Motile bacteria like proteus leave traces along their path Engineering these bacteria to make path traces of just the right width to diffract light plus also engineering them to make goo (kind of like biofilm) would create sparkly diffraction tracks possibly visible to the human eye which can detect
just one photon but presumably require more to register at the brain
Anyway just one proteus bacteria could make itself visible if it left the right width goo trail but also had the behavior of going on a raster path
--->---->--->---->--->(@@@@@@@)
---<----<---<---<---<-
--->--->--->--->--->--^
at refractive width this would be all glittery like a CD
PLUS proteus move thus the glittery CD appearance would shift n change as you watched it like a bacterial trip visual
There is an additional socially beneficial use I think the raster path would change on exposure to various trace chemicals thus it is potentially a sensitive massively parallel visual chemodetector like um, to detect naughty things at airports
I thought of this as I was trying to think of a new type of bacterial talent The ability to actually attract a larger host or food even as just one bacteria insects learn things thus I thought if the refractive bacteria were beneficial plus visible to insects they would recognize then transport n host the bacteria One thought was that bacteria that make Octopamine which is the reward chemical of honeybee brains would be favored with bee visits thus rapidly spreading the refractive bacteria possibly from a single bacterium octopamine releasing cytokines might be even more effective at tiny doses
the colonies would look like little glittery liquid gems
but If it escapes then there is sparkly iridescent goop on a dumpster near you