Saprotrophic nutrition

Mycelial cord made up of a collection of hyphae; an essential part in the process of saprotrophic nutrition, it is used for the intake of organic matter through its cell wall. The network of hyphae is referred to as a mycelium, which is fundamental to fungal nutrition.

Saprotrophic nutrition /sæprɵˈtrɒfɪk/ is a process of chemoheterotrophic extracellular digestion involved in the processing of dead or decayed organic matter. It occurs in saprotrophs or heterotrophs, and is most often associated with fungi (for example Mucor and Rhizopus) and soil bacteria. Saprotrophic microscopic fungi are sometimes called saprobes; saprotrophic plants or bacterial flora are called saprophytes (sapro- + -phyte, "rotten material" + "plant"). The process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae.^[1]

Various word roots relating to decayed matter (detritus, sapro-), eating and nutrition (-vore, -phage), and plants or life forms (-phyte, -obe) produce various terms, such as detritivore, detritophage, saprotroph, saprophyte, saprophage, and saprobe; their meanings overlap, although technical distinctions (based on physiologic mechanisms) narrow the senses. For example, usage distinctions can be made based on macroscopic swallowing of detritus (as an earthworm does) versus microscopic lysis of detritus (as a mushroom does).

Process

Explanation

As matter decomposes within a medium in which a saprotroph is residing, the saprotroph breaks such matter down into its composites.

• Proteins are broken down into their amino acid composites through the breaking of peptide bonds by proteases.^[2]
• Lipids are broken down into fatty acids and glycerol by lipases.^[2]
• Starch is broken down into simple disaccharides by amylases.^[2]

These products are re-absorbed into the hypha through the cell wall via endocytosis and passed on throughout the mycelium complex. This facilitates the passage of such materials throughout the organism and allows for growth and, if necessary, repair.^[1]

Conditions

In order for a saprotrophic organism to facilitate optimal growth and repair, favourable conditions and nutrients must be present.^[3] Optimal conditions refers to several conditions which optimise the growth of saprotrophic organisms, such as;

1. Presence of water: 80–90% of the fungus is composed of water by mass, and requires excess water for absorption due to the evaporation of internally retent water.^[3]
2. Presence of oxygen: Very few saprotrophic organisms can endure anaerobic conditions as evidenced by their growth above media such as water or soil.^[3]
3. Neutral-acidic pH: The condition of neutral or mildly acidic conditions under pH 7 are required. ^[3]
4. Low-medium temperature: The majority of saprotrophic organisms require temperatures between 1 °C and 35 °C, with optimum growth occurring at 25 °C.^[3]

The majority of nutrients taken in by such organisms must be able to provide carbon, proteins, vitamins and in some cases, ions. Due to the carbon composition of the majority of organisms, dead and organic matter provide rich sources of polysaccharides and disaccharides such as glucose, maltose, and starch.^[1]

In terms of nitrogen-rich sources, saprotrophs require combined protein for the creation of proteins, which is facilitated by the absorption of amino acids, and usually taken from rich soil. Although both ions and vitamins are rare, thiamine or ions such as potassium, phosphorus, and magnesium aid the growth of the mycelium.^[1]

See also

• Mycorrhizal fungi and soil carbon storage
• Chemoautotrophic nutrition
• Detritivore
• Holozoic nutrition
• Parasitic nutrition
• Photoautotrophic nutrition
• Photosynthesis
• Wood-decay fungus

Notes

• Clegg, C. J.; Mackean, D. G. (2006). Advanced Biology: Principles and Applications, 2nd ed. Hodder Publishing

References