mixotrophyand

Mixotrophy is a nutritional strategy in which an organism combines phototrophy with heterotrophy, enabling it to obtain energy and carbon from both light-driven carbon fixation and ingestion or uptake of organic compounds. In mixotrophy, organisms may perform photosynthesis and phagotrophy (ingesting particles or prey) or osmotrophy (absorbing dissolved organic molecules) within the same life stage or at different times.

Most commonly described in protists and algae, mixotrophy is found among various eukaryotic lineages, including certain chrysophytes, dinoflagellates, and euglenoids, as well as some ciliates. The classic example is Euglena gracilis, which retains photosynthetic plastids but can feed on bacteria or prey under low light or nutrient-poor conditions. Other photoautotrophic algae may switch to heterotrophy in response to nutrient limitation, and some mixotrophs rely primarily on photosynthesis when light is abundant and on ingestion when prey is available.

Ecological significance: Mixotrophy provides flexibility in nutrient-poor environments; it influences microbial food webs and biogeochemical cycles by coupling carbon fixation with consumption of prey and dissolved organic matter. In marine systems, mixotrophic phytoplankton can alter competition dynamics and bloom formation.

Evolution and metabolism: Mixotrophy arises from retention of plastids and metabolic pathways enabling heterotrophy, and may involve genetic exchange and endosymbiotic events. It highlights a continuum between phototrophy and heterotrophy rather than discrete categories.