The Diversity of Prokaryotic Organisms Chapter 11

Anaerobic Chemotrophs Found in soil, aquatic environments and the human body Organisms in this classification Anaerobic chemolithotrophs Anaerobic chemoorganotrophs

Anaerobic Chemotrophs Chemolithotrophs oxidize reduced inorganic chemicals to produce energy Use alternate terminal electron acceptor other that oxygen Usually carbon dioxide or sulfur Usually members of the domain Archaea

Anaerobic Chemotrophs Methanogens Members of Domain Archaea Produce energy by reducing hydrogen and using carbon dioxide as terminal electron acceptor This process creates methane and water Commonly found in sewage, swamps marine sediments and digestive tract of mammals Highly sensitive to oxygen Anaerobic chambers used for cultivation

Anaerobic Chemotrophs Some anaerobic chemoorganotrophs produce ATP via anaerobic respiration through the oxidation of organic molecules Also use terminal electron acceptor other than oxygen Sulfur and sulfate are common Other anaerobic chemoorganotrophs produce energy through fermentation Produce energy through substrate phosphorylation only

Anaerobic Chemotrophs Sulfur and sulfate-reducing bacteria use sulfur as terminal electron acceptors and oxidize organic material Reducing it to hydrogen sulfide Responsible for rotten egg smell These organisms essential for sulfur cycle in ecosystem Generally found in mud rich in organic matter and sulfur

Anaerobic Chemotrophs Members of genus Clostridium are Gram-positive rods Produce endospores Common inhabitant of soil Organisms in this genus ferment wide variety of compounds to produce energy Some organisms ferment amino acids in process of putrefaction

Anaerobic Chemotrophs Lactic acid bacteria are Gram-positive organisms that produce lactic acid as an end product of fermentation Includes Streptococcus, Enterococcus, Lactococcus, Lactobacillus, Leuconostoc Most organisms of this group can grow in aerobic environments but are obligate fermenters

Anaerobic Chemotrophs Propionibacterium species are Gram-positive rods Organisms produce propionic acid as end product of fermentation Essential in the production of Swiss cheese These organisms can also ferment lactic acid Can extract residual energy from waste product of other organisms

Anoxygenic Phototrophs Anoxygenic phototrophs oxidize hydrogen sulfide or organic molecules when making NADPH Many organisms inhabit restricted ecological niches Aquatic habitats such as bogs, lakes and upper layers of mud Includes purple bacteria and green bacteria

Anoxygenic Phototrophs Purple bacteria Gram-negative organisms Appear red, orange or purple due to pigments used in photosynthesis Purple sulfur bacteria found in habitats such as sulfur springs Prefer hydrogen sulfide to generate reducing power Most organisms strict anaerobes and phototrophs Some can grow aerobically and in absence of light

Anoxygenic Phototrophs Purple non-sulfur bacteria Found in variety of aquatic habitats Moist soil, bogs and paddy fields Prefer to use organic source of electrons in production of reducing power Distinguishes them from purple sulfur bacteria Remarkably diverse metabolism Most can grow aerobically and in absence of light

Anoxygenic Phototrophs Green bacteria Gram-negative organisms Typically green or brown Green sulfur bacteria Found in habitats similar to purple sulfur bacteria Use hydrogen sulfide as source of electrons Many lack flagella but have gas vesicles All are strict anaerobes

Anoxygenic Phototrophs Green non-sulfur bacteria Characterized by filamentous growth Metabolically resemble purple non-sulfur bacteria Use organic molecules to generate reducing power Can grow aerobically and in absence of light

Oxygenic Phototrophs Photosynthetic bacteria that use water as source of electrons Oxidation of water liberates oxygen Cyanobacteria thought to be earliest organism of group Cyanobacteria act as primary producers Harvest sunlight to produce organic compounds through conversion of carbon dioxide

Oxygenic Phototrophs The cyanobacteria Includes more than 60 genera Inhabit wide range of environments Aquatic to terrestrial Able to convert nitrogen gas to ammonia Nitrogen fixation Some organisms single celled Form multicellular associations called trichomes

Oxygenic Phototrophs Nitrogen-fixing cyanobacteria Important ecologically Can incorporate both nitrogen gas and carbon dioxide into organic material Supports growth of other organisms Helps control atmospheric carbon dioxide heterocyst Fixation occurs in thick-walled heterocyst Protects the break down of nitrogenase from oxygen

Aerobic Chemolithotrophs Obtain energy oxidizing reduced inorganic chemicals Uses oxygen as terminal electron acceptor Includes sulfur-oxidizing bacteria, nitrifiers and hydrogen-oxidizing bacteria

Aerobic Chemolithotrophs Sulfur-oxidizing bacteria are Gram-negative rods or spirals Grow in filaments Obtain energy through oxidation of reduced sulfur Including hydrogen sulfide, elemental sulfur and thiosulfate Molecular oxygen serves as terminal electron acceptor This produces sulfuric acid

Aerobic Chemolithotrophs Filamentous sulfur oxidizers live in sulfur springs, sewage polluted waters and on surface of aquatic sediments Causes bulking in sewage treatment facilities Interferes with the separation of solid sludge and liquid effluent

Aerobic Chemolithotrophs Unicellular sulfur oxidizers found in both terrestrial and aquatic environments Responsible for bioleaching through oxidation of metal sulfides producing sulfuric acid and liquid metal Some species produce enough acid to lower pH to 1.0

Aerobic Chemolithotrophs Nitrifiers Diverse group of Gram-negative bacteria Oxidize inorganic nitrogen to obtain energy Nitrogen such as ammonia and nitrite Important in the breakdown of ammonia containing waste Nitrogen polluted waters become hypoxic As nitrogen is oxidized oxygen is consumed Nitrifiers encompass two metabolically distinctive groups Ammonia oxidizers Nitrite oxidizers

Aerobic Chemolithotrophs Hydrogen-oxidizing bacteria are Gram-negative bacteria Obligate chemolithotrophs Tend to thermophilic Found primarily in hot springs Some members thrive at 95°C

Aerobic Chemoorganotrophs Oxidized organic compounds to obtain energy Use oxygen as terminal electron acceptor Include tremendous variety of organisms Chemoorganotrophs can be classified as Obligate aerobes Facultative anaerobes

Aerobic Chemoorganotrophs Obligate aerobes obtain energy using aerobic respiration exclusively None use fermentation Characteristic genera include Micrococcus Gram-positive cocci found in soil and dust Produce yellow pigmented colonies Mycobacterium Gram-positive bacterium Live on dead and decaying matter Pseudomonas Gram-negative rods Motile and often pigmented Common opportunistic pathogen Thermus and Deinococcus Both have scientific and commercial uses Thermus produces Taq polymerase Dinococcus used to clean up radioactive contamination

Aerobic Chemoorganotrophs Facultative anaerobes preferentially use aerobic respiration Can use fermentation as alternative in absence of oxygen Characteristic genera include Corynebacterium Gram-positive pleomorphic rods Inhabit soil, water and surface of plants Enterobacteriaceae Gram-negative rods Commonly referred to as enterics Reside in intestinal tract

Thriving in Terrestrial Environments Numerous genera that inhabit soil can form resting stages that enable survival in dry periods Endospores, cysts, fruiting bodies, and mycelium are examples of resting stage structures Bacillus and Clostridium species produce endospores Azobactor species produce cysts Myxobacteria species form fruiting bodies Streptomyces species form mycelium Endospores tend to be more resistant to environmental insult than cysts or fruiting bodies

Thriving in Terrestrial Environments Bacteria associated with plants use different means to obtain nutrients Agrobacterium produce plant tumors to gain nutrient These tumors are often fatal to plant Rhizobium have a mutually beneficial relationship with plants Organisms fix nitrogen that is used for a nutrient source for the plant

Thriving in Aquatic Environments Organisms produced numerous mechanisms for nutrient acquisition and retention Clustering within a sheath Bacteria form chains encased in tube which enables them to find favorable habitat Includes genera Sphaerotilus and Leptothrix Derive nutrient from other organisms Bdellovibrio prey on other organisms Bioluminescent bacteria establish relationships with other animals for food and protection Legionella live inside protected confines of protozoa

Thriving in Aquatic Environments Organisms produced numerous mechanisms for nutrient acquisition and retention Move by unusual means Spirochetes move via axial filaments in corkscrew motion Magnetotactic bacteria move by means of magnetic crystals aligning them with earth’s magnetism Formation of storage Spirillum species form volutin granules to store phosphate Certain marine bacteria store sulfur and nitrate for oxidation and reduction Gives advantage to bacteria in certain environments

Animals as Habitats Bodies of animals provide wide variety of ecological habitats for bacteria Skin inhabited by Staphylococcal species Significant component of skin flora Mucous membranes is inhabited by numerous genera including Bacteriods, Bifidobacterium, Campylobacter and Helicobacter, Neisseria and Treponema Bacteria that are obligate intracellular parasites including Rickettsia, Orientia and Ehrlicia reside in blood sucking arthropods Mainly ticks or lice Coxiella transmitted person to person without arthropod vector

Archaea that Thrive in Extreme Conditions Extreme halophiles are found in high salt environments Salt lakes, soda lakes and brines Most require 9% salt concentration Includes genera Halobacterium, Halorubrum, Natronobacterium and Natronococcus Extreme thermophiles are found in regions of volcanic and thermal vents as well as sulfurous fissures and hot springs Methanothermus grows at temperatures as high as 97°C Pyrolobus fumarii grows between 90°C and 113°C Sulfolobus species grow only above 50°C Also require pH between 1 and 6

Archaea that Thrive in Extreme Conditions Thermophilic extreme acidophiles grow at extremely high temperature and low pH Two significant genera Thermoplasma Grow optimally at pH of 2 Some species lyse at neutral pH Picrophilus Optimal growth below pH 1