Lecture 8: Aging and Differentiation

Question 1

Polar aging

Answer 1

Two bacterial poles differ in age. One pole arises from the septum of the parental cell and the other pole arises from a parental pole
-In E. Coli successive divisions have progeny with a mixture of polar ages
-Cells with very old poles accumulate damaged molecules and may cease replication and die

Question 2

Protein aggregate accumulation at bacterial poles

Answer 2

-Localization of protein aggregates driven by localization signals towards cellular poles.
-Chaperon proteins try to save salvageable cells and must remain in certain areas such as the poles to do so

Question 3

Determinant for positioning of protein aggregates

Answer 3

Nucleoid occlusion (Mechanism that prevents cellular division over bacterial chromosome)

Question 4

Cell differentiation in Caulobacter crescentus

Answer 4

-With sufficient nutrients swarmer cells lose flagella and develop into stalked cells causing asymmetry with daughter cell
Stalked cell allows bacteria to stick to surfaces

Question 4

Consequence of asymmetric distribution of protein aggregates

Answer 4

Rejuvenation of damage-free new-pole daughter cells

Question 5

Role of CtrA-P in Caulobacter crescentus

Answer 5

Binds to origin to inhibit DNA replication in order to regulate cell cycle

Question 6

Basic steps of phosphorelay system

Answer 6

1. Activation via environmental signal
2. Autophosphorylation (uses ATP, primes system, and is spontaneous)
3. Activation of protein kinase activity (Activates kinase to move phosphase)
4. Transfer of the phosphate to one or more intermediates
5. Phosphorylation of the response regulator

Question 7

Phosphorelay of histidine kinase

Answer 7

-Phosphate placed onto His- kinase
-Phosphate goes to an aspartate
-Phosphate goes to phospho-transpherase protein intermediate
-Phosphate sent to aspartate on response regulator

Question 8

Role of CtrA in swarmer cell

Answer 8

active transcription factor and inhibits origin of replication

Question 9

CtrA in stalked cell

Answer 9

Dephosphorylated and degraded by ClpXP

Question 10

PleC

Answer 10

Protein localized to the swarmer cell pole and dephosphorylates DivK

Question 11

Myxococcus response to starvation

Answer 11

Formation of a fruiting body from cells within that form spores.

Question 11

DivJ

Answer 11

Localized to the stalked cell poke and dephosphorylates DivK leading to CtrA-P dephosphorylation

Question 12

Bacterial Spores characteristics and function

Answer 12

-High resistance to adverse environmental conditions such as heat, radiation, and chemicals
-Only in a few bacteria
-Reversible
-Involved ordered expression of 60+ genes

Question 13

Bacterial Spore

Answer 13

-Structure containing a copy of a chromosome
-Mother cell helps spore maturate and eventually release it
-Spores germinate under suitable conditions to form new cells

Question 13

Stages of bacterial spore

Answer 13

1. Septum forms near one pole, DNA replicates and extends into an axial filament
2. Septum separates forespore from mother cell. DNA pumped through septum until each compartment gets a chromosome
3. Mother cell engulfs forespore surrounding it with a second membrane
4. Chromosomes of mother cell disintegrate
5. Forespore develops a cortex layer of peptidoglycan. Coat proteins deposited on outer membrane
6. Dipicolinic acid synthesized and calcium incorporated into spore coat
7. Mother cell releases spore

Question 13

Streptomyces

Answer 13

-Soil bacteria
-Plant pathogen
-Natural producer of many antibiotics

Question 13

SpoOA regulatory system

Answer 13

-Short peptide or stationary phase send signal
-Activation of kinase
-Transfer of phosphate between Spo factors (Phosphorelay)
-SpoOA-P activates expression of first level genes
-Asymmetric division and subsequent events

Question 13

Solution to Cyanobacterium paradox

Answer 13

-Differentiation of heterocyst cells for nitrogen fixation alone
-Heterocyst provides neighbors with nitrogen sources and gets carbon in return

Question 14

Cyanobacteria differentiation into nitrogen-fixing heterocyst paradox

Answer 14

Photosynthesis produces O2 but nitrogen fixation is sensitive to O2

Question 15

Developmental cycle of streptomyces coelicolor

Answer 15

1. In unfavorable conditions 1 or 2 germ tubes emerge from a spore and produce a substrate mycelium
   2a. After 48-72 hrs bld genes cause production of aerial hyphae
   2b. Tips of hyphae form a spiral compartment containing multiple copies of the genome
2. When growth stops, the compartment segments. Each segment changes shape and its wall thickens to become a desiccation-resistant spore