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How are bacteria classified into species when they reproduce by fission?
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Philosophy of biology
Detail of a Roman copy (2nd century bce) of a Greek alabaster portrait bust of Aristotle, c. 325 bce; in the collection of the Roman National Museum.
Classifying bacteria into species is challenging because, unlike higher organisms, they reproduce asexually through binary fission, which prevents the use of interbreeding as a defining criterion. Furthermore, horizontal gene transfer allows genetic material to move between different species, further complicating taxonomic boundaries.123
Because traditional biological species concepts do not apply, scientists rely on genetic and molecular methods to determine relatedness. These include:14
- DNA-DNA hybridization: Measures the similarity of DNA sequences between organisms to establish genetic relatedness.4
- DNA sequencing: Techniques such as whole genome sequencing and multilocus sequence analysis (MLSA) allow for precise identification, often resolving differences down to the intraspecies level.4
- DNA fingerprinting: Methods like repetitive element-PCR target specific genomic patterns to distinguish between bacterial populations.4
In practice, some researchers suggest that the bacterial species level is more comparable to the genus level in other organisms, with classification often focusing on ecotypes—genetically distinct populations that occupy specific ecological niches.1