Bacteria • Bacteria are one-celled organisms • visible only through a microscope.

• Bacteria live all around us and within us.• They are in the air ,water ,soil and food, the deepest parts

of the ocean and deep within Earth. and on plants and animals.

• Our lives are closely intertwined with theirs, • The health of our planet depends very much on their

activities• Bacteria inhabited Earth long before human beings or

other living things appeared

• The study of bacteria is called bacteriology, a branch of microbiology.

CHARACTERISTICS OF BACTERIA

• An average bacterium is about 1 to 2 micrometer long (1m =10^6 micrometer). Hundreds of thousands of

bacteria would fit on a rounded dot made by a pencil.

• Bacteria are procaryotes .They lack a true nucleus .Thier nucleus is made up of single circular DNA

• They occur in diverse shapes and types. As a group they carry out a broad range of activities and have different nutritional needs. They thrive in a variety of environments.

Structure of bacterial cell The cell wall :generally determines the shape of the bacterial cell and gives protection Some bacteria do not have much of a cell wall, while others have quite thick structures. Flagella :Many species of bacteria move about by means of flagella, hairlike structures that project through the cell wall. The flagellum’s rotating motion propels the bacterial cell toward nutrients and away from harmful substances.DNA is acting as Nucleus Most bacteria have a single coil of DNA, although some bacteria have multiple pieces. Bacterial cells often have extra pieces of DNA called plasmids, which the cell may gain or lose without dying. cytoplasm : Surrounding the DNA in a bacterial cell is, a watery fluid that is rich in proteins and other chemicals. cell membrane inside the wall holds together the DNA and the constituents of the cytoplasm.

Structure Flagella

Function(s) Swimming movement

Predominant chemical composition Protein

Pili

Sex pilus Stabilizes mating bacteria during DNA transfer by conjugation

Protein

Common pili or fimbriae Attachment to surfaces; protection against phagotrophic engulfment

Protein

Capsules (includes "slime layers" and glycocalyx)

Attachment to surfaces; protection against phagocytic engulfment, occasionally killing or digestion; reserve of nutrients or protection against desiccation

Usually polysaccharide; occasionally polypeptide

characteristics of typical bacterial cell structures

Cell wall

Gram-positive bacteriaPrevents osmotic lysis of cell protoplast and confers rigidity and shape on cells

Peptidoglycan (murein) complexed with teichoic acids

Gram-negative bacteria

Peptidoglycan prevents osmotic lysis and confers rigidity and shape; outer membrane is permeability barrier; associated LPS and proteins have various functions

Peptidoglycan (murein) surrounded by phospholipid protein-lipopolysaccharide "outer membrane"

Plasma membranePermeability barrier; transport of solutes; energy generation; location of numerous enzyme systems

Phospholipid and protein

Ribosomes Sites of translation (protein synthesis) RNA and protein

InclusionsOften reserves of nutrients; additional specialized functions

Highly variable; carbohydrate, lipid, protein or inorganic

Chromosome Genetic material of cell DNA

Plasmid Extrachromosomal genetic material DNA

Classification

Scientists classify bacteria into different types on the basis of.

1 shape. 2. oxygen use,

3. source of carbon, 4 .and response to a particular dye.

Etc .

shapeMost bacteria come in one of three shapes:

rod, sphere, or spiral. •Rod-shaped bacteria are called bacilli. •Spherical bacteria are called cocci,

•and spiral or corkscrew-shaped bacteria are called spirilla.

Some bacteria come in more complex shapes. A hairlike form of spiral bacteria is called

spirochete (see Spirochetes).

Aerobic and Anaerobic Bacteria.Aerobic bacteria require oxygen to support reproduction.

Camplylobacter jejuniEscherichia coli

Anaerobic bacteria reproduce in the absence of oxygen.Listeria (reduced oxygen levels)Clostridium perfringensClostridium botulinum

Facultative bacteria reproduce either in the presence or in the absence of oxygen.

SalmonellaShigellaStaphylococcus aureusBacillus cereus

Autotrophic and Heterotrophic Bacteria

All bacteria require carbon for growth and reproduction.

Autotrophs (“self-feeders”) get their carbon from CO2.Heterotrophs (“other feeders”) get carbon from organic nutrients

chemotrophs obtain energy by the oxidation of either inorganic or organic compounds lithotrophs : obtain electrons from inorganic compounds organotrophs : obtain their electrons from organic compounds

Some heterotrophic bacteria survive as parasites, growing within another living cell and using the nutrients and cell machinery of their host cells. Photo Autotrophs : Some autotrophic bacteria, such as cyanobacteria, use sunlight to produce sugars from CO2. Chemo autotrophs : depend on the breakdown of inorganic chemical compounds, such as nitrates and forms of sulfur for energy

Nutritional Type Energy Source Carbon Source Electron Source Examples

Photoautotrophic lithotrophs

Light CO2 Inorganic (H2O or H2S)

Cyanobacteria, some purple and green bacteria

Photoheterotrophic organotrophs

Light Organic compounds

Organic compounds

Some purple and green bacteria

Chemoautotrophic lithotrophs

Chemicals(H2, NH3, H2S)

CO2 Inorganic compounds

Bacteria and many archaea

Chemoheterotrophic organotrophs

Organic compounds

Organic compounds

Organic compounds

Most bacteria, some archaea

Gram-Positive and Gram-Negative Bacteria

Gram’s stain identifies bacteria as either Gram-positive

OR Gram-negative.

After staining, gram-positive bacteria hold the dye and appear purple, while gram-negative bacteria release the dye and appear red.

Gram-positive bacteria have thicker cell walls than gram-negative bacteria. Knowing whether a disease-causing bacterium is gram-positive or gram-negative helps a physician to prescribe the appropriate antibiotic.

• Endospores --Resistant survival forms produced in poor growth conditions. • This process is known as sporulation. • Bacterial spores are endospores in contrast to fungal spores• Unlike the spores of fungi, bacterial spores do not serve reproductive

function. • They are resistant to extreme environmental conditions such as high

temperatures, dryness, toxic chemicals (disinfectants, antibiotics), and UV radiation.

• The endospore is able to survive for long periods of time until environmental conditions again become favorable for growth.

• The endospore then germinates, producing a single vegetative bacterium. • Spores can be killed by sterilization methods such as autoclave and hot air

oven.• Some chemical disinfectants such as formaldehyde and ethylene oxide can

also kill spores. • Examples of sporulating bacteria Bacillus ,Clostridium

Endospores

Are all bacteria harmful?

• Much of our experience with bacteria involves disease. • Although some bacteria do cause disease, many kinds of

bacteria live on or in the human body and prevent disease. • Bacteria associated with the human body outnumber body

cells by ten to one. • In addition, bacteria play important roles in the

environment and in industry.

Disease causing bacteria opportunistic bacteria : they cause disease only when an opportunity is presented.

For example, cuts or injuries to the skin and protective layers of the body enable normally friendly bacteria to enter the bloodstream or other sterile parts of the body and cause infection especially when the immune system is weak

Opportunistic infections became more important in the late 20th century because of diseases such as acquired immunodeficiency syndrome (AIDS),

Cholera, one of the world’s deadliest diseases caused by the bacterium Vibrio cholerae.

After entering the body, the cholera bacteria grow in the intestines, often along the surface of the intestinal wall, where they secrete a toxin (poison).

This toxin causes massive loss of fluid from the gut, and an infected person can die of dehydration (fluid loss) unless the lost fluids, and the salts they contain, are replaced.

Tuberculosis is caused by Mycobacterium tuberculosis, which causes a disease of the lungs. Tuberculosis is responsible for more than 2 million deaths per year worldwide. TB bacterium is highly resistant to most antibiotics. In addition, the TB-causing bacteria readily spread from person to person.

New Bacterial DiseasesLegionnaires’ disease, a severe form of pneumonia, was first recognized in USA . It is caused by a previously unknown bacterium, Legionella pneumophila, which is most often transmitted through infected water

Lyme disease, a form of arthritis caused by the bacterium Borrelia burgdorferi, was first recognized in Lyme, Connecticut, in 1975. A bite from a deer tick that carries the bacteria transmits the disease to human beings.

Although E. coli is normally present in the human intestines, the variant E. coli O157:H7 produces toxins that cause bloody diarrhea and, in some cases, far more severe problems, including kidney failure and death. A person can become infected by eating contaminated meat. Thorough cooking kills the bacteria

Methicillin-resistant Staphylococcus aureus (MRSA) is a highly opportunistic, drug-resistant bacteria that originated in hospital settings and then spread widely.