Loose Ends on Loose Ends on Chapters Chapters

3,5,63,5,6

Loose Ends on Loose Ends on Chapters Chapters

3,5,63,5,6Summer Summer

MicrobiologyMicrobiology

Spore survival• Dipicolinic acid and Ca++ account for 15% of

the total spore mass• Dipicolinic acid theoretically may contribute to

the stability of the nucleic acids which is a contributory to the spore’s survival- The Ca and the dipicolinic acid may enhance the activity of DNA binding proteins that are vital to the spore’s ability to resist radiation

• Calcium contributes to the ability of the spore to resist destruction by oxidizing agents and dry heat – also steam

Spore Structure

Seven Steps and More in Spore Formation

Revisited• Stress or unfavorable environmental

conditions • Replication of DNA• Membrane begins to form to separate

cells – Forespore septum begins to show the formation of the forespore

• Membrane continues to grow and engulfs the DNA into the forespore

Spore formation Continued

• The cortex is laid down and Calcium and dipicolinic acid are accumulated here

• Protein coats then form around the cortex• The exosporium and then the spore coat

are made to surround the spore• At this point the spore structure is

completed

Spore Release• Lytic enzymes destroy the

sporangium releasing the spore• This process takes about 23 hours

in B. subtilis

Flagellar Structure• The M Ring is anchored in the cel

membrane of the bacterium.• A shaft that is attached to the hook and

flagellum extends form the shaft.• In Gram Positive cells the S ring is

attached to the cell wall and does not rotate

• In Gram Negative cells, the P and L rings act as a bearing for the rotating flagellum

Flagellar Motor Proteins• Mot A and Mot B• These form a proton channel for the

establishment of a proton gradient • The Motor proteins also assist in the

anchoring of the complex to cell wall peptidoglycans

• Fli G is the motor protein that generates flagellar rotation

Rotational symmetry of the C ring and a mechanism for the

flagellar rotary motor

• Dennis R. Thomas, David Gene Morgan, and David J. DeRosier

• Proc Natl Acad Sci U S A. 1999 August 31; 96(18): 10134–10139. PMCID: 17855

Reference• The cytoplasmic component of the

bacterial flagellar motor.• I H Khan, T S Reese, and S Khan• Proc Natl Acad Sci U S A. 1992 July

1; 89(13): 5956–5960

Chemoreceptors• MCP – Methyl accepting

chemotaxis proteins• Localized in patches at the ends of

the bacilli in E. coli• React to stimuli through a series of

steps utlizing proteins

Concepts• Conformation change in protein

structure• Methylation of proteins• Phosphorylation of proteins

Increase in nutrient binding

• Environmental stimulus – nutrient molecule

• Nutrient molecule in the gradient binds to the MCP protein( change in conformation)

• Che A is dephosphorylated – loses a phosphate

• Counterclockwise rotation occurs in the bacteria

No nutrient detected in the environment

• No nutrient binding• Che A is phosphorylated( gains a

phosphate group)• Phosphate is then donated to Che Y• Interacts with Fli switch to causes

clockwise rotation or tumbling – random and undirected

Two Component Phosphorelay System

• Two Component Phosphorelay System is similar in response to oxygen, light, hear and osmotic gradients.

Active Transport• Movement against the

concentration gradient from low concentration outside of the cell to higher inside the cyotplasm

• Requires the input of energy to drive the reaction forward

Active Transport and ATP- Binding Cassette

TransportersABC Transporters• Large group of transporters• Two hydrophobic domains in the membrane

and two nucleotide binding domains at the cytoplasmic surfaces

• The membrane spanning portions form a pore • The nucleotide binding domains bind ATP for

the hydrolysis of ATP to produce energy to drive molecules through the membrane

Salmonella ABC transporter

E. Coli and active transport

• The sugars arabinose, maltose galactose, and ribose are transported by this mechanism in bacteria

• Also amino acids may pass through the cell membrane in this manner

Porins• Porins are channels located in the

outer membrane of the Gram Negative bacteria

Omp F

Siderophore

Active transport• Uniport – One ion or molecule moves

against the concentration gradient• Symport – A concentration gradient

established by an ion, drives solute transport of another molecule against the concentration gradient

• Antiport – Sodium is pumped outward in response to an inward movement of protons

Importance of this mechanism

• The sodium pumped to the outside of the cell is also used in transport

• It binds to the outside of a different transport protein.

• When it binds it changes the shape of the protein

• The protein is then able to bind to molecules to move them into the cell

E. coli • Has multiple transport systems for

many nutrients• The diversity of these transport

system provides the ability to survive in diverse environments

Group Translocation• A molecule is transported ito the

cell while being chemically altered• This is energy dependent

PTS• Best characterized system is the

PTS• Phosphoenolpyruvate: sugar

phosphotransferase system• Transports sugars while

phosphorylating them

Components• Two enzymes( EI and EII)• Low Molecular weight – heat stable

protein( HPr)

Steps• High energy Phosphate is transferred

from phosphoenolpyruvate to EII with the help of EI and HPr

• The sugar molecule to be transported is phosphorylated as it goes across the membrane by EII

• EII is specific for the sugar that it transports

PTS