A good as well as obvious first step to take toward gaining an appreciation of microbial evolution is to develop an appreciation of microbiology generally. In part this is because there is terminology as well as concepts that are shared between the two disciplines, particularly those terms and concepts that originated within microbiology and which therefore are appropriately introduced within the context of microbiology. The other reason, far more subtle, is that it can be helpful to gain a "feel" for what microorganisms are, and what they do, before progressing towards understanding the particulars of their evolution. While the latter is unquestionably helpful, it is also much more difficult to impart. Indeed, part of the goal of this text is to provide some of this latter insight into the microorganism way of existence. In this chapter, though, I focus instead on the very basics of what microbiology is all about.

Overview Lecture


Table: Important Terms and Concepts from Microbiology.

Click Here for an Online Practice Quiz Covering the Following Terms

Algae Eukaryotic organisms that are photosynthetic and are not plants.
Non-plant photosynthetic organisms, often but not always used to describe eukaryotic organisms that are not plants yet photosynthetic; algae can be either unicellular or multicellular.
Bacteria Type of cellular organisms lacking nuclei.
Strictly, members of domain Bacteria or, more loosely, a synonym for prokaryote.
Bacteriophage A virus whose host range encompasses a subset of members of domain Bacteria.
"Phage" is short for bacteriophage, and phages also can be described as bacterial viruses.
Cyanobacteria Gram-negative, photosynthetic, producers of molecular oxygen (O2).
Photosynthetic bacteria (domain Bacteria) possessing the same kind of photosynthetic apparatus as that of chloroplasts in plants (chloroplasts in fact are cyanobacteria descendants).
Domain Archaea High-level taxon of prokaryotic organisms noted particularly for its members that inhabit extreme environments.
Formerly described as archaebacteria, these are prokaryotic organisms that are distinctly genetically different from members of domain Bacteria (but which are not necessarily 100% genetically isolated from members of domain Bacteria, and vice versa).
Domain Bacteria Taxon containing all cellular organisms whose chromosomes are not contained within a nuclear envelope (nucleus) and whose cell walls, if present, are peptidoglycan based.
Cellular organisms that otherwise are known as common prokaryotes including all that are known to cause disease.
Domain Eukarya Taxon containing all organisms whose chromosomes are contained within a nuclear envelope (nucleus).
Cellular organisms that are eukaryotes, which includes protists, animals, plants, fungi, and algae.
Endosymbiont Cell that lives inside of another cell, typically in a long-term relationship that is not damaging to the larger cell.
An symbiont, usually not parasitic, that lives within the cells of other organisms; endosymbiosis can become obligate for both the endosymbiont and host, e.g., mitochondria.
Eukaryote Cellular organism with chromosomal DNA that is enclosed within a membranous nucleus.
Cellular organisms that possess cell nuclei as well as other features distinguishing them from most prokaryotic organisms such as the nucleus-associated endomembrane system.
Gram negative Type of bacterium that possesses thin cell walls and an outer membrane.
Gram-negative bacteria in particular posses two membranes surrounding their cytoplasm, one inside the other, and with a periplasmic space in between. Gram-negative bacteria are also associated with endotoxin.
Gram positive Type of bacterium that possesses thick cell walls and no outer membrane.
Gram-positive bacteria as pathogens are notable particularly for the diversity of exotoxins they produce.
Helminth Parasitic worms, including parasitic flatworms and parasitic roundworms.
Infectious worms, a kind of animal, such as flukes, pinworms, and tapeworms.
Kingdom Monera Obsolete and polyphyletic taxon conaining the prokaryotes.
A poly- or paraphyletic eukaryotic taxon consisting of domains Bacteria and Archaea.
Kingdom Protista Obsolete and polyphyletic taxon of eukaryotic organisms excluding animals, plants, and fungi.
A poly- or paraphyletic eukaryotic taxon consisting of protists, unicellular algae, and, depending on author, various multicellular eukaryotes including algae and slime molds.
Mold Fungi that grow as filamentous, clonal colonies but which nonetheless can be viewed as microorganisms.
Molds among fungi contrast with yeasts as well as what are known as macrofungi or fleshy fungi, such as mushrooms.
Parasite Organism that lives in or on other organisms from which it is stealing resources and to which it is causing harm.
Strictly from the perspective of many individuals parasites are eukaryotic organisms capable of infecting or infesting in some manner another eukaryotic organism. From the perspective of ecology or evolutionary ecology, however, the more general definition provided above, or equivalent, is preferred.
Prions Infectious proteins, particularly which lack nucleic acids but nevertheless possess an ability to catalyze an increase in their own numbers.
A non-organismal infectious protein of animals as well as yeasts.
Prokaryote Cellular organisms that lack cell nuclei.
Term lacking taxonomic meaning but instead referring to cellular organisms whose cells lack nuclei.
Prophage Virus state during lysogeny.
Prophages are bacteriophages and are notable both as viral parasites of bacteria but also as viruses that give rise to what is known as lysogenic converstion.
Protist Eukaryotic organism that is neither animal, plant, nor fungus.
Protists include a substantial number of unicellular eukaryotes though various colonical or even multicellular organisms, such as algae, are included especially in kingdom Protista.
Provirus Particularly non-phage acellular organism that has integrated into the genome of its host.
Though use of the term provirus is preferable when describing non-phage viruses but legitimately can be used to describe phages as well as alternative to "prophage".
Symbiont Organism living in long-term, physically intimate association with another, much larger organism.
An organism that lives in intimate association with another organism, a host, over a significant portion of its life cycle.
Viroid Naked RNA (no capsid) pathogen that infects plants.
A RNA-based, non-encapsidated, obligate intracellular parasite of plants.
Virus Life form that is neither a cell nor consists of cells and which minimally consists of a combination of a nucleic-acid genome and protein coat.
An acellular, nucleic-acid-based genetic entity that obligately infects cells in order to replicate plus which possesses a mostly protein encapsidated form (a virion) by which cells are acquired.
Yeast Fungi that, in their mature form, exist as separate, individual cells.
Yeasts are diverse, polyphyletic (among fungi), and not always, depending on conditions, yeasts (i.e., see dimorphic fungi).