UCA_8B,7B_Day 7

Winogradsky column – Day 7

Group B8 (Laura Lucena Del Amo and Noelia Moares Fernández) 
Group B7(Pablo Lucas Ezequiel Garín Ortega and Alba Mejías Gallardo)

One week after the preparation of the Winogradsky column, both groups have observed significant changes in our columns.

The changes of the group B7 (column in darkness) are described with details below:

• We observed a huge amount of black sediments spread all over tube. This is caused by the reaction of H2S with Fe²⁺ resulting in HFe that presents a black color. 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, but there is a big bubble of gas that has separated in two the column. We think that these bubbles are formed by CO2 and CH4 probably due to the fermentation of the chemo-heterotrophs microorganisms.
• we think that in the zones with lighter colors, the microorganisms chemo-heterotrophs haven't proliferated.

After the observation of the tube, we have provoked the exit of the gas bubble to prevent the spillage.

Now, we will explain closely the changes observed in the tube exposed to sunlight of group B8:

• In the bottom of the column, we can observe an accumulation of black sediments. This indicates the proliferation of microorganisms able to breathe SO4^- and make the reactions commented previously in this zone.
• Also, we see bubbles in the middle of the colums. This gas may be N2 or H2S. We think that a part from these bubbles are formed by the sugar fermentation of micoorganisms chemoheterotrophs.
• In the top of the column, we see a fine laver of lighter color. It can be provoked by photoautrophic microorganisms (anaerobic). They provide oxygen to the rest of the tube, creating a gradient of oxygen. Due to this fact, we will find aerobic organisms close to the top and anaerobic microoorganisms in the bottom.

Finally, we return the columns to their previous places and we'll wait for new changes in next week.