osmotrophic

Osmotrophy is a nutritional mode in which organisms acquire energy and carbon by absorbing dissolved organic compounds directly across their cell membranes. Uptake is mediated by membrane transporters that import small molecules such as sugars, amino acids, organic acids, and other metabolites from the surrounding environment. In many cases, organisms secrete extracellular enzymes that hydrolyze larger polymers into soluble monomers before uptake, enabling rapid use of dissolved nutrients without phagocytosis.

Fungi provide a classic example of osmotrophy, especially in saprotrophic and some symbiotic lifestyles. They secrete enzymes (for example cellulases, proteases, and lignin-degrading enzymes) into their surroundings and absorb the resulting monomers through hyphal membranes. Other groups, including certain bacteria, archaea, and protists, also exhibit osmotrophy, particularly in aquatic or nutrient-rich soils where dissolved organic matter fuels heterotrophic growth.

Osmotrophy is distinct from phagotrophy, in which organisms ingest solid particles by engulfing them, and from photosynthesis-based nutrition. Many ecosystems rely on osmotrophic processes to recycle dissolved organic carbon and nutrients. In soils and streams, osmotrophic microbes contribute to decomposition and nutrient turnover by converting polymers to soluble compounds that can be taken up by a wider community.

While the term is most commonly applied to fungi, it is used more broadly in microbiology and protistology to describe any organism whose primary or significant feeding mode involves uptake of dissolved organic material rather than particulate food.