Clostridium pasteurianum as Industrial Microorganism for Efficient Production of 1,3-Propanediol: From Metabolic Engineering, to Fermentation and Product Separation

doi:10.12211/2096-8280.2024-030

Abstract

Abstract:

1,3-Propanediol (PDO) is an important chemical extensively used in material science and the cosmetics industry. The biomanufacturing of PDO offers numerous advantages, such as the renewability of raw materials and environmental friendliness. Among various microorganisms, Clostridium pasteurianum emerges as an ideal choice for industrial PDO production due to its safety, non-pathogenic nature, rapid glycerol metabolism, fast growth rate, independence from expensive culture medium components, and its inherent efficient metabolic pathway for PDO production. This review begins by introducing the current state and challenges of PDO biomanufacturing, followed by an in-depth discussion of the methods for producing PDO using C. pasteurianum. Special attention is paid to the glycerol metabolism mechanism, strategies for glycerol fermentation, and the design of the fermentation process. Notably, our research group has identified C. pasteurianum mutant strains and developed robust processes that have largely addressed the organism's traditional sensitivities to environmental conditions, especially regarding iron concentration and impurities of raw glycerol. In an electricity-aided fermentation process, PDO concentration as high as 120.6 g/L was achieved, with a productivity of 4.8 g/L/h and a yield reaching the theoretical maximum. We further discuss the natural limitations of genetic engineering in C. pasteurianum, exploring strategies based on rational genomic modification and directed evolution. Finally, the development of efficient downstream processing technologies is emphasized as crucial for realizing the cost-effective microbial production of PDO from renewable resources, since the industrial application of PDO requires a very high purity (>99.9%). The discussion on PDO downstream processing mainly focuses on evaporation, distillation, and extraction-based purification techniques. Through a comprehensive coverage of metabolic engineering, strain evolution, fermentation optimization, and product separation technologies, this review discusses about the characteristics and advantages of PDO production from C. pasteurianum, highlighting key considerations for advancing this microorganism as a new industrial chassis.

Key words: Biomanufacturing, Clostridium pasteurianum, 1,3-Propanediol, Crude Glycerol Fermentation, Downstream Separation and Purification

摘要：

1，3-丙二醇（PDO）是一种重要的化工原料，广泛应用于材料和化妆品等领域。生物制造 PDO具有原料可再生性和环境友好性等众多优点和广阔的发展前景。由于巴氏梭菌（Clostridium pasteurianum）菌株安全、非致病、代谢甘油速率快、生长快、不依赖昂贵的培养基组分、天然具备高效生产PDO代谢途径等条件，利用和改造巴氏梭菌作为工业底盘生产PDO呈现出得天独厚的优势。本文首先回顾了PDO的生物制造现状和挑战，随后深入探讨了采用巴氏梭菌生产PDO的方法，特别关注于巴氏梭菌的甘油代谢机制、甘油发酵的策略和发酵过程的工艺设计，值得一提的是本研究团队筛选到的巴氏梭菌突变体和随之开发的鲁棒工艺在一定程度上突破了传统巴氏梭菌对环境的要求，特别是对铁离子浓度的敏感性；在电辅助甘油发酵过程中，PDO 产量达到120.7 g/L，生产强度达到4.8 g/L/h，收率达到理论值；进一步阐述了巴氏梭菌基因工程改造方面的天然屏障，围绕着理性基因组改造和定向进化等几个方面进行了详细讨论；由于PDO产品纯度（>99.9%）通常有较高要求，因此开发高效的下游处理技术对于实现利用可再生资源发酵生产PDO的工业化应用至关重要，本文在分离工艺方面主要讨论了基于蒸发和蒸馏的PDO纯化技术、以及基于萃取的PDO纯化技术。通过对代谢工程、菌种进化、发酵过程优化以及产品分离等多个维度全方位分析，本文全面地解析了巴氏梭菌生产PDO的特点和优势，以及巴氏梭菌作为新型工业底盘微生物在未来发展过程中值得关注的问题。

关键词: 生物制造, 巴氏梭菌, 1，3-丙二醇, 粗甘油发酵, 下游分离纯化

CLC Number:

Q816

Jianming LIU, Chijian ZHANG, Bing ZHANG, Anping ZENG. Clostridium pasteurianum as Industrial Microorganism for Efficient Production of 1,3-Propanediol: From Metabolic Engineering, to Fermentation and Product Separation[J]. Synthetic Biology Journal, DOI: 10.12211/2096-8280.2024-030.

刘建明, 张炽坚, 张冰, 曾安平. 巴氏梭菌作为工业底盘细胞高效生产1，3-丙二醇-从代谢工程和菌种进化到过程工程和产品分离[J]. 合成生物学, DOI: 10.12211/2096-8280.2024-030.

Figures/Tables 5

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Substrate	End-product	Energy, reducing equivalents and product balances
Glycerol	PDO	Glycerol + NADHPDO
	Lactate	GlycerolLactate + NADH + ATP
	Acetate	GlycerolAcetate + CO₂ + 2ATP + 2NADH + FdH2
	Ethanol	GlycerolEthanol + CO₂ + ATP + FdH2
	Butyrate	2Glycerolbutyrate + 2CO₂ + 3ATP + 2NADH + 2FdH2
	Butyrate	*2Glycerolbutyrate + 2CO₂ + 3ATP + NADH + 3FdH2
	Butanol	2Glycerolbutanol + 2CO₂ + 2ATP + 2FdH2
	Butanol	*2Glycerol + NADHbutanol + 2CO₂ + 2ATP + 3FdH2
Glucose	Lactate	Glucose2Lactate + 2ATP
	Acetate	Glucose2Acetate + 2CO₂ + 4ATP + 2NADH + 2FdH2
	Ethanol	Glucose + 2NADH2Ethanol + 2CO₂ + 2ATP + 2FdH2
	Butyrate	Glucosebutyrate + 2CO₂ + 3ATP + 2FdH2
	Butyrate	*Glucose + NADHbutyrate + 2CO₂ + 3ATP + 3FdH2
	Butanol	Glucose + 2NADHbutanol + 2CO₂ + 2ATP + 2FdH2
	Butanol	*Glucose + 3NADHbutanol + 2CO₂ + 2ATP + 3FdH2

Substrate	End-product	Energy, reducing equivalents and product balances
Glycerol	PDO	Glycerol + NADHPDO
	Lactate	GlycerolLactate + NADH + ATP
	Acetate	GlycerolAcetate + CO₂ + 2ATP + 2NADH + FdH2
	Ethanol	GlycerolEthanol + CO₂ + ATP + FdH2
	Butyrate	2Glycerolbutyrate + 2CO₂ + 3ATP + 2NADH + 2FdH2
	Butyrate	*2Glycerolbutyrate + 2CO₂ + 3ATP + NADH + 3FdH2
	Butanol	2Glycerolbutanol + 2CO₂ + 2ATP + 2FdH2
	Butanol	*2Glycerol + NADHbutanol + 2CO₂ + 2ATP + 3FdH2
Glucose	Lactate	Glucose2Lactate + 2ATP
	Acetate	Glucose2Acetate + 2CO₂ + 4ATP + 2NADH + 2FdH2
	Ethanol	Glucose + 2NADH2Ethanol + 2CO₂ + 2ATP + 2FdH2
	Butyrate	Glucosebutyrate + 2CO₂ + 3ATP + 2FdH2
	Butyrate	*Glucose + NADHbutyrate + 2CO₂ + 3ATP + 3FdH2
	Butanol	Glucose + 2NADHbutanol + 2CO₂ + 2ATP + 2FdH2
	Butanol	*Glucose + 3NADHbutanol + 2CO₂ + 2ATP + 3FdH2

分离步骤	作用与功能	存在的问题	分离物质
离心和微滤	有效地去除所有微生物细胞（生物量）		生物质
低分子截留\|	有效地去除高含量的可溶性蛋白质，避免其会在水分蒸发过程中严重起泡，从而导致过程效率降低		可溶性蛋白
壳聚糖絮凝\|
活性炭吸附
纳滤	分离去除葡萄糖，避免葡萄糖在蒸发和蒸馏过程中发生沉淀		葡萄糖
离子交换吸附\|	有效地去除发酵液中的有机酸盐和无机盐，因为盐在水分蒸发过程中部分结晶，结晶盐的沉积导致蒸发器底部形成粘稠的浆液，进而导致高能耗和目标产品的低产量	树脂的快速饱和，需要大量的NaOH和HCl溶液进行再生	有机酸盐和无机盐
电渗析\|		电渗析的能源和材料成本通常非常高，阻碍了其在廉价大宗化学品的商业生产中的实际应
醇沉淀和稀释结晶		不足以有效去除在醇类中溶解度高的有机酸盐
蒸发	蒸发去除水分		水
蒸馏	液态混合物中各组分沸点不同，去除残留甘油		残余甘油

分离步骤	作用与功能	存在的问题	分离物质
离心和微滤	有效地去除所有微生物细胞（生物量）		生物质
低分子截留\|	有效地去除高含量的可溶性蛋白质，避免其会在水分蒸发过程中严重起泡，从而导致过程效率降低		可溶性蛋白
壳聚糖絮凝\|
活性炭吸附
纳滤	分离去除葡萄糖，避免葡萄糖在蒸发和蒸馏过程中发生沉淀		葡萄糖
离子交换吸附\|	有效地去除发酵液中的有机酸盐和无机盐，因为盐在水分蒸发过程中部分结晶，结晶盐的沉积导致蒸发器底部形成粘稠的浆液，进而导致高能耗和目标产品的低产量	树脂的快速饱和，需要大量的NaOH和HCl溶液进行再生	有机酸盐和无机盐
电渗析\|		电渗析的能源和材料成本通常非常高，阻碍了其在廉价大宗化学品的商业生产中的实际应
醇沉淀和稀释结晶		不足以有效去除在醇类中溶解度高的有机酸盐
蒸发	蒸发去除水分		水
蒸馏	液态混合物中各组分沸点不同，去除残留甘油		残余甘油

分离方法		作用与功能	存在的问题	提取率
液-液萃取	使用疏水有机溶剂乙酸乙酯	使用乙酸乙酯对生物合成的PDO进行溶剂萃取	从实际发酵液中回收PDO的最高分配系数仅达到0.14	12%
	基于化学反应的反应萃取	将PDO转化为疏水性PDO衍生物，有机溶剂溶剂萃取后，通过逆反应以获得PDO	反应物和萃取剂都有毒，发酵液中与PDO具有相似化学结构的其他物质（如2,3-丁二醇、甘油、乙醇等）也会与反应物发生反应	91%
	基于生物催化转化的反应萃取	利用与辛酸的酯化反应在脂肪酶催化下，将PDO转化为疏水酯	PDO和脂肪酸之间的反应效率低，需要重复三次脂肪酶催化的酯化反应	90%
两相盐析萃取	“K₂CO₃+K₂HPO₄”异丙醇盐析萃取系统	使用亲水有机溶剂的盐析萃取在从发酵液中回收亲水产品方面表现出显著更高的回收率	盐析萃取系统中形成两相所需的盐量大，且分离过程造成大量的废水排放	98%
	由乙醇和碳酸钠组成的盐析萃取系统	使用亲水有机溶剂的盐析萃取在从发酵液中回收亲水产品方面表现出显著更高的回收率		97%
	两步盐析萃取	第一步中，使用疏水性的正丁酸乙酯高效提丁酸，在第二步中，使用乙醇并添加NaH₂PO₄作为盐析剂，回收PDO		95%