Types of Microbes
June 30, 2021
The history of life stretches back untold eons. Today, there is a staggering array of organisms on Earth, with more species being discovered
The history of life stretches back untold eons. Today, there is a staggering array of organisms on Earth, with more species being discovered every year. The complexity of life, from the smallest microorganisms to the largest trees and animals, is astonishing. The most widespread family of organisms is the microbes.
There are several types of microbes, which include bacteria, archaea, protozoa, fungi, algae, lichens, slime molds, viruses, and prions. Most of these organisms can survive outside of a host in the air or soil, with the exception of viruses, which can only survive for a brief time outside their host cells.
Bacteria are unicellular organisms with a much simpler cell structure than other organisms. A key difference between bacteria and other biological organisms is that they have no membrane-bound organelles and a lack of nucleus.
The genetic material of bacteria is contained in a single loop of deoxyribonucleic acid (DNA). Notably, some bacteria have an extra circle of genetic material known as the plasmid. The plasmid is important for the bacteria that contain it, as it contains genes that confer an advantage, such as antibiotic resistance, over other species. Bacteria are classified into five types depending on their shape. These include bacilli (rod), cocci (spherical), vibrios (comma), spirilla (spiral), and spirochaetes (corkscrew.) Bacteria can exist as single cells, paired, in chains, or in clusters. Bacteria can be found in every habitat on Earth, from soil and the ocean to arctic snow. Bacteria also live inside the body, where they provide an essential function, as is evident by the gastrointestinal microflora. Bacteria also play an important role in several critical environmental processes such as the nitrogen cycle. Whereas some bacteria are involved in food production processes, others are pathogenic and have caused epidemics and pandemics over the course of human history.
Archaea are single-celled organisms that form the third domain of life. While these organisms are evolutionarily distinct from bacteria, they share several similarities to bacteria. There are some key biological differences between archaea and bacteria. These include a lack of peptidoglycan in the cell wall, as well as the presence of phytanyl instead of fatty acids on the cell membrane. The cell membrane of bacteria is always a lipid bilayer, whereas in archaea it can sometimes be a monolayer. Archaea also contain distinctive translation ribonucleic acids (tRNAs) and ribosomal RNAs (rRNAs). Archaea are obligate anaerobes that live in low-oxygen environments such as water or soil. Some examples of archaea include Aeropyrum pernix, Ignisphaera aggregans, and Metallosphaera sedula. Archaea can survive in some of the most inhospitable environments on Earth including salt deposits, deep-sea thermal vents, and hot springs. These are known as extremophiles.
Protozoa are single-cell eukaryotic organisms that belong to the Kingdom Protista. These organisms are often considered to be more complex than bacteria and archaea. The reproduction of protozoa is asexual and achieved by budding, fission, or schizogony; however, some protozoa are capable of sexual reproduction. A key difference between protozoa and bacteria/archaea is the presence of a nucleus. Protozoa are motile and capable of moving by cilia, flagella, or amoeboid movement. Amoeboid movement is achieved through the use of pseudopodia, which are temporary protrusions of the cell. Protozoa can reside in a wide range of moist habitats such as soil, marine environments, and freshwater. Some examples of protozoan species include Amoeba and Paramecium. Although very few protozoa cause disease, some are known to be parasitic in nature. Parasitic disease-causing protozoa include Plasmodium, which is the organism that causes malaria.