Regulation of Phagotrophy by Prey, Low Nutrients, and Low Light in the Mixotrophic Haptophyte Isochrysis galbana González Olalla, Juan Manuel Medina Sánchez, Juan Manuel Norici, Alessandra Carrillo Lechuga, Presentación Autotrophic processes Cell composition Enzymes Haptophyta Homeostasis Mixotrophy Nutritional status Phytoplankton Mixotrophy combines autotrophy and phagotrophy in the same cell. However, it is not known to what extent the phagotrophy influences metabolism, cell composition, and growth. In this work, we assess, on the one hand (first test), the role of phagotrophy on the elemental and biochemical composition, cell metabolism, and enzymes related to C, N, and S metabolism of Isochrysis galbana Parke, 1949. On the other hand, we study how a predicted increase of phagotrophy under environmental conditions of low nutrients (second test) and low light (third test) can affect its metabolism and growth. Our results for the first test revealed that bacterivory increased the phosphorous and iron content per cell, accelerating cell division and improving the cell fitness; in addition, the stimulation of some C and N enzymatic routes help to maintain, to some degree, compositional homeostasis. Under nutrient or light scarcity, I. galbana grew more slowly despite greater bacterial consumption, and the activities of key enzymes involved in C, N, and S metabolism changed according to a predominantly phototrophic strategy of nutrition in this alga. Contrary to recent studies, the stimulation of phagotrophy under low nutrient and low irradiance did not imply greater and more efficient C flux. 2025-01-22T13:08:24Z 2025-01-22T13:08:24Z 2021-03-04 journal article González-Olalla, J.M., Medina-Sánchez, J.M., Norici, A. et al. Regulation of Phagotrophy by Prey, Low Nutrients, and Low Light in the Mixotrophic Haptophyte Isochrysis galbana. Microb Ecol 82, 981–993 (2021). https://doi.org/10.1007/s00248-021-01723-w https://hdl.handle.net/10481/100025 10.1007/s00248-021-01723-w eng http://creativecommons.org/licenses/by-sa/4.0/ open access Atribución-CompartirIgual 4.0 Internacional Springer