1. Bacterial Cell Stucture

Question 1

What environmental extremes can bacteria survive in? 6

Answer 1

1. Found in air, water, soil and deep subsurface rocks
2. Acidic, alkaline, very hot and cold, and salty environments
3. Internal and external body surfaces
4. In Antartica, a lake hidden under the Taylor glacier for 1.5 million years had bacteria surviving at -5 degrees and 20% salinity
5. Yellowstone hot springs are 60-95 degrees and still full of bacteria
6. Enzymes from low temperature bacteria are used in washing powders

Question 2

How are bacteria identified using light microscopy? 6

Answer 2

1. Size and shape using gram stain
2. Cell arrangement, and there are lots of different stains for this
3. Motility, flagella help it move and find food etc
4. Spores, one per cell
5. Capsules, a layer of mucus enveloping bacteria
6. Helps resist desiccation and prevents phagocytosis and binding of antibodies by host

Question 3

Describe some common shapes and sizes of bacteria. 6

Answer 3

1. Coccus/cocci are round
2. Include staphylococcus aureus, which causes toxic shock, acne and boils, and streptococcus pneumoniae, which causes pneumonia
3. 0.5-1micrometer in diameter
4. Rod/vibrios are rod shaped
5. Include E. coli, bacillus cereus and vibrio cholerae
6. Up to 0.8 x 0.5 microns

Question 4

Describe some less common shapes and sizes of bacteria. 4

Answer 4

1. Spiral in a rigid helix eg spirillium
2. Found in water cooling towers and stagnant water
3. Spirochetes, which are flexible, helical and very long
4. Include treponema pallidum, syphilis, and borrellia burgdorferi, lymes disease

Question 5

Describe square bacteria. 6

Answer 5

1. Flat and rectangular with straight sides
2. Eg. Genus arcula (box)
3. Haloquadratum walsbyi was isolated from brine collected from shore of the Red Sea
4. Only grows in 20%+ salt solutions, 3.3M
5. Gram negative
6. Approx 6x6microns

Question 6

Describe bacteria that is star shaped. 5

Answer 6

1. Genus is Stella
2. Isolated from garden compost and horse manure in Moscow
3. Gram negative
4. Non motile
5. Only one species known

Question 7

Describe very big bacteria. 5

Answer 7

1. Epulopiscium fishelsoni, 0.6mm x 75microns wide
2. Lives in gut of surgeon fish
3. 85000 DNA copies spread through it, which makes transcription easier as it is difficult to transport proteins everywhere
4. Theomargarita namibiensis is 0.75 mm long
5. Has large gas vesicles to aid metabolism

Question 8

Describe the different forms of bacterial cell arrangement. 5

Answer 8

1. Streptococcus species are chains
2. Always divide in same plane and don’t separate
3. E. coli are rods, usually free living
4. Staphylococcus species are in clusters
5. Can divide on 3-4 different planes

Question 9

What is the importance of the gram stain? 6

Answer 9

1. Developed in 1884 by Christian gram
2. Differentiates bacteria on the basis of cell wall structure
3. Gram positive bacteria stains purple
4. Gram negative stains pink or red
5. We rely on this clinically
6. Gram positive bacteria have a much thicker layer of peptidoglycan

Question 10

Describe bacterial cell wall structure. 6

Answer 10

1. A gram positive bacterium has 20nm of peptidoglycan and teichoic acid
2. This is about 13/14 layers
3. Followed by the cytoplasmic membrane
4. A gram negative bacteria ha an outer membrane, followed by a periplasmic space
5. This contains 5-8nm of peptidoglycan
6. Followed by a cytoplasmic membrane

Question 11

Describe the gram stain method. 6

Answer 11

1. Prepare cells on slide and add crystal violet dye
2. Stain with iodine and cvi complex forms
3. Add acetone to dissolve the outer membrane
4. If the specimen is gram negative, the cvi complex leaves. It stays if specimen is gram positive
5. Counter stain with safranin
6. Gram negative changes from colourless to pink/red and gram positive remains purple

Question 12

Describe what happens to gram positive bacteria during the gram stain. 3

Answer 12

1. Cvi complex is trapped inside
2. Acetone leads to dehydration of peptidoglycan, sealing the cvi complex inside the cell
3. Peptidoglycan shrinks and tightens

Question 13

What happens to gram negative bacteria during the gram staining process? 5

Answer 13

1. Acetone dissolves outer membrane
2. Eventually penetrates inner membrane
3. Cvi complex is released and lost from cell
4. After the outer later is dissolved, the thin layer of peptidoglycan is not sufficient to retain the cvi complex
5. Eventually, the inner membrane breaks down

Question 14

What are the functions of peptidoglycan? 5

Answer 14

1. Rigid structure of wall gives cell shape.
2. Protection from osmotic lysis - penicillin attacks peptidoglycan so only works on gram positive
3. Withstands the high, internal osmotic pressure driven by cytoplasmic contents
4. Gram positive have high internal pressure - thick walls
5. Gram negative have low internal pressure and thin walls

Question 15

Describe bacterial cell ghosts. 2

Answer 15

1. Bacterial cell walls keep their shape after lysis eg cocci and rods
2. This is due to peptidoglycan in the wall

Question 16

What are pleomorphic cells? 6

Answer 16

1. Have variable shape eg mycoplasma pneumoniae
2. No peptidoglycan and surrounded by a membrane
3. Only live in eukaryotic cells
4. Never exposed to harsh conditions so doesn’t (need to) make ATP, some amino acids or peptidoglycan
5. Just inner and outer membranes - bag of cytoplasm
6. Are parasites of eukaryotes, not free living

Question 17

Describe the structure of peptidoglycan. 6

Answer 17

1. Gives strength and rigidity.
2. Grid like structure with many interlocking layers which are half sugar and half protein
3. N-acetyl muramic acid (NAM) and n-acetylglucosamine (NAG) make up the sugar backbone
4. A variety of amino acids keep the chains together and hold onto the ones above
5. These form peptide bridges
6. Without these it all falls apart and cells die quickly through lysis

Question 18

Explain the importance of bacteria. 6

Answer 18

1. Essential for carbon, nitrogen and sulphur cycles, and other environmental aspects
2. Essential commensalism bacteria eg. Bacteria help break down fibrous foods in the gut. We have 10x more bacterial than cells, and 100x more bacterial DNA
3. Basic research tool eg. Clones genes and makes mutations
4. Industrial uses, including fermentation of coco beans, wine, coffee and yeast
5. Can cause mild and fatal diseases
6. Also protect us from pathogens