On the 3rd day we did a serial dilution. A small amount of soil and SEM was added to a tube. SEM – Soil Extract Media – contains nutrients, atoms etc that were in the soil to help the bacteria survive. The tube was then placed on a rotator and then a daisy wheel (shown in the image), which mixed the contents slowly and not vigorously, again to ensure the bacteria didn’t die. The tube was then centrifuged to separate the liquid from the soil and with that liquid 6 different dilutions were made. 4 of the dilutions, (2 high dilutions and 2 low ones) were used in the next step along with the agar plates made on day 2. A pipette was used to transfer a specific amount of each dilution into 2 agar plates, one of a higher concentration and one with a lower concentration. A spreader was used to spread the liquid around the plates evenly, and it was done gently to prevent the agar – which has a jelly like consistency – from getting ruined.
