Five Types of Microorganisms
This chapter will look at different types of microorganisms. It will discuss their cell structure and functions. It will also discuss the position of microbes in food chains and their role in the biosphere.
Archaea were once thought to be a type of bacteria. After extensive research of their DNA and membrane structure, some scientists decided to put them into a separate group - Archaea. Another group of scientists is still not convinced and refers to them as Archaeabacteria.
Archaea are unicellular prokaryotes which make them bacteria-like organisms. Their DNA structure resembles the DNA of eukaryotic cells. Also, the cell walls of Archaebacteria are structurally different from the bacterial ones. Archaea live in environments that would not be suitable for most life forms. They can be found around hot geysers, volcanic vents, very salty lakes and on the ocean floor. Because Archaea thrive in such extreme conditions, they are sometimes called 'organism - extremists' or 'extremophiles. Archaeans can survive these extreme conditions due to their physiology. They synthesise different enzymes that keep their cells from being destroyed by high temperatures, salty or acidic water.
Because of their 'fondness' for extreme environmental conditions, Archaeans are believed to be the first living forms that appeared on Earth when it was still waterless, airless and a scorching hot planet.
Based on their habitat, all Archaeans can be divided into the following groups:
- Methanogens - methane-producing organisms;
- Halophiles - Archaeans that live in salty environments;
- Thermophiles - Archaeans that live at extremely hot temperatures;
- Psychrophiles - cold-temperature Archaeans.
Archaeans use different energy sources like hydrogen gas, carbon dioxide and sulphur. Some of them use sunlight to make energy, but not the same way as plants do. These creatures absorb sunlight using their membrane pigment, bacteriorhodopsin. This reacts with light, leading to the formation of the energy molecule, of adenosine triphosphate (ATP).
Compared with bacteria, Archaebacterial cell walls are composed of different polysaccharides and proteins, with no peptidoglycan. See image 1.
Cyanobacteria are aquatic, photosynthetic organisms. They can be unicellular or colonial. Cyanobacteria are sometimes called blue-green algae. Like other plants, they make their energy through photosynthesis, but besides that, they do not have anything in common with plants. Millions of years ago, the atmospheric oxygen that we depend on was generated by cyanobacteria. Most cyanobacteria live in water, damp soil and rocks.