L15: Bacterial Structure

What does it mean if a bacteria is cell wall defective

partial loss or change of the cell wall

Phylogeny

Evolution based methods of characterizing bacteria

Bacterial ribosome is composed of

70S ribosome

- 50s large subunit

- 30 s small subunit

What is as key part of a bacterial ribosome?

16s rRNA + 21 proteins

makes up small subunit of bacteria

Why is 16s rRNA important?

determines level of relatedness of different bacteria

Why is 16s RNA used to determine level of relatedness of different bacteria.

1. present in all bacteria

2. non transferrable

3. appropriate level of conservation

4. large enough

5. functionally stable

Parts of a phylogenetic tree

root, branch, node, clade

Root node is a ---- ancestor

common

Internal node is a ---- ancestor

common

Terminal node is the ---

actual bacteria

How is bacteria related in a dendrogram?

According to the distance between points

longer line = more differences

What are the 3 kingdoms?

Bacteria, Archaea, Eukarya

--- are the most common members of the microbiota present on body surfaces and found in pathogens

bacteria

---- are the most common members in the environment and gastrointestinal microbiota

Archea

Bacterial Toxonomy

Kingdom, phylum, class, order, family, genus, species

Basic structure of bacterial cell wall

Peptidoglycan

What is the makeup of the bacterial cell wall?

Peptidoglycan

NAG and NAM

peptide chain with 3 variant amino acids

Terminal D alpha cross links with 3rd amino acid on neighboring chain

What is the structure of peptidoglycan?

Alternating sugar molecules NAG and NAM

NAG

N acetyl glucosamine

NAM

N acetyl muramic acid

What is attached to NAM?

peptide chain with 3 amino acids and terminal D-ALA

How do peptidoglycan cross links form?

Between terminal D-ALA of one peptide chain and 3rd amino acid of neighboring peptide chain

True / False: the crosslink between terminal D-Ala and the 3rd amino acid can be direct or via a multi-amino acid bridges

True

What does cross linking between terminal D-ALA of one peptide chain and 3rd amino acid of another peptide chain add?

strength to the peptidoglycan (bacterial cell wall)

Gram staining divides bacteria into 2 different structural classes based on the --- and --- structure

cell wall and membrane structure

Gram positive bacterial cell wall

thick peptidoglycan

inner cytoplasmic membrane

Gram negative bacterial cell wall

outer membrane

thin peptidoglycan cell wall

inner cytoplasmic membrane

Gram positive bacteria stains

purple

Gram negative bacteria stains

pink/red

Steps of Gram Staining

crystal violet

iodine to aggregate crystal violet

Ethanol = collapses peptidoglycan and extracts lipid from the outer membrane

safranin = counterstain

What is the point of ethanol in gram staining?

Dehydration of water

Collapses the peptidoglycan cell wall

extracts lipids from outer membrane in gram negative bacteria

Purposes of adding ethanol to a gram negative staining

Ethanol destroys peptidoglycan and dissolves outer membrane = results in lack of color

Add safranin to stain gram negative cells red

What is the order of color for gram positive versus gram negative

Gram positive = purple, purple, purple

Gram negative = purple, colorless, red

Mycoplasma are the only bacteria that lack a —— and therefore ---- with gram reagents

lack a cell wall and do not stain well with gram reagents

The bacterial cell wall (peptidoglycan) prevents —— and confers bacterial cell --- and ---

prevents cell lysis

confers cell shape and arrangement

CWD bacteria

cell wall defective bacteria

Why do some bacteria undergo partial loss or change in cell membrane?

to increase survival without a cell wall

L form bacteria have ----

complete loss of bacterial cell wall

True / False: most bacteria lyse without a cell wall

What is the exception?

True

Mycoplasma = bacteria without a cell wall

What creates an L form of bacteria?

Low level antibiotic exposure = missed antibiotic dose

L form

Reformed bacteria

Undergoes a programmed change in the cell membrane to allow for survival without a cell wall

What confers a negative charge on bacteria?

Techoic acids

What can the bacterial cell wall have attached instead of cross links

proteins covalently attached to peptide side chain

Proteins covalently attached to peptide side chain are predominantly found in

gram positive bacteria

Steps in the peptidoglycan cell wall synthesis

1. NAM is synthesized from NAG

2. A pentapeptide chain is attached to N-AM

3. Undecaprenyl carreie transfers NAG-NAM peptide subunit to the outer membrane

4. Penicillin binding proteins carry out: - transglycosylation

- transpeptidation

- remove 5th ALA residue

Pentapeptide chain consists of

3 amino acids and 2 D-ALA residues

What carries the NAG-NAM pentapeptide chain to the outer membrane?

undecaprenyl carrier

Transglycosylation

The transfer of a sugar residue from one glycoside to another

Transpeptidation

formation of cross links between D-ALA and third amino acid

D-ALA is derived from L-ALA by a ---

racemase

Bacterial membranes are made up primarily of --- and ---

phosphatidylethanolamine

phsophatidylglycerol

Why does the bacterial membrane lyse when there is no peptidoglycan cell wall

bacterial membrane is made of phospholipids = phosphotidylethanolamine and phosphatidylglycerol

membrane phospholipids do not contain sterols

Bacterial membranes do not contain --- except for ---- which incorporate them from their environment into their membrane

sterols

except for mycoplasma which incorporate sterols from environment into membrane

Why do mycoplasma bacteria have sterols?

because they lack a bacterial cell wall

1. NAM is synthesized from NAG

2. A pentapeptide chain is attached to NAM, D- ALA is derived from a L-ALa by a racemase

3. Undecaprynyl carrier transfers the NAG - NAM peptide subunit to the outer membrane

4. Penicillin binding proteins (PBP) carry out

- transglycolation reactions = sugar bonds transpeptidation reactions = cross links (with or without added amino acids) and remove 5th ALA residue

Gram positive plasma membrane structure

- lipoproteins

- lipoteichoic acid

- membrane proteins

Gram negative membrane structure

Outer plasma membrane

peptidoglycan cell wall

Inner plasma membrane

The outer plasma membrane of gram negative bacteria is composed into -- leaflets

2 leaflets

How do the two leaflets of the outer plasma membrane of gram negative bacteria differ?

Outer leaflet = made of lipopolysaccharides

Inner leaflet = made of phosphatidylethanolamine and phosphatidylglycerol

Where are lipopolysaccharides located in bacteria?

(Outer leaflet) of outer membrane of gram negative bacteria

Lipopolysaccharides are

endotoxins

What bacteria caused endotoxic shock?

Gram negative bacteria

Why is the repeating oligosaccharide unit of a lipopolysaccharide important?

It is the antigenic portion recognized by the immune system

Lipopolysaccharide structure

Lipid A

Core polysaccharide

O specific oligosaccharide subunit

Why does gram negative bacteria cause endotoxic shock?

Lipid A (part of lipopolysaccharide) causes non-specific stimulation of the immune response

The outer membrane of gram negative bacteria contain --- and/or --- for transport

Porins and/or active transporters

Porins

water filled channels that allow hydrophilic molecules to pass through

Capsule

Discrete layer associated with individual cells

Functions of capsule

- Mediates adherence

- Protects from engulfment by phagocytes

- Protect from drying

Matrix

Slime layer / secreted layer

Helps to embed the cells

Functions of the matrix

Reserve carbohydrate for subsequent metabolism (between feast / famine episodes)

matrix for formation of biofilms

Pilli/Fimbraie

composed of proteins

used for conjugation, attachment, and mobility

Conjugation

DNA exchange

Flagella

Composed of flagellin

Power bacterial motility

What powers the bacterial motility of flagella?

Proton motive force

True / False: bacterial have a nucleus and organelles

False

What is the DNA material of bacteria?

Nucleoid = tightly coiled DNA without a membrane

True / False: the bacterial nucleiod is a nucleus

False - it does not have a membrane

it is tightly coiled DNA

SCM

structural maintenance complexes

Purpose of structural maintenance complexes

Maintain bacterial circular chromosome structure

help keep bacterial DNA tightly coiled

Bacterial chromosomes are ---- in structure

circular

What does bacteria use to replication DNA?

Gyres and topoisomerase IV

--- and ---- allow for bacterial DNA replication at the origin of replication

gyrase and topoisomerase IV

---- and --- target DNA gyrase

Quinolones and fluoroquinolones

Bacteria have extrachromosomal ----

plasmids

Plasmids

extrachromosomal elements in bacteria

Plasmids replicate and are segregated into ---

daughter cells

Plasmids are important genes and play a role in --- and ---

virulence and antibiotic resistance