Chapter 19: Bacteria

How Human are you?

• There are more microbial cells in our bodies than there are human cells!

• Of the 100 trillion cells that make-up the human body 90 trillion are bacterial

• Humans are ~90% Bacterial• Everyone has about 1 kg in weight of bacteria in

their gut. • Each gram of feces contains 100,000,000,000

(100 billion) microbes.• Human adults excrete their own weight in fecal

bacteria every year.

Classifying ProkaryotesDOMAIN BACTERIA – Kingdom Eubacteria

•Single-celled prokaryote

•Have peptidoglycan (protein carbohydrate) cell walls

•Can form colonies of clumps or filaments.

•Three basic shapes: Cocci (round), bacilli (rod) & spirilla (spiral)

Strepto – occurs in chains.

Staphylo – occurs in clusters..

Basic StructureCell wall – protects the cell & gives it shape.

Outer membrane – protects the cell against some anibiotics (only present in gram-negative)

Cell membrane – regulates movement of materials into & out of the cell; contains enzymes important to cellular respiration.

Plasmid – circular piece of DNA that contains some genes obtained through genetic recombination.

Capsule & Slime layer – protect the cell & assist in attaching the cell to other surfaces.

Ribosome

Cell Membrane

Cell Wall

Pilli

Flagella

DNA (circular)Peptidoglycan

Classifying ProkaryotesDOMAIN ARCHAEA – Kingdom Archaebacteria

•Genes that resemble eukaryotic genes & some that resemble prokaryotes.

•Have unusual lipids in their cell membranes

•Found in EXTREME environments!

•Cell walls lack peptidoglycan

•Have introns in their DNA

•Single-celled prokaryote

ArchaebacteriaMethanogens

•Convert H2 & CO2 into methane CH4

•Anaerobic bacteria

•Found in bottoms of swamps, sewage & intestinal tracts of animals.

Extreme Halophiles

•Salt loving

•Found in Great Salt Lake & Dead Sea

Thermoacidophiles

•Live in extreme acidic & hot environment

Prokaryote Evolution•Fossil Evidence indicates bacteria existed about 3.5 billion years ago.

•Eukaryotes existed about 2.5 billion years ago.

•Bacteria evolved to adapt to almost any environment, from ocean trenches to thermal vents.

Identifying Prokaryotes

Prokaryotes are identified by characteristics such as:

•the way they obtain energy

•shape

•type of cell wall

•the way they move

V. Ways Bacteria are Identified

I. Shapes of Bacteria:

a. Bacilli - rod-shaped

b. Cocci - round shaped

Staphylococcus - cocci in

clusters

Streptococcus - cocci in chains

Diplococcus - cocci in pairs

c. Spirilla - spiral shaped Ex: Treptonema pallidum

Metabolic DiversityChemoheterotrophs – organisms that must take in organic molecules for both energy and a supply of carbon.

Photoheterotrophs – organisms that are photosynthetic, but still need to take in organic compounds as a carbon source.

Chemoautotrophs – make organic carbon molecules from carbon dioxide and other inorganic compounds using energy from chemical reactions.

Photoautotrophs – use energy from sunlight to convert carbon dioxide and water to carbon compounds.

Releasing EnergyObligate aerobes – organisms that require a constant supply of oxygen in order to live. EX: Mycobacterium tuberculosis, the bacterium that causes tuberculosis.

Obligate anaerobes – do not require oxygen; some may be killed by O2! EX: Clostridium botulinum, found in soil and can grown in canned food causing fatal food poisoning.

Facultative anaerobes – can survive with or without O2. EX: E. coli, can live in the large intestines and contaminated water.

Growth & ReproductionBinary Fission – bacterium doubles in size, it replicates its DNA and divides in half.

Growth & ReproductionConjugation – the process by which two living bacteria bind together and one bacterium transfers genetic information to the other.

Sex pili

Growth & ReproductionEndospore – protects the cell against harsh environmental conditions, such as heat and drought. May allow the bacterium to survive for thousands of years.

Importance of BacteriaDecomposers – break down the nutrients in dead matter & atmosphere.

Nitrogen – Fixing Bacteria (Nitrogen fixation)

•Live freely & symbiotically with plants

•Rhizobium; converts N2 into a form of nitrogen plants can use.

•Found in legumes (bean type plants)

Importance of BacteriaPhylum Cyanobacteria

•Photosynthetic

•Encased in jelly-like substance & cling together

•Contain enzymes for fixing atmospheric nitrogen & make it available to plants.

•Some thrive on phosphates & nitrates in lakes & ponds.

Importance of BacteriaPhylum Cyanobacteria

Eutrophication or Population Bloom – the sudden increase in the number of cyanobacteria due to a high availability of nutrients.

When cyanobacteria die, they are decomposed by heterotrophic bacteria. This increase in heterotrophic bacteria depletes O2 in the water, harming other organisms that live there.

Human Uses of Bacteria•Food – baking & beverages

•Clean up oil spills, rivers & streams

•Make pharmaceuticals

•Aid in digestion

Bacteria & DiseasePathogen – bacteria that cause disease or a disease causing agent.

Exotoxins – toxic proteins secreted by bacterial cells, includes some of the most potent poisons known.

Clostridium botulinum – one gram of the exotoxin that causes botulism could kill 1,000,000 people!

Staphylococcus aureus – harmless, found on skin; if it enters the body through a wound it can cause layers of skin to slough off, vomiting, severe diarrhea & deadly toxic shock syndrome.

Bacteria & DiseaseEndotoxins – are NOT secretions; but components of cell walls in bacteria: glycolipids, which are large molecular complexes of polysaccharides & lipids.

All endotoxins induce the same general symptoms: fever, aches and sometimes a dangerous drop in blood pressure (shock).

Salmonella – produces endotoxins that cause food poisoning & typhoid fever.

Bacteria & DiseaseLyme Disease

•Most widespread pest carried disease in U.S.

•Caused by Borrelia burgdorferi, a bacterium carried by ticks that live on deer & field mice.

•Antibiotics can cure the disease if administered within a month of exposure.

•If untreated, it can lead to arthritis, heart disease & nervous disorders.

Bacteria & DiseaseYersinia pestis – the bacterium that causes bubonic plague throughout Europe. Carried by fleas.

It also played a role in battle, when armies hurled the bodies of plague victims into enemy ranks.

Bacteria & DiseaseBacillus anthracis

•Found naturally in soil where grazing animals such as sheep, cattle & goats are located.

•Easy to obtain, grow & it forms hardy endospores that can survive for years.

•Upon entering the bloodstream, anthrax will actively metabolize & multiply.

•Anthrax will release 3 proteins that combine to form a toxin that destroys body tissues & cells of the immune system.

•Modes of entry: cutaneous, inhalation, ingestion

Bacteria & DiseaseBacillus anthracis

Bacteria & Disease

AntibioticsAntibiotics are drugs that combat bacteria by interfering with various cellular functions

Some bacteria are antibiotic-resistant and destroy antibiotics, or prevent entry of the antibiotic into the cytoplasm.

AntibioticsBacteria can be tested for their sensitivity to antibiotics by growing them in a petri dish with paper disks containing different antibiotics.

As the antibiotics diffuse into the agar, the bacteria’s growth will be inherited by the antibiotics if the bacteria are sensitive to that antibiotic.