초록
<P><B>Abstract</B></P> <P>Anaerobic microflora enriched for dark fermentative H<SUB>2</SUB> production from a mixture of glucose and xylose was used in batch cultivations to determine the effects of sudden short-term temperature fluctuations on H<SUB>2</SUB> yield and microbial community composition. Batch cultures initially cultivated at 55 °C (control) were subjected to downward (from 55 °C to 35 °C or 45 °C) or upward (from 55 °C to 65 °C or 75 °C) temperature shifts for 48 h after which, each culture was transferred to a fresh medium and cultivated again at 55 °C for two consecutive batch cycles. The average H<SUB>2</SUB> yield obtained during the first cultivation at 55 °C was 2.1 ± 0.14 mol H<SUB>2</SUB> mol<SUP>−1</SUP> hexose equivalent. During the temperature shifts, the obtained H<SUB>2</SUB> yields were 1.8 ± 0.15, 1.6 ± 0.27 and 1.9 ± 0.00 mol H<SUB>2</SUB> mol<SUP>−1</SUP> hexose equivalent at 35 °C, 45 °C and 65 °C, respectively, while no metabolic activity was observed at 75 °C. The sugars were completely utilized during the 48 h temperature shift to 35 °C but not at 65 °C and 45 °C. At the end of the second cycle after the different temperature shifts, the H<SUB>2</SUB> yield obtained was 96.5, 91.6, 79.9 and 54.1% (second cycle after temperature shift to 35 °C, 45 °C, 65 °C and 75 °C, respectively) when compared to the average H<SUB>2</SUB> yield produced in the control at 55 °C. Characterization of the microbial communities present in the control culture at 55 °C showed the predominance of <I>Thermoanaerobacteriales</I>, <I>Clostridiales</I> and <I>Bacilliales</I>. The microbial community composition differed based on the fluctuation temperature with <I>Thermoanaerobacteriales</I> being most dominant during the upward temperature fluctuations and <I>Clostridiales</I> being the most dominant during the downward temperature fluctuations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optimum H<SUB>2</SUB> production depends on the resilience of the microbial community. </LI> <LI> H<SUB>2</SUB> production at 35 and 45 °C decreased but rapidly recovered at 55 °C. </LI> <LI> H<SUB>2</SUB> production decreased at 65 °C and stopped completely during 75 °C shift. </LI> <LI> H<SUB>2</SUB> production recovered better after 65 °C than after 75 °C temperature shift. </LI> <LI> The major microbial genera were <I>Clostridium</I> spp. and <I>Thermoanaerobacterium</I> spp. </LI> </UL> </P>