Microbiology Week 6: Microbial Metabolic Diversity

Anaerobic chemotrophs

organisms that harvest energy by oxidizing chemicals

Chemolithotrophs

oxidized reduced inorganic chemicals to obtain energy,

Use alternative electron acceptor,

Most in domain Archaea

Methanogens

methane-producing archaea,

Oxidize H2 gas to generate ATP,

CO2-terminal electron acceptor,

Very sensitive to O2,

Found in sewage, rice paddies, Digestive tracts

Anaerobic Chemoorganotrophs

anaerobic chemotrophs; can undergo anaerobic respiration or fermentation

Chemoorganotrophs

oxidize organic compounds to obtain energy,

Sulfur, sulfate used as a Terminal electron acceptor,

Sulfur and sulfate-reducing bacteria

-Produce hydrogen sulfide

-H2S is corrosive to metals

-Important in sulfur cycle

-Genera include Desulfovibrio

Anaerobic chemoorganotrophs- Fermentation

-Many anaerobic bacteria ferment

-glucose is the energy source

-pyruvate is the terminal electron acceptor

-Organic compounds are electron acceptors

Clostridium

Gram-positive, endospore-forming rods,

Endospores tolerate O2,

germinate when conditions improve,

Spores survive in improperly processed canned goods

Lactic acid bacteria

produce lactic acid,

can grow in aerobic environments; but only ferment,

lack catalase,

some pathogenic

examples include streptococcus, S. thermophilus

Lactobacillus

rod-shaped, common in mouth, vagina,

lower pH in vagina mucosa -inhibits pathogenic microbes,

fermented foods -lower pH, used to make cheese

Propionibacterium

gram-positive pleomorphic rods,

produce propionic acid via fermentation,

can ferment lactic acid,

Found in intestinal tract, anaerobic microenvironments on skin

Anoxygenic Phototrophs

-Earliest photosynthesizers

-Use hydrogen sulfide or organic compounds (not water) to make reducing power

-Do not generate O2

-Phylogenetically diverse (live in bogs, lakes, upper layers of mud)

-CO2-carbon source

-H2S-electron source

Purple Bacteria

-Gram negative; appear red, orange, or purple

-Photosynthetic apparatus in cytoplasmic membrane

-folds increase surface area

Purple sulfur bacteria

-May have gas vesicles to control depth

-Most store sulfur in intracellular granules

-Preferentially use H2S to generate reducing power

Purple Non-Sulfur Bacteria

-Use organic molecules instead of H2S as source of electrons

-Lack gas vesicles

-May store sulfur, granules form outside cell

Green bacteria

filamentous anoxygenic phototrophic bacteria

- Form multicellular arrangements

-Exhibit gliding motility

-Many have chlorosomes

-Metabolically diverse

oxygenic phototrophs

Photosynthetic organisms that produce O2

Cyanobacteria

-Earliest oxygenic phototrophs

-Began producing oxygen ~3 BYA

-Water is the electron source for reducing power

-Play essential role as primary producers

-Harvest sunlight to convert CO2 into organic compounds

-Diverse group of Gram-negative bacteria

-Many convert N2 to ammonia: nitrogen fixation

Cyanobacteria shape and examples

-Morphologically diverse

-Unicellular: cocci, rods, spirals

-Multicellular: filamentous associations: trichomes

-May have gas vesicles for vertical movement in water

-Large numbers can accumulate in freshwater habitats (blooms)

-Chloroplasts of algae, plants evolved from ancient cyanobacteria

Aerobic chemolithotrophs

gain energy by oxidizing reduced inorganic chemicals

Sulfur-oxidizing bacteria

-Gram-negative rods/spirals, may form filaments,

-obtain energy by oxidizing hydrogen sulfide and thiosulfate with O2 as a terminal electron acceptor.

-important in sulfur cycle

-Filamentous and unicellular lifestyles

Filamentous Sulfur Oxidizers

-sulfur springs, sewage polluted waters

-store sulfur as intercellular granules

Beggitoa filaments

move by gliding motility

Thiothrix immobile filaments

progeny cells detach; move via gliding motility

Nitrifiers

-diverse group of gram negatives

-oxidize inorganic nitrogen compounds for energy

-Concern to farmers using ammonium nitrogen

-Can deplete water of O2 if wastes are high in ammonium

Ammonium oxidizers

nitrosomonas, nitrosococcus

ammonium + terminal electron acceptor (02) -- NO2 + water and H+

Nitrite oxidizers

Nitrobacter, Nitrococcus

Hydrogen-Oxidizing Bacteria

-Aquifex, Hydrogenobacter- obligate chemolithotrophs

-Thermophilic, inhabit hot springs

-One of the earliest bacterial forms to exist on earth

-O2 requirements low

-H2 (energy source)

-1/2 O2 (terminal electron acceptor)

Aerobic chemoorganotrophs

-oxidize organic compounds, use O2 as the final electron acceptor, generate some CO2 as waste product , and some are obligate aerobes

-Some inhabit specific environments, other ubiquitous

Obligate Aerobes

Micrococcus: Gram positive cocci

-Found in soil, skin, dust particles

-Pigmented colonies

-Tolerate dry, salty conditions

Mycobacterium

-Acid fast bacteria

-Mycolic acid in cell wall prevents Gram-staining

-Acid-fast staining used

-Pleomorphic rods

-M. tuberculosis, M. Leprae

Pseudomonas

-Gram negative rods; oxidase positive

-Often produce green/blue pigments

-strict aerobes; do not ferment

-metabolic diversity important in degradation

-Ability sometimes come from plasmids

-Widespread: soil, water, mostly harmless

-obligate aerobe

Thermus

-Stain gram positive but have unusual cell walls

-Themophilic

-source of heat-stable enzymes: Taq polymerase in PCR reaction

-obligate aerobe

Deinococcus

-extraordinarily radiation resistant

-Dose shatters genome into many fragments, yet enzymes repair damage

facultative anaerobes

-Prefer aerobic respiration if oxygen is available

-in its absence they ferment

Corynebacterium

-Gram-positive pleomorphic rods

-Wide-spread

-Often club-shaped and form V shapes or palisades

-Generally facultative anaerobes; some strict aerobes

Enterics (enterobacteria)

-Gram-negative rods

-Ferment glucose

-Mostly found in normal intestinal microbiota

Typhoid fever

caused by salmonella typhi,

Facultative anaerobe

Bulbonic plague

caused by Yersinia pestis,

Facultative anaerobe

Coliforms

ferment lactose by producing acid and gas (E.coli)