2- Bacteria
paste previous notes here
Flagella Structure
helical in shape
consists of
• Filament composed of flagellin.
• Reversible rotating machine
• increases or decreases rotational speed relative to the strength of the proton motive force
• Note: flagella rotate either clockwise (CW) or counterclockwise (CCW) relative to the cell.
Chemotaxis
Chemotaxis is the movement of a bacterium in response to chemical gradients.
Attractants cause CCW rotation.
• Flagella bundle together
• Push cell forward
• “Run”
Repellents (or absence of attractants) cause CW rotation.
• Flagellar bundle falls apart.
• “Tumble” – Bacterium briefly stops, then changes direction.
Bacterial Taxonomy
Bacteria named using the binomial system
genus + species
Genus: group of closely related species
Species: group of organisms sharing common features while differing considerably from other organisms
Strain vs serotype
Strain: Distinct subtype of species that differs genetically, and often phenotypically, from other subtypes.
Serotype (or serovar): Strain identified by serotyping (identifying surface antigens particular to a subspecies)
Pangenome = extra genes that a species can acquire that
The pan genome represents the entire set of genes found across all strains within a bacterial species. It consists of:
Core Genome: Genes present in all strains of a species, encoding essential housekeeping and metabolic functions.
Accessory (Dispensable) Genome: Genes present in some but not all strains, often acquired through horizontal gene transfer (e.g., conferring antibiotic resistance, virulence, or novel metabolic pathways).
Unique Genes: Genes exclusive to a single specific strain.
Bacteria are typically classified according to shared characteristics:
• Morphology (colony appearance on a plate)
• Gram colouring
• Size and shape (rod or coccus, single, chain or cluster, …)
• Presence of structures (such as magnetosomes or flagella)
• Metabolic traits (energy source, enzymatic capacities,…)
• DNA sequence