Approaches to distinguishing bacteria from mineral particles in microscopic imaging IEEE aerospace conference

Biologists use microscopy as the gold standard for identification of the presence of microbial life in terrestrial environments. Even when DNA analysis is used to identify strains and genetic population diversity, microscopic imaging is typically used to verify the presence of live organisms and obtain information about their sizes and morphologies. With identified microbes, a variety of microscopic techniques, particularly fluorescence imaging, are used for identification of features such as proteins, lipids, and nucleic acids. For identification of microbial life in situ, the challenge is extended to include discrimination of potential live cells from non-living objects of similar size. We present here a survey of analyses that can be made from microscopic images to make this distinction. The techniques include measurement of refractive index, Brownian motion, gravitational settling, autofluorescence, induced fluorescence, and induction of various forms of taxis.

1. Introduction

NASA has recently announced plans for a potential Europa Lander mission, with science goals that would include the search for extant life. Any extant life on Europa or elsewhere in the solar system is likely to be microbial, with maximum dimensions in the range of 0.2 to and at concentrations of the order of 100/mL. There will likely be additional background material of abiotic origin, with many particles in a similar size range. The ability to discriminate between such particles and possible living organisms would be a key requirement of any suite of instruments intended to detect extant life. In the case of moons orbiting outer planets, such as Enceladus, Europa, or Ganymede, the limits of mission data volume, data rate, and round trip time for communications make it desirable to allow an on-board computer to make preliminary evaluation of data in order to prioritize transmission of the most compelling data.