The yeast Yarrowia lipolytica is an industrially important microorganism with distinctive physiological and metabolic characteristics. A variety of external factors (e.g., pH, temperature, and nutrient availability) influences the behavior of the yeast and may act as stress conditions which the cells must withstand and adapt. In this mini review, the impacts of environmental factors on the morphology and metabolite production by Y. lipolytica are summarized. In this regard, detailed insights into the effectors involved in the dimorphic transition of Y. lipolytica, the cultivation conditions employed, as well as the methods applied for the morphological characterization are highlighted. Concerning the metabolism products, a special focus is addressed on lipid and citric acid metabolites which have attracted significant attention in recent years. The dependence of lipid and citric acid productivity on key process parameters, such as media composition and physico-chemical variables, is thoroughly discussed. This review attempts to provide a recent update on the topic and will serve as a meaningful resource for researchers working in the field.

Yarrowia lipolytica, a non-conventional yeast with a promising biotechnological potential, is able to undergo metabolic and morphological changes in response to environmental conditions. The effect of pH perturbations of different types (pulses, Heaviside) on the dynamic behavior of Y. lipolytica W29 strain was characterized under two modes of culture: batch and continuous. In batch cultures, different pH (4.5, 5.6 (optimal condition), and 7) were investigated in order to identify the pH inducing a stress response (metabolic and/or morphologic) in Y. lipolytica. Macroscopic behavior (kinetic parameters, yields, viability) of the yeast was slightly affected by pH. However, contrary to the culture at pH 5.6, a filamentous growth was induced in batch experiments at pH 4.5 and 7. Proportions of the filamentous subpopulation reached 84 and 93 % (v/v) under acidic and neutral conditions, respectively. Given the significant impact of neutral pH on morphology, pH perturbations from 5.6 to 7 were subsequently assayed in batch and continuous bioreactors. For both process modes, the growth dynamics remained fundamentally unaltered during exposure to stress. Nevertheless, morphological behavior of the yeast was dependent on the culture mode. Specifically, in batch bioreactors where cells proliferated at their maximum growth rate, mycelia were mainly formed. Whereas, in continuous cultures at controlled growth rates (from 0.03 to 0.20 h) even closed to the maximum growth rate of the stain (0.24 h), yeast-like forms predominated. This pointed out differences in the kinetic behavior of filamentous and yeast subpopulations, cell age distribution, and pH adaptive mechanisms between both modes of culture.