Fungal extracellular enzyme activity

Extracellular enzymes or exoenzymes are synthesized inside the cell and then secreted outside the cell, where their function is to break down complex macromolecules into smaller units to be taken up by the cell for growth and assimilation. These enzymes degrade complex organic matter such as cellulose and hemicellulose into simple sugars that enzyme-producing organisms use as a source of carbon, energy, and nutrients. Grouped as hydrolases, lyases, oxidoreductases and transferases, these extracellular enzymes control soil enzyme activity through efficient degradation of biopolymers.

Upon senescence, plant residues, animals and microorganisms enter the dead organic matter pool and become a source of nutrients and energy for other organisms. Extracellular enzymes target macromolecules such as carbohydrates (cellulases), lignin (oxidases), organic phosphates (phosphatases), amino sugar polymers (chitinases) and proteins (proteases) and break them down into soluble sugars that are subsequently transported into cells to support heterotrophic metabolism.

Biopolymers are structurally complex and require the combined actions of a community of diverse microorganisms and their secreted exoenzymes to depolymerize the polysaccharides into easily assimilable monomers. These microbial communities are ubiquitous in nature, inhabiting both terrestrial and aquatic ecosystems. The cycling of elements from dead organic matter by heterotrophic soil microorganisms is essential for nutrient turnover and energy transfer in terrestrial ecosystems. Exoenzymes also aid digestion in the guts of ruminants, termites, humans and herbivores. By hydrolyzing plant cell wall polymers, microbes release energy that has the potential to be used by humans as biofuel. Other human uses include waste water treatment, composting and bioethanol production.

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