Microorganisms: Characteristics, Classification, and Lifestyles
Microorganisms
Microorganisms are living things that can only be seen with a light or electron microscope. They are everywhere where there is moisture, temperature, and food suitable for development and reproduction. Leeuwenhoek gave them that name.
Characteristics
They are extremely small, and their physiological and ecological properties are peculiar. They have active metabolism (influencing the environment they live in), reproduce quickly (high number; the proliferation of microorganisms causes excessive pollution), and have ease of dispersion (they are ubiquitous; microorganisms are everywhere).
Classification
Whittaker, in 1969, proposed five kingdoms: Monera (bacteria and cyanobacteria, prokaryotes), Protists (unicellular algae and protozoa, eukaryotic plant or animal), and Fungi (yeasts and molds). Viruses are considered acellular (they are the smallest and lack metabolism itself; they are obligate parasites).
Lifestyle
Microorganisms need to produce energy for vital functions. Types of microorganisms:
- Autotrophs (can synthesize compounds from simple molecules): Photosynthetic (the energy source is sunlight captured by pigments) and Chemosynthetic (energy is obtained from chemical reactions).
- Heterotrophic (take food from outside, as organically produced): Saprophytic (decomposing organic matter in the medium; they cause putrefaction, play a hygienic role in the biosphere, and recycle matter; they perform useful alcoholic and lactic fermentations that yield products of industrial or nutritional interest), Symbionts (live with other organisms, providing them with food and obtaining benefits, i.e., the bacteria that decompose matter and synthesize a necessary vitamin, B6), Guests (inside the body without causing damage, they take advantage of substances necessary for the receptor, e.g., bacteria inside the mouth, respiratory tracts, vagina…), and Parasites (obtain food from another living being, causing injury or illness; they are pathogenic microorganisms, bacteria, fungi, mycoplasma…).
The Flora in Humans
All microorganisms live in direct contact with us. They may cause diseases, but under normal conditions, they are indispensable. They are divided into those living on the skin or those in cavities like the mouth, nose, or vagina. They feed on sebaceous and sweat glands and keratinous scales of the skin’s surface. Some may be pathogens, such as staph, which can enter a wound and infect it, or infect hair follicles, originating in pimples and boils. Hygiene significantly reduces them, but excessive hygiene can be harmful. The nose and mouth are suitable places for the growth of microorganisms.
In the mouth, the fermentation of sugars causes tooth decay. The large intestine and rectum are home to many microorganisms, such as colibacteria and streptococci, and are beneficial (vitamin E).
Protozoa
Protozoa are unicellular eukaryotic microorganisms. They reproduce by binary division or bipartition, and some require a host to live. Nutrition is heterotrophic (although Euglena possesses chlorophyll). They move by cilia, flagella, and pseudopodia. They are parasites of humans or live in the aquatic environment (plankton). There are four types:
- Amoebas: Move by pseudopodia. There are free amoebas and guests of the digestive tract that do not cause illness (e.g., Entamoeba histolytica, which causes diarrhea and dysentery).
- Flagellates: Have flagella. They can live in the gut, urogenital tract (pathogens of the woman’s vagina and urethra and prepuce of the male, considered STDs); the most dangerous are those in the bloodstream (e.g., Trypanosoma).
- Sporozoa: They are motionless, have complicated life cycles, and are parasites. For example, Toxoplasma.
- Ciliates: Move with cilia; the best known is Paramecium.
Fungi
Fungi are heterotrophic beings. They include:
- Yeasts: Unicellular, round, reproduce by budding, important in the fermentation of wine and bread. For example, Candida albicans.
- Moulds: Filaments consisting of several cells, not single-celled, small size, produce diseases such as ringworm or athlete’s foot.