Gas vesicles (GVs) are cylindrical or spindle-shaped protein nanostructures filled with air and used for flotation by various cyanobacteria, heterotrophic bacteria, and Archaea. Recently, GVs have gained interest in biotechnology applications due to their ability to serve as imaging agents and actuators for ultrasound, magnetic resonance and several optical techniques. The diameter of GVs is a crucial parameter contributing to their mechanical stability, buoyancy function and evolution in host cells, as well as their properties in imaging applications. Despite its importance, reported diameters for the same types of GV differ depending on the method used for its assessment. Here, we provide an explanation for these discrepancies and utilize electron microscopy (EM) techniques to accurately estimate the diameter of the most commonly studied types of GVs. We show that during air drying on the EM grid, GVs flatten, leading to a ~1.5-fold increase in their apparent diameter. We demonstrate that GVs' diameter can be accurately determined by direct measurements from cryo-EM samples or alternatively indirectly derived from widths of flat collapsed and negatively stained GVs. Our findings help explain the inconsistency in previously reported data and provide accurate methods to measure GV dimensions.

中文翻译：

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通过电子显微镜测量气体囊泡尺寸

气体囊泡（GV）是充满空气的圆柱形或纺锤形蛋白质纳米结构，可用于各种蓝细菌，异养细菌和古细菌进行浮选。近年来，由于GV能够用作超声，磁共振和多种光学技术的成像剂和致动器，因此它们在生物技术应用中引起了人们的兴趣。GV的直径是决定其机械稳定性，浮力功能和宿主细胞进化以及它们在成像应用中的性能的关键参数。尽管它很重要，但相同类型GV的报告直径因其评估方法而异。这里，我们提供了这些差异的解释，并利用电子显微镜（EM）技术准确估算了最常研究的GV类型的直径。我们显示，在EM格栅上风干期间，GV变平，导致其表观直径增加约1.5倍。我们证明，可以通过直接从冷冻EM样品进行直接测量来准确确定GV的直径，或者可以间接地从平坦塌陷和负染GV的宽度间接得出。我们的发现有助于解释先前报告的数据的不一致之处，并提供测量GV尺寸的准确方法。直径可以通过直接从冷冻EM样品中进行测量来准确确定，也可以间接地从扁平塌陷和阴性染色的GV的宽度中间接得出。我们的发现有助于解释先前报告的数据的不一致之处，并提供测量GV尺寸的准确方法。直径可以通过直接从冷冻EM样品中进行测量来准确确定，也可以间接地从扁平塌陷和阴性染色的GV的宽度中间接得出。我们的发现有助于解释先前报告的数据的不一致之处，并提供测量GV尺寸的准确方法。