How does water influence the growth of spirulina bacteria?

The name spirulina describes the genus of edible aquatic cyanobacteria performing photosynthesis. The chlorophyll is responsible for the green color which is why spirulina used to be called green-blue algae. However, it is now widely known that they are bacteria, not algae. Today, scientist know of 35 different species belonging to the genus spirulina.

My “board game” is supposed to be a competition between living spirulina, an interaction of spirulina with different environments. I will be focusing on the growth of spirulina and which type of water favors it. Therefore, I took a tube of spirulina (the exact species is unknown to me) bacteria in a liquid, divided the content into four parts and inserted each part into a tube with minerals and different types of water. The four samples respectively consisted of: 1. Spirulina in its normal medium in which it had been delivered/bought, 2. Spirulina in its original liquid, added to normal pond water from a side branch of the Ilm river, 3. Spirulina in sterilized and filtered pond water (sterilized by boiling it; filtered through a coffee filter), 4. Spirulina added to distilled water bought in a drug store. [[File:20170524_183100a.sfdhkl.jpg|400px|thumb|left|Day 1 in the different tubes]] The tubes were kept hanging from a shelf close to a window where some sun’s rays could enter on warm days. The “minerals” which I had added to each one of the four tubes were: sodium chloride (NaCl = normal cooking salt), some baking soda/sodium bicarbonate/natron and some potassium (in German: Kaliumdihydrogenphosphat).

After one week in the tubes during which I hadn’t changed anything except for shaking the tubes every (other) day and opening them every two days, I went to the bio-lab to observe the different liquids containing spirulina under the microscope.

06/01/2017: Under the microscope (lense PL4 / 0.10) [edited on the 06/06/2017] I observed and described the spirulina bacteria based on wrong assumptions. I was not aware of the obvious fact that all green spirulina bacteria are able to do photosynthesis and therefore alive. This is why I do not recommend reading the italic paragraph below.

My observations are based on the assumption that straight, but spiral spirulina bacteria of a normal green color are healthy and alive while clumsy bits, broken spirals or pieces floating around in the sample are dead. I often saw broken pieces sticking together, tied to each other. This supports the observation that spirulina bacteria untouched by others / freely staying in the medium are healthy and alive. Apparently, unhealthy, destroyed or dead spirulina are a darker color. 1. Spirulina: In the original surrounding, I observe many clumsy/broken bits of spirulina. Some living bacteria can be perceived, but primarily strange green structures that might be compared to very small dried apples with their skin, but in a rectangular form. Inside of these rectangular organisms are little organisms looking like dried flowers. In this sample, there are a lot of spirulina bacteria knotted together. All in all, the spirulina do not seem very lively. 2. There are many seemingly dead spirulina organisms that twisted to circles or half-circles or that broke. Only a few bacteria appear alive. In another sample of the same tube are less dead organisms, but not many organisms anyway. The water does not seem very clear which is no surprise as it is taken from the river. 3. In this sample, I can see that the water is taken from a natural surrounding (the pond) because the water is not extremely clear and a few other organisms are in the sample as well. These other organisms are bigger than spirulina and have a different form. Some look like small dried flowers or snowflakes, others like little algae or plants. Overall, there are probably more living than dead spirulina. 4. The water is very clean as it is distilled water – it does not seem to contain other easily perceivable organisms or dirt. There is not much “going on” in this sample – a few living and some dead spirulina are visible. In conclusion, even though I could remark some differences between the samples, the water does not seem to highly influence spirulina. I might try a different experiment in which some spirulina are kept without CO2 and others with the inflow of oxygen…