Bradley James A, Amend Jan P, LaRowe Douglas E
Department of Earth Sciences, University of Southern California, Los Angeles, CA, United States.
Department of Biological Sciences, University of Southern California, Los Angeles, CA, United States.
Front Microbiol. 2018 Feb 13;9:180. doi: 10.3389/fmicb.2018.00180. eCollection 2018.
Marine sediments constitute one of the most energy-limited habitats on Earth, in which microorganisms persist over extraordinarily long timescales with very slow metabolisms. This habitat provides an ideal environment in which to study the energetic limits of life. However, the bioenergetic factors that can determine whether microorganisms will grow, lie dormant, or die, as well as the selective environmental pressures that determine energetic trade-offs between growth and maintenance activities, are not well understood. Numerical models will be pivotal in addressing these knowledge gaps. However, models rarely account for the variable physiological states of microorganisms and their demand for energy. Here, we review established modeling constructs for microbial growth rate, yield, maintenance, and physiological state, and then provide a new model that incorporates all of these factors. We discuss this new model in context with its future application to the marine subsurface. Understanding the factors that regulate cell death, physiological state changes, and the provenance of maintenance energy (i.e., endogenous versus exogenous metabolism), is crucial to the design of this model. Further, measurements of growth rate, growth yield, and basal metabolic activity will enable bioenergetic parameters to be better constrained. Last, biomass and biogeochemical rate measurements will enable model simulations to be validated. The insight provided from the development and application of new microbial modeling tools for marine sediments will undoubtedly advance the understanding of the minimum power required to support life, and the ecophysiological strategies that organisms utilize to cope under extreme energy limitation for extended periods of time.
海洋沉积物是地球上能量限制最为严苛的栖息地之一，其中的微生物能以极其缓慢的新陈代谢在超长的时间尺度上存续。这一栖息地为研究生命的能量极限提供了理想环境。然而，对于那些能够决定微生物是生长、休眠还是死亡的生物能量学因素，以及那些决定生长与维持活动之间能量权衡的选择性环境压力，我们还了解得不够充分。数值模型对于填补这些知识空白至关重要。然而，模型很少考虑微生物可变的生理状态及其能量需求。在此，我们回顾了已有的关于微生物生长速率、产量、维持和生理状态的建模架构，然后提供了一个整合所有这些因素的新模型。我们结合其未来在海洋次表层的应用来讨论这个新模型。理解调节细胞死亡、生理状态变化以及维持能量来源（即内源性与外源性代谢）的因素，对于该模型的设计至关重要。此外，对生长速率、生长产量和基础代谢活性的测量将使生物能量学参数得到更好的限制。最后，生物量和生物地球化学速率测量将使模型模拟得到验证。新的海洋沉积物微生物建模工具的开发与应用所提供的见解，无疑将推动我们对维持生命所需的最小能量，以及生物体在极端能量限制下长期应对所采用的生态生理策略的理解。
