Cell Aggregation and Aerobic Respiration Are Important for Zymomonas mobilis ZM4 Survival in an Aerobic Minimal Medium
Cell Aggregation and Aerobic Respiration Are Important for Zymomonas mobilis ZM4 Survival in an Aerobic Minimal Medium
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DOI：
10.1128/aem.00193-19
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发表时间：
2019-05-01
影响因子：
4.4
通讯作者：
McKinley, James B.
中科院分区：
文献类型：
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作者：
Jones-Burrage, Sara E.;Kremer, Timothy A.;McKinley, James B.
运动发酵单胞菌从葡萄糖生产乙醇的产量接近理论最大产量，使其成为工业乙醇生产中酿酒酵母的潜在替代品。一个潜在有用的工业特征是能够形成称为絮凝物的多细胞聚集体，它可以快速沉降，并且比单细胞表现出更高的对有害化学物质的抵抗力。虽然已经描述了自发形成絮状运动发酵单胞菌突变体，但对于诱导运动发酵单胞菌絮状形成的自然条件或所涉及的遗传因素知之甚少。在这里，我们发现野生型运动发酵单胞菌响应有氧生长条件形成絮凝物，但仅在基本培养基中。我们鉴定了一个纤维素合酶基因簇和一个二鸟苷酸环化酶，它们对于絮凝物的形成和在最低需氧培养基中的存活至关重要。我们还发现NADH脱氢酶2是有氧呼吸链的关键组成部分，对于在最低需氧培养基中的生存非常重要，为该酶提供了生理作用，而此前已发现该酶在富氧培养基中是不利的。在基本培养基中补充维生素也能促进存活，但不会抑制絮凝物的形成。 重要性 运动发酵单胞菌细菌以其厌氧发酵生活方式而闻名，在这种生活方式中，它将葡萄糖转化为乙醇，其产量超过了酵母。然而，运动发酵单胞菌也具有有氧生活方式，这让研究人员感到困惑，因为它的生长不良、有毒乙酸和乙醛的积累以及不利于有氧生长的呼吸酶的属性。在这里，我们证明了运动发酵单胞菌的一种主要呼吸酶和形成多细胞聚集体（称为絮凝体）的能力对于生存很重要，但仅限于在含有生长所需的最低营养成分的培养基中的有氧生长期间。维生素或酵母提取物等补充剂可促进有氧生长，并在某些情况下抑制絮凝物的形成。我们认为运动发酵单胞菌可能需要有氧呼吸和絮凝物形成才能在缺乏酵母提取物等补充剂中的保护因子的自然环境中生存。
Zymomonas mobilis produces ethanol from glucose near the theoretical maximum yield, making it a potential alternative to the yeast Saccharomyces cerevisloe for industrial ethanol production. A potentially useful industrial feature is the ability to form multicellular aggregates called flocs, which can settle quickly and exhibit higher resistance to harmful chemicals than single cells. While spontaneous floc-forming Z mobilis mutants have been described, little is known about the natural conditions that induce Z. mobilis floc formation or about the genetic factors involved. Here we found that wild-type Z. mobilis forms flocs in response to aerobic growth conditions but only in a minimal medium. We identified a cellulose synthase gene cluster and a single diguanylate cyclase that are essential for both floc formation and survival in a minimal aerobic medium. We also found that NADH dehydrogenase 2, a key component of the aerobic respiratory chain, is important for survival in a minimal aerobic medium, providing a physiological role for this enzyme, which has previously been found to be disadvantageous in a rich aerobic medium. Supplementation of the minimal medium with vitamins also promoted survival but did not inhibit floc formation.IMPORTANCE The bacterium Zymomonas mobilis is best known for its anaerobic fermentative lifestyle, in which it converts glucose into ethanol at a yield surpassing that of yeast. However, Z. mobilis also has an aerobic lifestyle, which has confounded researchers with its attributes of poor growth, accumulation of toxic acetic acid and acetaldehyde, and respiratory enzymes that are detrimental for aerobic growth. Here we show that a major Z mobilis respiratory enzyme and the ability to form multicellular aggregates, called flocs, are important for survival, but only during aerobic growth in a medium containing a minimum set of nutrients required for growth. Supplements, such as vitamins or yeast extract, promote aerobic growth and, in some cases, inhibit floc formation. We propose that Z mobilis likely requires aerobic respiration and floc formation in order to survive in natural environments that lack protective factors found in supplements such as yeast extract.