Lab 1 Flashcards
Why add cellulose powder to the Winogradsky column?
It is a source of carbon
Why add calcium sulphate to the Winogradsky column?
It is a source of sulphur
Describe Clostridium and its role in the column.
Non-sulphur, fermentative obligate anaerobic bacteria
- Breaks down cellulose into glucose subunits
- Ferment glucose
- Energy, ethanol and organic acids by products
Describe Desulfovibrio and its role in the column (black zone)
Sulphur-reducing, chemoheterotrophic obligate anaerobic bacteria
- Uses by products from lower layer as C source
- Sulphate final e- acceptor
- Produces H2S - creating gradient (high at the top)
Describe Chlorobium and its role in the column. (green zone)
Green sulphur, photoautotrophic obligate anaerobic bacteria
- Uses CO2 from calcium carbonate as C source
- H2S as e- donor
- Light as E source
- Can tolerate higher energy conc. than lower layer
Describe Chromatium and its role in the column. (red zone)
Purple sulphur, photoautotrophic bacteria
- Uses CO2 from calcium carbonate as C source
- H2S as e- donor
- Light as E source
- Proliferate in region further away from H2S
Describe Rhodomicrobium and its role in the column.
Purple non-sulphur photoheterotrophic bacteria
- low sulphur levels
- Absence of O2 and presence of light (E source)
- Fix CO2 -> organic molecules
- Organic molecules or ethanol as e- donor
Describe Beggiatoa and its role in the column.
Sulphur oxidising bacteria (micro-aerophilic zone)
- Oxidise sulphur
- H2S as E and oxidises sulphuric acids
- E used to fix carbon and produce OM (organic molecules)
Describe Cynobacteria (and algae) and its role in the column.
Aerobic photosynthetic microbes
- Light as E source (release O2)
- uses energy to fix CO2 and produce OM
- Maintains O2 gradient
What is a Winogradsky column used for
To study a variety of soil organisms in a microcosm (replicate environmental situation) and test the effect of changing one factor on the interactive system.
Also demonstrates that the success of one organism often dependent on the success of others.
What is the basic composition of the column
(from high to low sulphide conc., anaerobic to aerobic, bottom to top)
Black zone - non-sulphur bacteria and sulphur reducing bacteria
Green zone - green sulphur bacteria
Red zone - Purple sulphur bacteria
Rust zone - Purple non-sulphur bacteria
O2 dominant mud - sulphur oxidising bacteria
Water - Algae, diatoms, cyanobacteria, protists
How do the layers of the column interact
The lower layers provide carbon and sulphur. Cellulose is hydrolysed to simple sugars which are fermented to release acids. Acids react with carbonate to release CO2 for photosynthetic organisms. Decomposition products like citrate, pyruvate and acetate are used by pond organisms
Describe specification in Rhizobium-legume symbiosis
A single strain of Rhizobium will only infect certain species of legumes (cross-inoculation group). Depends on both plant and Rhizobium.
Describe nodule formation
Rhizobium enters through root hairs and grows within an infection thread, spreading through the root hair into the root. Tetraploid cells stimulated to divide and form nodule - bacterial cells bud off from infection thread, surrounded by plant membrane into cytoplasm of tetraploid cells -> divide and become swollen, misshapen, branched cells (bacteroids).
What is the role of bacteroids
- Fix nitrogen
- Incapable of cell division
