Diversity of Prokaryotes

Exam 2

Based on growth and nutrient requirement prokaryotes are divided into these groups

Anaerobic chemotrophs

Anoxygenic phototrophs

Oxygenic phototrophs

Aerobic chemilithotrophs

Aerobic chemoorganotrophs

Anaerobic chemotrophs

Found in soil, wetlands, digestive tract of humans, and ruminant mammals.

Two groups of chemotrophs

Anaerobic chemolithotrophs

Anaerobic chemoorganotrophs

Chemolithotrophs

Oxidize reduced inorganic chemicals to produce their energy

Methanogens

Found in sewage, swamps, marine sediments, digestive tract of mammals and hydrothermal vents where temperatures are above 100 degrees C. They are anaerobic members of Archaea that produce energy by reducing hydrogen and use carbon dioxide as terminal electron acceptor to produce methane and water. 

Chemotrophs can obtain energy by

Oxidation organic matter (chemoorganotrophs) or inorganic matter (chemolithotrophs)

Examples of anaerobic chemotrophs

Clostridia, streptococci, lactobacilli, propionibacterium

Genus Clostridia are

Gram-positive rods, produce endospores, and are common inhabitant of soil. They ferment a wide variety of compounds to produce energy

Lactic acid bacteria are

Gram-positive and produce lactic acid as an end product of fermentation. They include streptococcus, enterococcus, lactococcus, lactobacillus, and leuconostoc. Most organisms in this group can grow in aerobic environments but are obligate fermenters. 

Propionibacterium species are

Gram positive rds that produce propionic acid as end product of fermentation. These bacteria are essential in the production of swiss cheese.

Anoxygenic phototrophs

Oxidize hydrogen sulfide or organic molecules to make NADPH.

Examples of anoxygenic phototrophs

Purple bacteria

Green bacteria

Purple bacteria

Gram negative and appear red, orange, or purple due to their pigments used in photosynthesis

Purple sulfur bacteria

Prefer hydrogen sulfide to generate reducing power

Purple non sulfur bacteria

Prefer to use organic matter as their source of electrons for reducing power which distinguishes them from purple sulfur bacteria.

Green bacteria are 

Gram negative and are typically green or brown. 

Green sulfur bacteria are

Found in habitats such as sulfur springs, similar to purple sulfur bacteria

Use hydrogen sulfide as source of electrons

Many lack flagella but have gas vesicles

All are strict anaerobes

Filamentous anoxygenic phototrophic bacteria are

Metabolically similar to purple non-sulfur bacteria

They use organic molecules to generate reducing power

They grow aerobically and in the absence of light

Photosynthetic bacteria use

Water as source of electrons and release oxygen

Cyanobacteria

Included more than 60 genera and inhabit a wide range of environments, aquatic and terrestrial. Can be single celled or multicellular

Aerobic chemolithotrophs

Obtain energy by oxidizing reduced inorganic chemicals.

Aerobic chemolithotrophs include 3 groups:

Sulfur-oxidizing bacteria, nitrifying bacteria, hydrogen-oxidizing bacteria.

Aerobic chemoorganotrophs

Oxidize organic compounds to obtain energy

Aerobic chemoorganotrophs can be classified as

Obligate aerobes

Facultative anaerobes