biologia - Studia

CHARACTERIZATION OF ALPHA-AMYLASE FROM BACILLUS SUBTILIS STRAIN
Results and discussion
1. The maximum specific increase rate
The maximum specific increase rate of the Bacillus subtilis strain used,
was determined by the relation dx/dt=µx
where x = quantity of biomass
t = time of growth
µ = specific increase rate
By separating the variables and integration we obtain:
Ln·x 0 /x = µ(t-t 0 )
Thus, by the graphic presentation of the values for Ln·x 0 /x depending on
the time we obtained a line, with the slope indicating the specific increase rate. The
dependence between the optical density at 600 nm and the quantity of biomass in
the sample is considered to be a linear one. Knowing the quantity of biomass (0.15
mg) corresponding to an absorbance of 1.42, the absorbance of the samples at 600
nm was correlated with the quantity of biomass, using the data in Table 1.
Table 1.
Data used for calculating the maximum specific increase rate
Time (h) Absorbance at 600 nm Dry cell mass (mg) Ln· x 0 /x
2 0.227 0.023979 0.024527
2.5 0.365 0.038556 0.499474
3 0.581 0.061373 0.964328
3.5 0.61 0.064437 1.013036
4 0.835 0.088204 1.327009
4.5 0.79 0.083451 1.27161
5 1.235 0.130458 1.718403
5.5 1.452 0.15338 1.880274
6 1.58 0.166901 1.964757
6.5 1.828 0.193099 2.110555
7 1.95 0.205986 2.175162
Based on the data in Table 1 we drawn the graphic in figure 1. We
calculated this way the slope of the line, which is actually the maximum increase
rate (µ max ). For the Bacillus subtilis strain, this value was of µ max =0.504 h -1 , which
is considered to be a normal value for a cell culture.
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