Biology Reference
In-Depth Information
Fig 6.1:
Example of a spring inside the town of Kampala, the capital of Uganda.
Spring water is used for drinking, cooking and bathing. Please note the
concrete slab and the fencing behind the spring in order to try to protect the
intake area
6.2.2 Bacteria growth and size measurements
To conduct experiments, a sterile forceps was used to pick a bead from the vial and into 25
ml of nutrient broth and then incubated for 24 hours at 37 °C while shaking at 150 rpm on an
orbital shaker. Then, 5 ml each of the bacteria solution was further inoculated into four
Erlenmeyer flasks containing 250 mL of nutrient broth and again grown for 24 hours on an
orbital shaker at 150 rpm for 24 hours to obtain a cell concentration of ~10
9
cells/ml. Bacteria
were washed and centrifuged (4600 rpm) three times in Artificial Ground Water (AGW),
which was prepared by dissolving 526 mg/L CaCl
2
.2H
2
O and 184 mg/L MgSO
4
.7H
2
O, and
buffering with 8.5 mg/L KH
2
PO
4
, 21.75 mg/L K
2
HPO
4
and 17.7 mg/L Na
2
HPO
4
. The final
pH-value of the suspensions ranged from 6.6 to 6.8, while the electrical conductivity ranged
from 980 to 1024 S/cm.
To determine
width
and
length
of the
E. coli
cells, a light microscope (Olympus BX51) in
phase contrast mode, with a camera (Olympus DP2) mounted on top and connected to a
computer, was used to take images of cells. Per
E. coli
strain 30 different images were
imported into an image processing program (DP-Soft 2) and the average cell width and cell
length were determined. The equivalent spherical diameter (ESD) was determined as the
geometric mean of average length and width (Rijnaarts et al., 1993).
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