Prokaryotes (Bacteria)

Prokaryotes

·        Classification of prokaryotes has dramatically changed due to analysis of the genomes of various types of cells:

·        The description of these organisms as members of Kingdom Monera, has been abandoned and replaced with a three domain system.  These Domains are as follows:

·        Domain Bacteria

·        Domain Archaea

·        Domain Eukarya

·        The domains bacteria and archaea contain the prokaryotic organisms.

·        Domain Eukarya include the protists and the other multicellular kingdoms

·        Bacteria are the smallest "living" organisms

·        Are prokaryotic cells

·        Lack Nucleus

·        DNA is naked. - a single loop - not bound into a chromosome.

·        May contain plasmids (small circular fragments of DNA)

·        Lack membrane-bound organelles

·        Usually have an outer Cell Wall.

·        Sometimes have an Outer Capsule - These stain red in a Gram Stain test and are called Gram Negative bacteria.

·        Those without an outer capsule stain blue in the gram stain test and are called Gram Positive Bacteria

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Are prokaryotic cells

Lack Nucleus Bacteria are the smallest "living" organisms

DNA is naked. - a single loop - not bound into a chromosome.

May contain plasmids (small circular fragments of DNA)

Lack membrane-bound organelles

Usually have an outer Cell Wall.

Sometimes have an Outer Capsule –

×These stain red in a Gram Stain test and are called Gram Negative bacteria.

×Those without an outer capsule stain blue in the gram stain test and are called Gram Positive Bacteria

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BACTERIAL CLASSIFICATION:

o       Bacteria are classified generally by 3 characteristics

o       The bacterial cell shape

o       The bacterial cell arrangements

o       Ability to accept a Gram stain

Bacterial Shape:

 

·        Bacteria have 4 basic shapes:

1.      Spherical - cocci

2.    Rod-shaped – bacilli

3.    Bent rod shaped - Vibrios

4.    Spiral – spirilli

 

Bacterial Arrangement:

 

·        Bacteria have 3 basic arrangements:

1.      Occurring singly = “Mono” arrangement

2.    Occurring in pairs = “Diplo” arrangement

3.    Occurring in long chains = “Strepto” arrangement

4.    Occurring in clusters = “Staphlo” arrangement

 

 

 

Gram Staining:

 

o       Bacteria can be categorized by their ability to accept a gram stain.

o       Bacteria are exposed to several staining agents; Crystal Violet, Gram’s Iodine, and safranine.

§        If the bacteria possesses a cell capsule, it will retain a pink color.  This is referred as to a “Gram Negative” bacteria

§        If the bacteria lacks a cell capsule it will retain a blue color.  This is referred to as a “Gram Positive” bacteria

 

Gram positive bacteria	Gram negative bacteria

 

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How Bacteria obtain energy:

·        Two major categories:

1.      Autotrophs - Make their own energy - 2 types Phototrophic autotrophs - Get energy from sunlight

·        Chemotrophic autotrophs - Get energy from inorganic molecules (eg. Sulfides)

2.    Heterotrophs - Energy obtained from other organisms

·        Chemotrophic heterotrophs - obtain energy by dissolving/absorbing organic material

·        Phototrophic heterotrophs - meet some energy needs from photosynthesis, but must absorb organic compounds.

Bacterial Respiration:

·        3 major categories

1.      Obligate aerobes. - Must have O₂ in order to live

2.    Obligate anaerobes - Must live in an O₂ free environment

3.    Facultative anaerobes - Can live with or without O₂.

Bacterial Reproduction:

 

·        Bacteria reproduce through binary fission.

·        Can engage in primitive sexual reproduction called conjugation.

·        A bridge is formed between 2 bacteria

·        Plasmids are shared across bridge, thus exchanging genetic information.

·        In times of harsh conditions, bacteria can form endospores, to encapsulate themselves in a dormant state, until conditions improve.

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Motility

Some bacteria are motile - can move by either thrashing, secreting lubricating secretions or through use of a flagellum.

Flagellated bacteria

 

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Archaea

Evolutionary Relationships

Analysis of molecules found within the cells suggests that eukaryotes are more closely related to archaea than to bacteria.

Major Groups of Archaea

Three major groups of archaea are found in extreme habitats.

o       Methanogens are found in anaerobic environments.such as marshes and in the intestinal tracts of animals. They produce methane as a result of cellular respiration.

o       Halophiles are found in environments with high salt concentration such as the great salt lake or soil with a high salt concentration.

o       Thermoacidophiles live in hot, acidic environments such as hot springs and hydrothermal vents.