Stop using the generic term “bacteria” as a lazy catch-all. This article will establish a clear framework with easy-to-understand analogies to help you grasp relevant concepts effortlessly.
I. Core logic: hierarchy from macro to micro
These six terms are not parallel concepts. Similar to the hierarchy of Country – Province – City – Subdistrict – Household – Residence, they follow a clear descending scale from macro to micro, from collective groups to individual units.
To put it simply: the sequence Microbiota → Genus → Species → Strain represents a gradual narrowing from large collective populations down to precisely defined individual microbial units.
In contrast, thallus (bacterial cell body) and colony refer respectively to the living physical form of microbes and the visible trace left by their proliferation, falling into the category of morphological descriptions.
II. Precise identification of six microbe-related terms
- Microbiota: shared accommodation for microbes
Definition: A mixed population of various microorganisms (including bacteria, fungi, etc.) coexisting in the same environment.
Key feature: It does not require identical species; the only criterion is sharing the same habitat.
Examples: Gut microbiota (containing hundreds of species such as bifidobacteria and lactic acid bacteria), soil microbiota.
- Genus: the family surname of microorganisms
Definition: A group of microorganisms with close genetic relatedness and similar characteristics; its Latin scientific name starts with a capital letter.
Key point: They share the same “family surname” but different given names—similar in traits yet not identical.
Examples: Bifidobacterium (including Bifidobacterium infantis, Bifidobacterium longum); Influenzavirus (including influenza A and influenza B viruses).
- Species: the Full Given Name of a Microorganism
Definition: A population with identical traits and stable heredity, whose Latin scientific name consists of a genus name plus a species epithet (the species epithet is written in lowercase).
Key point: Members share both the same “family surname” and “given name”, serving as the basic unit of taxonomic classification.
Examples: Escherichia coli (E. coli), Saccharomyces cerevisiae (the yeast used for bread making and brewing alcohol).
- Strain: The ID number of a microorganism
Definition: Individuals belonging to the same species but isolated from different sources with subtle genetic or phenotypic differences, distinguished by letters or numbers.
Key point: Different strains within one species can have drastically different functions.
Examples: Escherichia coli O157:H7 (pathogenic strain) versus Escherichia coli Nissle 1917 (probiotic strain); Bifidobacterium animalis subsp. lactis BB 12® in yogurt (BB 12® is the strain designation).
- Bacterial cell (Thallus): the physical body of a microbe
Definition: The living organism itself of a microorganism, which can be unicellular (e.g., bacteria) or multicellular (e.g., mold hyphae).
Key point: It has nothing to do with taxonomic classification and merely refers to the physical entity of the microbe.
Examples: A single Escherichia coli cell observed under a microscope, the green fuzz growing on moldy bread.
- Colony: The collective dormitory of microbes
Definition: A visible aggregate formed by microbial proliferation on solid culture medium (such as petri dishes).
Key point: It is a growth trace rather than the microbe itself; its morphological features (color, size, shape, etc.) serve as the basis for microbial identification.
Examples: Golden round spots in a petri dish (potentially Staphylococcus aureus), the milky viscous layer on the surface of yogurt.
No more loosely using the blanket term “bacteria” from now on! Accurately distinguishing these microbe-related terms will not only help you understand popular science articles and pick suitable probiotics, but also grant you genuine insight into the wondrous microscopic universe that lives and evolves alongside us.
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