Micro Ch11

Methanogens

Members of Domain Archaea Produce energy by oxidizing 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

a. Aerobic Chemolithotrophs

Obtain energy-oxidizing reduced inorganic chemicals Oxygen as terminal electron acceptor Sulfur-oxidizing bacteria, nitrifiers and hydrogen-oxidizing bacteria

sheathed bacteria

form chains of cells incased in a sheath, enables cells to attach to solid objects in favorable habitats whilde sheltering them from attack of predators

prosthecate bacteria

have single polar prostheca called a stalk at the tip of the stalk in a holdfast, cells divide by binary fission

symbionts

..., organisms that live together and in which the association is of mutual advantage

Sulfur-oxidizers

...Sulfur-oxidizing bacteria Gram-negative rods or spirals Grow in filaments Energy through oxidation of reduced sulfur Hydrogen sulfide, elemental sulfur and thiosulfate Molecular oxygen serves as terminal electron acceptor This produces sulfuric acid An example of this is: S + 1 O + H O H2SO (energy (terminal source) electron) Filamentous sulfur oxidizers live in sulfur springs, sewage-polluted waters and on surface of aquatic sediments Cause bulking in sewage treatment facilities Interferes with separation of solid sludge and liquid effluent

Obligate aerobes

...obtain energy using aerobic respiration exclusively 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

Facultative anaerobes

...preferentially use aerobic respiration Can use fermentation as alternative in absence of oxygen May also use anaerobic respiration if the correct TEA is available Characteristic genera include Corynebacterium Gram-positive pleomorphic rods Inhabits soil, water and surface of plants Enterobacteriaceae Gram-negative rods Commonly referred to as enterics Reside in intestinal tract

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 An example of this is: NH + 1 O NO- + H O + 2H (energy (terminal electron source) acceptor) Nitrifiers Nitrogen polluted waters become hypoxic As nitrogen is oxidized, oxygen is consumed Nitrifiers encompass two metabolically distinctive groups Ammonia oxidizers Nitrite oxidizers An example of this is: NO + O NO (energy source) (terminal electron acceptor)

Green non-sulfur

Filamentous Anoxygenic Phototrophic 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

What is a heterocyst?

Fixation occurs in thick-walled heterocyst Protects the break down of nitrogenase from oxygen

ii. Purple sulfur and non-sulfur bacteria

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

Purple bacteria

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

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

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 trichomesNitrogen-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

Anaerobic Chemoorganotrophs - Fermentation

Other anaerobic chemoorganotrophs produce energy through fermentation Produce energy through substrate phosphorylation only Lactic acid bacteria Gram-positive organisms Produce lactic acid as fermentation end product Streptococcus, Enterococcus, Lactococcus, Lactobacillus, Most in this group can grow in aerobic environments but are obligate fermenters

Anoxygenic Phototrophs

Oxidize hydrogen sulfide or organic molecules when making NADPH Many inhabit restricted ecological niche Aquatic habitats such as bogs, lakes and upper layers of mud Includes purple bacteria and green bacteria An example is: 6 CO2 + 12 H2 S C6 H12 O6 + 12 S + 6 H2 O (carbon (electron source) source) ...

Anaerobic Chemoorganotrophs - Respiration

Some chemoorganotrophs produce ATP via anaerobic respiration through oxidation of organic molecules( glucose) Use terminal electron acceptor other than oxygen Sulfur and sulfate are common Sulfur and sulfate-reducing bacteria use sulfur as terminal electron acceptors and oxidize organic material Reduce it to hydrogen sulfide Responsible for rotten egg smell Essential for sulfur cycle in ecosystem Generally found in mud rich in organic matter and sulfur An example of this reaction is: Organic compounds + S CO + H S (energy source) (terminal electron acceptor)

Anaerobic Chemolithotrophs

anae, inorganic chemicals for energy source, use CO2 and S for terminal elecron acceptor, usually archaea (methanogens)