Lecture 7: Internal and External Structures

Adaptation

Adjustment of a microorganism’s structure or behavior in response to environmental changes.

Asymmetric septation

Unequal cell division that produces two cells of different sizes or functions, such as in spore formation.

Bacterial microcompartments

Protein-based compartments inside bacteria that house specific metabolic pathways.

Biofouling

The unwanted accumulation of microorganisms on surfaces, such as pipes or ship hulls.

C-ring

A structure at the base of the bacterial flagellum that interacts with the motor and controls direction of rotation.

Capsule

A polysaccharide or protein outer layer that protects bacteria from phagocytosis and desiccation.

Carboxysomes

Protein-enclosed microcompartments in cyanobacteria that contain enzymes for carbon fixation.

Chemoreceptor

Membrane receptor proteins that detect chemical gradients and guide chemotaxis.

Chemotaxis

Directed movement of a cell toward or away from chemical stimuli.

Chlorosomes

Light-harvesting complexes containing bacteriochlorophyll in green sulfur bacteria.

Coat

Outer protein layer of a bacterial endospore that provides resistance to environmental stresses.

Cortex

A thick layer of peptidoglycan located beneath the spore coat in bacterial endospores.

Dipolconic acid

A molecule abundant in bacterial endospores that contributes to heat resistance and DNA stabilization.

Engulfment

The process during sporulation where one cell membrane engulfs another, forming a forespore.

F-pilus

A specialized pilus in bacteria that mediates conjugation by transferring plasmid DNA between cells.

Filament

The long helical structure made of flagellin that extends from the bacterial cell and provides motility.

Flagellum

A whip-like appendage composed of filament, hook, and basal body that propels bacterial movement.

Gas vesicles

Protein-bound compartments in aquatic microbes that provide buoyancy control.

Glycocalyx

A protective sugar-rich layer outside the cell wall, including capsules and slime layers.

Hook

A curved protein structure that connects the filament to the basal body of the flagellum.

Horizontal gene transfer (HGT)

The movement of genetic material between organisms outside of reproduction.

Magnetosomes

Membrane-bound crystals of magnetic minerals in bacteria that allow alignment with Earth’s magnetic field.

Membrane bushings

Ring-like proteins in the bacterial flagellum that stabilize the rod as it rotates through the membranes.

Nanowire

Conductive pili-like structures used by certain bacteria to transfer electrons to external surfaces or partners.

Phycobilisomes

Light-harvesting complexes found in cyanobacteria and red algae, rich in phycobiliproteins.

Pilus

A hair-like appendage on bacteria involved in adhesion, motility, or genetic exchange.

Polyhydroxybutyrate (PHB) granules

Carbon and energy storage inclusions in bacteria.

Polyphosphate (volutin) granules

Storage inclusions containing phosphate polymers used in metabolism and stress resistance.

Rotor

The rotating component of the flagellum motor that drives filament movement.

Run, tumble

The alternating swimming behaviors of bacteria during chemotaxis; runs move straight, tumbles reorient direction.

Signal layer

A loose layer of extracellular polysaccharides forming a hydrated barrier around cells.

Small, acid-soluble proteins

Proteins in bacterial endospores that bind and protect DNA from damage.

Stator

The stationary component of the flagellar motor that provides torque through proton or sodium flow.

Sulfur granules

Energy storage inclusions composed of elemental sulfur in certain bacteria.

Twitching motility

A type of bacterial surface movement powered by extension and retraction of type IV pili.