Metabolic shifts induced by pH variation in <i>Yarrowia lipolytica</i> biofilm

The yeast Yarrowia lipolytica adapts its metabolite production based on cultivation conditions, with the pH value playing a critical role. At pH 3, most Y. lipolytica strains produce polyols, while at pH 5, they accumulate predominantly organic acids. Yarrowia lipolytica has demonstrated the ability to transition from a planktonic, free-floating state to an immobilized state as a biofilm. This study aims to clarify the effects of pH level and carbon sources on the physiological state of Y. lipolytica when grown in a biofilm state. These pH variations were applied to the same biofilm culture to assess the capacity of given Y. lipolytica cells to undergo metabolic shifts and recovery under changing environmental conditions. Interestingly, a pH shift from 3 to 5 leads-as expected-to a metabolic shift from polyols to citric acid. However, the shift back to pH 3 does not revert to polyols as major products. This study not only revealed an unexpected production pattern but also provided benefits for the industrial process in general. Understanding biofilm cultivation methods supports continuous bioprocesses using the immobilized nature of biofilm. pH-alternating experiments reveal how environmental condition fluctuations affect biofilm culture physiology.