Data from: Extant life detection using label-free video microscopy in analog aquatic environments

The ability of microbial morphology, active motion, and refractive index
to serve as biosignatures was investigated by in situ video microscopy in
a wide range of extreme field sites where such imaging had not previously
been performed. These sites allowed for sampling seawater, sea ice brines,
cryopeg brines, hypersaline pools and seeps, hyperalkaline springs, and
glaciovolcanic cave ice. In all samples, except the cryopeg brine, active
motion was observed without any sample treatment. Active motion was
observed in the cryopeg brines when samples were subjected to temperature
gradient above in situ. Levels of prokaryotic motility were, in general,
low in the field samples collected at temperatures < 4ºC.
Non-motile cells could be distinguished from microminerals by differences
in passive motion (e.g., density measured by sinking/floating), refractive
index and/or absorbance, or morphology in the case of larger eukaryotes.
Dramatic increases in the fraction of motile cells were seen with simple
stimuli such as warming or the addition of L-serine. Chemotaxis and
thermotaxis were also observed in select samples. An open-source,
autonomous software package with computational requirements that can be
scaled to spaceflight computers was used to classify the data. These
results demonstrate the utility of volumetric light microscopy for life
detection, but also suggest the importance of developing methods to
stimulate cells in situ and process data using the restrictions imposed by
mission bandwidth, as well as instruments to capture cell-like objects for
detailed chemical analysis.