Biomedical Engineering Reference
In-Depth Information
and also simple nutritional needs. They are small cells, 1 to 5 μm in diameter, which
reproduce asexually, each mature cell producing 6, 8, or, more rarely, 16 autospores. Species
from the
Scenedesmus
gender are largely distributed in water and soil. Cells are cylindrical
with rounded or sharp extremities. They can be found laterally united in 4, 8 or 16 - more
rarely - cells. They reproduce by autocolonies formation [22].
Algal cultures were stored at 4ºC, in sterilized test tubes, and renewed with algae
proceeding from successive experiments performed in sterile conditions.
3.2. Growth Medium
Table 1
presents the composition of the culture medium. As autoclaving leads to the
precipitation of certain mineral salts [8], four concentrated solutions (Table 2) were prepared
separately and aseptically filtered through 0.45 μm Gellman Sciences membranes. All
solutions were prepared with dechlorinated tap water, which was previously sterilized by
filtration. The only source of specific inorganic carbon was NaHCO
3
, besides the CO
2
present
in the sterile air bubbled into the medium.
Table 1. Composition of the synthetic medium
Concentration (mg l
-1
)
Constituent
NaNO
3
525
NaHCO
3
50
KH
2
PO
4
626
K
2
HPO
4
266
MgSO
4
.
7H
2
O
500
CaCl
2
.
2H
2
O
55.87
Na
2
EDTA
50
NaOH
22.1
FeSO
4
.
7H
2
O
4.98
Table 2. Composition of the concentrated inorganic solutions
Concentration (g l
-1
)
Constituent
Solution
NaNO
3
5.25
1
NaHCO
3
0.5
1
KH
2
PO
4
6.26
1
K
2
HPO
4
2.66
1
MgSO
4
.
7H
2
O
5.0
2
CaCl
2
.
2H
2
O
0.559
2
Na
2
EDTA
50
3
NaOH
22.1
3
FeSO
4
.
7H
2
O
4.98
4
One of the factors affecting microorganism growth is pH. Experiments aiming at
determining kinetic parameters must be performed at constant or approximately constant pH.
According to Mitchell and Slaughter [25], control of pH is also very important since in many
cases it changes during the development of a microbial population. Phosphate buffers are
