ASTID

Unambiguous Detection of Extraterrestrial Microbial Metabolic Activity Using Differential Electrochemical Detection (2)

PI: Samuel Kounaves

The ideal microbial life detection instrument for use beyond Earth must be based on absolutely minimal assumptions about the nature of the organism. For example, the organic chemistry, internal structure, and internal components of microbial life might be significantly different from terrestrial microorganisms and cannot be accurately predicted. However two properties of microbial life that are likely to be universal and require no prior
assumptions of specific properties are (1) an ability to reproduce itself in a self regulated form, and (2) the ability to maintain some degree of isolation of its internal compartment from the surrounding environment. In addition, we will assume that any microbial life will require water and carbon. During the process of reproduction, the organism’s metabolism, mediated by its membrane processes, will, by necessity change the surrounding chemical and redox environment. Thus, an appropriate instrument must be capable of detecting such changes, rapidly and free of extraneous or non-biogenic interferences. We propose to demonstrate a new detection technique via a prototype instrument dubbed the Microbial Detection Array (MDA). A substantial portion of the MDA, the sensor array, is heritage-based and already space qualified. The MDA is designed to provide a response to minute chemical and physical changes occurring in one of two identical chambers via differentially monitored electrochemical sensor arrays. Minimal metabolism will alter the physico-chemical steady state in one chamber such that a difference between the sensor arrays will result in a signal. This detection system makes minimal assumptions about the nature of the microorganism, assuming only that after addition of water the it will reproduce and in the process cause changes in its immediate surroundings by consuming or generating, metabolizing, and transporting in both directions, a number of molecules and ionic species. The experiment begins by placing a
homogenized split-sample of soil into each chamber, adding pure water,
sterilizing at a high temperature incompatible with any form of terrestrial life, and zeroing. In the absence of any metabolically active organism in either chamber, no signal will be detected. The “inocula-tion” of one chamber with a minimal of viable microorganisms, which proceed to multiply, will produce a significant metabolically generated disequilibrium in the system (compared to the control) to provide a detectable signal. Replication of the experiment and positive results would lead to the conclusion of biologically induced changes. Changes resulting from non-biological chemical reactions of whatever type are canceled out by the control. The replication of the procedure, split
sample, and minimal inoculation protocol, eliminate non-biogenic causation. In addition to detecting microbes, the sensor array will also characterize the chemical composition and electrochemistry of the sample.