초록
<P><B>Background</B></P><P>Pure bacterial strains give better yields when producing H<SUB>2</SUB> than mixed, natural communities. However the main drawback with the pure cultures is the need to perform the fermentations under sterile conditions. Therefore, H<SUB>2</SUB> production using artificial co-cultures, composed of well characterized strains, is one of the directions currently undertaken in the field of biohydrogen research.</P><P><B>Results</B></P><P>Four pure <I>Clostridium</I> cultures, including <I>C. butyricum</I> CWBI1009, <I>C. pasteurianum</I> DSM525, <I>C. beijerinckii</I> DSM1820 and <I>C. felsineum</I> DSM749, and three different co-cultures composed of (1) <I>C. pasteurianum</I> and C. <I>felsineum</I>, (2) <I>C. butyricum</I> and <I>C. felsineum</I>, (3) <I>C. butyricum</I> and <I>C. pasteurianum</I>, were grown in 20 L batch bioreactors. In the first part of the study a strategy composed of three-culture sequences was developed to determine the optimal pH for H<SUB>2</SUB> production (sequence 1); and the H<SUB>2</SUB>-producing potential of each pure strain and co-culture, during glucose (sequence 2) and starch (sequence 3) fermentations at the optimal pH. The best H<SUB>2</SUB> yields were obtained for starch fermentations, and the highest yield of 2.91 mol H<SUB>2</SUB>/ mol hexose was reported for <I>C. butyricum</I>. By contrast, the biogas production rates were higher for glucose fermentations and the highest value of 1.5 L biogas/ h was observed for the co-culture (1). In general co-cultures produced H<SUB>2</SUB> at higher rates than the pure <I>Clostridium</I> cultures, without negatively affecting the H<SUB>2</SUB> yields. Interestingly, all the <I>Clostridium</I> strains and co-cultures were shown to utilize lactate (present in a starch-containing medium), and <I>C. beijerinckii</I> was able to re-consume formate producing additional H<SUB>2</SUB>. In the second part of the study the co-culture (3) was used to produce H<SUB>2</SUB> during 13 days of glucose fermentation in a sequencing batch reactor (SBR). In addition, the species dynamics, as monitored by qPCR (quantitative real-time PCR), showed a stable coexistence of <I>C. pasteurianum</I> and <I>C. butyricum</I> during this fermentation.</P><P><B>Conclusions</B></P><P>The four pure <I>Clostridium</I> strains and the artificial co-cultures tested in this study were shown to efficiently produce H<SUB>2</SUB> using glucose and starch as carbon sources. The artificial co-cultures produced H<SUB>2</SUB> at higher rates than the pure strains, while the H<SUB>2</SUB> yields were only slightly affected.</P>