Hoicyzk L10-13

Question 1

What are the four functions caused by bacterial development?

Answer 1

1. Stress survival = Conversion of cells into resting cells with low metabolic activity and high resistance to stress.
2. Physiological specialisations = Occurrence and formation of cells that possess physiological features complementary to the normal vegetative cells.
3. Cell dispersal = Production of cells that either actively use flagella / surface associated motility or passively by the wind, water or animals.
4. Symbiotic relationship = Interaction with other cells can leads to the establishment of a symbiotic relationship .

Question 2

What is the genome structure of myxococcus?

Answer 2

10Mb large genome - about 3x the size of E.coli. Contains 200 two component systems, 181 transcriptional regulators, 100 Ser/Thr kinases, 43 sigma factors and 8 chemosensory systems.

Question 3

What are some characteristics of Myxococcus xanthus?

Answer 3

Form groups of cells called rafts as well as individual cells that can move on their own. Has biofilm formation and developmental differentiation causing cell death, kinship, altruism and cooperation. Contains both bacterial motor systems and prokaryotic signalling processes so can communicate with nearby cells to combat stress.

Question 4

How does Myxococcus grow?

Answer 4

As a swarm with a million organisms that cooperatively feed on other bacteria. They are predators. Uses motor systems to move to the surface in order to find and kill their prey. In low nutrients, the behaviour changes so swarm contracts forming mounds that will form fruiting bodies.

Question 5

What does developmental differentiation lead to in myxococcus?

Answer 5

80% of cells undergo autolysis to liberate nutrients so that cells that eventually differentiate into spores can successfully complete their differentiation. 15% of cells will differentiate into spores that are highly resistant to heat, desiccation, radiation etc. They develop a thick carbon hydrate spore coat and possess 2N genome so replicate quicker. 5% will differentiate into peripheral rods, cells that stay vegetative but hardly divide. Interpreted as scout cells that initiate swarm development when cell encounters nutrients

Question 6

How are fruiting bodies formed in Myxococcus?

Answer 6

Starts as growing cells which undergo aggregation forming a mound where cells are lysed together. This undergoes sporulation which forms a full fruiting body with peripheral rods and cores of spores.

Question 7

What orchestrates fruiting body formation in Myxococcus?

Answer 7

The C signal. CsgA from Myxococcus and HSD10 from humans are cardiolipin phosphor-lipases that produce diacylglycerol (DAG) through oxidation. CsgA is 227 amino acids long which undergoes cleavage where one half can interact with receptor on the other side of the membrane to line up membranes. This is the C signal. A DAG-containing lipid extract initiates development differentiation in a csgA mutant. SocA is another alcohol dehydrogenase in Myxococcus. Without CsgA there are no fruiting bodies but over expression of SocA allowed formation once again.

Question 8

What is TraA in myxococcus?

Answer 8

A recognition protein that interacts with a carbohydrate receptor on an adjacent cell. They become for a brief time, one interconnected cell where material can be swapped.
Cells expressing different TraA alleles do not exchange outer membrane so that only related bacteria can swap material. This is the kin system.

Question 9

What are cyanobacteria?

Answer 9

Large, diverse group of photosynthetic prokaryotes found in oceans, lakes and soil. Gram -ve photoautotrophs so fix CO2 in Calvin cycle. Show gliding motility none having flagella. Some groups show complex differentiation and polymorphic cell cycles which are nutritionally controlled, most importantly by the availability of nitrogen. Lack a source of “fixed” nitrogen e.g. ammonium ions NH4+ results in formation of specialised cells (heterocysts) to convert (“fix”) atmospheric N2 to ammonium ions.

Question 10

What are the major groups of cyanobacteria?

Answer 10

1. Chroococcacaen = Unicellular rods or cocci. Non motile. Divide by simple binary fission.
2. Pleurocapsalean = Unicellular but form cell aggregates. Unique mode
3. Oscillatorian = Filaments of cells called Trichomes. Filaments break up into motile units of a few cells called Hormogonia
4. Hetercystous = Filaments of cells called Trichomes. Trichomes contain heterocysts and also produce resting cells called Akinetes and produce Hormogonia.

Question 11

What are properties of heterocysts?

Answer 11

• Terminally differentiated cells which cannot divide once formed so finite life span
• Have no Calvin cycle and do not fix CO2
• Fix atmospheric nitrogen to ammonium using nitrogenase – an oxygen sensitive enzyme
• Contain low content of photosynthetic membranes and only contain photosystem 1 so no O2 generation
• Thick outer envelope layers thought to restrict diffusion of oxygen into cell which might damage nitrogenase.

Question 12

How is gene regulation controlled during development in heterocysts?

Answer 12

Early events are controlled by NtcA, a regulatory protein which monitors the N - status of the cell. NtcA controls HetR - a DNA binding protein which aids transcription at het gene promoters which contain genes needed for correct spacing of heterocyst and genes encoding envelope polysaccharides which help keep out oxygen.

Question 13

How does bacteria respond to nutrient stress?

Answer 13

Production of the stringent response alarmone ppGpp and ppGppp and the subsequent activation of regulons that i.e. increase nutrient uptake, transcribe chaperones, reprogram the metabolism, etc. One of the most effective strategies during severe forms of stress is the formation of resting cells (spores, cysts, etc.). These cells are metabolic dormant and possess increased resistance against physical and chemical stress.

Question 14

What is the structure of a bacillus endospore?

Answer 14

They contain an outer coat, an inner coat, a cortex, a core and a nucleoid. Multiple layers including the spore cortex composed of peptidoglycan and the inner and outer spore coats surround the spore core containing the compacted chromosome. The core also contains 5-15% dry weight dipicolinic acid (DPA).

Question 15

What are the adaptations of a bacillus endospore?

Answer 15

• Dehydrated core – heat and radiation resistance
• Small acid soluble spore proteins (SASPs) – protect DNA from heat, chemicals and radiation
• Ca(II)DPA – stabilises DNA
• Coat – resistant to organic solvents, chemicals

Question 16

What are the differences between endospore and myxospore formation?

Answer 16

During the formation of endospores (i.e. Bacillus species) the cell undergoes an unequal division resulting in a mother cell and the prespore cell. During the formation of myxospores (i.e. Myxococcus species) the entire cell will become spherical and turn into a spore. Glycerol spores are spore-like entities that are formed by Myxococcus cells in response to substances such as glycerol that interfere with cell growth. They are similar but also different from fruiting body spores.

Question 17

What are antibiotics?

Answer 17

Natural or synthetic agents that kills or inhibits the growth of microorganisms. There are 3 types: antiseptics, disinfectant and antibiotics. Antiseptics and Disinfectants are used to kill bacteria, viruses and protozoa but too toxic for internal use. Antiseptic = skin. Disinfectant = inanimate surfaces. Antibiotics are low molecular mass compounds that kill or inhibit the growth of bacteria and can be ingested or injected into the human body with minimal side effects.

Question 18

What are the requirements for antibiotics?

Answer 18

Killing/inhibition
- Intact immune system bacteriostatic compounds OK
- Defective immune system need bactericidal compounds
Selective toxicity:
- Exploit differences between host and pathogen
- Glycopeptides cause deafness therefore only for serious infections
Pharmacokinetics:
- Distribution of compound in the body
- Some compounds do not reach all areas of the body if ingested/injected

Question 19

What makes a good antibiotic?

Answer 19

One with few side effects with a broad spectrum BUT may destroy natural flora allowing other organisms. The ideal target for antibiotics is present in bacterium but not in humans.

Question 20

What are the targets for antibiotics in bacterium?

Answer 20

1. Cell wall biosynthesis
2. Nucleic acid biosynthesis
3. Protein synthesis
4. Cytoplasmic membrane function

Question 21

How do antibiotics target cell wall biosynthesis?

Answer 21

Peptidoglycan unique to bacteria. Essential for cell viability in most bacteria. Inhibitors:
Cycloserine: inhibits incorporation of alanine into cell wall precursor
Phosphomycin: prevents UDP-NAG&raquo_space;UDP-NAM
Bacitracin: stops recycling of bactoprenol (quite toxic so only topical use).
Beta-lactams: penicillin, methicillin, cephalosporins. Some of the most useful antibiotics (over half of all antibiotics used). All have a four membered beta-lactam ring. Structural alterations effect (pharmacokinetics, spectrum of activity, bacterial resistance mechanisms). All bind to and inhibit Penicillin Binding Proteins (PBPs). PBPs are cytoplasmic membrane proteins involved in transpeptidation and transglycosylase reactions.
Glycopeptides: vancomycin, teichoplanin
Bind to D-ala-D-ala and prevent transpeptidation and transglycosylase reactions. Vancomycin drug of last resort for some multiply resistant strains of Staphylococcus aureus

Question 22

How do antibiotics target nucleic acid synthesis?

Answer 22

Synthesis of precursors =
Sulfonamides and trimethoprim inhibit tetrahydrofolic acid production (they are substrate analogues). THF is necessary for nucleic acid synthesis. Mammals cannot make THF (required in diet) and so are resistant.
DNA replication =
Quinolones bind to and inhibit DNA gyrase. Supercoiling – gyrase.
RNA synthesis =
Rifampin inhibits RNA polymerase. Used primarily on drug resistant Mycobacterium tuberculosis.

Question 23

How do antibiotics target protein synthesis?

Answer 23

Good target, as ribosomes of bacteria are different from humans. Macrolides (erythromycin), lincosamides (clindamycin) and chloramphenicol:
Bind 50S subunit of ribosome, block transfer of peptides. Widely used. Complication with clindamycin due to killing of resident anaerobic microflora (allows Clostridium difficile to grow and produce toxins).
Aminoglycosides (kanamycin, gentamycin):
Bind 30S subunit and prevent 50S binding. Effective bactericidal but side effects (kidney function hearing loss).
Tetracyclines:
Bind 30S subunit and prevent alignment of aminoacylate tRNA with mRNA. Extremely widely use -> Resistance very common.

Question 24

How do antibiotics target cytoplasmic membrane function?

Answer 24

Gramicidin forms cation channel, H+ leaks. Cell cannot maintain PMF.Polymyxins act on Gram-negative bacteria.

Question 25

What are new antibiotics?

Answer 25

Synercid and Linezolid. Synercid is a mixture of dalfopristin and quinupristin. Both streptogramins (bind to 50S subunit of ribosome and prevent elongation of peptide chain). However used for many years in animal feeds so resistant bacteria already developed. Linezolid Oxazolidinone (bind to 50S subunit of ribosome preventing initiation of protein synthesis). However resistance already found.