lecture 6 Flashcards
bacterial motility intro to pili/fimbriae
types of flagella (4)
monotrichous (single flagella that is on one polar end of the cell)
amphitrichous (two flagella on opposite ends of the cell)
lophotrichous (multiple flagella on both polar ends of the cell)
peritrichous (multiple flagella all around the cell)
what is motility?
what is positive motility?
Microbes are so small that it is difficult to distinguish between real motility and brownian movement (movement caused by particles around them)
Positive motility is caused by flagella
The structure of a flagella is usually the same across organisms but where it sits on a cell and what it helps the cell do, makes the flagella a defining characteristic
2 types of motility pattern
RUN
flagella filaments are left handed helices (anticlockwise) that form a bundle. they can move the cell in a straight line in one direction
TUMBLE
if you reverse and go clockwise, it forces the flagella in a right handed helix and breaks the bundle up completely. It tumbles randomly so it isn’t controlled. It tumbles until it spins the flagella the other way again which makes it move forward again and run
–> the bacteria alternates between runs and tumbles to move
define the tactic behaviour of a bacteria
Choosing between runs and tumbles is a very random process
This allows a cell to move through the environment and sense it, to work out if they’re moving towards a place they want to be in.
move through env and sense the env (tactic behaviour of bacteria)
4 tactic responses
Aerotaxis - towards/away from a gradient
Chemotaxis - towards/away from a chemical they want to have or avoid
Magnetotaxis - following lines of magnetism. They can line up structure in their cells to be able to sense and move towards magnetic fields, to get compounds for their growth
Phototaxis - moving towards light
testing tactic response (chemotaxis)
To see if bacteria is motile and whether it can sense the chemicals in its environment.
Insert a capillary tube with a specific chemical inside it, into a bacterial culture, and study the response of bacteria.
The chemical can be an attractant, repellent, or neutral.
how do bacteria sense the nutrient conc in the env?
To sense the environment, it uses a set of transmembrane proteins (methyl accepting chemotaxis proteins)
MCP detect and measure very specific changes in the environment
MCP proteins interact with cytoplasmic proteins to change the tactic behaviour of a cell
They alternate between runs and tumbles to regulate the direction of their swims.
MCP interact with cytoplasmic proteins Che.
Che interact with rings of motor to regulate the direction
how do chemotaxis recognise signals?
MCP (transducer proteins) are very specific to what they sense and can send signals inside the cell
(E coli has 5 transducer proteins, so it can sense only 5 different compounds in its environment)
To send signals:
MCP interacts with sensor kinase CheA
When MCP is activated, it causes the CheA to autophosphorylate itself
If the chemical is an attractant, we get a decrease in phosphorylated CheA
(vice versa for repellent, increase of CheA)
how do chemotaxis control the motor switch?
CheA-P acts as a kinase to another protein CheY and phosphorylates it
CheY can only bind to the flagellar motor when it’s phosphorylated
Binding of CheY-P changes anticlockwise to clockwise motion, causing the bacteria to tumble
CheZ is another protein, this one constantly dephosphorylates CheY - turns flagella motion back to anticlockwise
increased repellent conc – increased CheA-P – increased CheY-P – more tumbling less running – gets away from repellent
how do chemotaxis adapt to the changing concentrations?
Cell needs to remember what it’s seen and integrate the signals from the MCP proteins. it does so by methylation of MCP
CheR constantly methylates MCP (makes it insensitive to attractant)
CheB (methylesterase) is phosphorylated by CheA-P (increases its activity and demethylates MCP)
low conc of attractant –> high CheA-P, high CheB-P (demethylates MCP, increases sensitivity to attractant)
high conc of attractant –> low CheA-P, low CheB-P (methylates MCP, decreases sensitivity to attractant, increases autophosphorylation of CheA)
define bacterial memory
methylation of MCP is a bacterial memory (y desensitising MCP, the cell remembers previous conc, alters behaviour to new env)
high conc attractant –> methylated MCP, short runs and tumbles to stay in the env
low conc attractant –> methylated MCP, long runs and less tumbles to leave the env
define MCP receptors and the different numbers of putative chemoreceptor genes
Diff organisms have different numbers of compounds that we can detect
sequence of cytoplasmic domains of all these receptors are highly conserved
sequences of periplasmic sensing domains vary significantly between species and between receptors
each receptor binds different ligands
each species has different optimum niches
explain gliding
Moving without flagella - gliding
Cell pulls along slime extruded on the outside
Common in cyanobacteria
This is along a surface not in a liquid.
genes required for gliding
3 Gld proteins (components of an atp-biinding-cassette transporter)
5 Gld proteins are lipoproteins in the cytoplasmic membrane or OM
so it’s the movement of the 2 membranes that allows the cell to move forward
If we disrupt these genes, we disrupt the ability of the organism to do move, we increase resistance to bacteriophages that infect wild-type cells, and lose the ability to digest the insoluble polysaccharide chitin)
define chitin and its characteristics
Chitin is insoluble and can’t enter the cell so the cell digests chitin by gliding along its surface and get its energy
Motility and gliding action comes at a cost - makes it more susceptible to other pathogens
