The capacity to sense gradients efficiently and acquire information about the ambient environment confers many advantages such as facilitating movement toward nutrient sources or away from toxic chemicals. The amplified dispersal evinced by organisms endowed with motility is possibly beneficial in related contexts. Hence, the connections between information acquisition, motility, and microbial size are explored from an explicitly astrobiological standpoint. By using prior theoretical models, the constraints on organism size imposed by gradient detection and motility are elucidated in the form of simple heuristic scaling relations. It is argued that environments such as alkaline hydrothermal vents, which are distinguished by the presence of steep gradients, might be conducive to the existence of “small” microbes (with radii of ≳0.1 μm) in principle, when only the above two factors are considered; other biological functions (e.g., metabolism and genetic exchange) could, however, regulate the lower bound on microbial size and elevate it. The derived expressions are potentially applicable to a diverse array of settings, including those entailing solvents other than water; for example, the lakes and seas of Titan. The article concludes with a brief exposition of how this formalism may be of practical and theoretical value to astrobiology.

中文翻译：

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天体生物学环境中由梯度检测和扩散对微生物大小施加的理论约束

有效感知梯度和获取周围环境信息的能力赋予了许多优势，例如促进向营养源移动或远离有毒化学物质。具有运动性的生物体表现出的扩大扩散在相关背景下可能是有益的。因此，从明确的天体生物学角度探索了信息获取、运动性和微生物大小之间的联系。通过使用先前的理论模型，以简单的启发式缩放关系的形式阐明了梯度检测和运动性对生物体大小的限制。有人认为，碱性热液喷口等环境以陡峭梯度的存在为特征，原则上可能有利于“小”微生物（半径≥0.1 μm）的存在，当只考虑以上两个因素时；其他生物学功能（例如，代谢和基因交换）可以调节微生物大小的下限并提高它。派生的表达式可能适用于各种不同的环境，包括那些需要除水以外的溶剂的环境；例如，泰坦的湖泊和海洋。文章最后简要说明了这种形式主义如何对天体生物学具有实践和理论价值。