Stabilization of the colonies and appearance of organic molecules

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

Third blog post:

In the last posts, we described the possible bacteria colonies present in our Winogradsky column: from sulphate reducing bacteria to cyanobacteria. In our second post, we detailed the progresses in the first three weeks, and in the present entry we will conclude with all our progresses after two months of research.

One month after the last registers of our column, we can observe that the metal sulphides precipitate is much more concentrated than before: this is to say that the column is darker than before. However, purple sulphur bacteria colonies has developed considerably too. Furthermore, we can appreciate the appearance of a small new layer. This layer seems to have the same colour as the mud we used at the start of the experiment. Occam’s razor would say that the obvious answer is that it’s mud. The question here is why did it appear after all this time, when there were metal sulphides there before. Methane going up, as we’ll see later, could have stirred all the components of the column. We could have stirred them while breaking the methane gap. Or, a more complex answer would be that those sulphides are being decomposed. Could be the action of bacterias, either using the sulfides, or altering the equilibrium it might have with the H₂S. As we already said on our last post, purple sulphur bacteria use the H₂S on their metabolism. According to Le Chatelier’s principle, by using H₂S, the equilibrium constant of formation of those sulphides would decrease, and more H₂S would be formed, consuming sulphides.

But the most important new in our Winogradsky column is the creation of a gap which divides the mud in two parts: this gap keeps one piece of mud raised and suspended in the air, as we can observe in this image:

This is due to the production of methane, which is produced by a process called methanogenesis or bio-methanation, carried out by some microorganisms from the domain Archaea. This was something important and new in our research: we finally obtained organic substances, which are an indisputable evidence of the presence of life. Methane (CH₄) is the simplest organic molecule, as it contains only one carbon atom and four hydrogen atoms. The origin of this carbon atom can be cellulose or calcium carbonate; the two carbon sources we added (it is impossible to determinate it qualitatively). Methane is a waste molecule produced by living beings, and its presence is a clear sign of cellular metabolism. Last exoplanetary researches established the presence of a small concentration of methane in the surface of Mars (approximately 0’01ppm); a very small concentration but not insignificant. Another important fact about the significance of the role of this bacteria in the possible appearance of life is its presence in hydrothermal vents, which are one of the cribs of life on earth. The expulsion of gas methane though this chimney evidence the presence of this microorganisms. To sum up, the appearance of this gas gap in our column is a great new in our research, as we finally can demonstrate the formation of organic molecules. Nevertheless, we cannot determinate quantitatively the concentration of methane in this camera, so we can’t confirm that this gas is pure methane: it can coexist with other inorganic molecules, such as CO₂ (coming from the metabolism of some microorganisms) or even H₂O vapour, among other molecules. But we can confirm that most of this gas is methane, as we can smell an unpleasant scent when we extract the gas from this bag.

In relation to the rest of the Winogradsky column, we cannot make any clear distinction respect to our last posts: most of the column stills being dark, but the purple sulphur bacteria colonies have increased in number and size. The methane gas gap has been removed to fix again both parts of the mud, and a new colour layer has appeared. Attending to the evolution trajectory of the colonies, we do not expect any significant news: maybe purple sulphur bacteria colonies can reach a higher size, and we may observe the appearance of new methane gas gaps spread through the bottom of the column. Therefore, this is the final appearance of our Winogradsky column:

Pablo González García &
                                                                               José Manuel Bellido Gutiérrez

                                                                                  Group 4B