Zymomonas mobilis를 이용한 목질계 에탄올 생산을 위한 균주 개선에 관한 연구 동향

Recent Progress in Strain Development of Zymomonas mobilis for Lignocellulosic Ethanol Production

Abstract

자이모모나스 모빌리스(Zymomonas mobilis)는 수십 년 동안 생화학적 발효 기술을 통한 수송용 에탄올을 생산하기에 적합한 산업용 미생물로 각광을 받아왔다. 최근 이 균주의 포스트 게놈 시대 도래 및 미국 듀폰사(DuPont, USA)의 세계 최대 산업용 목질계 에탄올 생산 시설 완료 등은, 이 미생물을 이용한 산업적 에탄올 생산 공정 가시화를 위한 다양한 연구들을 파생시키고 있다. 특히, 산업용 셀룰로오스 에탄올 발효공정에 이용되는 미생물은 다양한 독성 발효 저해물질 및 물리적 스트레스에 보다 쉽게 노출 될 수 있다. 따라서 본 논문은 이 미생물이 보유한 최신 생리학적 이해와 관련 된 정보와 다양한 환경적 스트레스에 견딜 수 있는 산업적 강건성 및 산업용 균주 개발 방법에 대한 사례 및 이 균주를 이용한 가격 경쟁적인 목질계 에탄올 생산 공정 개발에 필요한 균주 개발에 대한 미래 지향적 연구 방향에 대하여 기술하였다.

Zymomonas mobilis has been recognized as a potential industrial ethanologen for many decades due to its outstanding fermentation characteristics, including high ethanol tolerance, fast sugar uptake rate, and high theoretical ethanol yield. With the emergence of the postgenomic era and the recent announcement of DuPont's world largest cellulosic ethanol production process, research on this bacterium has become even more important to harness successful application not only for use in the bioethanol process but also in other biochemical processes, which can be included in bio-refinery. As an important industrial microorganism, Z. mobilis will likely be exposed to various stressful environments, such as toxic chemicals, including the end-product ethanol and fermentative inhibitory compounds (e.g., furan derivatives, organic acids, and lignin derivatives in pretreatment steps), as well as physical stresses, such as high temperature during large-scale ethanol fermentation. This review focuses on recent information related to the industrial robustness of this bacterium and strain development to improve the ethanol yield and productivity in the lignocellulosic ethanol process. Although several excellent review articles on the strain development of this bacterium have been published, this review aims to fill gaps in the literature by highlighting recent advances in physiological understanding of this bacterium that may aid strain developments and improve the ethanol productivity for lignocellulosic biomass.

Fig 1. A) Transmission electron microscopic image of flagellated cells of the wild type strain Z. mobilis ZM4; B) flocculent cells of the mutant strain ZM401 image stained by calcofluor white, the source adapted from Jeon et al. [22].

Fig 2. Schematic diagram of cell flocculating mechanims in Z. mobilis ZM401 caused by a single point mutation in phophodiesterase domain which allow to increase intracellular level of c-di-GMP. The increased intracellular c-di-GMP subsequently results in increase in cellulose synthsis and decrease in motility. The increased cellulose synthesis metabolism with increased cell flocculation phenotype finally contributed to the enhanced volumatric ethanol productivity due to the acetate and vanillin resistance. DGC: Diguanyl cylase; PDE: Phophodiesterase.

Table 1. The list of Z. mobilis strains genome sequenced

Table 2. The list of heterologous genes expressed in Z. mobilis to broaden its substrate usages for ethanol production

Table 3. Effect of lignocellulosic inhibitory compounds on specific rates of xylose uptake, ethanol production, and ethanol yield of Z. mobilis ZM4 (pZB5) at 30℃ and initial pH 6 investigated by Kim et al. [25]

Table 4. List of genes from Z. mobilis involved in stress responds confirmed by various techniques