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 iron-containing 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

Radish sprout, displaying root hairs

1. Legume roots release flavonoids (organic micronutrients)

2. Rhizobia attracted to flavonoids3. Rhizobia releases nodulation

factors, causinga. Cell division of root hairsb. 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 onTrifolia 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 Biofuels1. Manure and cellulose are put into a digester without oxygen2. Anaerobic decomposition by bacteria which occur naturally in the manure3. Manure and cellulose broken down into organic acids and alcohol by

acidogenic bacteria4. Organic acids and alcohol are broken down by acetogenic bacteria into

carbon dioxide, hydrogen, and acetate5. Finally, methanogenic bacteria convert (#4) to methane6. 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