초록
<P><B>Abstract</B></P> <P>Hydrogen-yielding fermentation conducted in bioreactors is an alternative method of hydrogen production. However, unfavourable processes can seriously inhibit bio-hydrogen generation during the acidogenic step of anaerobic digestion. Here, ascomycetous yeasts were identified as a major factor inhibiting the production of bio-hydrogen by fermentation. Changes in the performance of hydrogen-producing bioreactors including metabolic shift, quantitative changes in the fermentation products, decreased pH, instability of the microbial community and consequently a dramatic drop in bio-hydrogen yield were observed following yeast infection. Ascomycetous yeasts from the genera <I>Candida, Kazachstania</I> and <I>Geotrichum</I> were isolated from hydrogen-producing bioreactors. Yeast metabolites secreted into the growth medium showed antibacterial activity. Our studies indicate that yeast infection of hydrogen-producing microbial communities is one of the serious obstacles to use dark fermentation as an alternative method of bio-hydrogen production. It also explains why studies on hydrogen fermentation are still limited to the laboratory or pilot-scale systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ascomycetous yeasts have been identified as a new factor inhibiting hydrogen fermentation. </LI> <LI> The yeasts disturb a number of parameters in H<SUB>2</SUB>-yielding bioreactors. </LI> <LI> The antibacterial activity of yeasts requires an acidic environment. </LI> <LI> Secreted products of yeast metabolism are responsible for the antibacterial effect. </LI> <LI> The candidate inhibitory factor is 1,3-beta-glucosidase. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>