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Microbiology, Chapter 17

Microbiology, Chapter 17


Produced without organisms; occurring in the absence of life.

Archaean eon

The second eon (major time period) of Earth's existence, from 3.8 to 2.5 gigayears (Gyr, 109 years) before the present. The earliest geological evidence for life dates to this eon.

banded iron formation (BIF)

A geological formation consisting of layers of oxidized iron (Fe3+) which indicates formation under oxygen-rich conditions.

biosignature (biological signature)

A chemical indicator of life.


The area containing the sum total of all life on Earth.

candidate species

A newly described microbial isolate that may become accepted as an official species.


The recognition of different forms of life and their placement into different categories.


The evolution of two species in response to one another.

dichotomous key

A tool for identifying organisms, in which a series of yes/no decisions successively narrows down the possible categories of species.


Bacteria that grow within the crystals of solid rock.


An organism that lives as a symbiont inside another organism.


An intimate association between different species in which one partner population grows within the body of another organism.

genomic island

A region of DNA sequence whose properties indicate that it has been transferred from another genome. Usually comprises a set of genes with shared function, such as pathogenicity or symbiosis support.

genus name

A taxonomic rank consisting of closely related species.

greenhouse effect

The trapping of solar radiation heat in the atmosphere by CO2; a cause of global warming.

Hadean eon

The first period of Earth's existence, from 4.5 to 3.8 gigayears (109) ago.

horizontal gene transfer

The passage of genes from one cell into another mature cell.


The recognition of the class of a microbe isolated in pure culture.

informational gene

A DNA sequence that encodes a product essential for transcription or translation.


A microbe that has been obtained from a specific location and grown in pure culture.

isotope ratio

The ratio of amounts of two different isotopes of an element. The isotope ratio may serve as a biosignature if the ratio between certain isotopes of a given element is altered by biological activity.

metabolist model

A model of early life in which the central components of intermediary metabolism arose from self-sustaining chemical reactions based on inorganic chemicals.


A microscopic fossil in which calcium carbonate deposits have filled in the form of ancient microbial cells.

molecular clock

The use of DNA or RNA sequence information to measure the time of divergence among different species.


A group of organisms that includes an ancestral species and all of its descendents.


A symbiotic relationship in which both partners benefit.


The naming of different taxonomic groups of organisms.

operational gene

A DNA sequence that encodes a product not essential for transcription or translation but involved in cell functions such as metabolism, stress response, or pathogenicity.


The hypothesis that life forms originated elsewhere and "seeded" life on Earth.


A symbiotic relationship in which one member benefits and the other is harmed.

phylogenetic tree

A diagram depicting estimates of the relative amounts of evolutionary divergence among different species.


A measurement of genetic relatedness. The classification of animals based on their genetic relatedness.

probabilistic indicator

A means of quickly identifying microbes in the clinical setting, based on a battery of biochemical tests performed simultaneously on an isolated strain.


A level of taxonomic hierarchy, such as phylum, class, order or family.

reductive evolution

The loss or mutation of DNA encoding unselected traits.


A catalytic RNA molecule.

RNA world

A model of early life in which RNA performed all the informational and catalytic roles of today's DNA and proteins.

small-subunit rRNA

A ribosomal RNA found in the small subunit of the ribosome. Its gene is often sequenced for phylogenetic comparisons.


A single, specific type of organism, designated by a genus and species name.


A mass of sedimentary layers of limestone produced by a marine microbial community over many years.


An evolutionary process by which two or more species become intimately associated.


The intimate association of two unrelated species.


A category of organisms grouped together based on genetic relatedness.


The description of distinct life forms and their organization into different categories.

unrooted tree

A phylogenetic tree showing only the relative distances between different species, without indicating which of these diverged earliest from the common ancestor.

vertical transmission

The passage of genes from parent to offspring.

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