Bacterial Structure and Pathogenesis: Capsules, Flagella, Pili, and Biofilms

Comprehensive flashcards covering bacterial appendages (capsules, flagella, pili), biofilm formation, motility mechanisms, and virulence strategies based on biology lecture handouts.

What is the primary role of the 'Housekeeping' sigma ($\sigma$) factor in bacterial transcription?

It initiates the transcription of most genes needed for basic cell function.

Under what specific conditions are alternative sigma factors activated in bacteria?

Conditions such as starvation, sporulation, stationary phase, nitrogen metabolism, and heat-shock response.

In a Maneval's stain preparation, what constitutes a negative stain and what is its purpose?

An acidic stain, such as India ink or Congo red, is used to stain the background surrounding the cells.

What is the function of a positive stain in the capsule staining procedure?

A basic dye, such as crystal violet or methylene blue, is used to stain the bacterial cell itself.

Why is heat-fixing omitted during the preparation of a capsule stain?

To prevent the capsule from shrinking or being destroyed.

What is the 'halo effect' observed in a successful capsule stain?

The nonionic capsule does not take up acidic or basic stains, appearing as a clear, bright halo between the dark-stained background and the colored bacterial cell.

Which organism produces a polypeptide capsule rather than a polysaccharide one?

Bacillus anthracis

What are the three main models for bacterial glycan synthesis and export?

The Wzx/Wzy-dependent pathway, the ABC transporter-dependent pathway, and the Synthase-dependent pathway.

In Neisseria meningitidis, which genetic region is specifically involved in capsule synthesis?

Region A

What are the two primary mechanisms Azotobacter uses to protect the oxygen-sensitive nitrogenase enzyme?

A third protein that reversibly complexes to the nitrogenase for conformational protection, and the production of an oxygen-retarding alginate capsule.

How does Azotobacter vinelandii physically adapt its alginate capsule under high oxygen stress?

It produces alginate with a higher molecular weight and a different chemical structure, specifically greater L-guluronic acid content, making the capsule thicker and more compact.

What criteria are used to isolate Azotobacter from soil using an enrichment culture?

Using a nitrogen-free broth medium with mannitol as the sole carbon and energy source.

What species-specific pigment does Azotobacter vinelandii produce that is visible under UV light?

A yellow-green fluorescent pigment.

What percentage of a biofilm's biomass is typically accounted for by the exopolysaccharide (EPS) matrix?

$$50-90\,\%$$

What are the five steps of bacterial biofilm formation?

(A) Reversible attachment, (B) Irreversible attachment, (C) EPS synthesis/secretion, (D) Maturation, and (E) Dispersal.

How is bacterial motility quantified in the Crystal Violet Biofilm Assay?

By solubilizing bound crystal violet and measuring absorbance at $590\,nm$ to quantify the biofilm density.

Define the Monotrichous flagellar arrangement.

A single, polar flagellum.

Define the Amphitrichous flagellar arrangement.

A single flagellum at each of the two opposite ends of the cell.

Define the Lophotrichous flagellar arrangement.

A tuft or cluster of flagella arising from the same location on the bacterial surface.

Define the Peritrichous flagellar arrangement.

Flagella distributed over the entire surface of the bacterium.

What chemical indicator is used in Motility Test Medium to visualize bacterial movement?

2,3,5-triphenyltetrazolium chloride (TTC), which is reduced to an insoluble red pigment called formazan.

What powers the rotation of the bacterial flagellar motor in most aerobic bacteria?

The proton motive force (PMF), which is the electrochemical potential of protons ($H^+$).

What are the two specific components of the proton motive force (PMF)?

Electrical potential difference (membrane potential) and a chemical potential difference (pH gradient).

What is the consequence of damaging the fliA gene in Escherichia coli?

The loss of motility because fliA encodes the specific sigma factor ($\sigma^{28}$) essential for transcribing flagellar genes like fliC.

In bacterial chemotaxis, what are the roles of CheY and CheB?

CheY controls the switching of the flagellar motor (rotation direction), and CheB is involved in chemoreceptor adaptation to stimuli.

How do type IV competence pili facilitate natural transformation in Vibrio cholerae?

They bind to extracellular double-stranded DNA at their tips and then retract to bring the DNA to the cell surface for internalization.

What enzyme produced by Proteus mirabilis is responsible for increasing urine pH and inducing crystalline biofilms?

Urease, which breaks down urea into ammonia and carbon dioxide.

What morphological differentiation occurs when Proteus mirabilis switches from swimming to swarming?

Short, rod-shaped vegetative cells differentiate into very long, nonseptate, polyploid, hyperflagellated swarmer cells.

How do pathogenic bacteria like Salmonella capture iron from the host's transferrin or lactoferrin?

By deploying siderophores, which are high-affinity iron-binding molecules designed to strip $Fe^{3+}$ from host proteins.

What is the function of the ActA protein in Listeria monocytogenes?

It recruits and activates the Arp2/3 complex and VASP to induce actin polymerization, creating an actin tail that propels the bacterium into adjacent cells.

Which surface proteins does Listeria monocytogenes use for adhesion and entry into host cells?

Internalin A (InlA) and Internalin B (InlB).