Chapter 11

Sulfur - oxdizing bacteria

Are gram negative rods or spirals, grow in filaments. Obtain energy by oxidizing elemental sulfur and reduced sulfur compounds, including hydrogen sulfide and thiosulfate. O2 as a terminal electron acceptor, generating sulfuric acid S (energy source )+ 1 (1/2)O2 (terminal acceptor) + H2O --------> H2SO4

Thriving in Terrestrial Environments *Endospore Formers - bascillus,clostridium*

Bacillus species include both

Clostridium (Anaerobic chemoorgantrophs - Fermentation)

*Endospore - forming obligate anaerobes. Inhabitants of soil. Gram-positive. * Common in soils inhabitants and vegetative cells live in the anaerobic microenvironments created when aerobic organisms consume available O2. Endospores tolerate O2, survive long periods of heat, drying, chemicals irradiation that would kill vegetative bacteria. Germinate when conditions improve Diverse metabolism; some cause diseases.

Cyanobacteria

A diverse group of photosynthetic gram - negative bacteria that inhabit a wide range of environments, including fresh water and marine habitats, soils, and the surfaces of rocks.

Hydrogen - oxdizing bacteria - Aquiflex, Hydrogenobacter (Aerobic Chemolithotrophs)

Thermophilic bacteria that oxidize hydrogen gas as energy source. One of the earliest bacterial forms to exist on earth. Phylum : Aquifacae

*Thermus* (Aerobic Chemoorganotrophs: Obligate Aerobes)

Thermus aquaticus is the source of Taq polymerase (used in PCR). Stain Gram-negative. Phylum: Deinococcus - Thermus

Sulfur - and Sulfate - Reducing Bacteria environment

generally live in mud that has ogranic material and oxidized sulfur compounds.

Today anaerobic habitats common

Aerobes contribute by depleting O2 Mud and tightly packed soil limit the diffusion of gases and any O2 that penetrates is quickly converted to water by aerobically respiring organisms. Aquatic environments may also become anaerobic, limiting oxygen Huaman body (especially intestinal tract). Even the skin and oral cavity which are routinely exposed to O2, have anaerobic environments.

Filamentous anoxygenic phototrophic bacteria - Chloroflexus (Anoxygenic Phototrophs)

Characterized by their filamentous growth. Gram-negative Phylum: Chloroflexi

Anaerobic Chemoorganotrophs - Aanerobic Respiration

Chemoorganotrophs - oxidize organic compounds such as glucose to obtain energy. Those that grow anaerobically often use *sulfur or sulfate as a terminal electron acceptor. *

Green - Sulfur Bacteria examples

Chlorobium Pelodicyton

filamentous anoxygenic phototrophic bacteria

Chloroflexus best studied, especially therophilic strain found in hot springs.

Purple sulfur bacteria examples

Chromatium Thiospirillum Thiodictyon

*Pseudomonas* (Aerobic Chemoorganotrophs: Obligate Aerobes)

Common environment bacteria that as a group, can degrade a wide varitey of compounds Phylum: Proteobacteria

Cyanobacteria (oxygenic photortophs)

Earliest oxygenic phototrophs Use water as a source of electrons for reducing power. The carbon source is CO2 Carbon dioxide. harvest sunlight to convert CO2 into organic compounds. People thought they were algae called blue-green algae. Many convert N2 to ammonia: nitrogen fixation

Purple sulfur bacteria - Chromatium Thiosirillum , Thiodictyon (Anoxygenic Phototrophs)

Form colored masses in sulfur - rich aquatic habitats and use sulfur compounds as a source of electrons when making reducing power. Gram - negative Phyum: Proteobacteria

Green Sulfur bacteria - Chlorobium, Pelodictyon (Anoxygenic Phototrophs)

Found in habitats similar to those preferred by the purple sulfur bacteria. Gram - negative Phylum: Chlorobi

Purple Bacteria (Anoxygenic phototrophs)

Gram - negative; apper red, organe, or purple Photosynthetic apparatus in cytoplasmic membrane *Unlike other anoxygenic phototrophs* *Folds increase surface area*

Methangens

Group of archaea that generate ATP by oxidizing hydrogen gas, using *CO2 as a terminal electron acceptor*. Generates methane (CH4), a colorless, odorless, flammable gas *4 H2(energy source) + CO2 (terminal electron acceptor) -> CH24 + 2 H2O* *Can also use alternative energy sources such as formate, methanol, or acetate.* Found in anaerobic environments where H2 and CO2 are both available. *Oxidized H2 gas to generate ATP (oxidize means to lose e -)*

Purple non - sulfur bacteria - Rhodobacter, Rhodopseudomonas (Anoxygenic Phototrophs)

Grow in aquatic habitats, preferentially using organic compounds as a source of electrons for reducing power. Many are metabolically versatile. Gram - negative. Phylum: Proteobacteria

Others - Heliobacterium

Have not been studied extensively Phylum: Firmicutes

Anabaena, Synechococcus (Oxygenic Phototrophs - Cyanobacteria)

Important primary producers. Some fix N2. Gram negative Phylum: Cyanobateria

purple sulfur bacteria (Anoxygenic phototrophs)

Large cells; cell motile May have gas vesicels to control depth Most store sulfur in intracellular granules Preferentially use H2S to generate reducing power *other inorganic (H2) or organic (pyruvate) compounds* Some can grow aerobically in absence of light *Oxidize reduced inorganic, organic compounds*

*The Enterobacteriaceae - Escherichia, Enterobacter, Klebsiella, Proteus, Salmonella, Shigella, Yersinia* (Aerobic Chemoogranotrophs - Facultative Anaerobes)

Most reside in the intestinal tract. Those that ferment lactose are coliforms; their presence in water serves as an indicator of fecal pollution. Gram - negative Phylum: Proteobacteria

Anaerobic Chemolithotrophs

Obtain energy by oxidizing inorganic chemicals such as hydrogen gas (H2) to obtain energy. *Alternative electron acceptor:* carbon dioxide and sulfur. Relatively few anaerobic chemolithotrophs have been discovered, most are members of the domain Archaea. *Methanogens are one group*, Volta experiment.

Nitrite oxidizer

Nitrobacter Nitrococcus

Ammonium Oxidizers

Nitrosomonas Nitrosococcus

Propionibacterium (Anaerobic chemoorgantrophs - Fermentation)

Obligate anaerobes that produce proponic acid as their main fermentation end product. Used in the production of Swiss cheese. Gram - positive Phylum: Actiobacteria

Nitrifiers - Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrococcus(Aerobic Chemolithotrophs)

Oxidize ammonia or nitrite as energy sources. This converts certain fertilizers to a form easily leached from soils. and depletesO2 in water polluted with ammonia - containing wastes. Genera that oxidize nitrite prevents the toxic buildup of nitrate. Gram-negative Phylum: Proteobacteria

Aerobic chemoorgaphs

Oxidize organic compounds to obtain energy, using O2 as a termianl electron acceptor; organic compounds (energy soruce) + O2 (termianl electron acceptor) ------> CO2 + H2O

Filamentous sulfur oxidizers - Beggiatoa, Thiothrix(Aerobic Chemolithotrophs)

Oxidize sulfur compounds as energy sources. Found in sulfur springs and sewage - polluted waters. Gram-negative Phylum: Proteobacteria

Unicellular sulfur oxidizers - Thiobacillus, Acidithiobacillus (Aerobic Chemolithotrophs)

Oxidize sulfur compounds as energy sources. Some species produce enough acid to lower the pH to 1.0 Gram-negative Phylum: Proteobacteria

Lactic acid bacteira - Streptococcus, Enterococcus, Lactococcus, Lactobacillus, Leuconostoc (Anaerobic chemoorganotrophs - Fermentation)

Produce lactic acid as the major end prodcut of the their fermentative metabolism. Aerotolerant anaerobes. Several genera are used by the food industry. Gram- positive. Phylum: Firmicutes

*Deniococcus* (Aerobic Chemoorganotrophs: Obligate Aerobes)

Resistant to the damaging effects of gamma radiation. Stains Gram - Positive Phylum: Deinococcus - Thermus

Non-sulfur bacteria examples

Rhodobacter Rhodopseudomonas Rhodospirillum

Cornelius B. van Niel (1897 - 1985)

Studied photosynthetic purple bacteria *demonstrated requriement of light for growth* *No evolution of oxygen* *Oxidize hydrogen sulfide during CO2 fixation* Noted remarkable similarity of photosyntheic reactions in all photosynthetic organisms *purple sulfur bacteria use hydrogen sulfide instead of H2O* *Produce oxidized sulfur compounds instead of O2* *Indicated O2 from plants and algae comes from water, not CO2*

Anaerobic Chemotrophs

The first 1.5 billion years that prokaryotes inhabited Earth, the atomosphere was anoxic(lacked O2). Early chemotrophs probably used pathways of anaerobic respiration, using terminal electron accpetors such as *carbon dioxide or elemental sulfur* other may have used fermentation.

*Vibrio* (Aerobic Chemoogranotrophs - Facultative Anaerobes)

Typically found in marine environments because most species require at least low levels at Na+ for growth. Gram-negative Phylum: Proteobacteria

Oxygenic Phototrophs

Use water as a source of electrons for reducing power, generating O2 6CO2 + 6H2O -------> C6H12O6 + 6O2 (carbon source) (electron source )

*Mycobacterium* (Aerobic Chemoorganotrophs: Obligate Aerobes)

Waxy cell wall resists staining: acid - fast Phylum: Actinobacteria

Aerobic Chemoorganotrophs: Obligate Aerobes: Micrococcus

Widely distributed; common labortory contaminants, Gram - positive Phylum: Actinobacteria

*Corynebacterium* (Aerobic Chemoogranotrophs - Facultative Anaerobes)

Widespread in nature. Gram - positive Phylum: Actinobacteria

Methanogens environment

are commonly found in sawmps, marine sediments, rice paddies and the digestive tracts of humans and other animals. Is part of the 10 cubic feet of gas discharged from a cow's digestive system each day! *ARE VERY SENSITIVE TO O2*

primary producers

harvest the energy of sunlight using it to convert CO2 into organic compounds.

Anaerobic Chemoorganotrophs - Fermentation

obtain energy by fermentation, producing ATP only by substrate-level phosphorylation glucose -------> pyruvate ---------> lactic acid (energy source) (terminal electron acceptor)

anoxygenic phototrophs

use hydrogen sulfide or organic compounds as a source of electrons. Do not generate O2 6CO2 + 12 H2S -------> C6H12O6 + 12S + 6 H2O (carbon dioxide) (Electron source: H2S)

Sulfur - and Sulfate - Reducing Bacteria

when sulfur compounds are used as terminal electron acceptors, they *become reduced to form hydrogen sulfide*, the compound *responsible for the rotten - egg smell of many anaerobic environments*. organic compounds + S --------> CO2 + H2S (energy source) (terminal electron acceptor) *H2S is corrosive to metals* *Important in sulfur cycle* *At least a dozen recognized genera, Desulfovibrio most studied Gram-negative curved rods * most of the sulfur-reducing bacteria are either mesophiles or thermophiles