BIO3710 Chapter 3 Bacteria Cell Structure and Cell Wall

most common cell shapes

cocci and rods, though less common are possible

determination of cellular arrangement

plane of division

separation after division

characteristics of cocci bacteria

sphere

diplococci (pairs)

streptococci (chains)

staphylococci (clusters)

tetrads (4 cocci in a square)

sarcinae (8 cocci in a cube)

Rods (Bacilli) characteristics

singe rod

coccobacilli (very short rods)

vibrios (comma-shaped rods)

Bacterial shape: Spirillum

rigid helix

Bacterial shape: Spirochete

flexible helix

Bacterial shape: Mycelium

filamentous, multinucleate

bacterial shape: pleomorphic

variable shape

smallest size bacteria

mycoplasma 0.3 um

average size rod

1.1 - 1.5 × 2-6 um (E. coli)

very large size bacteria

600 × 80 um (Epulopiscium fishelsoni)

organization of bacterial cell

cell envelope (3 layers)

cytoplasm

external structures

plasma membrane

selectively permeable barrier, mechanical boundary of cell, nutrient and waste support, location of many metabolic processes ( respiration, photosynthesis) detection of environmental cues for chemotaxis

gas vacuole

an inclusion that provides buoyancy for floating in aquatic environment

ribosomes

protein synthesis

inclusions

storage of carbon, phosphate, and other substances; site of chemical reaction (microcompartments); movement

nucleoid

localization of genetic material (DNA)

periplasmic space

in typical Gram-negative bacteria, contains hydrolytic enzymes and binding proteins for nutrient processing and uptake; in typical Gram-positive bacteria, may be smaller or absent

cell wall

protection from osmotic stress, helps maintain cell shape

capsules and slime layers

resistance to phagocytic adherence to surfaces

fimbriae and pili

attachment to surfaces, bacterial conjugation and transformation, twitching

flagella

swimming and swarming motility

endospore

survival under harsh environmental conditions

bacterial cell envelope

plasma membrane, cell wall, and surrounding layers

Fluid Mosaic Model of Plasma membrane

peripheral protein in plasma membrane

loosely connected proteins

integral protein of plasma membrane

embedded in membrane

hopanoid in plasma membrane

bacterial version of cholesterol

bacterial cell wall

rigid structure just outside plasma membrane

made of peptidoglycan

2 types (G+ and G-)

Functions of Cell Wall

maintain shape of bacteria

protect cell from osmotic lysis and toxic materials

can contribute to pathogenicity

peptidoglycan

meshlike polymer of identical subunits forming long strands

two alternating sugars in peptidoglycan

N-acetylglucosamine (NAG)

N-acetylmuramic (NAM)

Gram-Positive (G+)

thick peptidoglycan

small or no periplasm

many contain teichoic acids

Gram-Negative (G-)

thin peptidoglycan

large periplasm

outer membrane of lipids, lipoproteins, and lipopolysaccharides (LPS)

cytoskeleton

homologues of 3 eukaryotic cytoskeletal elements in bacteria

cytoskeleton in eukaryotes

microfilaments (actin)

microtubules (tubulin)

intermediate filaments (lamin and keratin)

cytoskeleton in bacteria

Mreb and Mbl- maintain cell shape in rods

FtsZ- forms ring at center of dividing cell

CreS- forms curve shape of Caulobacter crescentus

Plasma membrane infoldings in Intracytoplasmic membranes

photosynthetic bacteria

highly respiratory bacteria

Anammoxosome in Planctomycetes

organelle serving as site of ammonia oxidation

bacterial cell inclusions

aggregation of organic or inorganic substances

granules, crystals, or globules

free in cytoplasm or enclosed in shell

storage or reduces osmotic pressure

quantity varies with nutritional status of cell

storage inclusion

store nutrient or metabolic end product

glycogen

long branched chain of glucose units

Poly-beta-hydroxybutyrate

carbon storage

form distinct bodies able to be viewed with light microscope

industrial use - biodegradable plastics

polyphosphate granules

phosphate storage

metachromatic granules- appear red or blue when stained with blue dyes

sulfur globules

storage reservoir for sulfur

gas vacuoles

provide buoyancy to aquatic organisms

regulate buoyancy to float at proper depth

Aggregates of gas vesicles

single protein subunits assembled into cylinder

impermeable to water

permeable to gases

Magnetosomes

found in aquatic bacteria

intracellular chains of magnetite (Fe3O4) particles enclosed in plasma membrane

tiny magnets used to orient to earth’s magnetic field

MamK cytoskeletal protein

helps form magnetosome chain

Ribosomes

found throughout cytoplasm and near plasma membrane

composed of proteins and RNA molecules

Nucleoid

region with chromosomes and proteins

chromosomes in bacteria

most circular and double stranded

how are the chromosomes longer than the length of the cell?

supercoiling

Nucleoid-associated proteins (HU and condensins)

Plasmids

small extrachromosomal self replicating DNA

circular (common) or linear (rare)

single or multi copy

episomes

plasmids integrated into and replicated with the chromosomes

curing

loss of a plasmid

spontaneously or by treatment

conjugative plasmids

transport themselves to other bacteria

F factor: fertility factor

R factor: resistance factor

Bacteriocin

encoding plasmids

virulence plasmids

more pathogenic plasmids

metabolic plasmids

genes for enzymes that degrade substances

TOL plasmids

degradation of aromatic compounds

why are gas vacuoles bound by proteins rather than lipid membrane?

gas vacuoles are more permeable

benefits plasmids give a bacterial cell

antibiotic resistance genes in plasmids

virulence plasmids can make bacteria more pathogenic

code to metabolize certain components

what would happen if the creS gene was removed

it would alter the shape of the bacteria

what would happen if the ftsZ was removed

would not be able to form the septum to divide

inclusions containing carbon are commonly found in the form of __________

poly-beta-hydroxybutyrate

certain bacteria accumulate magnetite in _______ that can be used to sense _______

magnetosomes; earths magnetic field

glycocalyx

outside cell wall

capsules and slime layers

capsules

usually made of polysaccharides

visible in light microscope

resistant to phagocytosis

protective to dessication

exclude virus and detergent

slime layers

similar to capsules but less organized

used for motility

S layers

Layers of protein or glycoprotein

S Layer in G-

outside outer membrane

S layer in G+

peptidoglycan surface

S layer function

protect from ion and pH fluctuation

promote adhesion and protect from host

self assemble

pili/fimbriae

short appendages, thinner than flagella

slender tubes of helical protein subunits

attach to solid surface

type IV in G- bacteria

motility

uptake of DNA during transformation

sex pili

larger, coded by conjugative plasmids

flagella

motility and attachment to surfaces

virulence factor

Distribution of Flagella

monotrichous- one

amphitrichous- one at each pole

lophotrichous- cluster at pole(s)

petritrichous- all over

flagella filament

cell surface to tip

hollow cylinder of flagellin subunits

capping protein at end

flagella basal body

embedded in the cell

rings drive flagellar motor

flagella hook

flexible link of filaments to basal body

flagella synthesis

complex (20 to 30 genes)

type III like secretion system

• flagellin subunits transported through hollow core

• spontaneously aggregate using filament cup

• grows at the tip, not the base

swimming motility

flagella rotates like propellar

powered by motor in basal body (Proton Motive Force)

swimming counterclockwise

cell moves forward (run)

swimming clockwise

cell moves randomly (tumble)

Biased random walk

bacteria move randomly without chemical gradient

Attractant→ longer runs toward attractant

Repellant→ longer runs away from repellant

swarming motility

on moist surface as bacteria group behavior

produce molecules to aid movement

spirochete motility

corkscrew shape flexes and spins

endoflagella

multiple flagella form axial fibril in periplasm that wraps around cell

twitching

type IV pili

short jerky motions when cells in contact

pili extend (contact surface) and retract (oull cell forward)

gliding

smooth motions

endospore

dormant cell formed when nutrients are low

resistant to heat, radiation, chemicals, and desiccation

endospore structure

many layers

thin exosporium covers spores

thick layer of proteins form spore coat

core has nucleoid and ribosomes

what makes endospore so tough?

Ca2+and dipicolinic acid in the core

dehydrated core

protection from spore coat and exosporium

function of Ca2+ and dipicolinic in endospore

interact with small acid-soluble DNA-binding proteins (SASPs) to protect DNA

sporulation process

10 hours

1. axial filament formation

2. septum formation and forespore development

3. engulfment of forespore

4. cortex formation

5. coat synthesis

6. completion of coat synthesis, increase in refractility and heat resistance

7. lysis of sporangium, endospore liberation

germination activation

spore prepare for germination

germination

environmental nutrients detected

breakdown of peptidoglycan

release of Ca2+ and dipicolinic acid

increased metabolic activity

water uptake

germination outgrowth

emergence of vegetative cell