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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