Department of Biochemistry and Molecular Biology, The Pennsylvania State University , 305 South Frear Laboratory, University Park, Pennsylvania 16802, United States.
J Proteome Res. 2013 Oct 4;12(10):4316-26. doi: 10.1021/pr400266m. Epub 2013 Sep 9.
The bioavailability of terminal electron acceptors (TEAs) and other substrates affects the efficiency of subsurface bioremediation. While it is often argued that microorganisms exist under "feast or famine", in the laboratory most organisms are studied under "feast" conditions, whereas they typically encounter "famine" in nature. The work described here aims to understand the survival strategies of the anaerobe Geobacter sulfurreduces under TEA-starvation conditions. Cultures were starved for TEA and at various times sampled to perform global comparative proteomic analysis using iTRAQ to obtain insight into the dynamics of change in proteins/enzymes expression associated with change in nutrient availability/environmental stress. Proteins varying in abundance with a high level of statistical significance (p < 0.05) were identified to understand how cells change from midlog to (i) stationary phase and (ii) conditions of prolonged starvation (survival phase). The most highly represented and significantly up-regulated proteins in the survival phase cells are involved in energy metabolism, cell envelope, and transport and binding functional categories. The majority of the proteins were predicted to be localized in the cell membranes. These results document that changes in the outer and cytoplasmic membranes are needed for survival of Geobacter under starvation conditions. The cell shuts down anabolic processes and becomes poised, through changes in its membrane proteins, to sense nutrients in the environment, to transport nutrients into the cell, and to detect or utilize TEAs that are encountered. Under TEA-limiting conditions, the cells turned from translucent white to red in color, indicating higher heme content. The increase in heme content supported proteomics results showing an increase in the number of cytochromes involved in membrane electron transport during the survival phase. The cell is also highly reduced with minimal change in energy charge (ATP to total adenine nucleotide ratio). Nonetheless, these proteomic and biochemical results indicate that even under TEA starvation cells remain poised for bioremediation.
末端电子受体 (TEA) 和其他基质的生物可利用性会影响地下生物修复的效率。虽然人们常说微生物处于“饱食或饥饿”状态，但在实验室中，大多数生物都是在“饱食”条件下进行研究的，而在自然界中，它们通常会遇到“饥饿”。这里描述的工作旨在了解 TEA 饥饿条件下厌氧菌 Geobacter sulfurreducens 的生存策略。将培养物饥饿 TEAs，并在不同时间取样，使用 iTRAQ 进行全局比较蛋白质组分析，以深入了解与营养物质可用性/环境胁迫变化相关的蛋白质/酶表达变化的动态。鉴定丰度变化且具有高水平统计显著性 (p < 0.05) 的蛋白质，以了解细胞如何从中对数期转变为 (i) 静止期和 (ii) 长时间饥饿 (存活期) 条件。在存活期细胞中，表达水平最高且显著上调的蛋白质主要参与能量代谢、细胞包膜和运输及结合功能类别。大多数蛋白质预测定位于细胞膜中。这些结果表明，在饥饿条件下，Geobacter 细胞膜的内外层都需要发生变化才能存活。细胞停止合成代谢过程，并通过改变其膜蛋白，准备感应环境中的营养物质，将营养物质运输到细胞内，并检测或利用遇到的 TEA。在 TEA 限制条件下，细胞从半透明的白色变为红色，表明血红素含量增加。血红素含量的增加支持蛋白质组学结果表明，在存活期，参与膜电子传递的细胞色素数量增加。细胞也高度还原，能量电荷（ATP 与总腺嘌呤核苷酸的比值）几乎没有变化。尽管如此，这些蛋白质组学和生物化学结果表明，即使在 TEA 饥饿的情况下，细胞仍然为生物修复做好准备。
