Enriching ruminal polysaccharide-degrading consortia via co-inoculation with methanogenic sludge and microbial mechanisms of acidification across lignocellulose loading gradients

• Published in: Applied microbiology and biotechnology Vol. 102; no. 8; pp. 3819 - 3830
• Main Authors: Deng, Yuying, Huang, Zhenxing, Ruan, Wenquan, Miao, Hengfeng, Shi, Wansheng, Zhao, Mingxing
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2018; Springer; Springer Nature B.V
• Subjects: Acetic acid; Acidification; Anaerobic digestion; Anaerobic microorganisms; Archaea; Bacteria; Bacteroidales; Biomedical and Life Sciences; Biotechnology; Cellulase; Cellulose; Chemical properties; Consortia; Environmental aspects; Environmental Biotechnology; Fatty acids; Fermentation; Inoculation; Life Sciences; Lignocellulose; Methanogenic bacteria; Microbial activity; Microbial colonies; Microbial Genetics and Genomics; Microbiology; Microbiota; Microorganisms; Oxidation; Oxidizing agents; Propionic acid; rRNA 16S; Sludge; Slurries; Substrates; Xylanase; Anaerobic acidification; Co-inoculated consortia; Lignocellulose digestion
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-018-8877-9

Using lignocellulosic materials as substrates, ruminal microbiota were co-inoculated with anaerobic sludge at different loading rates (LR) to study the microbial community in the semi-continuous mode. The results indicated that the highest CH 4 yield reached 0.22 L/g volatile solid at LR of 4 g/L/day, which obtained 56–58% of the theoretical value. In the steady stage with LR of 2–4 g/L/day and slurry recirculation, copies of total archaea increased. Especially the Methanobacteriales increased significantly ( p  < 0.05) to 3.30 × 10 8 copies/mL. The microbial communities were examined by MiSeq 16S rRNA sequencing. Enriched hydrolytic bacteria mainly belonged to Clostridiales , including Ruminococcus , Ruminiclostridium , and Ruminofilibacter settled in the rumen. High-active cellulase and xylanase were excreted in the co-inoculated system. Acid-producing bacteria by fermentation were affiliated with Lachnospiraceae and Bacteroidales . The acidogen members were mainly Spirochaetaceae and Clostridiales . Syntrophic oxidation bacteria mainly consisted of Synergistetes, propionate oxidizers ( Syntrophobacter and Pelotomaculum ), and butyrate oxidizers ( Syntrophus and Syntrophomonas ). There had no volatile fatty acid (VFA) accumulation and the pH values varied between 6.94 and 7.35. At LR of 6 g/L/day and a recirculation ratio of 1:1, the hardly degradable components and total VFA concentrations obviously increased. The total archaea and Methanobacteriales then deceased significantly to 8.56 × 10 5 copies/mL and 4.14 × 10 3 copies/mL respectively ( p  < 0.05), which resulted in the inhibition of methanogenic activities. Subsequently, microbial diversity dropped, and the hydrolytic bacteria and syntrophic oxidizers obviously decreased. In contrast, the abundances of Bacteroidales increased significantly ( p  < 0.05). Acetate, propionate, and butyrate concentrations reached 2.02, 6.54, and 0.53 g/L, respectively, which indicated “acidification” in the anaerobic reactor. Our study illustrated that co-inoculated anaerobic sludge enriched the ruminal function consortia and hydrogenotrophic methanogens played an important role in anaerobic digestion of lignocelluloses.