mixotroph

Mixotrophy is a nutritional strategy in which a single organism combines autotrophy, typically through photosynthesis, with heterotrophy, the ability to ingest or absorb organic matter. Mixotrophs can obtain carbon and energy from inorganic sources via photosynthesis and from organic sources by consuming prey or absorbing dissolved organic compounds. The balance between these modes can shift with light, nutrients, and ecological conditions.

There are different forms of mixotrophy. Phagotrophic mixotrophs actively ingest prey such as bacteria or small algae to supplement their carbon and nutrient supply, especially when light or nutrients are limiting. Phototrophic mixotrophs rely primarily on photosynthesis but take up organic compounds or prey opportunistically. Some organisms use kleptoplasty, retaining and using plastids stolen from prey to temporarily sustain photosynthesis.

Among mixotrophs, protists such as certain flagellates and amoebae are well known. Euglena gracilis is a classic example that can photosynthesize and also feed on bacteria. In marine systems, many dinoflagellates, chrysophytes, and other protists exhibit mixotrophy, leveraging both energy pathways to adapt to variable light and nutrient regimes. This flexibility allows mixotrophs to occupy ecological niches where strict phototrophs or heterotrophs would be disadvantaged.

Ecological significance of mixotrophy includes its impact on nutrient cycling and carbon flow in aquatic ecosystems. Mixotrophs can influence prey populations, herbivory dynamics, and the transfer of energy through food webs, particularly in environments with limited nutrients or fluctuating light. Ongoing research aims to quantify the relative contributions of autotrophic and heterotrophic nutrition in different mixotrophic lineages.