摘要
混菌发酵系统中微生物菌群和代谢路径有效调控是制取中链脂肪酸的关键.本研究以厌氧发酵重要参数pH为调控因子,考察pH对秸秆初次和二次厌氧发酵中有机酸生成的影响规律,并采用16S rRNA高通量测序分析微生物群落变化,解析pH调控与产酸性能和微生物群落之间的关系.结果表明, pH调控对秸秆初次发酵产酸性能有显著影响,酸性和中性条件有利于链延长反应,产物以丁酸和己酸为主(80%以上).然而,碱性条件严重抑制链延长反应,产物以乙酸(93.2%)和丙酸(5.5%)为主,无己酸生成.二次发酵结果表明,在酸性条件下(pH 5.6)二次发酵链延长无法进行,而pH从5.6调至7.0后,己酸浓度从1.88 g/L快速升高到11.8 g/L.微生物群落分析表明,链延长直接相关的菌属,如Clostridium Ⅳ, Clostridium Ⅺ, Clostridium ⅪVa, Clostridium ⅪVb, Clostridium XⅧ和Clostridium sensu stricto等,在中性和酸性条件下的丰度显著高于碱性条件.另外,二次发酵中pH调节并未显著改变链延长相关菌群的丰度,表明链延长微生物活性恢复是产己酸的诱因.本研究发现可为混菌发酵体系内复杂微生物群落的定向调控生产中链脂肪酸提供借鉴.
Anaerobic fermentation of waste biomass via microbial chain elongation for producing medium-chain fatty acids(MCFAs)is becoming an emerging and economically viable technology. However, due to the large abundant of microbial species and great diversity of microbial metabolic pathways in open cultures, how to achieve the high yields of MCFAs is an important topic. In this study, the effect of pH, as an important parameter for process control, on the production and composition of volatile fatty acids(VFAs) in two cycles of anaerobic chain elongation process with cornstalk as feedstock was investigated, and the 16S rRNA high throughput sequencing was employed to elucidate the mechanism of pH affecting chain elongation process. The results showed that p H significantly influenced the VFAs production and their spectra. At pH5.6, the VFAs production was 10.0 g/L, which was increased to 15.9 g/L at pH 7.0, and was further increased to 18.8 g/L at pH 9.0. In addition, the metabolic pathways and the VFAs composition in anaerobic fermentation were greatly changed with pH regulation. Under acidic and neutral conditions(pHs of 5.6 and 7.0), the chain elongation was enhanced, and butyrate and caproate were the major products accounting for more than 80%. Specially, under the neutral condition, the caproate concentration reached(3.49±0.17) g/L. However, the pH of 9.0 seriously inhibited the chain elongation, and the major fermentation products were acetate(93.2%) and propionate(5.5%). The second-cycle fermentation with supplementing additional ethanol as an electron donor indicated that pH played the more important role in the chain elongation process for a high level MCFAs production. In the second cycle, the chain elongation reaction did not occur under the acidic conditions. However, when the pH was adjusted from 5.6 to 7.0, the chain elongation reaction was significantly stimulated, and the caproate concentration quickly increased from 1.88 to 11.8 g/L. The results of microbial community analysis showed that the fermentative bacteria of Firmicutes were the dominate population under the neutral pH condition accounting for 49.9%, which was far higher than those under the acidic and alkaline conditions. The strains relating to the chain elongation, such as Clostridium Ⅳ, Clostridium Ⅺ, Clostridium ⅪVa, Clostridium ⅪVb, Clostridium XⅧ and Clostridium sensu stricto, were enriched under the neutral and acidic conditions, but not under the alkaline condition. It should be noted that the well-known pure culture bacteria relating to chain elongation, such as Clostridium Kluyveri, were not found in this study. In the second cycle, no significant difference on the relative abundance of strains relating to chain elongation was found between neutral and acidic conditions, suggesting that these strains could survive under the acidic conditions but their activity was inhibited. When the pH was adjusted from 5.6 to 7.0, their activities could quickly recover to produce caproate. The above findings provided an effective regulating strategy for selective production of MCFAs from waste biomass with open cultures of microbial consortia.
作者
朱孔云
党超
张雷
李爱民
Kongyun Zhu;Chao Dang;Lei Zhang;Aimin Li(Key Laboratory of Industrial Ecology and Environmental Engineering(Ministry of Education),School of Environmental Science and Technology,Dalian University of Technology,Dalian J16024,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2020年第26期2903-2913,共11页
Chinese Science Bulletin
基金
国家自然科学基金(51978123)资助。
关键词
秸秆
链延长
中链脂肪酸
pH影响
微生物群落
cornstalk
chain elongation
medium chain fatty acids
pH effects
microbial community
