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What is Bacteria?
Domain Bacteria
• A Large and Diverse group of organisms that
consist of prokayotic cells (have no nucleus)
• Their cells wall contains the protein
peptidoglycan
• Grow everywhere on Earth
Species belonging to
the Domain Bacteria
are classified based on:
(1) Cell Shape
(2) Respiration Type
(3) How they obtain
Energy
(4) How they
Reproduce
Classifying Bacteria
(1) Cell Shape There are three basic bacterial shapes:
– Bacilli are rod shaped
– Cocci are spherical shaped and
– Spirilla are spiral shaped (also called
spirochetes)
• These may occur as individual cells, pairs
(Diplococcus), in chains (Streptococcus)or as
clumps or clusters (Staphylococcus)
(2) Bacterial Respiration
• Obligate aerobes need a constant O2 supply
• Obligate anaerobes must live in the absence of O2
– EG: Clostridium botulinum. The toxin (poison) it produces effects nerves and paralyses breathing muscles
• Facultative anaerobes use fermentation of organic molecules for energy like obligate anaerobes do but are not harmed by oxygen.
• This respiratory diversity allow bacteria to live in all of the environments of the biosphere
(3) How the Bacteria Obtains Energy
• AUTOTROPHS
– Phototrophic autotrophs use light energy to
produce carbohydrates.
– Chemotrophic autotrophs use inorganic
chemicals such as hydrogen sulfide, nitrites,
ammonia, sulfur and iron for energy.
• HETEROTROPHS
– Many bacteria and all fungi and animals are chemotropic heterotrophs which means they get energy from breaking down organic molecules
– Some bacteria are photosynthetic heterotrophs which means that they can obtain energy both ways
(4) Bacterial Reproduction1. Binary
Fission
(asexual)
2. Conjugation
(sexual)
• A bacterial donor containing a conjugative plasmid forms a connection with neighboring cell.
• A single stranded copy of the plasmid genome is made.
• The single stranded copy is sent through the pilus to the recipient cell.
conjugation
Importance of Bacteria
• Food production
– EG: cheese, yogurt, buttermilk, sour cream,
and sauerkraut
• Industry
– EG: petroleum digestion, waste and poison
removal, mining minerals, and drug synthesis
• Human Symbiosis
– EG: intestinal bacteria to digest cellulose or
produce vitamins (in humans bacteria
produce vitamin K in the large intestine)
Bacteria and the Environment
• Bacteria fill the ecological role of decomposer
• Bacteria that recycle and decompose (break
down) dead material can be called saprophytes.
• Sewage decomposition is accomplished largely
by encouraging and controlling bacterial growth.
The products are H2O, N2, CO2, and solid
leftovers that can be used to fertilize crops.
• Nitrogen fixation is accomplished in nature only
by cyanobacteria notably Rhizobium in root
nodules of legumes. These live associated with
many types of plants and convert N2 from the air
into a form plants can incorporate into amino
acids.
Lyme disease
caused by Borrelia
burgdorferi, a type
of bacterium called
a spirochete
E. coli bacillus
Salmonella enteriditis
E. coli on alfalfa sprout
Neisseria gonorrhoeae
Bacillus anthracis
Domain Archaea
• Discovered in 1977 and originally classified as “bacteria”
• Classified as their own domain in 1990
• Like “traditional” bacteria this group of organisms consist
of prokaryotic cells
• Are biochemically different than Bacteria (are NOT
considered bacteria)
• Live in extreme environments (considered
extremophiles)
– Extreme heat (>100ºC)
– Acidic and Alkaline Environments
– High Salinity (high salt concentration)
– Extreme Pressure (up to 200 atmospheres)
• Produce methane gas
• Reproduce by binary fission
– Although recently archaea that reproduce sexually have been
discovered
• Obligate anaerobes
– Although recently aerobic archaea have been discovered
Species belonging to
the Domain Archaea
are classified based on:
(1) Cell Shape
(2) Respiration Type
(3) How they obtain
Energy
(4) How they
Reproduce
However, recent discoveries
and the wide range of diversity
in species among this Domain
are leading to the emergence of
Kingdoms and possibly distinct
new Domains
Stay tuned….
