared to the benchmark fermentation. The highest dry cell weight reached in 24 hours within aerobic cultivations was 4.65 g L-1. Although cell densities were not as high as expected, these results provide information about the aerobic cultivation of W. coagulans.