Microbes in the environment

F2, p. 304

Microbes in ecosystems

F.2.1, p. 304

Did you know?

• “Just one gram of soil contains 5000 to 7000 different species of bacteria.”– http://www.buzzle.com/articles/facts-about-

the-soil.html

Good news!

• You only have to know 5!

Bacteria

• Play several major roles in different nutrient cycles– Both in land and in water

• Involved in P, S, C and N cycles

Decomposing

• Bacteria break down dead organisms

• Nutrients released– Nutrients return to the environment

Producers

• Use raw energy (Ex: sunlight) to create organic molecules and nutrients– Used by bacteria and other organisms

• Includes:– Photosynthetic bacteria (cyanobacteria)– Chemosynthetic bacteria (in the nitrogen

cycle)

Nitrogen cycle

F.2.2, p. 304

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

Nitrogen cycle

• Nitrogen moves through the environment

• Major reserves are:– Atmosphere– Living things

• Nitrogen must go through chemical reactions during the cycle

Nitrogen

• Comes in two forms:– Pure element, N2 (gas)

– Fixed (as part of a compound)

Atmospheric nitrogen

• N2, gas• Three covalent bonds between the

atoms– Very difficult to break– Not reactive– Very few organisms have the enzyme for

breaking the triple bond

• Can’t be used by organisms

Fixed nitrogen

• Nitrogen as part of a compound– Nitrite (NO2

-), nitrate (NO3-), ammonium

(NH4+)

• NO3-, nitrate, is essential for all

organisms– An important part of DNA and protein

Importance of nitrogen fixing bacteria

• Where do animals get nitrogen from?– Plants, amino acids, DNA

• Where do plants get nitrogen from?– NOT the atmosphere– Usually NO3

-, NH4+, which is created by

bacteria

• ALL organisms get fixed nitrogen from bacteria

Nitrogen fixation

p. 304-305

Nitrogen fixation

• Nitrogen is fixed by:– Lightening– Manufacturing– Microbes

Lightening

• High temperatures cause N2 and O2 to combine

• A series of reactions creates NO3-

• P. 304

Haber process

• N2 and H2 reacted at high pressure and temperature

• NH3 (ammonia) produced

• Used to manufacture plant fertilizer– Mixed with the soil for plant nutrition

Microbes fixing nitrogen

• Two examples:– Azotobacter

• Free-living

– Rhizobium• Live in plant root nodules

Root nodules

• Mutualistic relationship– The plant gets fixed nitrogen– The bacteria get an anaerobic environment

Microbial nitrogen fixation

• N2 --> NH3

• Requires ATP

• Azobacter (free living) and Rhizobium (Root nodules) fix nitrogen– Have nitrogenase, the enzyme that fixes N

– Breaks the strong N2 triple bond to produce NH3

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

Nitrification and denitrification

F.2.4, p. 305

Nitrification

• Two steps:– NH3 --> NO2

-

– Ammonia --> Nitrite• Nitrosomonas bacteria

– NO2- --> NO3

-

– Nitrite --> Nitrate• Nitrobacter bacteria

• Releases energy• Occurs quickly

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

NO3- uses

• NO3- assimilated by plants

– Pumped into root hairs by active transport

• Passed on to animals/heterotrophs through the food chain

• Used for amino acids/proteins and DNA

Denitrification

• NO3- --> N2 + H2O

• Example: Pseudomonas denitrificans• Anaerobic respiration

– NO3- is the electron receptor instead of O2

• Anaerobic soils encourage denitrification– Bad drainage/flooding causes– Denitrification exacerbates the problem

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

Ammonification

• Also called putrification– Organic matter (feces and dead

organisms) are decomposed by bacteria

• The nitrogen in the organisms is converted into ammonia (NH3)

– The NH3 then goes through nitrification

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

Nitrogen Cycle

Name each process:

Name the bacteria carrying out each process

Sewage and fertilizer waste

F.2.5, p. 305

Sewage

• Household - Feces, kitchen waste

• Industrial - chemicals, heavy metals

• Farm - fertilizers

• All cause water pollution– Radically change the aquatic environment

Downstream pollution

• Graph on p. 306

Downstream pollution

• Table on p. 306

Steps for contamination

1. Waste discharged, eutricifation2. Algea bloom, then die off3. Decomposers break down dead algae and use

up oxygen. Oxygen levels decrease.4. Extreme cases: Oxygen levels are too low and

fish/aquatic life is killed (hypoxic zone)5. Dead organisms are broken down, using oxygen

and creating a high concentration of nutrients (eutrification)

6. Extreme cases: nutrients cause another algae bloom, cycle repeats

BOD

• ‘Biochemical oxygen demand’

• The level of oxygen in a water sample is recorded over 5 days

• Less oxygen = More O2 demand (BOD) = more microbes = more contamination– The contamination feeds the microbes– The microbes demand oxygen

BOD levels

• If BOD is too high, fish and other organisms might die– Not enough O2 in the water– ‘oxygen sag’

• Caused by decomposing bacteria– Use up O2

Oxygen Sag

Stopping the cycle

• When the pollutants are broken down and diluted enough, the river can recover– Several kilometers from source of pollution

• Key: improving oxygen levels, avoiding fish kills

Sewage treatment

F.2.6, p. 307/145

Treating raw sewage

• Bacteria are used to treat harmful/polluting substances

• Two kinds:– Trickle filter bed p. 145 SG– Reed bed . 145 SG

Biofuels

F.2.7, p. 308

Gasohol

• Gasoline + ethanol

• Ethanol comes from yeasts digesting sugar– Sugar from sugar can/sugar beets

Fig. 27-22c

(c)

Biomass

• Some microbes convert biomass to fuel– Biomass = Total mass of the living material

in an area, minus water– Measured in kg/m2

– Usually refers to plants

Biogas

• Bacterial fermentation

• Biomass --> CH4, methane, natural gas

• Several species of bacteria used together

Methanognesis

F.2.8, p. 308

Acetogenesis

• Aerobic bacteria break down waste into lipids, proteins, fats

• Oxygen used up

• Acetogenic bacteria (anaerobic) produce acetate

METHANOGENESIS

• Acetate converted into CH4

• Uses methanogens (archaea)– Obligate anaerobes – Occurs in a sealed tub

Advertisements

• In groups, create illustrated advertisements for the following products:

1. Trickle-filter bed

2. Reed-filter bed

3. Gasohol

4. Biogas/CH4

Advertisements: Include the following

• Target audience/demographic• A diagram of the process and

equipment• Important reaction equations involved• The bacteria involved in each process

– Include specific environment conditions (ex: anaerobic tank)

• The benefits of the product/process