초록
<P><B>Background</B></P><P>Currently, the most promising microorganism used for the bio-production of butyric acid is <I>Clostridium tyrobutyricum</I> ATCC 25755<SUP>T</SUP>; however, it is unable to use sucrose as a sole carbon source. Consequently, a newly isolated strain, <I>Bacillu</I>s sp. SGP1, that was found to produce a levansucrase enzyme, which hydrolyzes sucrose into fructose and glucose, was used in a co-culture with this strain, permitting <I>C. tyrobutyricum</I> ATCC 25755<SUP>T</SUP> to ferment sucrose to butyric acid.</P><P><B>Results</B></P><P><I>B.</I> sp. SGP1 alone did not show any butyric acid production and the main metabolite produced was lactic acid. This allowed <I>C. tyrobutyricum</I> ATCC 25755<SUP>T</SUP> to utilize the monosaccharides resulting from the activity of levansucrase together with the lactic acid produced by <I>B.</I> sp. SGP1 to generate butyric acid, which was the main fermentative product within the co-culture. Furthermore, the final acetic acid concentration in the co-culture was significantly lower when compared with pure <I>C. tyrobutyricum</I> ATCC 25755<SUP>T</SUP> cultures grown on glucose. In fed-batch fermentations, the optimum conditions for the production of butyric acid were around pH 5.50 and a temperature of 37°C. Under these conditions, the final butyrate concentration was 34.2±1.8 g/L with yields of 0.35±0.03 g <SUB>butyrate</SUB>/g <SUB>sucrose</SUB> and maximum productivity of 0.3±0.04 g/L/h.</P><P><B>Conclusions</B></P><P>Using this co-culture, sucrose can be utilized as a carbon source for butyric acid production at a relatively high yield. In addition, this co-culture offers also the benefit of a greater selectivity, with butyric acid constituting 92.8% of the acids when the fermentation was terminated.</P>