Abstract
The detection of microbial colonization in geophysical systems is becoming of interest in various disciplines of Earth and planetary sciences, including microbial ecology, biogeochemistry, geomicrobiology, and astrobiology. Microorganisms are often observed to colonize mineral surfaces, modify the reactivity of minerals either through the attachment of their own biomass or the glueing of mineral particles with their mucilaginous metabolites, and alter both the physical and chemical components of a geophysical system. Here, we hypothesise that microorganisms engineer their habitat, causing a substantial change to the information content embedded in geophysical measures (e.g., particle size and space-filling capacity). After proving this hypothesis, we introduce and test a systematic method that exploits this change in information content to detect microbial colonization in geophysical systems. Effectiveness and robustness of this method are tested using a mineral sediment suspension as a model geophysical system; tests are carried out against 105 experiments conducted with different suspension types (i.e., pure mineral and microbially-colonized) subject to different abiotic conditions, including various nutrient and mineral concentrations, and different background entropy production rates. Results reveal that this method can systematically detect microbial colonization with less than 10% error in geophysical systems with low-entropy background production rate.
Highlights
Microorganisms have always been found to inhabit most of the natural geophysical systems on Earth even in extreme environmental conditions
Note that biomass-affected suspensions had S(Q[L]|P[L]) and S(Q[d0]|P[d0]) relatively similar to those of biomass-free suspensions at G > 64 s−1, implying that the capacity for microorganisms to increase the entropy of a geophysical system had been constrained by high turbulence energy dissipation rates
We put forth a method that makes use of measurable physical characteristics to detect microbial colonization in a geophysical system by exploiting the capability of microorganisms to change the information content of their habitat
Summary
Microorganisms have always been found to inhabit most of the natural geophysical systems on Earth even in extreme environmental conditions (e.g., hyperthermophile, piezophile, alkaliphile, and acidophile[1]). Studies have shown that the characteristics of soil crusts and sediment formed through microbiological activity are very different from those formed by physical processes[6, 14, 15] These observations led us to hypothesise that microorganisms, when engineering their habitat, can change the information content and orderliness of a geophysical system to a state different from its abiotic state. Lovelock[16, 17] suggests the possibility of using information embedded in a system to detect biological activity, this life detection theory has not yet been tested and validated to its entirety It has not yet been systematically tested if measures or quantifiers of geophysical characteristics can provide sufficient information for life detection; or, if background entropy production and other abiotic factors The effectiveness and robustness of the proposed approach was tested and validated against 105 experiments conducted with different sediment suspension types (e.g., pure mineral suspensions, nutrient-affected mineral suspensions, and nutrient-affected and microbially-colonized suspensions) in waters subject to different mineral and nutrient concentrations, and different background entropy production rates
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