Deciphering Molecular Mechanism Underlying Self-Flocculation of Zymomonas mobilis for Robust Production
Deciphering Molecular Mechanism Underlying Self-Flocculation of Zymomonas mobilis for Robust Production
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DOI：
10.1128/aem.02398-21
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发表时间：
2022-04-25
影响因子：
4.4
通讯作者：
Bai, Feng-Wu
中科院分区：
文献类型：
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作者：
Cao, Lian-Ying;Yang, Yong-Fu;Bai, Feng-Wu
抗逆性是微生物细胞工厂稳健生产的先决条件，特别是对木质纤维生物质的生物精炼，以生产生物燃料、生物能源和用于可持续社会经济发展的生物基化学品，因为在预处理过程中会释放各种抑制剂，通过对纤维素组分的酶解来破坏顽固的木质素-碳水化合物复合体，以生产糖，而且它们的解毒成本太高，无法生产大宗商品。尽管对单个胁迫的耐受性已经得到了深入的研究，但由于微生物细胞不可避免地在生产条件下同时遭受多种胁迫，这一进展似乎并不显著。运动发酵单胞菌通过Entner-Doudoroff途径厌氧代谢糖，而较低的生物量积累产生的ATP较少，从而引导更多的糖形成产品，从而提高产量，使其成为适合作为微生物细胞工厂的宿主，以生产大宗商品，主要成本来自原料消耗。细菌细胞的自絮凝表现出许多优点，如增强了对环境压力的耐受性，这是通过使用浓缩底物获得高产品效价的先决条件。本研究以ZM4单细胞模式菌株ZM401为研究对象，探讨了ZM401自絮凝表型的分子机制。ZM401和ZM4的比较研究表明，ZMO1082多T区的单核苷酸缺失引起的移码使其与ZMO1083的开放阅读框融合，编码细菌纤维素合成酶的催化亚基BCSA，从而催化纤维素的生物合成。此外，ZMO1055开放阅读框的单核苷酸多态突变编码了具有明显二鸟苷环化酶/磷酸二酯酶活性的双功能GGDEF-EAL蛋白，导致Ala526Val替换，从而降低了体内降解环二鸟酸的特异性磷酸二酯酶活性，导致激活纤维素生物合成的信号分子在细胞内积累。这些发现对于改造其他具有自絮凝表型的移动酵母单细胞菌株以实现稳健生产具有重要意义。重要的抗逆性是微生物细胞工厂稳健生产的先决条件，特别是对木质纤维生物质的生物精炼，以生产生物燃料、生物能源和用于可持续社会经济发展的生物基化学品，因为在预处理过程中会释放各种抑制剂，通过酶解纤维素成分来破坏用于制糖的顽固的木质素-碳水化合物复合体，而且它们的解毒成本太高，无法生产大宗商品。虽然对个体胁迫的耐受性已经得到了深入的研究，但由于微生物细胞不可避免地在生产条件下同时遭受多种胁迫，这一进展似乎不那么显著。当微生物细胞自我絮凝时，由于增强的群体感应与形态变化相关的生理和代谢优势，微生物细胞通过一般的应激反应对多种胁迫具有更强的耐受性。因此，阐明这种自絮凝表型背后的分子机制，对于通过合理的设计使微生物细胞具有独特的多细胞形态，提高其生产性能具有重要意义。
Stress tolerance is a prerequisite for microbial cell factories to be robust in production, particularly for biorefinery of lignocellulosic biomass to produce biofuels, bioenergy, and bio-based chemicals for sustainable socioeconomic development, since various inhibitors are released during the pretreatment to destroy the recalcitrant lignin-carbohydrate complex for sugar production through enzymatic hydrolysis of the cellulose component, and their detoxification is too costly for producing bulk commodities. Although tolerance to individual stress has been intensively studied, the progress seems less significant since microbial cells are inevitably suffering from multiple stresses simultaneously under production conditions.Zymomonas mobilis metabolizes sugar anaerobically through the Entner-Doudoroff pathway with less ATP generated for lower biomass accumulation to direct more sugar for product formation with improved yield, making it a suitable host to be engineered as microbial cell factories for producing bulk commodities with major costs from feedstock consumption. Self-flocculation of the bacterial cells presents many advantages, such as enhanced tolerance to environmental stresses, a prerequisite for achieving high product titers by using concentrated substrates. ZM401, a self-flocculating mutant developed from ZM4, the unicellular model strain of Z. mobilis, was employed in this work to explore the molecular mechanism underlying this self-flocculating phenotype. Comparative studies between ZM401 and ZM4 indicate that a frameshift caused by a single nucleotide deletion in the poly-T tract of ZMO1082 fused the putative gene with the open reading frame of ZMO1083, encoding the catalytic subunit BcsA of the bacterial cellulose synthase to catalyze cellulose biosynthesis. Furthermore, the single nucleotide polymorphism mutation in the open reading frame of ZMO1055, encoding a bifunctional GGDEF-EAL protein with apparent diguanylate cyclase/phosphodiesterase activities, resulted in the Ala526Val substitution, which consequently compromised in vivo specific phosphodiesterase activity for the degradation of cyclic diguanylic acid, leading to intracellular accumulation of the signaling molecule to activate cellulose biosynthesis. These discoveries are significant for engineering other unicellular strains from Z. mobilis with the self-flocculating phenotype for robust production. IMPORTANCE Stress tolerance is a prerequisite for microbial cell factories to be robust in production, particularly for biorefinery of lignocellulosic biomass to produce biofuels, bioenergy, and bio-based chemicals for sustainable socioeconomic development, since various inhibitors are released during the pretreatment to destroy the recalcitrant lignin-carbohydrate complex for sugar production through enzymatic hydrolysis of the cellulose component, and their detoxification is too costly for producing bulk commodities. Although tolerance to individual stress has been intensively studied, the progress seems less significant since microbial cells are inevitably suffering from multiple stresses simultaneously under production conditions. When self-flocculating, microbial cells are more tolerant to multiple stresses through the general stress response due to enhanced quorum sensing associated with the morphological change for physiological and metabolic advantages. Therefore, elucidation of the molecular mechanism underlying such a self-flocculating phenotype is significant for engineering microbial cells with the unique multicellular morphology through rational design to boost their production performance.