BACTERIA

Bacteria • Cells are prokaryotic and amongst the smallest known cells ( length

0.5-20 µm ).

• Lack a nucleus

• DNA is naked, a single loop not bound in a chromosome

• May contain plasmids (small circular fragments of DNA)

• Have ribosomes, but no other organelles.

• DNA present as a long circular molecule.

Structure of a Bacteria

Classification

• All bacteria are prokaryotes, which can be placed in one of two kingdoms:

• Archaebacteria: “Ancient Bacteria”

• Archaebacteria “True Bacteria”

Archaebacteria

• “Archae” means primitive or early

• Oldest organisms on the plant ~ 3 billion yrs old

• Live in extreme conditions: Environments in which no other organisms can survive

Environments of Archaebacteria

• These bacteria are characterized as living in extreme conditions that have:

• High temperatures (Thermophiles)• Low temperatures (Psychrophiles)• High Salt concentrations (Halophiles)• High acidity • Environments with no oxygen (anerobic)

Archaebacteria

Thermophilic bacteria thrive in volcanic vents Halophilic bacteria thrive in salty

lakes

Eubacteria

• All other bacteria.• Strong cell walls and less complicated genetic

makeup.• Live in many habitats• Most common form of life on earth• Can be bad (pathogens) or good (digestion)• Organisms: Bacteria, Cyanobacteria

How to Classify Bacteria

• Shape

• Cell walls

• How they move

• How they obtain Energy

Cell Shape

• One way that bacteria can be identified is by their shape:

Lactobacilli: rod-shaped Spirochaeta: spiral Enterococci: spherical

Rod-shaped, called Bacilli Spiral, called Spirilla or Spirochetes

Spherical

Coccus

• Spherical shaped bacteria are called Cocci

Single cells - monococci

Pairs - diplococci

Chains - streptococci

Bacillus • Rod shaped Bacteria are called Bacilli

Exists as: Single Cells In pairs (diplobacilli) In chains (streptobacilli).

Spirilla • Spiral shaped bacteria are called Spirilla • Spirillum (Singular)

Plural is spirilli.Exist only as single cells.

Cell Wall• The chemical nature of a

cell wall can be studied by a method known as Gram Staining

• Hans Christian Gram: inventor of Gram Staining

Gram Staining• Gram stains contain of two dyes

• Crystal Violet (Purple)• Safranine (Red)

• Gram-positive bacteria: cells with only 1 thick layer of carbohydrate and protein molecules took up the crystal violet dye.

• Gram-negative bacteria: cells wall contains a second layer of lip and carbohydrate took up the crystal violet dye.

a)Gram positive:

Appears violet after

Gram’s stain

b) Gram negative:

Appears red after Gram’s stain

GRAM STAIN It is the most important differential stain used in bacteriology because

it classified bacteria into two major groups:

Bacterial Movement

• Some bacteria propel themselves by the means of 1 or more whip-like structures called a flagella

• Some bacteria produce a thick layer of slime to glide about

• Others remain stationary

• Bacteria can be identified by studying how them move:

How bacteria obtain Energy

• Autotrophs: Organisms that make their own energy

• Phototrophic Autotrophs: Bacteria that get there energy from sunlight

• Chemotropic Autotrophs: Bacteria that obtain

their energy from inorganic molecules

– Inorganic molecules: Hydrogen sulphide, nitrites, sulphur and iron

Examples of Autotrophic Bacteria

Phototrophic autotroph: Cyanobacteria Chemotrophic Autotrophs: Ecoli bacteria

How Bacteria obtain Energy

• HETEROTROPHS: Energy is obtained from other organisms

• Chemotrophic heterotrophs: obtain energy by dissolving and absorbing organic material

• Phototrophic heterotrophs : obtain sunlight for energy, but need organic compound for nutrition.

Examples of Heterotrophic Bacteria

Chemotrophic heterotroph: Salmonella

Bacterial Respiration and Fermentation

• Bacteria need a constant supply of energy to perform their life activities

• Energy is supplied by the process of:

– Respiration: A process that involves oxygen and the breakdown of food molecules to release energy

– Fermentation: the process that enables cells to carry out energy production in the absence of oxygen

Bacterial Respiration

• Bacteria can be classified into three categories based on their need for oxygen

1. Obligate aerobe: Must have O2 to live

2. Obligate anaerobes: Must live in O2 free environment 3. Facultative anaerobes: Can live with or without O2

RECAP QUESTIONSHow would this bacteria be classified accordingto shape?

Is this bacteria a Gram-positive or Gram-negative bacteria?