Bacterial Morphology

Exam 1 - Lec 2 - Intro to Bacterial Cell Architecture

What is the key difference between prokaryotes and eukaryotes?

eukaryotes are very complex:

• nucleus + lots of other organelles

• multiple linear chromosomes

• replication (nucleus), transcription (nucleus), & translation (cytoplasm) happen separately

prokaryotes are simple:

• NO defined nucleus (or other membrane-enclosed organelles)

• single circular chromosome

• replication, transcription, & translation happen simultaneously → rapid growth & adaptability

What specific cellular characteristics do bacteria possess that eukaryotes do not?

Bacteria:

• peptidoglycan, 70S ribosomes, 1 RNA polymerase (5 subunits)

Eukaryotes:

• NO peptidoglycan, 80S ribosomes, 3 RNA polymerases (12-14 subunits)

Why is it important to understand the different structural characteristics of bacteria and eukaryotes?

helps vets pick drugs that target bacteria but NOT eukaryotes

T/F: Prokaryotes possess NO internal structures.

FALSE - no nucleus/ organelles but do have many internal structures

(thylakoid membranes for photosynthesis, carboxysomes for CO₂ fixation, ect)

T/F: Prokaryotes have vast organismal diversity.

TRUE - largest biomass of living organisms

What factors contribute to prokaryote organismal diversity?

Nutritional versatility:

• can digest carbs, hydrocarbons, organic acids, etc

Metabolic diversity:

• N fixation, sulfur reduction/oxidation (different e^- acceptors), photosynthesis, etc

What are the 8 defining characteristics of prokaryotic cells?

1. Lack of nucleus → chromosome localized in nucleoid

2. Complex cell wall → rigid support, protects from turgor pressure

3. Simple internal structure → no membrane-bound organelles

4. Single circular chromosome

5. Asexual reproduction → binary fission = quick (exponential) population growth

6. Size and scale → 0.1-5 micrometers (much smaller than eucarya)

7. Metabolic diversity → utilize MANY energy sources, highly adaptable & survives anywhere

8. Genetic adaptability → rapidly adapts through mutations, horizontal gene transfer

What are the 3 common bacterial shapes?

1. Cocci → spherical

2. Bacilli → rod-shaped

3. Spirilla → spiral-shaped

Cocci are _______ in shape and can appear in ______ or ______.

spherical

clusters

chains

T/F: Bacilli can be found in various environments.

TRUE - so many spp (E. coli, Clostridium spp, B. anthracis, Salmonella spp)

What are some common cocci species?

Staphylococcus aureus (mastitis, skin infections)

Staphylococcus intermedius (skin & ear infections)

Streptococcus agalactiae (subclinical mastitis)

Streptococcus suis (meningitis, arthritis in swine)

Spirilla are _______ in shape and often ______.

spiral

motile

The unique shape of Spirilla aids in their _________.

locomotion

What are some common Spirilla species?

Leptospira spp

Borrelia burgdorferi (Lyme disease)

T/F: The shape and structure of bacteria are not imperative for identifying the type of infection.

FALSE

What are some common bacterial arrangements?

staphylococcus (clusters)

diplococci (pairs)

streptobacilli (chains)

Why is understanding the different cellular components of bacteria essential for veterinarians?

directly informs diagnosis, treatment, and prevention of bacterial infections

What do structures such as cell walls, membranes, capsules, pili, and flagella do for bacteria?

influence their ability to cause disease, evade the immune system, and resist antibiotics → important in determining virulence

Awarness of bacterial cell structure supports effective _________ & _________, therefore helping vets protect both animal and __________.

biosecurity practices

vaccine strategies

public health

Flagella are tail-like structures primarily used for _________ in _________ habitats.

motility

aqueous

Aside from motility, what other purposes do flagella serve?

adhesion & host-cell invasion

Flagella allow bacteria to perform _________.

chemotaxis

What is chemotaxis?

movement toward an attractant (nutrients) or away from a repellent

T/F: Production of flagella is extremely easy and energy sparing for bacteria.

FALSE - extremely energetically expensive (grow 2% more slowly)

Monotrichous

1 flagellum

Peritrichous

flagellum all over the surface

Lophotrichous

flagella in clumps (bundled)

Amphitrichous

one flagellum at both ends

Polar flagella normally assist with ________ while lateral flagella normally assist with __________.

chemotaxis

adherence

Flagella are made up of ______ parts.

3

What are the 3 parts of flagella?

1. Basal body (anchored in cell wall)

2. Filament (the “tail”)

3. Hook (connects filament to the cell)

The filament is comprised of individual protein subunits called ________.

flagellin (also called H-antigen in sterotyping)

T/F: Flagellins are highly immunogenic.

TRUE - one of the most recognizable bacterial proteins by host immune system (used a lot for vaccines)

Some bacteria (Salmonella enterica) use ________ to randomly switch between different types of flagellin proteins.

phase variation

What is the purpose of phase variation?

to avoid immune detection → “disguise itself”

Flagellar motor consists of _________ which turns ___________ by default.

plain filaments

counterclockwise

What does counterclockwise rotation of plain filaments do for the cell?

allows several peritrichous flagella to bundle together and propel the cell smoothly forward

T/F: Complex filaments can only rotate clockwise.

TRUE - though much less common

What signals the flagellar motor to switch to a clockwise rotation?

chemotaxis signaling molecule

What is the result of flagellar motors switching to clockwise rotation?

dissociation of pertitrichous flagellar bundle, resulting in a “tumble” → reorientation of the cell

What is tactic response?

the ability to move in response to environmental stimuli (sensory control of swimming behavior)

Environmental change is sensed by a sensory protein, generally ________ sensing the __________ environment.

transmembrane proteins

external (some spp may have additional cytoplasmic receptors)

What are examples of different tactic responses?

• Chemotaxis → chemical stimuli

• Phototaxis → light stimulus

• Aerotaxis → oxygen

• Magnetotaxis → magnetic field

What are the 2 important considerations of the tactic response?

1. Length of run

2. Direction of run

Bacteria measure the _________ over time.

chemoeffector

If bacteria sense a/an __________, tumble frequency _________.

attractant

decreases (runs are longer)

If bacteria senses a/an ___________, tumble frequency _________.

repellent

increases (runs are shorter)

Spirochetes have ________ flagella.

internal

Where is the flagella of spircochetes located?

in the periplasm between inner & outer membrane → periplasmic flagella

How are flagella oriented within spirochetes?

wrap around the length of the cell and overlap in the middle

Rotation of axial filaments of spirochetes creates ____________.

“cork-screw” movement

The ability of spirochetes to swim using cork-screw movement allows the pathogen to be ___________ and __________ in human/animal hosts.

highly invasive

virulent

Pili are also called _______.

fimbriae

What are pili?

protein filaments on the cell surface

Pili are _________, ___________, and __________ than a flagellum.

shorter, straighter, more fragile

T/F: Pili are usually present in low numbers on the surface of bacteria.

FALSE - large numbers

Pili are found almost exclusively in which type of bacteria?

Gram negative

Pili mediate various functions including:

1. Adhesion

2. Conjugation (sex pili)

3. Twitchin motility & social motility (Type IV pili)

4. Phage receptor

Like flagellum, pili are also _________.

immunogenic

What type of pili are used for adhesion?

type I

Pili are important ________ factors.

colonization (virulence factors involved in colonization & invasion portion of disease)

T/F: Pili are NOT produced at initial colonization.

TRUE

Adhesion is mediated by proteins located at the tip of the pili called

adhesins

What is the purpose of adhesins on the tip of pili?

recognize and bind to specific receptors on the surface of cells or other substrates

Different pili types mediate attachment to __________ substrates.

different

Different pili types can be responsible for

host and tissue specificity

Some adhesins of bacterial pathogens bind to _________ or ___________ in cell surface receptors.

glycolipids

oligosaccharides

Why is it important to note that some bacterial pathogen adhesins bind to glycolipids?

animal cell membranes contain glycolipids & glycoproteins → natural receptors for pathogens

Many strains of E. coli, Salmonella, & Shigella have pili that attach specificially to the _____________ on cell membranes.

mannose glycoside residue

Pili are important for _______ transfer of genetic information via __________.

horizontal

conjugation

Sex pili are coded for by the _________.

F plasmid

The F plasmid is typically the ________ factor.

competitive → determines virulence, antibiotic resistance, etc

What is a plasmid?

small extrachromosomal DNA molecule within in a cell that is physically separated from chromosomal DNA and can replicate independently.

T/F: Plasmids are required for survival.

FALSE - are NOT required (non-genomic DNA)

The sex pilus grows from the ______ cell and mediates cell-cell contact between itself and the _____ cells.

male (donor of genetic info)

female (recipient of genetic info)

T/F: Conjugation requires cell-to-cell contact.

TRUE

The donor (male) and recipient (female) will __________ after conjugation since single stranded DNA is transferred.

both retain a plasmid → donor keeps ½, recipient keeps ½

What is one important plasmid-encoded function that sex pili can facilitate?

virulence

Many bacterial pathogens are _________ because of genes carried on plasmids.

ONLY pathogenic → not a pathogen without key plasmid proteins

What are a couple of examples of pathogens that are only pathogenic due to their plasmids?

Bacillus anthracis, Salmonella enterica, Yersinia pestis, Rhodococcus equi, E. coli