Insights into the microbiomes for medium-chain carboxylic acids production from biowastes through chain elongation

Bioconversion of medium-chain carboxylic acids (MCCAs) from biowastes through anaerobic mixed-culture fermentation is undergoing a revolution in terms of mitigating the lower fossil fuels requirement and increasing biowaste treatment capacity. Benefiting from hydrophobicity and high energy density of MCCA, this high-valuable biofuel exhibits easier separation and wider application than traditional volatile fatty acid products. The biggest bottleneck for efficiently and simultaneously producing MCCAs by mixed-culture fermentation is complicated or even entangled microbial interaction. Therefore, this review aimed to supply guidelines to understand and steer these microbiomes toward the controllable ones. The metabolic pathway of chain elongation and associated cooperating and competing pathways were firstly discussed to understand the primary microbial interaction in mixed-culture fermentation. In an attempt to inspect the overall performance of mixed-culture CE reactor, the typical microbial community and its variation influenced by reactor parameters were also identified. The methods of in-line extraction of MCCAs for relieving toxicity inhibition on microbiome were also summarized regarding the difficulties lied in continuous MCCAs production. Finally, the future research directions of MCCAs production via mixed-culture fermentation would be proposed to help steer these novel bioproduction processes toward full-scale applications.

通过厌氧混合培养发酵从生物废弃物中制备中链羧酸（medium-chain carboxylic acids, MCCAs）的生物转化技术，在降低化石燃料需求、提升生物废弃物处理能力方面正迎来革新。得益于MCCAs的疏水性与高能量密度，这类高价值生物燃料相较于传统挥发性脂肪酸产物，具备分离难度更低、应用场景更广的优势。通过混合培养发酵高效同步制备MCCAs的最大瓶颈，在于复杂甚至错综的微生物相互作用。因此，本综述旨在提供指导框架，以帮助理解并调控这些微生物群落，使其朝着可控化方向发展。本文首先探讨了链延长代谢通路及其相关的协同与竞争通路，以此阐明混合培养发酵过程中的核心微生物相互作用机制。为考察混合培养链延长反应器的整体运行性能，本文还分析了典型微生物群落及其受反应器参数影响的变化规律。针对MCCAs连续生产中存在的技术难题，本文总结了在线提取MCCAs以缓解其对微生物群落毒性抑制作用的相关方法。最后，本文将提出通过混合培养发酵制备MCCAs的未来研究方向，以助力这类新型生物制备工艺实现规模化应用。