Prokaryotes
1) Diversity of nutritional and metabolic adaptations
a. There is greater amount of nutritional diversity among prokaryotes than among all
eukaryotes. Every type of nutrition observed in eukaryotes is seen in prokaryotes,
plus there are some nutritional modes that are unique to prokaryotes.
b. There are four major modes of nutrition in prokaryotes
i. Photoautotrophs – photosynthetic organisms. Capture light energy and
use it to drive the synthesis of organic compounds using CO2. Example:
Cyanobacteria
ii. Chemoautotrophs – Need only CO2 as a carbon source. Oxidize
inorganic cubstances (hydrogen sulfide H2S), ammonia (NH3), and ferrous
ions (Fe2+) instead of light energy. This mode of nutrition is unique to
prokaryotes.
iii. Photoheterotrophs – uses light energy but must obtain their carbon in
organic form. Many marine prokaryotes use this mode of nutrition.
iv. Chemoheterotrophs – must consume organic molecules for both energy
and carbon. Found widely among prokaryotes as well as protists, fungi,
animals, and some parasitic plants.
Mode of Nutrition
Autotroph
Photoautotroph
Chemoautotroph
Heterotroph
Photoheterotroph
Chemoheterotroph
Energy Source
Carbon Source
Types of Organisms
Light
CO2
Inorganic Chemicals
CO2
Photosynthetic
prokaryotes, plants,
certain protists
Certain prokaryotes
(Ex. Sulfolobus)
Light
Organic Compounds
Organic Compounds
Organic Compounds
Certain prokaryotes
(Ex. Rhodobacter,
Chloroflexus)
Many prokaryotes
(Clostridium) and
protists, fungi,
animals, and some
plants
2) Metabolic relationships to Oxygen
a. Prokaryotic metabolism varies in respect to oxygen
b. Obligate aerobes – use O2 for cellular respiration and cannot grow without it
c. Facultative anaerobes – use O2 if it is present but can also grow by fermentation
in an anaerobic environment
3)
4)
5)
6)
d. Obligate anaerobes – are poisoned by O2. Some live exclusively by
fermentation, others extract chemical energy by anaerobic respiration.
i. Anaerobic respiration – uses substances other than oxygen as the final
electron acceptor of ETC’s.
Nitrogen fixation
a. Process in which atmospheric nitrogen is converted into ammonia.
b. This “fixed” nitrogen can be incorporated into amino acids and other organic
molecules.
c. This ability causes prokaryotes to play an important role in the nitrogen cycle of
ecosystems.
Chemical Recycling
a. Prokaryotes play a crucial role in the ecosystem/biosphere
b. The atoms that make up all living things were at one time part of inorganic
compounds
c. Ecosystems depend on the continual recycling of chemical elements
d. Chemoheterotrophic prokaryotes function as decomposers. They break down
corpses, dead vegetation, and waste products.
e. The action of these decomposers unlock supplies of carbon, nitrogen, and other
elements that would otherwise be inaccessible.
Symbiotic Relationships
a. Symbiosis – an ecological relationship between organisms of different species
that are in direct contact. If the symbiotic organisms differ in size, the larger
organism is called the host and the smaller organism is called the symbiont.
b. Mutualism is a type of symbiotic relationship where both organisms benefit
i. Ex. Many eukaryotic organism depend on mutualistic prokaryotes. Many
of these live in the intestines.
c. Commensalism – one organism benefits while neither harming nor helping the
other in any significant way (rare in nature)
d. Parasitism – one organism (a parasite) benefits at the expense of the host
organism
Pathogenic Prokaryotes
a. Prokaryotes cause about half of all human diseases
b. Usually cause illness by producing exotoxins or endotoxins
c. Exotoxins – proteins secreted by prokaryotes. Can cause disease even if the
prokaryotes that make them are not present. Ex. Clostridium botulinum
d. Endotoxins – lipopolysaccharide components of the outermembrane of gramnegative bacteria. Released only when the bacteria die and their cell walls break
down. Ex. Salmonella
e. The discovery of antibiotics has greatly reduced the threat of pathogenic
prokaryotes. Antibiotic resistance is currently evolving in many strains of
prokaryotes.
7) Research and Technology
a. Bioremediation – use of organisms to remove pollutants from soil, air, or water.
i. Ex. Anaerobic bacteria and archaea decompose the organic metter in
sewage, converting it to material that can be used as landfill or fertilizer
after chemical sterilization.