Effects of substrate loading and co-substrates on thermophilic anaerobic conversion of microcrystalline cellulose and microbial communities revealed using high-throughput sequencing

Abstract

Batch tests were conducted to investigate the effect of co-substrates, including glucose, xylose and starch, on thermophilic anaerobic conversion of microcrystalline cellulose using mixed culture enriched from anaerobic digestion sludge (ADS). Up to 30.9% of cellulose was utilized with xylose as co-substrate. When using glucose as co-substrate, cellulose conversion rate reached the maximum of 0.048 g/l/h at cellulose loading of 5.0 g/l. Illumina high-throughput sequencing of the 16S rRNA gene revealed that the thermophilic consortium exclusively consisted of Clostridium (more than 70% of all sequences). Growth of Thermoanaerobacterium over Clostridium would inhibit cellulose conversion capacity of the consortium. But the growth of Thermoanaerobacterium could be repressed by pH higher than pH 6.0. Co-substrates caused noticeable variation of bacterial community structure. Predominance of Thermoanaerobacterium over Clostridium was observed when monosugars (glucose and xylose) were used as co-substrate without pH control. Starch was ineffective as co-substrate because it competed with cellulose for Clostridium. Highlights: Co-substrate could affect cellulose conversion rate and community structure. Cellulose loading could affect cellulose conversion rate but not community structure. Clostridium was the cellulolytic constituent in the community. Thermoanaerobacterium growth over Clostridium inhibits cellulose conversion and repressed by pH > 6. Thermoanaerobacterium dominates when using monosugar co-substrate without pH control. © 2012 Hydrogen Energy Publications, LLC.