You many never know if Mars has indigenous microscopic life.
The recent "Sky & Telescope" issue [Jan/2007] has an article
on the "possible" transfer of microbial life from Earth to Mars resulting
from the Gulf of Mexico asteroid impact.
So any bacteria found on Mars today maybe of Earth origin,
even halophiles.

It is halophiles [salt-loving bacteria] that I will focus on.
Could halophiles be found in the buried salt-deposits on the Columbia Hills
in Gusev Crater?
Have you seen those old Spirit images of the inside of the trenches it gouged out on the hills?
Weren't those white deposits salt deposits? And they were possibly buried deep enough for protection
from deadly UV rays and hydrogen peroxide sterilization.

Hmmm...If only Spirit had a more powerful microscope.

cheers.

Jacob