Microbiology – Alcamo Lecture: Bacterial Structures

-Not all bacteria have all structures

Shapes of Bacteria• 3 Different Shapes:

Bacilli• Rod shaped• Most occur singly, but some form long

chains called Streptobacilli• Examples:

– Typhoid fever– Anthrax– Diptheria

Cocci• Usually sphere shaped but can be oval• Diplococci – cocci that remain in pairs

– Examples – Gonorrhea, Menengitis• Streptococci – cocci in chains

– Examples - Strep throat, Tooth decay• Staphylococcus – irregular grape-like

cluster of cells– Examples – Food poisoning, staph skin

infections

Spiral Bacteria• Vibrios – curved rods - look like a

comma– Example - Cholera

• Spirilla – corkscrew shape with flagella– Example – Rat Bite fever

• Spirochetes – corkscrew shape but no flagella– Example - syphilis

Flagella• Used by some bacteria to achieve

motion• Made of long rigid strands of protein

called flagellin• Protein strands are permanently coiled• Permits the flagellum to rotate and

propel the bacterium forward

Flagella• Complicated structure: Filament

attached to hook-like shaft which is inserted through cell wall and attached to cell membrane

Flagella

Monotrichous

Lophotrichous

Amphitrichous

Peritrichous

Axial Filament• Only spirochete• One flagella attached at both ends of

flexible spiral MO• Motion effected by cell spinning around

filament

Pili• Look like short flagella but have nothing

to do with motion• Very tiny protein “Hairs” that enable MO

to stick to surfaces - like “Velcro”

Pili• Pili aid in transfer of genetic material

between bacteria

• Pili anchor bacteria to surfaces like living tissue

• Can enhance MO’s disease effect

• Example - gonorrhea

Capsule• Some bacteria secrete a layer of

polysaccharides and proteins that stick to its surface

• Sticky and gelatinous• Serves as a buffer between the bacteria

and its environment– Protects bacteria against dehydration– Protects bacteria against host’s immune

system

Glycocalyx• Some bacteria produce a Slime Layer• Complex sugar, made inside cell wall secreted

as liquid, polymerizes to jelly like substance• Cavities – S. mutans attaches itself to teeth by

using the sugar a person eats – creates an acid that breaks down tooth enamel

Cell Wall• All bacteria have a cell wall except

mycoplasmas• Semi-rigid structure, protects, gives

shape• Amount of chemical “Peptidoglycan”

determines characteristics of cell wall• If a lot: Thick, G+ stain reaction, sensitive

to penicillin and lysozyme in tears, saliva, mucous

• If small: thinner, G- stain reaction, not sensitive to penicillin or lysozyme

• If MO is pathogenic, disease more difficult to cure

Cell Membrane• Boundary layer of the cell inside of cell wall• Contains Cytoplasm, controls molecular traffic

in and out of the cell• Triple layer structure, 60% proteins, 38% lipids

(phospholipid bilayer), 2% sugars• Antimicrobials (detergents, alcohol, some

antibiotics) dissolve cell membrane

cell membrane animation

Cytoplasm

Gelatinous mass of proteinscarbohydrateslipidsnucleic acidssaltsions water

Important Structures in Cytoplasm

• Ribosomes – protein synthesis• Inclusion Bodies – globules of starch

or lipids – store nutrients• Bacterial Chromosome – closed loop of

DNA without a membrane or proteins (nucleoid region)

• Plasmids – smaller, separate molecules of DNA – few genes but do give bacteria drug resistance (R genes)

Endospores• Some Gram + bacteria produce highly

resistant structures - spores– Bacteria grow, mature and reproduce as

vegetative cells– Then the bacterial chromosome replicates

and the cell membrane grows in to seal off a developing spore

– Next, thick layers of peptidoglycan form to protect the cell

– Finally, the cell wall of the vegetative cell disintegrates and the spore is released

Endospores• Very resistant to poor environmental

conditions:– Extreme temperatures – boiling water– Chemicals – 70% alcohol– Spores have even been recovered alive

from an Egyptian mummy’s intestines

• Examples of spore formers – anthrax, botulism, tetanus

• “Sporulation” is spore formation - DNA + some cytoplasm wrapped in spore case formed by cell membrane

• “Germination” occurs when good environmental conditions return – vegetative cell

Kingdom Classification

Archaeobacteria• Have existed on earth longer than any

other living organism• They are different from eubacteria:

– No peptidoglycan in cell wall– Different lipids in cell membrane– Different ribosomal RNA– Now archaeobacteria and eubacteria are

classified as different kingdoms

Archaeobacteria• 3 Types:

– Methanogens – rods that live in anaerobic conditions and produce methane gas – common in marshes and the guts of cows and humans

– Thermoacidophiles – resistance to acid and high temperatures – live in hot springs and ocean vents

– Extreme Halophiles – thrive in high salt environments (Great Salt Lake)