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Biology mini assignment - Roles of Micro-organisms in Decomposition
3B
Chen Shu Jun(2)
Dinah Chua(?)
Lim Yan Chun(33)
Tan Jun Wei(35)
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Process
Autolysis is the process by which a cell self-destructs (if necessary) for the healthiness of the entire organism. It is uncommon in adult organisms and usually occurs in injured cells or dying tissue. Autolysis occurs when a lysosome allows the digestive enzymes out of its membranes. The cell then, in effect, digests itself.
Putrefaction is the decomposition of animal proteins, especially by anaerobic microorganisms. Decomposition is a more general process. It results usually in amines such as putrescine and cadaverine, which have a putrid odor. Material that is subject to putrefaction is called putrescible.
Next, scavangers are the next agent in decomposition. Animals like insects play a very important role in decomposition, provided that the body is accessible to them.
Decomposition
It is the reduction of the body of an organism or its faeces into simpler forms of matter. Decomposition begins at the moment of death. At this moment, two processes will take place, autolysis and putrefaction.
Decomposers
Decomposers feed on dead and decaying organisms and their faeces, secreting enzymes onto their food source and breaking down the complex organic compounds into simpler or gaseous inorganic compounds.
For e.g. Gases like Carbon dioxide, hydrogen sulpide, water vapour and salts like nitrates, phosperous and potassium ions. These are reused by plants during photosynthesis. The decomposers only absorb a small amount of energy and nutrients for their own use, the remaining nutrients are released into the surrounding soil, air and water.
Microorganisms
Bacteria
Bacteria are the smallest living organisms and the most numerous during decomposition. They are responsible for most of the decomposition and heat generation. They use a broad range of enzymes to chemically break down a variety of organic materials. Most of these bacteria have the ability to move on their own, in other words, they are motile.
Bacteria are found in :
--nature (soil, human and animals)
In the beginning of the decomposition process (0-40ç), mesophilic bacteria predominate, they can be found in the top soil. As the compound heats above 40ç, thermophilic bacteria take over. The microbial populations during this phase are dominated by members of the genus Bacillus. The diversity of bacilli species is fairly high at temperatures from 50-55ç but decreases dramatically at 60ç or above. Once the temperature cools down, mesophilic bacteria predominate again.
--sewage treatment plants
Bacteria present in the sewage secrete enzymes to digest the solid organic matter into soluble harmless substances and gas carbon dioxide. Some bacteria feed on these digested products. The liquid that results from this bacteria digestion is filtered and pathogens (An agent that causes disease, especially a living microorganism such as a bacterium or fungus.) removed before it is discharged into the rivers or seas.
The digested solid, or sludge, is removed, dried, and used as fertilizers.
Fungi
They are the ones responsible for the decomposition of many complex plant polymers in soil and compost. They break down tough debris, enabling bacteria to continue the decomposition process once most of the cellulose has been exhausted. They can also attack organic residues that are too dry, acidic or low in nitrogen for bacteria decomposition.
Most fungi live on dead or dying material and obtain energy by breaking down organic matter in dead plants and animals, thus they are classified as saprophytes. During both mesophilic and thermophilic phases of decomposition, fungi are numerous strive well. Fungi will live on the outer layer of the compost when the temperatures are high.
Protozoa
They are unicellular microscopic organisms. They are found in water droplets but they play a rather minor role in decomposition. They obtain food from organic matter just like bacteria. They are larger and more complex in their activities as compared to bacteria. However, their main role in decomposition is to act as secondary consumers ingesting bacteria and fungi.
Actinomycetes
Actinomycetes resembles fungi but are actually filamentous bacteria that give the soil its smell. They lack nuclei, but they grow multi-cellular filaments. They play an important role of degrading complex organics, such as cellulose, lignin, chitin and proteins. They also secrete enzymes to break down tough debris. They exist in both the mesophilic and thermophilic stages. Only the most resistant compounds remain in the last stages of decomposition. They form long, thread-like filament that appears only towards the end of the decomposition process. Sometimes they appear as circular colonies that gradually expand in diameter.
Rotifers
They are microscopic multi-cellular organisms. They are found in films of water in compost. They feed on organic matter and also ingest bacteria and fungi.