BS1040 Topic 1 Lecture 2 Biological Classification and Taxonomy: Key Concepts and Methods
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What is biological classification?
The arrangement of organisms into taxonomic groups based on observed similarities.
Why do we classify organisms?
To organize diversity describe relationships and help identify new organisms.
What is taxonomy?
The scientific study of naming defining and classifying biological groups.
What is a taxon?
A group of organisms given a taxonomic rank.
What is the basic unit of classification?
The species.
Who developed the binomial naming system?
Carl Linnaeus (1707-1778)."
What is binomial nomenclature?
A two-part Latin naming system: Genus species (e.g. Escherichia coli).
How should scientific names be written?
In italics with the genus capitalized and species lowercase.
After first mention how is the name abbreviated?
G. species (e.g. E. coli).
What is the hierarchy of taxonomic ranks?
Domain Kingdom Phylum Class Order Family Genus Species.
What is the genus of Canis familiaris (dog)?
Canis.
What family does Canis belong to?
Canidae.
How are species defined in higher organisms?
By morphology ,reproductive isolation and shared gene pool.
Why is species definition more complex in bacteria?
They reproduce asexually and exchange genes horizontally.
What is a type strain?
The strain on which a species' description is based.
What are the main approaches to bacterial classification?
Phenetic numerical and phylogenetic (cladistic).
What does phenetic classification rely on?
Observable similarities regardless of evolutionary relationship.
Give examples of phenetic traits.
Cell shape staining growth conditions motility and metabolism.
Who developed numerical taxonomy?
Peter Sneath and Robert Sokal (1963).
What is numerical taxonomy?
Quantitative phenetic classification using many measurable characteristics.
What is a phenogram or dendrogram?
A tree diagram showing relationships based on overall similarity.
What is an Operational Taxonomic Unit (OTU)?
A group of similar organisms often defined by >=97% sequence similarity.
What does cladistics group organisms by?
Shared characteristics derived from a common ancestor
What does a cladogram show?
Evolutionary relationships between organisms.
What is LUCA?
The Last Universal Common Ancestor of all living cells.
What are nodes and branches in a phylogenetic tree?
Nodes = divergence points; branches = evolutionary change over time.
What are the three domains in Woese's classification?
Archaea Bacteria and Eukarya.
What was Woese's classification based on?
16S/18S rRNA gene sequencing.
How has genomics revolutionized classification?
Through whole genome sequencing bioinformatics and cheaper technology.
What complicates bacterial classification?
Horizontal gene transfer between species.
Why was Clostridium difficile reclassified as Clostridioides difficile?
Genetic sequencing showed it was phylogenetically distinct from other Clostridium species.
Why is defining bacterial species difficult?
Genomes can differ by up to 7% even within a single species.
What are the genomic thresholds for defining a bacterial species?
>=95% rRNA (16S) sequence identity and >=95% whole-genome similarity.
What must microbial species definitions consider?
Both phylogeny and ecology (shared niche or disease).
What are common bacterial subdivisions below species?
Subspecies serovars pathotypes strains and isolates.
Why are typing systems important?
For identification epidemiology and outbreak investigation.
What is serotyping based on?
Antigenic differences on bacterial surfaces (O H K antigens).
What system is used for Salmonella serotyping?
The Kauffman-White scheme (O and H antigen combinations).
What is MLST (Multilocus Sequence Typing)?
A method that compares sequence variations in conserved housekeeping genes.
Why is MLST valuable?
It's reproducible, quantitative and allows global comparison of bacterial strains.
Which species was MLST first developed for?
Neisseria meningitidis.
How many Staphylococcus aureus MLST strains were recorded in Sept 2025?
47 746
Why is classification important in microbiology?
It organizes diversity identifies relationships aids identification and underpins epidemiology.
What are the key classification methods?
Phenetic numerical and phylogenetic approaches.
Why is bacterial typing important?
To track evolution transmission and outbreaks of infectious diseases.