pH shifting adaptive evolution stimulates the low pH tolerance of Pediococcus acidilactici and high L-lactic acid...

L-lactic acid fermentation at low pH reduces the use of neutralizers during fermentation and the generation of solid wastes in purification processes. Most lactic acid bacteria exhibit weak tolerance and poor cell viability at low pH. This study proposes a pH shifting adaptive evolution method to improve the low-pH tolerance of an engineered Pediococcus acidilactici strain. In the first stage, cells were cultured at a moderate pH to maintain the cell viability, then shifted to a low pH to enhance low-pH tolerance. Long-term pH shifting evolution culture of the engineered P. acidilactici between the moderate and low pH resulted in a 43 % increase in L-lactic acid production at pH 4.6 (110.4 g/L) and a 2.1-fold increase at pH 4.4 (80.7 g/L) compared to the parental strain when using wheat straw as a feedstock. This pH-shifting adaptive evolution strategy provides an effective tool for improving the low-pH tolerance of lactic acid bacteria.