what is an anaerobe?

1

Anaerobic Metabolism

Methanogenesis

Sulfate reduction

Nitarte reductionAcetogenesis

fermentation

syntrophism

Iron reduction

Absence of O2

What is an anaerobe?

Is the distinction between aerobes andanaerobes based on energymetabolism or sensitivity to oxygen? Yes to both questions in part.

Define an organism by its growth inrelation to oxygen. semi-solid medium presence of an oxygen gradient.

Growth response to oxygen

Anaerobe Facultative MicroaerophileAerobe

Oxidized

Reduced

Factors influencing organismsability to grow with oxygen Cellular

Cell density Inoculum age Prior exposure to oxygen

Medium Components: sulfur and other oxidizable

compounds Medium handling

Reactive oxygen species

Aerobically, respiratory flavoproteinsand ubiquinone oxidoreductases form: Superoxide anion (O2

-) Hydrogen peroxide (H2O2)

These can react with iron in the cell toform hydroxyl radical (•OH)

Hydroxyl radical responsible for much ofthe damage to cells

Protective enzymes

Hydrogen peroxide Catalase: 2 H2O2 --> 2 H2O + O2

Peroxidase: NAD(P)H + H+ + H2O2 -->2H2O + NAD(P)+

Superoxide dismutase (SOD) O2

- + O2- + 2 H+ --> H2O2 + O2

Singlet oxygen Quenched by carotenoids

2

Oxygen tolerance

Aerobes: generally have catalase,superoxide dismutase, peroxidases andother protective enzymes

Microaerophiles: usually have low levelsof above enzymes

Anaerobes: many of them have theabove enzymes, but they still oxygensensitive.

Interesting features aboutanaerobes Acetogens live in well-drained, oxic soils and

in termite guts with steep oxygen gradients. Sulfate reducers:

Desulfovibrio termitidis uses O2 at a rate of 1570µmol O2 per min per mg of cells (Periplasmic oxygen reductionby Desulfovibrio species Arch. Microbiol. (2001) 176(4):306-9)

Faster than many aerobes Cohen found sulfate reduction occurs together

with oxygenic photosynthesis in algal mats Judy Wall’s group found cytochrome oxidase in

genome of sulfate reducer.

New protective system foranaerobes

O2 O2-

Metal

Rubredoxinred

Rubredoxinox

NAD(P)H + H+

NAD(P)+

H2O2

2 H2ONAD(P)+

NAD(P)H + H+

Value is no O2 is made

Superoxidereductase

Peroxidase

What makes anaerobessensitive to oxygen?

Expose Bacteroides thetaiotaomicron to air Disrupts key enzymes in central metabolism

Fumarate and pyruvate can’t be metabolized

Cells can’t make ATP

Anaerobes depend on highly oxygensensitive enzyme systems to generate energy

Disrupt these then cell dies

Electron DonorBenzoateFatty AcidsEthanolHydrogen

Electron acceptors

O2 Fe+3 NO3- SO4- CO2

e-

Preference of electron acceptors in Nature

CO2SO4-NO3-Fe+3O2

Contaminant

FlowX

3

4) Methanogenic Bacteria

3) Acetogenic Bacteria

2) Syntrophic Bacteria

1) Fermentative Bacteria

Anaerobic metabolic groups of Prokaryotesinvolved in the oxidation of organic mater

Lake

18-Sep-06

Dissolved oxygen (mg/L)0 2 4 6 8

Depth (m

)

0

2

4

6

8

10

12

14

16

18

20

22

24

Temperature (oC)

26 27 28 29 30 31

Redox potential (mV)

-200 -100 0 100 200 300 400

DO TemperatureDO SaturationRedox

16-Jan-07


0

2

4

6

8

10

12

14

16

18

20

22

24

Temperature (oC)

26 27 28 29 30 31


-300 -200 -100 0 100 200 300 400

12-Mar-07


0

2

4

6

8

10

12

14

16

18

20

22

24

Temperature (oC)

26 27 28 29 30 31


-300 -200 -100 0 100 200 300 400

Evaluation of temporal variation of dissolved oxygen and related parameters at Guajataca

Sotomayor, D., G. A. Martínez, and F. Pantoja-Agreda. Limnological Assessment of two Reservoirs of Puerto Rico. 2007. Proceedings. 30th Congress of the International Association of Theoretical and Applied Limnology. August 12-18, Montreal, Canada. In Press.

Sotomayor, D., G. A. Martínez, and F. Pantoja-Agreda. Limnological Assessment of two Reservoirs of Puerto Rico. 2007. Proceedings. 30th Congress of the International Association of Theoretical and Applied Limnology. August 12-18, Montreal, Canada. In Press.

DO (mg/L)

0 2 4 6 8 10

Water colum

n position

Surface

Mid Depht

Bottom

Cidra Patillas Carraizo La Plata Lucchetti Caonillas Cerrillos Guajataca Dos Bocas Toa Vaca

Concentration of dissolved oxygen at three water column depths in selected reservoirs of Puerto Rico.

4

What is syntrophism?

Is a special mutualistic association that requires a symbiotic cooperationbetween two different types of prokaryotes.

Syntrophic bacteria and a hydrogen consumerSulfate reducer

Methanogen

∆G0' (kJ/mol)

C7H5O2 + 7H2O 3CH3COO + HCO3 + 3H2 + 3H+ 70.5

C7H5O2 + 4.75H2O 3CH3COO + 0.25HCO3 + 0.75CH4 + 2.25H+ -31.2

Benzoate

Go to paper

2) Syntrophic Bacteria

Sulfate Reducers

Complete or incomplete

CO2

Sulfate reducersDesulfovibrio, Desulfotomaculum, DesulfobacterDesulfobulbus, Desulfococcus, Desulfonema,Desulfosarcina

Methanogens

5

MethanogensEstan limitados a H2, CO2

compuestos organicos de 1 C,methylamines o acetato para laproduccion de metano.

Polysaccharides, sugars, proteins, lipids, etc.

Intermediates of fermentation

CO2 + HS-

H2 + CO2

Formate

CH4

Acetate

CH4

HS-

Fermentative, syntrophic, sulfate-reducing, and methanogenic prokaryotes

Where can we find these microorganisms?

1 2 3 4

Conclusion Reactive oxygen species destroy cellular

components Cells have protective enzymes Oxygen tolerance depends on balance

between rate of generation of reactivespecies vs. the rate of detoxification

Anaerobes may also have protectiveenzymes, but they rely on very oxygen-sensitive systems for energy generation

References Cypionka, H. 2000. Ann. Rev. Microbiol. 54: 827-848. Jenny Jr., F.E., Verhagen, M.F.J.M., Cui, X., and Adams,

M.W. 1999. Science. 286: 306-309. Krekeler, D., and Cypionka, H. 1995. FEMS Microbiol.

Ecol. 17: 271-278. Lumppio, H.L., Shenvi, N.V., Summers, A.O., Voordouw,

G., and Kurtz Jr., D.M. 2001. J. Bacteriol. 183: 101-108. Morris, J.G. 1975. Adv. Micro. Physiol. 16: 169-246. Imlay, J.A. 2002.. Adv. Microb. Physiol. 46: 111-153.

what is an anaerobe?

Documents