Studies on growth kinetics and plasmid stability of a recombinant Escherichia coli expressing a Schistosoma mansoni antigen
A 13 kDa Schistosoma mansoni tegumental antigen (Sm13) was cloned and expressed in Escherichia coli. The fermentation product of 55 kDa corresponds to the maltose binding protein-recombinant Sm13 fusion protein (MBP-rSm13). The growth conditions for maximum IPTG inducible MBP-rSm13 production was investigated by examining the following parameters: innoculum size, agitation, temperature of induction and concentration of the inducer, IPTG. The maximum MBP-rSm13 production was achieved by two steps-fermentation. First, the recombinant strain was cultivated in a 37 °C orbital shaker, at 160 rpm, for 3 hours. The MBP-rSm13 was then induced by adding 0.3 mM IPTG and placing the culture in a 28 °C orbital shaker for 2 hours. Under these conditions the MBP-rSm13 production yield was approximately 50% of total intracellular proteins and the degradation by bacterial intracellular proteases seemed to be minimized. The plasmid stability was also studied during the fermentation of the Sm13-expressing E. coli in non induced and induced conditions. In both conditions there was a slightly plasmid loss before induction, however after the addition of IPTG the loss was increased. The rate of plasmid loss was 5.5 and 13.5 before and after IPTG induction respectively.
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