Transcript Microbes and the Environment

Microbes and the
Environment
Option F.2
Microscopic Producers
•
Convert inorganic molecules into organic molecules.
Algae and some bacteria use chlorophyll to trap energy
from sunlight. Chemoautotrophic bacteria use chemical
energy stored in bonds to convert CO2 to carbohydrate.
Cyanobacteria – oldest known fossils (3.5
BYA); filamentous blue-green bacteria;
inhabit most known environments
Volvox – freshwater alga, eyespots allow
phototaxis, forms colonies of up to 50,000
cells
Diatoms – unicellular alga surrounded by a
silicate cell wall (frustule); bilaterally or
radially symmetrical
Thiobacillus ferrooxidans – converts
energy in chemical bonds of sulfur- and ironcontaining compounds
Microscopic Decomposers
•
Break down organic molecules in decaying matter, releasing inorganic
nutrients back into the ecosystem
•
Fungi, bacteria, protozoa
Nitrogen fixation
1. Industrial nitrogen fixation: burning of fossil fuels to produce fertilizer
2. Mutualistic nitrogen fixation: bacteria forms symbiotic relationship (root nodules)
with a host plant and fix nitrogen for it (Rhizobium).
3. Free-living nitrogen fixation: live freely in soil (Azotobacter)
Root nodule formation
1. Legume roots release flavonoids
(organic micronutrients)
2. Rhizobia attracted to flavonoids
3. Rhizobia releases nodulation
factors, causing
a.
b.
Radish sprout,
displaying root hairs
Cell division of root hairs
Redirection in growth
Root nodule formation
• The ability of legumes (soybean, peas,
peanuts, beans, clover, radish, lentils,
carob) to obtain nitrogen from
Rhizobia makes them easy to cultivate
Root nodule on
Pisum sativum
(common pea)
Root nodule on
Trifolia repens
(white clover)
The nitrogen cycle
•
Nitrification: bacteria convert ammonia into nitrites and nitrites are converted into
nitrates
•
Active transport of nitrates: nitrates taken in by roots
•
Plants and animals: plants use nitrates to make their own proteins; animals feed on
plants, digest and rearrange proteins to make their own proteins
•
Death and excretion: products of digestion and dead bodies contain molecules
which contain nitrogen
•
Putrefaction: decomposers break down complex proteins and release nitrogen gas
into the atmosphere
•
Denitrification: bacteria remove nitrates and nitrites and put nitrogen gas back into
the atmosphere
Conditions which favor nitrification and
denitrification
• Nitrification
– Ammonia into nitrite (carried
out by Nitrosomonas)
– Nitrite into nitrate (carried out
by Nitrobacter)
– Available oxygen (aerobic)
– Neutral pH
– Warm temperature
• Denitrification
– Carried out by Pseudomonas
denitrificans and others (nitrates
back into the atmosphere)
– No available oxygen (anaerobic)
– High nitrogen input
– Negative impacts
Consequences of releasing raw sewage and nitrate
fertilizer into rivers
• High nitrates and phosphates fertilize
the algae present in water
• Increased growth of algae (algal bloom)
• Algae are decomposed by aerobic
bacteria which use up the oxygen in the
water (high biochemical oxygen
demand, or BOD)
• Water becomes deoxygenated and fish
and other organisms die
• Too much of a good thing?
Sewage treatment by saprotrophic
bacteria
• Stages of sewage
treatment:
– Inorganic materials
are removed and
organic matter is left
– 90% of the organic
matter is removed by
saprotrophic bacteria
Trickling filter system
• Water trickled over a bed of stones
• Saprotrophic bacteria adhere to the stones and act on the sewage
trickled over them until it is broken down
• Cleaner water trickles out of the bottom of the bed
• This flows to another tank where the bacteria are removed
• The water is further treated with chlorine to finish the disinfectant
process
Reed bed
•
•
•
•
Waste water provides water and the nutrients to the growing reeds
Reeds are then harvested for compost
Breakdown of organic waste is again accomplished by saprotrophic bacteria
Nitrate and phosphates released as a result of bacterial action are used as
fertilizer by the reeds
• Advantages: relatively easy to maintain, no chemicals
• Disadvantage: can only handle small sewage flow
Production of Biofuels
1. Manure and cellulose are put into a digester without oxygen
2. Anaerobic decomposition by bacteria which occur naturally in the manure
3. Manure and cellulose broken down into organic acids and alcohol by
acidogenic bacteria
4. Organic acids and alcohol are broken down by acetogenic bacteria into
carbon dioxide, hydrogen, and acetate
5. Finally, methanogenic bacteria convert (#4) to methane
6. Ammonia and phosphate are byproducts and can be used as high-quality
fertilizer
Production of Biofuels
Conditions to be kept constant in
digester:
• No free oxygen
• Temperature (95 degrees F)
• pH (not too acidic)
Benefits:
• Reduced water pollution
• Reduced methane emissions
• Cheaper
• Fertilizers with less odor
• Reduced dependency on
foreign oil
• Reduced dependency on fossil
fuels