Astrobiology (general)

Theoretical Constraints Imposed By Gradient Detection And Dispersal On Microbial Size In Astrobiological Environments

By Keith Cowing
February 10, 2021
Filed under
Theoretical Constraints Imposed By Gradient Detection And Dispersal On Microbial Size In Astrobiological Environments
The signal-to-noise ratio (S/N) as a function of the cell size R (in µm) for Earth-analogs. The curves reflect the various ambient gradients and attendant pathways for perceiving them. Red, green and blue are used to demarcate chemical, thermal and light gradients, respectively. The dotted and dashed lines (for all colours) indicate the spatial and temporal means for identifying gradients. The solid blue line represents the S/N for detecting the direction of the light source via gradient sensing. All results were obtained by combining (9) with (2)-(8).

The capacity to sense gradients efficiently and acquire information about the ambient environment confers many advantages like 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 paper concludes with a brief exposition of how this formalism may be of practical and theoretical value to astrobiology.

Manasvi Lingam

Comments: Accepted for publication in Astrobiology; 39 pages; 2 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Biological Physics (; Cell Behavior (q-bio.CB)
Cite as: arXiv:2102.05009 [astro-ph.EP] (or arXiv:2102.05009v1 [astro-ph.EP] for this version)
Submission history
From: Manasvi Lingam
[v1] Tue, 9 Feb 2021 18:23:36 UTC (134 KB)
Astrobiology, Microbiology,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻