Roghair Mark, Liu Yuchen, Adiatma Julius C, Weusthuis Ruud A, Bruins Marieke E, Buisman Cees J N, Strik David P B T B
Sub-department of Environmental Technology, Wageningen University & Research, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.
Bioprocess Engineering, Wageningen University & Research, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
ACS Sustain Chem Eng. 2018 Jun 4;6(6):7499-7506. doi: 10.1021/acssuschemeng.8b00200. Epub 2018 Apr 17.
Chain elongation is an open-culture fermentation process that facilitates conversion of organic residues with an additional electron donor, such as ethanol, into valuable n-caproate. Open-culture processes are catalyzed by an undefined consortium of microorganisms which typically also bring undesired (competing) processes. Inhibition of competing processes, such as syntrophic ethanol oxidation, will lead to a more selective n-caproate production process. In this study, we investigated the effect of n-caproate concentration on the specific activity of chain elongation and competing processes using batch inhibition assays. With "synthetic medium sludge" (originally operating at 3.4 g/L n-caproate), syntrophic ethanol oxidation was proportionally inhibited by n-caproate until 45% inhibition at 20 g/L n-caproate. Hydrogenotrophic methanogenesis was for 58% inhibited at 20 g/L n-caproate. Chain elongation of volatile fatty acids (volatile fatty acid upgrading; the desired process), was completely inhibited at 20 g/L n-caproate with all tested sludge types. "Adapted sludge" (operating at 23.2 g/L n-caproate) showed a 10 times higher volatile fatty acid upgrading activity at 15 g/L n-caproate compared to "nonadapted sludge" (operating at 7.1 g/L n-caproate). This shows that open cultures do adapt to perform chain elongation at high n-caproate concentrations which likely inhibits syntrophic ethanol oxidation through hydrogenotrophic methanogenesis. As such, we provide supporting evidence that the formation of n-caproate inhibits syntrophic ethanol oxidation which leads to a more selective medium chain fatty acid production process.
链延长是一种开放式培养发酵过程，该过程利用乙醇等额外的电子供体促进有机残留物转化为有价值的己酸盐。开放式培养过程由未定义的微生物群落催化，这些微生物通常也会引发不期望的（竞争性）过程。抑制诸如互营乙醇氧化等竞争性过程，将导致更具选择性的己酸盐生产过程。在本研究中，我们使用批次抑制试验研究了己酸盐浓度对链延长和竞争性过程比活性的影响。对于“合成培养基污泥”（最初在3.4 g/L己酸盐浓度下运行），互营乙醇氧化受到己酸盐的比例抑制，直至在20 g/L己酸盐浓度下抑制率达到45%。在20 g/L己酸盐浓度下，氢营养型产甲烷作用受到58%的抑制。对于所有测试的污泥类型，挥发性脂肪酸的链延长（挥发性脂肪酸升级；期望的过程）在20 g/L己酸盐浓度下完全受到抑制。“适应污泥”（在23.2 g/L己酸盐浓度下运行）在15 g/L己酸盐浓度下的挥发性脂肪酸升级活性比“未适应污泥”（在7.1 g/L己酸盐浓度下运行）高10倍。这表明开放式培养确实能够适应在高己酸盐浓度下进行链延长，这可能通过氢营养型产甲烷作用抑制互营乙醇氧化。因此，我们提供了支持性证据，即己酸盐的形成抑制互营乙醇氧化，从而导致更具选择性的中链脂肪酸生产过程。
