Bacterial Motility

Question 1

Brownian motion

Answer 1

random movement of molecules suspended in a fluid due to the collision with the fast moving particles in the fluid

Question 2

why don’t all bacteria move in a culture on a slide

Answer 2

stuck to the slide, run out of energy, dead

Question 3

types of flagella

Answer 3

monotrichous, amphitrichous, lophotrichous, peritrichous

Question 4

monotrichous

Answer 4

one flagella

Question 5

amphitrichous

Answer 5

2 flagella - one on each end

Question 6

lophotrichous

Answer 6

more than one flagella at each pole - mono or bipolar

Question 7

peritrichous

Answer 7

have flagella protruding all over

Question 8

motility pattern of bacteria

Answer 8

alternating between running for a few seconds and tumbling for a fraction of a second

Question 9

running movement description

Answer 9

motor turns anti clockwise, flagellar filaments with left handed helices form a bundle and propel the cell in a new direction

Question 10

tumbling movement description

Answer 10

quick reversal of motor to clockwise rotation -> twist into right handed helix - bundle falls apart rapidly - causes bacteria to move in a random direction

Question 11

Aerotaxis

Answer 11

movement towards oxygen

Question 12

chemotaxis

Answer 12

movement usually towards nutrients but also away from toxins

bacteria sense changes in nutrient conc in the environment

Question 13

magnetotaxis

Answer 13

movement along lines of magnetism - certain bacteria with iron in cells -> find iron to make energy from

Question 14

phototaxis

Answer 14

movement towards light

Question 15

tactic responses (4 types)

Answer 15

chemotaxis, phototaxis, magnetotaxis, aerotaxis

Question 16

tactic responses - response to attractants and repellents

Answer 16

bacteria sense changes in nutrient conc in environment

when capillary with chemical attractant inserted into culture -> lots of bacteria accumulate inside and around the capillary tube

when capillary with repellent -> v little bacteria found in or around it

Question 17

function of methyl-accepting chemotaxis proteins (MCP) or transducer proteins

Answer 17

detect and measure changes in the environment - for very specific compounds, and interact with cytoplasmic proteins: CHE proteins

Question 18

function of Che proteins

Answer 18

interact with rings of the motors - regulating direction in which it turns: dictates running or tumbling by switching the direction from ccw to cw

Question 19

chemotaxis full mechanism description

Answer 19

1) MCP interacts with sensor kinase CheA -> autophosphorylates

2) attractant: decreases CheA-P
repellent: increase in CheA-P

3) CheA-P phosphorylates CheY -> CheY-P binds to flagellar motor (not CheY)

4) CheY-P change ccw to cw -> tumble

5) CheZ, a phosphatase - dephosphorylates CheY-P -> continue ccw

6) attractants decrease CheY-P due to less CHeA-P = less switching and longer runs. repellents increase CheY-P as there is more CheA-P formed -> more tumbles

Question 20

chemotaxis - methylation adaptation explanation

Answer 20

• over time cell integrates attractants/repellents via constant methylation of MCP by CheR
• fully methylated MCP is insensitive to attractant
• CheA-P phosphorylates CheB (methylesterase) -> CheB-P -> demethylates MCP
• Low conc attractant: high CheA-P, High CheB-P = demethylation of MCP increase sensitivity to attractant = longer runs
• high conc attractant: low CheA-P, low CheB-P = high demethylation of MCP = insensitive to attractant -> increase autophosphorylation of CheA -> more likely to tumble to not swim out of the favourable environment

Question 21

how many transducers are in E. coli

Answer 21

5 - each detect different compounds

Question 22

bacterial memory

Answer 22

methylation of MCP

Question 23

methylation of MCP effects

Answer 23

high conc attractant - methylated MCP (more CheA-P = shorter runs and more tumbling to stay in good environment

high conc repellent - methylated MCP less CheA-P = longer runs and less tumbling to leave bad environment

(essentially the CheA-P released is reversed after the MCP becomes methylated by CheR)

Question 24

traits of mcp receptors

Answer 24

sequences of cytoplasmic domains of all these receptors are highly conserved

sequences of periplasmic sensing domains vary significantly from species to species and from receptor to receptor

each receptor binds diff ligands

each species have diff optimum niches

Question 25

example of gliding motility in bacteria

Answer 25

F. johnsoniae - latex spheres added to it bind to and are rapidly propelled along cells = suggests that adhesive molecules move laterally along the cell surface during gliding

Question 25

which genes control the ability to glide?

Answer 25

Gld genes:

3 Gld proteins are components of an ATF-Binding-Cassette (ABC) transporter

5 Gld proteins are lipoproteins in the cytoplasmic membrane or outer membrane

disruption of these genes = loss of motility but ups resistance to bacteriophages that infect wild type cells + loss of the ability to digest the insoluble polysaccharide chitin

Question 26

what is gliding?

Answer 26

moving without flagella, cell pulls along slime extruded on the outside

Question 27

how does twitching motility work?

Answer 27

type IV pilus
- extends from the cell surface then is retracted, drags the cell along the surface
- powered by ATP hydrolysis
- retraction proteins control the direction of movement

Question 28

how does a cell move using gas vesicles, and which kinds of cell?

Answer 28

planktonic bacteria e.g. cyanobacteria, and some archaea

• protein vesicles contain gas -> cell = buoyant
• float up to oxygenated water + light
• vertical migration in aquatic systems like lakes

Question 29

what are fimbriae/pili?

Answer 29

surface appendages - multi subunit proteins + not flagella!

Question 30

what are fimbriae/pili needed for?

Answer 30

• host-pathogen interactions
• colonisation + virulence
• host and tissue specificity (tropism)
• biofilm formation
• adhere to other cells and surfaces
• aid resistance in immune cell phagocytosis
• act as antigens
• agglutination
• specialised pili: genetic exchange between bacteria

Question 31

most important types of pili/fimbriae?

Answer 31

type I and IV

Question 32

structure + size of fimbriae/pili?

Answer 32

thinner and shorter than flagella

2-5 micrometers long

hundreds to thousands per cell

Question 33

How does the immune system recognise pathogenic bacteria?

Answer 33

fimbriae are antigenic - called Colonisation Factor Antigens (CFA)

• secretory antibodies (IgA) block bacterial colonisation
• circulating antibodies (IgG/IgM) lead to phagocytosis

Question 34

What is the process for invading host tissues?

Answer 34

fimbriae/pili loosely associate + adhere to mucosal membranes, invade into or through submucosal epithelial cells

Question 35

explain the process of fimbriae/pili assisted adhesion -> colonisation

Answer 35

TYPE iv PILI WITH ADHESIVE TIP PROTEIN
- pili establish initial contact to host cell (membranes are negatively charged: avoid electrostatic repulsion, resist flushing by moving contents of intestine/urine)
- the pilus’ adhesive tip protein binds to a receptor (glycolipid/glycoprotein)
- type IV pili depolymerise and shortens
- pulls bacterium close to host cell
- additional adhesins bind to host cell
- colonisation can begin!!