saprotrophy

Saprotrophy is a nutritional mode in which an organism obtains energy and carbon from dead or decaying organic matter by secreting extracellular enzymes that break down complex polymers into smaller, soluble compounds that can be absorbed.

Most saprotrophs are fungi, particularly basidiomycetes and ascomycetes that decompose leaf litter, wood, and other detritus. Bacteria and some protists also exhibit saprotrophic lifestyles. Saprotrophs rely on the breakdown of organic matter rather than extracting nutrients from living hosts, though some organisms are facultative saprotrophs and can switch to other modes of nutrition when opportunity or substrates arise.

Ecologically, saprotrophy drives decomposition and nutrient cycling and is a key component of the carbon cycle. Saprotrophic enzymes include cellulases, hemicellulases, lignin-modifying enzymes such as lignin peroxidases and laccases, proteases, and chitinases. By mineralizing organic matter, saprotrophs release inorganic nutrients and make them available to other organisms, including plants.

Differentiating saprotrophy from parasitism and predation helps clarify ecological roles. Saprotrophs feed on dead material, whereas parasites extract nutrients from living hosts. Some fungi are primarily saprotrophic but may become pathogenic or form mutualisms under certain conditions, and some wood-decay fungi exemplify classic saprotrophy, breaking down lignocellulose in dead wood.

Examples include white-rot and brown-rot fungi that decompose wood, various soil-dwelling fungi, and many soil bacteria that degrade plant and animal detritus. Saprotrophy is widespread across ecological systems and underpins soil fertility and ecosystem productivity.