bacteria. structure of a bacterium peptidoglycan cell wall cell membrane ribosome pilidna flagellum

BACTERIA

Structure of a Bacterium

Peptidoglycan

Cellwall

Cellmembrane

Ribosome

PiliDNAFlagellum

Structure of a BacteriumCapsule: some have a sticky gelatinous

capsule around the cell wall (these bacteria are more likely to cause disease)

Cell wall: gives the cell shape; composed of a peptidoglycan (sugar-protein complex)

Plasma membrane: surrounds the cell and regulates what enters and leaves

Structure of a Bacterium

Pilus: hairlike structures emerging from the cell surface; helps bacteria stick to a surface or exchange DNA between bacterial cells

Flagellum: long, whiplike structure that enables movement

Structure of a Bacterium

Chromosome: single DNA molecule arranged as a circular chromosome; not enclosed in a nucleus

Plasmid: small circular chromosome piece containing a few genes

Classifying Bacteria

Bacteria are classified according to:ShapeArrangementGram stain

Classifying Bacteria

ShapeSpherical - CocciRod - BacilliCorkscrew - Spirillae

Classifying Bacteria

ArrangementSingularPairs – Diplo Chains – StreptoClusters – Stapylo

Classifying Bacteria

Gram stainStaining method involving two dyesThe dye absorbed by the bacteria depends

on properties of the cell wallBacteria are either Gram positive or Gram

negativePositive stain bluish-purpleNegative stain reddish-pink

Prokaryote Cell Wall Structure

peptide sidechains

cell wallpeptidoglycan

plasma membrane

protein

Gram-positive bacteria

Gram-negative bacteria

peptidoglycan

plasmamembrane

outermembrane

outer membrane of lipopolysaccharides

cell wall

peptidoglycan = polysaccharides + amino acid chainslipopolysaccharides = lipids + polysaccharides

That’simportant foryour doctorto know!

Gram-Positive bacteria

Metabolism

Obligate aerobes – must have oxygen to survive

Obligate anaerobes – cannot live if oxygen is present

Facultative anaerobes- can live either with or without oxygen

Archaebacteria&

Bacteria

Classification3 Domain system

reflects a greater understanding of evolution & molecular evidenceBacteria: EubacteriaArchae: ArchaebacteriaEukaryotes:

Protists Plants Fungi Animals

Prokaryote

Eukaryote

Classification of Bacteria

All bacteria are prokaryotesVery simple organismsAll are unicellular In general, they are smaller than

eukaryotesCircular DNA which is not enclosed in a

nucleusLack membrane-bound organelles

Classification of Bacteria

ArchaebacteriaEubacteria

Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria

Archaebacteria

a.k.a. Extremophiles Live in oxygen-free environments Obtain energy from sun or inorganic

molecules

Archaebacteria: Thiobacilli

Heat- and acid-loving bacteria Live in sulfur springs

Archaebacteria: Thiobacilli

Consume sulfur Combine it with oxygen to produce

energy Produce sulfur dioxide as by-product

Archaebacteria: Thiobacilli

Sulfur dioxide can combine with water to form sulfuric acid

Archaebacteria: Halobacteria

Salt-loving bacteria Live in saturated salt water like the

Great Salt Lake

Archaebacteria: Halobacteria

Produce purple pigments Use purple pigment to carry out

photosynthesis the way plants use chlorophyll

Archaebacteria: Alkalophytes

Live in aquatic environments with high pH

Forms the food basis upon which thousands of large organisms are dependent

Lake Nakuru

Archaebacteria: Methane Bacteria

Cannot live in the presence of oxygen Live in stomachs of cows and sewage

treatment ponds

Archaebacteria: Methane Bacteria

Obtain energy from CO2 and hydrogen gas

Archaebacteria: Deep Subsurface Bacteria

Live in rocks beneath Earth’s surface (as deep as 3,000 feet)

Archaebacteria: Deep Subsurface Bacteria

Obtain energy from H+ produced from reaction between minerals in rock and groundwater seeping in

Classification of Bacteria

ArchaebacteriaEubacteria

Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria

Heterotrophic Eubacteria

Obtain food from other living organismsparasites

Obtain food from dead organisms or organic wasteRecycle nutrients in decomposing organic

material

Classification of Bacteria

ArchaebacteriaEubacteria

Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria

Autotrophic Eubacteria

Obtain energy from lightPerform photosynthesis

Autotrophic Eubacteria

CyanobacteriaMost contain blue-green pigment (but some

are red or yellow)Form chains: not unicellular

Classification of Bacteria

ArchaebacteriaEubacteria

Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria

Chemosynthetic Eubacteria

Obtain energy from breakdown of inorganic substances (S and N compounds)

Key for agriculture:Convert atmospheric N to a form plants can

use

Reproduction in Bacteria

Can reproduce rapidly (every 20 minutes)

Luckily, most run out of nutrients and water before the colony gets very large

Most reproduce by binary fissionBacterium copies its chromosomeOld chromosome and copy attach to the

plasma membrane at opposite endsCell grows and becomes larger

Reproduction in Bacteria

Most reproduce by binary fissionGrowth causes two chromosomes to

separatePartition forms and separates the cell into

twoEach new cell has one copy of the original

chromosomeCreates two cells genetically identical to one

another

Genetic Exchange in Bacteria

ConjugationSexual form of bacterial reproductionOne bacterium passes all or part of its

chromosome to another cellTransfer occurs across piliCreates two bacteria genetically different

from one anotherThey then reproduce by binary fission

Transduction: Transfer of genes from one bacterium to another by a bacteriophage.

Ex. Toxin gene in Corynebacterium diphtheriae

Genetic Exchange in Bacteria

Transformation: Taking in DNA from the outside environment.

Ex. Rough Streptococcus pneumoniae transformed into smooth S. pneumoniae. Bacterial species in biofilm communities.

Genetic Exchange in Bacteria

Survival

If conditions become less than ideal some bacteria can form endospores

Tough outer covering resistant to:Drying outTemperature extremes (boiling water)Harsh chemicals

Survival

Closturidium botulinumProduces a deadly toxinEndospores can withstand boiling

temperaturesCanned foods must be pressure cooked to

kill the endospores

Six week old infant with botulism, which is evident as a marked loss of muscle tone, especially in the region of the head and neck.

Survival

Closturidium tetaniObligate anaerobe that produces a deadly

neurotoxinEndospores are found on nearly every

surface on the planetWhen endospores get into a moist,

oxygen-free environment (such as inside a puncture wound) they germinate

Reason for getting a tetanus shot

Tetanus

Survival

Bacillus anthracisAka. AnthraxEndospores live in soilWhen inhaled they germinate

Decomposers

Break down dead organisms and recycle the nutrients that make them

Without decomposition we would run out of the molecules necessary for life

Nitrogen-fixation

Plants and animals need nitrogen to make protein

The atmosphere is mostly nitrogen but plants and animals can’t use it

Nitrogen-fixation

Nitrogen-fixing bacteria convert nitrogen in the atmosphere into nitrogen plants can take up with their roots

Animals get their nitrogen by eating plants

Biotechnology

Production of foods like butter, cheese, and yogurt

Cleaning up oil spillsSynthesizing drugs and chemicals

Digestion

Much of what we eat would pass through our bodies without being digested if we didn’t have bacteria in our digestive tracts

They break down plant matter and synthesize vitamins for us

Bacterial Diseases

Bacteria cause illness one of two ways:Breaking down host cells or tissues for foodNormal metabolic processes generate

toxins

Bacterial Diseases

Most food-borne illnesses are caused by bacteria:E. coli comes from infected, undercooked

beefSalmonella comes from infected,

undercooked poultry (meat and eggs)Botulinum causes botulism – a deadly form

of food poisoning

Controlling Bacteria

Antibiotics are drugs that kill bacteria (NOT VIRUSES)

Controlling Bacteria

Most bacteria like warm, moist, dark conditions

Exposing them to other conditions kills them or slows reproduction

Controlling Bacteria

Examples: Cooking foods makes it too hot for most

bacteria to surviveRefrigerating or freezing foods makes it too

cold for them to reproduceDrying foods makes it impossible for

bacteria to reproducePickling causes bacterial cells to burst