Nutrient data:

·         Mud: 30g

·         Cellulose: 0’5g

·         Sugar (glucose): 0’5g

·         Iron sulphate (FeSO₄): 0’1g

·         Agar: 0’11g

·         Calcium carbonate: 0’5g

·         Sodium chloride: 0’54g

·         Water

Second blog post:

With this research, we intended to demonstrate how could some microorganisms of the natural environment of Cádiz marsh develop in a Winogradsky column, thanks to the addition of some kinds of different metabolites, such as calcium carbonate, sodium chloride, iron sulphate, cellulose or glucose, among others. We wanted to study how could they grow in an environment with different concentrations of oxygen (while the column gets deeper, the concentration of oxygen decreases) and sulphate (while we get near to the surface, the concentration of sulphate is lower).

The very first days, we appreciated the apparition of bacteria colonies. This was demonstrated because of the colour layers:

        

As we described, the surface is richer in oxygen, so the microorganism that grow in this zone are aerobic, microaerophiles or facultative anaerobic. Some weeks later, we will observe the presence of cyanobacteria; a kind of photosynthetic archaea. It is known that this microorganism was the responsible of the appearance of the present day’s oxidant atmosphere 2.400 million of years ago. Immediately below, there is an orange-yellow-brown liquid. We have four hypotheses for this:

·         Option A: Iron Chloride (FeCl₃). In this molecule, iron is in its oxidized form (Fe³⁺). Iron sulphate is dissociated in Fe²⁺ and SO₄^2-. Fe²⁺ can be oxidized with water molecules (or simply with other molecules present in the column) to Fe³⁺, and this cation can react with chloride ions coming from NaCl, forming iron chloride. This reaction is not very likely because of the high solubility of this molecule. In addition, this reaction is not spontaneous even in standard conditions (ΔG=37’9KJ/mol).

·         Option B: Iron sulphate can be dissociated in Fe²⁺ (which has a yellow colour) and SO₄^2-. Part of the ferrous ions can be oxidized into Fe³⁺ (which has an orange colour), and the solution of the top of the column will be a mixture of both ions.

·         Option C: Iron oxides. Iron sulphate can be dissociated in dissolution, resulting in two different ions. It can also react with water to form iron monoxide (FeO) and sulphuric acid (H₂SO₄). Iron monoxide, when diluted, acquires an orange-red colour too. Also, iron (Fe) can be oxidised because of the action of water to form Fe₂O₃, another orange-red compound.

In conclusion, the orange solution can be a result of a mixture of these substances.

According to the rest of the column, which has a black coloration with some red tones, we can obtain some conclusions. First, we must talk about sulphate reducing bacteria (there are several kinds of bacteria which are based on this metabolism). They transform iron sulphate into hydrogen sulphide (H₂S), which, in natural conditions, can react with several kinds of metals to form metal sulphides such as FeS, with a black-brown coloration (which gives the shown coloration of the column) and a rotten egg odour. The purple coloration is due to the purple sulphur bacteria, which take advantage of the hydrogen sulphide obtained in the degradation of iron sulphate to participate in the photosynthesis. These bacteria are microaerophilic or anaerobic: some of the bacteria included in this group can tolerate oxygen (but they do not use it in their metabolism) or they must not be around oxygen (it is considered a poison for them). Thus, they can live in zones poor in oxygen (as it is the bottom of the column) and carry out photosynthesis, using non-organic-carbon metabolites. In the following pictures, we can see this first bacteria: