UCA_8B,7B_Day 8

Winnogradsky column - Day 8

Group B8(Laura Lucena Del Amo, Noelia Moares Fernández)
GroupB7(Pablo Lucas Ezequiel Garin Ortega, Alba Mejías Gallardo)

We are back one week later to discuss about the changes that we have observed in both columns, the column exposed to sunlight (B8) and the column kept in darkness in which we added glucose (B7).

In the column exposed to sunlight (B8), which had Rio San Pedro sediment + 0.3 g paper + 0.1 g CaSO4, we find these characteristics:

• The column is darker in the bottom, with black sediments. This probably is caused by the FeS precipitate, produced by anaerobic microorganisms from Fe (provided by the Rio San Pedro sediment) and SO4 (from the CaSO4). 
• The top of the tube is much lighter than the bottom, due to the proliferation of photoautotroph microorganisms. These organisms produce O2, which helps keeping a gradient of oxygen.
• Because of this gradient of oxygen aerobic microorganisms will grow close to the top of the column and anaerobic microorganisms will grow in the bottom.
• There are a few of little bubbles in the column, they may be bubbles of N2 (from the sediment) as well as bubbles of H2S (mostly in the bottom).
• The main difference observed this week is that we can perceive two different sides of the tube in the middle:

1. One side lighter ( with an orange hue), this is the side exposed to sunlight. The explanation of this phenomenon is based in the fact that there might have proliferated photoorganoheterotrophic bacteria in the medium.
2. The other side is darker, the same that we observed last week. There might be chemoorganoheterotroph microorganisms.

While in the B7 tube, kept in darkness (absence of light) and in which we added Rio San Pedro sediment + 0.3 g paper + 0.1 g CaSO4 + glucose, we find these changes:

• This week's column is way darker than the last one due to the breathing of the H₂S reacting with Fe²⁺ and obtaining HFe, which gives the black tone. This reaction is produced by anaerobic microorganisms. The Fe²⁺ comes from the sediment of San Pedro river, and the H₂S is caused by the fermentation of present sugar in the column.
• Many small bubbles appear, we think that these bubbles are formed by CO2 and CH4 probably due to the fermentation of the chemo-heterotrophs microorganisms.
• The main difference observed this week is:

1. There aren´t accumulation of fumes and it has been generated a layer of dirty water on the top. In this water seems to have been suspended micro-organisms, although it may also be sediment of San Pedro river.