Prem Eva Maria, Schwarzenberger Alessa, Markt Rudolf, Wagner Andreas Otto
Department of Microbiology, Universität Innsbruck, Innsbruck, Austria.
Front Microbiol. 2023 Apr 5;14:1087043. doi: 10.3389/fmicb.2023.1087043. eCollection 2023.
Aromatic compounds like phenyl acids (PA) can accumulate during anaerobic digestion (AD) of organic wastes due to an increased entry of lignocellulose, secondary plant metabolites or proteins, and thermodynamic challenges in degrading the benzene ring. The effects of aromatic compounds can be various - from being highly toxic to be stimulating for methanogenesis - depending on many parameters like inoculum or molecular characteristics of the aromatic compound. To contribute to a better understanding of the consequences of PA exposure during AD, the aim was to evaluate the effects of 10 mM PA on microbial communities degrading different, degradation phase-specific substrates in thermophilic batch reactors within 28 days: Microcrystalline cellulose (MCC, promoting hydrolytic to methanogenic microorganisms), butyrate or propionate (promoting syntrophic volatile fatty acid (VFA) oxidisers to methanogens), or acetate (promoting syntrophic acetate oxidisers to methanogens). Methane production, VFA concentrations and pH were evaluated, and microbial communities and extracellular polymeric substances (EPS) were assessed. The toxicity of PA depended on the type of substrate which in turn determined the (i) microbial diversity and composition and (ii) EPS quantity and quality. Compared with the respective controls, methane production in MCC reactors was less impaired by PA than in butyrate, propionate and acetate reactors which showed reductions in methane production of up to 93%. In contrast to the controls, acetate concentrations were high in all PA reactors at the end of incubation thus acetate was a bottle-neck intermediate in those reactors. Considerable differences in EPS quantity and quality could be found among substrates but not among PA variants of each substrate. spp. was the dominant methanogen in VFA reactors without PA exposure and was inhibited when PA were present. VFA oxidisers and spp. were abundant in VFA assays with PA exposure as well as in all MCC reactors. As MCC assays showed higher methane yields, a higher microbial diversity and a higher EPS quantity and quality than VFA reactors when exposed to PA, we conclude that EPS in MCC reactors might have been beneficial for absorbing/neutralising phenyl acids and keeping (more susceptible) microorganisms shielded in granules or biofilms.
像苯酸（PA）这样的芳香族化合物在有机废物的厌氧消化（AD）过程中可能会积累，这是由于木质纤维素、次生植物代谢产物或蛋白质的输入增加，以及降解苯环时的热力学挑战。芳香族化合物的影响可能多种多样——从剧毒到刺激产甲烷作用——这取决于许多参数，如接种物或芳香族化合物的分子特征。为了有助于更好地理解厌氧消化过程中PA暴露的后果，本研究旨在评估10 mM PA对嗜热间歇反应器中降解不同的、特定降解阶段底物的微生物群落的影响，为期28天：微晶纤维素（MCC，促进水解微生物到产甲烷微生物）、丁酸盐或丙酸盐（促进互营挥发性脂肪酸（VFA）氧化菌到产甲烷菌）或乙酸盐（促进互营乙酸盐氧化菌到产甲烷菌）。评估了甲烷产量、VFA浓度和pH值，并对微生物群落和胞外聚合物（EPS）进行了评估。PA的毒性取决于底物类型，而底物类型又决定了（i）微生物多样性和组成以及（ii）EPS的数量和质量。与各自的对照相比，MCC反应器中的甲烷产量受PA的影响小于丁酸盐、丙酸盐和乙酸盐反应器，后者的甲烷产量降低了高达93%。与对照相反，在培养结束时，所有PA反应器中的乙酸盐浓度都很高，因此乙酸盐是这些反应器中的瓶颈中间体。在不同底物之间可以发现EPS数量和质量存在显著差异，但在每种底物的PA变体之间没有发现差异。在没有PA暴露的VFA反应器中， spp.是主要的产甲烷菌，当存在PA时会受到抑制。在有PA暴露的VFA试验以及所有MCC反应器中，VFA氧化菌和 spp.都很丰富。由于MCC试验在暴露于PA时比VFA反应器显示出更高的甲烷产量、更高的微生物多样性以及更高的EPS数量和质量，我们得出结论，MCC反应器中的EPS可能有利于吸收/中和苯酸，并使（更易受影响的）微生物在颗粒或生物膜中得到保护。
