Chapter 22Lecture Outline

Microbes and the Global Environment

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Biogeochemical Cycles All living organism elements flow in cycles

Rate of cycling varies Biomass vs. organic Environment: atmospheric, land, or ocean

Lack of necessary elements limits growth IronPhosphorusFixed nitrogenMicronutrients

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Biogeochemical Cycles Elements move from large sources to sinks

Reservoirs provide both Ocean important for carbon, nitrogen Land important for sulfur

Oxidation state governs element reactivityNitrogen gas plentiful, fixed nitrogen rare

Measure elements in atmosphere viaChemical reactionsRadioactivity measurements

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Carbon Cycle

Aerobic carbon cyclingPhotosynthesis fixes CO2 into biomass

Produces O2 and organic carbon compounds

Lithotrophs also reduce CO2 to biomass

Respiration returns CO2 to atmosphere Net gain of O2, loss of CO2 in photic zone

Major reservoir is oceanAtmospheric reservoir

is much smaller

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Carbon Cycle

Anaerobic carbon cyclingLower cycling rate than aerobic cycles

Less iron, and less redox potential than oxygen

Subsurface environment Soil, benthos, rock

Fermentation, lithotrophic respiration Incomplete breakdown of biomass carbon Formation of peat, oil, gas

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Carbon Cycle Human activity accelerates CO2 release

Ocean absorbs most CO2

Increased photosynthesis absorbs CO2

Forests, ocean environments

Atmospheric CO2 levels risingRole of newly

discovered microbesunclear

E.g., annamox bacteria

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Nitrogen Cycle Multiple oxidation

states of NitrogenMore than for any

other biological molecule

Prokaryotes crucial for nitrogen conversionOnly natural nitrogen fixers

Haber process doubled biological fixation

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The “Nitrogen Triangle”

Both reduced and oxidized N used for biomass

NITRIFICATION

ATMOSPHERIC N2

REDUCEDNITROGEN

OXIDIZEDNITROGEN

FIXATION DENITRIFICATION

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Nitrogen Cycle—N2 Fixation N2 NH3 NH4

+

NH4+ is rapidly assimilated into amino acids

Catalyzed by nitrogenaseOnly works anaerobicallyOccurs in all ecosystems

Klebsiella, Clostridium, Pseudomonas in soil

Rhizobium within legumes Cyanobacteria in oceans,

freshwater

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Nitrogen Cycle—Nitrification NH4

+ NO2- NO3

-

Oxidation of NH4+ provides electrons, energy

In soil, one species oxidizes NH4+ to NO2

- Nitrosomas

2nd species oxidizes NO2- to NO3

-

Nitrobacter

Excessive fertilizer use causes nitrate runoffEutrophication of streamsDanger to water supplies

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Nitrogen Cycle—Denitrification NO3

- NO2- NO N2O N2

Dissimilatory nitrate reduction Nitrate is anaerobic electron acceptor

N2O (nitrous oxide) buildup if much NO3- present

Prevalent in hypoxic ocean waters Greenhouse gas

In some environments, NO3- NH4

+ Anaerobic sludge, cow rumen H2 gas available as electron donor

Other Geochemical Cycles

Sulfur Phosphate Iron and other metals

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Hydrologic Cycle Water precipitates from

atmosphereWater vapor evaporates

from land, ocean Water flowing over ground picks up nutrients

Carbon, nitrogen runoff allows respirationRespiring microbes deplete O2 in water

BOD = Biochemical Oxygen Demand

High BOD anoxic runoff hypoxic coasts fish die-offs

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Wastewater Treatment Natural treatment

Wetlands filter water Slow water passage Bacteria in wetland denitrify water

Municipal treatmentReduce nutrients to

reduce BOD Allow microbes to grow,

digest nutrients Aerate to restore

oxygen levels

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Municipal Wastewater Treatment Preliminary, primary treatments

Remove solid debris, sediment Secondary treatment

Microbial treatment to eliminate organic content Anaerobic treatment by methanogens

Release CH4, recover gas as fuel

Aerobic treatment Zooglia, Flavobacterium, Pseudomonas, Nocardia Ciliates, amoebas, nemaotdes, rotifers

Possible tertiary treatment to kill pathogens Release into river

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Concept QuizCarbon is oxidized from biomass to CO2 by the process of

a. Respiration

b. Photosynthesis

c. Lithotrophy

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Concept QuizNitrification is the process by which

a. N2 gas is converted to NH4+

b. NH4+ is oxidized to NO3

-

c. NO3- is reduced to N2O