L2 basic bacteriology and bacterial genetics

Question 1

What are some common shapes of bacteria?

Answer 1

-Cocci
- Rod
- Spirilla
Unusual shapes:
- Spiral
- Budding
- Filamentous
- Square

Question 2

What are the functions of the cell membrane?

Answer 2

Selective permeability: prevents leakage and functions as gateway for transport of nutrients in and out of the cell.

Transmembrane proteins: transport, bioenergetics and chemotaxis.

Energy conservation: site of generation and use of the proton motive force.

Question 3

What does the structure of the cell wall for gram-positive bacteria?

Answer 3

Peptidoglycan layer (20-80nm) that provides strength to the cell wall, and protects the cell from external environment. Gram-positive bacteria have more layers of peptidoglycan than gram-negative bacteria.

Question 4

What does the structure of the cell wall for gram-negative bacteria?

Answer 4

Peptidoglycan layer (7-8nm), as well as lipopolysaccharides (LPS). LPS is composed of fatty acids and polysaccharides as well as endotoxin (lipid A).

Question 5

What are some cell surface structures and their roles?

Answer 5

Capsule and slime layer: polysaccharide layer, assist in attachment to surfaces, protects against phagocytosis, and resists desiccation.

Fimbriae (gram-negative): filamentous protein structures on cell surface. enable organisms to stick to surfaces.

Pili: on the surface of bacteria. Facilitate genetic exchange between cells (conjugation)

Endospores: some gram-positive bacteria can produce them. Survival mechanism to protect DNA in harsh environments. Resistant to heat, chemicals, and radiation.

Flagella (locomotion): a tail-like structure that assists in swimming. Different arrangements and movement by rotation. Directed movement in response to chemical or physical changes.

Question 6

What are the essential cations and anions for most microorganisms?

Answer 6

K+: required by enzymes for activity
Mg2+: stabilizes ribosomes, membranes, and nucleic acids
Ca2+: helps stabilize cell walls in microbes, plays key role in heat stability of endospores
Na+: required by some microbes

Question 7

Cell nutrition?

Answer 7

Trace metals: iron, copper, manganese, zinc, cobalt -> biochemical functions

Growth factors: vitamins and amino acids -> coenzymes

Question 8

What is binary fission?

Answer 8

Asexual reproduction, where the cell divides into 2 identical parts.

Question 9

What does the time required for cell division depend on?

Answer 9

Nutrients, temp, pH, levels of oxygen

Question 10

What are the different phases of the growth of a cell?

Answer 10

Lag: the interval between inoculation of culture and beginning of growth.
Exponential: cells in this phase are typically in the healthiest state.
Stationary: growth rate is zero. Either an essential nutrient is used up, or the waste product of the organism accumulates in the medium.
Death: if incubation continues after cells reach the stationary phase, the cells will eventually die.

Question 11

How does temperature affect microbial growth?

Answer 11

Rate of enzymatic reactions. If the temp is too high the enzymes will denature.

Question 12

Give examples of organisms that are classified by their growth temperature optima.

Answer 12

Psychrophile: low temp
Mesophile: midrange temp
Thermophile: high temp
Hyperthermophile: very high temp

Question 13

How does pH affect microbial growth?

Answer 13

some organisms have evolved to grow best at low or high pH, but most organisms grow best between 6-8 (neutrophils).

Question 14

Give examples of organisms that are classified by their growth pH optima

Answer 14

Acidophiles: grow best at low pH (<6)
Alkaliphiles: grow best at high pH (>9)
Neutrophiles: grow best at neutral pH (6-8)

Question 15

How do varying levels of oxygen affect microbial growth for different kinds of bacteria?

Answer 15

Aerobes: require oxygen to live

Anaerobes: do not require oxygen and may even be killed by exposure to it

Facultative organisms: can live with or without oxygen

Microaerophiles: can use oxygen only when it is present at levels reduced form that in air

Aerotolerant anaerobes: can tolerate oxygen and grow in its presence even though they cannot use it.

Question 16

What is transformation? Explain the process.

Answer 16

Bacteria and other microorganisms take up foreign DNA from their surroundings and incorporate it into their own genome.

Pili/fimbriae on bacteria facilitate the uptake of extracellular DNA. Once the DNA has attached to the surface it is transported across the bacterial cell membrane. This often involves the formation of a pore or channel through which the DNA passes through. The foreign DNA integrates into the recipient cells’ genome, via homologous recombination or site-specific recombination. Ince integrated, the DNA may contain genes that confer new traits or functions to the bacterium. These genes can be expressed and incorporated into the bacteriums cellular processes leading to phenotypic changes.

Question 17

What is transduction? Explain the process.

Answer 17

Transfer of DNA from one bacterium to another by bacteriophage. This is a mechanism of horizontal gene transfer.

Becateriohage infects the bacterial cell by attaching to its surface and injecting its genetic material. The phage’s DNA integrates into the bacterial genome. Once inside, the phage DNA replicates using the cell’s resources and enzymes (which may result in the production of new phage particles). Newly formed phage particles containing fragments of DNA are released from the original host cells, causing them to lyse (burst). These phages can then infect other bacterial cells. When the pahge infects new bacterial cell, the genetic material is carries is introduced to recepient cell. Bacterial DNA can integrate into the new hosts genome , potentially conferring new traits or genetic variation.

Question 18

What is conjugation? Explain the process.

Answer 18

Mechanisms of horizontal gene transfer where genetic material (plasmid) is transferred between bacteria.

A bacterium that possesses a conjugative plasmid that acts as the donor cell. The conjugative plasmid contains the genes necessary for conjugation. The donor cell extends a thin, hollow appendage called a conjugation pilus. The pilus is encoded by genes on the conjugative plasmid. The pilus of the donor cell makes contact with a recipient cell. The pilus attaches to specific receptors on its cell surface. Once attached the pilus retracts, pulling the two cells closer. This process forms a conjugation bridge. Through the conjugation bridge, the donor cell transfers a copy of the conjugative plasmid to the recipient cell. Plasmid DNA is transferred from donor to recipient often through a pore or channel formed by proteins encoded by plasmid. Once inside the recipient cell, the transferred plasmid can exist as an independent genetic element, separated from the recipient’s chromosomal DNA. It can replicate autonomously and express the genes it carries, including those encoding specific traits or antibiotic resistance.