Bacteria are the most used organisms for studying the proteome and the genome. Once, understood on this organisms ( since they are easy to grow up, relatively cheap and they multiply rapidly), thanks to informatics tools it is possible to encounter the human homologous ( since the human genome has been already sequenced).
The most used growing medium for bacteria is agar-agar. This one comes from red algae ( Phylum Rodophyta), for e.g. the ones that belong to the next genders: Gelidium, Euchema, Gracilaria.
In order to obtain the agar-agar, you have to identify the algae, previously mentioned; recollect them and boil them. Once they have been submitted to this process, a gelatinous, transparent liquid will appear, which is agar. This will happen even though for the ones that don’t have the sea close, so they can made it , there are two other options left:
The first one is to buy it on a naturist shop (in Spain is around 20 € for 100 g).
The second option that I “personally developed” is the gelatin. This is a medium that contains all the nutrients necessary for the normal bacterial development (further on a mention about the selective mediums will be made) and it is cheaper. Even though there is a small inconvenient: the bacteria got buried on the medium (because they consume it) and as the time passes by the bacterial manipulation get worse. This is why I recommend to select the interest bacterial colony and to grow it on a new plate after one week as much.
You simply have to follow the instructions that are written on the package:
- Heat water on a recipient.
- Add the package content to the recipient and stir the mixture vigorously until the solute (the gelatin grains) stops being observed anymore and the dissolution becomes homogenous.
- When the dissolution is still hot, it has to be poured on the recipients where the bacteria will be grown (so many recipients as necessary for the experiment, but not forgetting the control plat, where no microorganisms are expected to grow).
- Once the plate is ready, they have to be hermetically closed (in this way a possible contamination is avoided), and placed on the fridge overnight, so the gelatin can solidify.
Some typical examples to understand the microbial populations are: to touch the plate that you introduced on the fridge (it will appear the microbiota present on the cutaneous surface), to spread a small sample of liquid from a lake, river or puddle or by taking a sample of the ground and mix it with water, so you can spread it over the plate and observe this way the different phenotype of the bacterial colonies.