Prem Eva Maria, Mutschlechner Mira, Stres Blaz, Illmer Paul, Wagner Andreas Otto
Department of Microbiology, Universität Innsbruck, Technikerstraße 25d, 6020, Innsbruck, Austria.
Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000, Ljubljana, Slovenia.
Biotechnol Biofuels. 2021 Jan 20;14(1):27. doi: 10.1186/s13068-020-01855-0.
Lignin intermediates resulting from lignocellulose degradation have been suspected to hinder anaerobic mineralisation of organic materials to biogas. Phenyl acids like phenylacetate (PAA) are early detectable intermediates during anaerobic digestion (AD) of aromatic compounds. Studying the phenyl acid formation dynamics and concomitant microbial community shifts can help to understand the microbial interdependencies during AD of aromatic compounds and may be beneficial to counteract disturbances.
The length of the aliphatic side chain and chemical structure of the benzene side group(s) had an influence on the methanogenic system. PAA, phenylpropionate (PPA), and phenylbutyrate (PBA) accumulations showed that the respective lignin intermediate was degraded but that there were metabolic restrictions as the phenyl acids were not effectively processed. Metagenomic analyses confirmed that mesophilic genera like Fastidiosipila or Syntrophomonas and thermophilic genera like Lactobacillus, Bacillus, Geobacillus, and Tissierella are associated with phenyl acid formation. Acetoclastic methanogenesis was prevalent in mesophilic samples at low and medium overload conditions, whereas Methanoculleus spp. dominated at high overload conditions when methane production was restricted. In medium carbon load reactors under thermophilic conditions, syntrophic acetate oxidation (SAO)-induced hydrogenotrophic methanogenesis was the most important process despite the fact that acetoclastic methanogenesis would thermodynamically be more favourable. As acetoclastic methanogens were restricted at medium and high overload conditions, syntrophic acetate oxidising bacteria and their hydrogenotrophic partners could step in for acetate consumption.
PAA, PPA, and PBA were early indicators for upcoming process failures. Acetoclastic methanogens were one of the first microorganisms to be impaired by aromatic compounds, and shifts to syntrophic acetate oxidation coupled to hydrogenotrophic methanogenesis occurred in thermophilic reactors. Previously assumed associations of specific meso- and thermophilic genera with anaerobic phenyl acid formation could be confirmed.
木质纤维素降解产生的木质素中间体被怀疑会阻碍有机物质厌氧矿化生成沼气。苯乙酸（PAA）等苯酸是芳香族化合物厌氧消化（AD）过程中早期可检测到的中间体。研究苯酸形成动态以及伴随的微生物群落变化有助于理解芳香族化合物厌氧消化过程中的微生物相互依存关系，可能有助于应对干扰。
脂肪族侧链长度和苯侧基的化学结构对产甲烷系统有影响。PAA、苯丙酸（PPA）和苯丁酸（PBA）的积累表明相应的木质素中间体被降解，但由于苯酸未得到有效处理，存在代谢限制。宏基因组分析证实，嗜温菌属如Fastidiosipila或互营单胞菌属以及嗜热菌属如乳杆菌属、芽孢杆菌属、地芽孢杆菌属和蒂氏菌属与苯酸形成有关。在中低负荷条件下，嗜温样品中乙酸裂解产甲烷作用普遍存在，而在高负荷条件下甲烷产生受限，甲烷袋形菌属占主导。在嗜热条件下的中碳负荷反应器中，尽管从热力学角度乙酸裂解产甲烷作用更有利，但互营乙酸氧化（SAO）诱导的氢营养型产甲烷作用是最重要的过程。由于乙酸裂解产甲烷菌在中高负荷条件下受到限制，互营乙酸氧化细菌及其氢营养型伙伴可以介入消耗乙酸。
PAA、PPA和PBA是即将发生过程故障的早期指标。乙酸裂解产甲烷菌是最早受到芳香族化合物损害的微生物之一，嗜热反应器中发生了向与氢营养型产甲烷作用耦合的互营乙酸氧化的转变。先前假设的特定嗜温和嗜热菌属与厌氧苯酸形成的关联得到了证实。
