The Winogradsky Column

Question 1

Basics of the Winogradsky column

Answer 1

• simple and economical means of growing a variety of soil and aquatic microorganism
• provides a gradient of oxygen allowing for aerobic and anaerobic life

Question 2

Setup

Answer 2

• mixing surface sediment from an estuary and 0.5g calcium sulfate and some organic material e.g. shredded filter paper
• mixture placed in 500ml measuring cylinder filled with fresh water
• kept in the dark for 2 days and then exposed to daylight for 2-4 weeks

Question 3

Why is calcium sulphate
added

Answer 3

• sulphate will serve as an electron accepting for anaerobic respiration by some bacteria
• this will reduce it, forming sulphide which can serve as a source of electrons for the anoxygenic bacteria

Question 4

What is the function of the filter paper

Answer 4

• source of organic carbon and energy for heterotrophic bacteria
• metabolism of these bacteria then use up the oxygen in the mud creating an anaerobic environment for the sulphate reducing bacteria and eventually anoxygenic photosynthesis
• sugars released after cellulose decomposition are fermented to release acids that react with carbonate to release CO2 for photosynthesis

Question 5

Why is the column left in the dark for the first few days

Answer 5

• allows dark heterotrophic processes to dominate the system (not oxygen producing photosynthesis)
• reducing conditions are created which favour development of anaerobic anoxygenic bacteria

Question 6

What purpose does the reduced sulphur serve for the photosynthetic sulphur bacteria

Answer 6

• serves as a source of electrons
• form sulphur granules, a reserve material for future oxidation and NADH production

Question 7

Structure of column

Answer 7

• bottom = surface sediment with CaSO4 and shredded filter paper
• anaerobic zone, green photosynthetic bacteria, purple photosynthetic bacteria stuck to the wall of the vessel
• aerobic zone, cyanobacteria and algae

Question 8

Photoautotrophic purple and green bacteria

Answer 8

• carry out anoxygenic photosynthesis
• photopigment bacteriochlorophyll a
• use sulphide as the electron donor in photosynthesis
• use CO2 derived from fermentation in the sediment

Question 9

Purple bacteria

Answer 9

• photopigments located on intracytoplasmic unit membrane systems
• live well below the surface, absorb infrared wavelengths
• can store sulphur granules as reserve material for future oxidation

Question 10

Green bacteria

Answer 10

• photopigments in chlorobium vesicles or chlorosomes joined to cell membrane
• underneath purple bacteria as they are non-motile, and cannot store sulphur so needs to be at a level where sulphide production is not exhausted at maximum photosynthesis (purple bacteria can adjust itself to the diurnal changes)