Dissecting microbial community structure and acidogenic fermentation pathways of rumen microorganisms fermenting office paper under mesophilic and thermophilic temperatures by massive sequencing

This study aimed the hydrolysis and fermentation of paper with recovery of H2 and VFAs using a natural microbial consortium in lysimeters. Serial dilutions of rumen fluid in natura (F.N.) were performed to obtain the fermentative non-methanogenic purified consortium (F.P.). Then, the consortium was used as inoculum in lysimeters under 2 different conditions of mass of paper (g) and temperature of incubation (oC), under the same paper’s moisture content (80%), at pH 5.5: L1 (500 g; 80%; 35 oC) and L2 (1000 g; 80%; 55 oC). For monitoring the lysimeters in relation to paper hydrolysis and fermentation, analyses of biogas (H2, N2, CO2 e CH4) and the compounds’ concentrations in the leachate, such as, total sugars, chemical oxygen demand, volatile fatty acids (VFA’s) and alcohols were performed. Alcalinity, pH and total solids content of the leachate were also monitored. High-throughput sequencing was used to characterize the phylogenetic composition and functional potential of microbial consortium. The effect of temperature, mass of paper and paper’s moisture content was evaluated on the microbial community and on the metabolisms performed by the microorganisms at each condition. Hydrogen production was detected in lysimeters with 35 mmol (L1) and 3 mmol (L2). In L1, high concentration of acetic acid, of 17.000 mg/L, respectively, were due to the likely occurrence of homoacetogenesis. Under thermophilic condition L2, the hydrogen production was detected in low volume, and the highlight was the production of ethanol and methanol, with concentrations around 2.300 and 5.600 mg/L, respectively. The most abundant microbial genus in each sample sequenced were: Prevotella in the rumen fluid in natura (F.N.) Dysgonomonas in the purified consortium and L1 (35o C) and Thermicanus in L2 (55o C). In conclusion, moisture content of 80% promoted paper hydrolysis and fermentation by microorganisms; temperature was the principal parameter that influenced the structure of microbial community, confirmed by the different metabolic route observed under mesophilic and thermophilic conditions; and the production yields of the compounds were not influenced by the mass of paper added to the lysimeters.

本研究旨在利用天然微生物菌群，在渗漏池（lysimeters）中实现纸张的水解与发酵，并回收氢气（H₂）与挥发性脂肪酸（VFAs）。首先对天然瘤胃液（F.N.）进行系列稀释，以获得发酵型非产甲烷纯化菌群（F.P.）。随后，将该菌群作为接种物，在两种不同纸张质量（g）与培养温度（℃）条件下的渗漏池中开展实验，所有实验组均维持纸张含水率80%、pH值5.5：实验组L1（500 g；80%；35 ℃）与实验组L2（1000 g；80%；55 ℃）。为监测渗漏池内纸张的水解与发酵过程，本研究对沼气（H₂、N₂、CO₂与CH₄）组分及渗滤液中的相关化合物浓度进行了分析，涵盖总糖、化学需氧量（COD）、挥发性脂肪酸（VFAs）与醇类；同时同步监测了渗滤液的碱度、pH值与总固体含量。采用高通量测序技术对微生物菌群的系统发育组成与功能潜力进行表征，评估了纸张质量、培养温度与纸张含水率对不同条件下微生物群落结构及微生物代谢途径的影响。实验结果显示，在L1组渗漏池中检测到氢气产量为35 mmol，L2组为3 mmol。L1组中乙酸浓度高达17000 mg/L，该现象推测源于同型产乙酸作用。在嗜热条件下的L2组中，氢气产量较低，而乙醇与甲醇为主要产物，浓度分别约为2300 mg/L与5600 mg/L。各测序样本中丰度最高的微生物属分别为：天然瘤胃液（F.N.）中的普雷沃氏菌属（Prevotella），纯化菌群与L1组（35 ℃）中的戴森戈莫纳斯菌属（Dysgonomonas），以及L2组（55 ℃）中的热卡菌属（Thermicanus）。综上，80%的纸张含水率可有效促进微生物对纸张的水解与发酵；温度是影响微生物群落结构的核心参数，中温与嗜热条件下观测到的不同代谢途径验证了这一结论；添加的纸张质量对目标化合物的产率无显著影响。