BACTERIA

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


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


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


ShapeSpherical - CocciRod - BacilliCorkscrew - Spirillae


ArrangementSingularPairs – Diplo Chains – StreptoClusters – Stapylo


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


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


Consume sulfur Combine it with oxygen to produce

energy Produce sulfur dioxide as by-product


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




Heterotrophic Eubacteria

Obtain food from other living organismsparasites

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

material




Autotrophic Eubacteria

Obtain energy from lightPerform photosynthesis

Autotrophic Eubacteria

CyanobacteriaMost contain blue-green pigment (but some

are red or yellow)Form chains: not unicellular

http://www.e2bn.net/e2bn/microweb/microweb/photomicrographs/blue%20green%20algae.jpg




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 BacteriaCan reproduce rapidly (every 20

minutes)Luckily, most run out of nutrients and

water before the colony gets very largeMost reproduce by binary fission

Bacterium copies its chromosomeOld chromosome and copy attach to the

plasma membrane at opposite endsCell grows and becomes larger

Reproduction in BacteriaMost reproduce by binary fission

Growth causes two chromosomes to separate

Partition forms and separates the cell into two

Each new cell has one copy of the original chromosome

Creates two cells genetically identical to one another

Genetic Exchange in BacteriaConjugation

Sexual 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.

SurvivalClosturidium tetani

Obligate anaerobe that produces a deadly neurotoxin

Endospores are found on nearly every surface on the planet

When endospores get into a moist, oxygen-free environment (such as inside a puncture wound) they germinate

Reason for getting a tetanus shot

Tetanus

SurvivalBacillus anthracis

Aka. AnthraxEndospores live in soilWhen inhaled they germinate

DecomposersBreak down dead organisms and

recycle the nutrients that make themWithout decomposition we would run

out of the molecules necessary for life

Nitrogen-fixationPlants and animals need nitrogen to

make proteinThe atmosphere is mostly nitrogen but

plants and animals can’t use it

Nitrogen-fixationNitrogen-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 DiseasesMost 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)


Most bacteria like warm, moist, dark conditions

Exposing them to other conditions kills them or slows reproduction


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

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BACTERIA