Magnetic resonance imaging of biofilm mass transport processes with gadolinium tracers

生物膜是由密集的细菌组成的城市，它们通过排泄粘稠的胶状物质而粘在一起。值得注意的是，这些黏糊糊的群落在一系列重要的生物技术应用中提供了巨大的潜力，例如污水处理、生物燃料生产和微生物燃料电池发电。它们在控制自然环境的化学方面也起着重要作用。然而，为了使生物膜发挥作用，反应物（例如污水处理厂的污水）必须有效地通过生物膜，在那里它们被细菌处理。值得注意的是，生物膜的工作速率是由这些反应物通过生物膜的速率控制的。因此，对于工程师和微生物学家来说，能够测量反应物供应的速率是至关重要的。至关重要的是，这些数据对我们理解生物膜的工作方式和提高生物膜性能的能力至关重要。虽然存在测量生物膜中运输的工具，但它们不能测量所需的所有参数（例如，有些仅限于高分子质量或低分子质量的反应物），有些是侵入性的，可能会破坏生物膜，改变结果。然而，磁共振成像（MRI）在弥合这一技术差距方面具有巨大的潜力。核磁共振成像是非侵入性的，因此它确实使我们能够看到生物膜内部，测量反应物的运动，而不会以任何方式损害生物膜。问题是，虽然MRI可以测量生物膜中水的运动（它可以用作其他低分子质量化合物运动的代理），但测量高分子质量分子是困难的。然而，这是可以改变的。通过用顺磁离子（钆）标记这些分子，分子突然变得很容易在MRI上看到。这项技术已经应用于临床研究，在临床研究中，钆被用来使分子在人类和其他哺乳动物组织中很容易地可见。在这里，我们的目标是证明顺磁标记的分子可以用来跟踪生物膜内的质量运输。在本研究中，我们将对来自实验室废水处理生物反应器和自然系统的生物膜中一系列商用钆标记分子的运输进行成像。将使用校准方案将MRI数据转换为实际钆浓度，使我们能够确定每个时间间隔内每个图像像素中的钆浓度。由此，计算每个生物膜中每个钆标记分子的扩散系数。3D模型也将用于生成扩散系数在每个生物膜的地图。如果成功，这项技术将是一个宝贵的工具，为微生物学家和工程师提供必要的运输数据，以利用这些复杂生物群落的全部力量。

Biofilms are dense cities of bacteria which adhere together by excreting a slimy, glue-like substance. Significantly, these slimy communities offer huge potential in an array of important biotechnological applications, such as sewage treatment, biofuel production and the generation of electricity in microbial fuel cells. They also play an important role in controlling the chemistry of the natural environment. For a biofilm to function, however, reactants (e.g. the sewage in sewage treatment plants) must be efficiently transported through the biofilm where they are processed by bacteria. Significantly, the rate at which the biofilm can operate is controlled by the rate at which these reactants move through the biofilm. Consequently, it is vital for engineers and microbiologists to be able to measure the rate of reactant supply. Critically, this data is essential to our understanding of the way biofilms work and our ability to enhance biofilm performance. Whilst tools for measuring transport in biofilms exist, they cannot measure all the parameters needed (for example, some are restricted to either high or low molecular mass reactants) and some are invasive, potentially damaging the biofilm, altering results. Magnetic resonance imaging (MRI), however, has tremendous potential to bridge this technology gap. MRI is non-invasive and so it quite literally enables us to look inside the biofilm and measure the movement of reactants without harming the biofilm in any way. Problematically, while MRI can measure the movement of water in biofilms (which can be used as a proxy for the movement of other low molecular mass compounds), measurement of high molecular mass molecules is difficult. This, however, can change. By labeling these molecules with a paramagnetic ion (in this case gadolinium), the molecule suddenly becomes easily visible with MRI. This technology is already applied in clinical research, where gadolinium is used to make molecules readily visible in human and other mammalian tissues. Here, we aim to demonstrate that paramagnetically labeled molecules can be used to track mass transport within biofilms. In this investigation, we will image the transport of a range of commercially available gadolinium labeled molecules in biofilms from laboratory wastewater treatment bioreactors and from natural systems. A calibration protocol will used to convert MRI data into actual gadolinium concentrations, enabling us to determine the concentration of Gd in each image pixel at each time interval. From this, diffusion coefficients for each gadolinium labeled molecule in each biofilm will be calculated. A 3D model will also be used the generate maps of diffusion coefficients throughout each biofilm. If successful, this technology would be an invaluable tool providing microbiologists and engineers alike with essential transport data needed to harness the full power of these complex biological communities.