Levy Amalie T, Lee Kelvin H, Hanson Thomas E
Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware, USA Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, USA.
School of Marine Science and Policy, University of Delaware, Newark, Delaware, USA Department of Biological Sciences, University of Delaware, Newark, Delaware, USA Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, USA
Appl Environ Microbiol. 2016 Oct 14;82(21):6431-6439. doi: 10.1128/AEM.02111-16. Print 2016 Nov 1.
Microbial sulfur metabolism, particularly the formation and consumption of insoluble elemental sulfur (S), is an important biogeochemical engine that has been harnessed for applications ranging from bioleaching and biomining to remediation of waste streams. Chlorobaculum tepidum, a low-light-adapted photoautolithotrophic sulfur-oxidizing bacterium, oxidizes multiple sulfur species and displays a preference for more reduced electron donors: sulfide > S > thiosulfate. To understand this preference in the context of light energy availability, an "energy landscape" of phototrophic sulfur oxidation was constructed by varying electron donor identity, light flux, and culture duration. Biomass and cellular parameters of C. tepidum cultures grown across this landscape were analyzed. From these data, a correction factor for colorimetric protein assays was developed, enabling more accurate biomass measurements for C. tepidum, as well as other organisms. C. tepidum's bulk amino acid composition correlated with energy landscape parameters, including a tendency toward less energetically expensive amino acids under reduced light flux. This correlation, paired with an observation of increased cell size and storage carbon production under electron-rich growth conditions, suggests that C. tepidum has evolved to cope with changing energy availability by tuning its proteome for energetic efficiency and storing compounds for leaner times.
How microbes cope with and adapt to varying energy availability is an important factor in understanding microbial ecology and in designing efficient biotechnological processes. We explored the response of a model phototrophic organism, Chlorobaculum tepidum, across a factorial experimental design that enabled simultaneous variation and analysis of multiple growth conditions, what we term the "energy landscape." C. tepidum biomass composition shifted toward less energetically expensive amino acids at low light levels. This observation provides experimental evidence for evolved efficiencies in microbial proteomes and emphasizes the role that energy flux may play in the adaptive responses of organisms. From a practical standpoint, our data suggest that bulk biomass amino acid composition could provide a simple proxy to monitor and identify energy stress in microbial systems.
微生物硫代谢，特别是不溶性元素硫（S）的形成和消耗，是一种重要的生物地球化学引擎，已被应用于从生物浸出、生物采矿到废物流修复等各种领域。嗜温绿菌（Chlorobaculum tepidum）是一种适应低光照的光合自养硫氧化细菌，能氧化多种硫物种，并且对还原性更强的电子供体表现出偏好：硫化物>S>硫代硫酸盐。为了在光能可用性的背景下理解这种偏好，通过改变电子供体身份、光通量和培养持续时间，构建了光合硫氧化的“能量景观”。分析了在此“能量景观”中生长的嗜温绿菌培养物的生物量和细胞参数。根据这些数据，开发了一种用于比色蛋白质测定的校正因子，能够更准确地测量嗜温绿菌以及其他生物的生物量。嗜温绿菌的总氨基酸组成与能量景观参数相关，包括在较低光通量下倾向于使用能量成本较低的氨基酸。这种相关性，再加上在富电子生长条件下观察到的细胞大小增加和储存碳产生增加，表明嗜温绿菌已经进化到通过调整其蛋白质组以提高能量效率并储存化合物以备不时之需，来应对不断变化的能量可用性。
微生物如何应对和适应不断变化的能量可用性是理解微生物生态学和设计高效生物技术过程的一个重要因素。我们通过一个析因实验设计探索了模式光合生物嗜温绿菌的反应，该设计能够同时对多种生长条件进行变化和分析，即我们所说的“能量景观”。在低光照水平下，嗜温绿菌的生物量组成向能量成本较低的氨基酸转变。这一观察结果为微生物蛋白质组中进化出的效率提供了实验证据，并强调了能量通量在生物体适应性反应中可能发挥的作用。从实际角度来看，我们的数据表明，总生物量氨基酸组成可以提供一个简单的指标来监测和识别微生物系统中的能量压力。
