Saprotroph

A saprotroph is an organism that feeds on dead organic matter or waste by excreting chemicals to digest it, rather than eating it directly (as detritivores do). It is most often performed by fungi (e.g. Mucor) and soil bacteria. Microscopic saprotrophs are sometimes called saprobes.^[1] In fungi, saprotrophic digestion is usually done by actively transporting such materials through endocytosis within the internal mycelium and its constituent hyphae.^[2]

Process

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.^[3]
Lipids are broken down into fatty acids and glycerol by lipases.^[3]
Starch is broken down into pieces of simple disaccharides by amylases.^[3]
Cellulose, a major portion of plant cells, and therefore a major constituent of decaying matter is broken down into glucose

These products are re-absorbed into the hypha through the cell wall by 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.^[2]

Conditions

In order for a saprotrophic organism to facilitate optimal growth and repair, favourable conditions and nutrients must be present.^[4] Optimal conditions refers to several conditions which optimise the growth of saprotrophic organisms, such as;

Presence of water: 80–90% of the mass of the fungi is water, and the fungi require excess water for absorption due to the evaporation of internally retained water.^[4]
Presence of oxygen: Very few saprotrophic organisms can endure anaerobic conditions as evidenced by their growth above media such as water or soil.^[4]
Neutral-acidic pH: The condition of neutral or mildly acidic conditions under pH 7 are required. ^[4]
Low-medium temperature: The majority of saprotrophic organisms require temperatures between 1 and 35 °C (34 and 95 °F), with optimum growth occurring at 25 °C (77 °F).^[4]

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 disaccharides and polysaccharides such as maltose and starch, and of the monosaccharide glucose.^[2]

References

Citations

^ "saprobe". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.) - "The word saprophyte and its derivatives, implying that a fungus is a plant, can be replaced by saprobe (σαπρός + βίος), which is without such implication."
^ ^a ^b ^c Clegg & Mackean (2006, p. 296) states the purpose of saprotrophs and their internal nutrition, as well as discussing the main two types of fungi that are most often referred to. It also describes, visually, the process of saprotrophic nutrition through a diagram of hyphae, referring to the Rhizobium on damp, stale whole-meal bread or on rotting fruit.
^ ^a ^b ^c Clegg & Mackean (2006, p. 296), fig 14.16—Diagram detailing the re-absorption of substrates within the hypha.
^ ^a ^b ^c ^d ^e Clegg & Mackean (2006, p. 296), fig 14.17—A diagram explaining the optimal conditions needed for successful growth and repair.

General and cited references

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

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