A GLIMPSE TO BLACK BACTERIA...

Billion year-old bacteria. Credit: BBC Bacteria. Mars. You might not see much of a relationship between the two terms. But according to leading scientists from the Mars Society and other organizations, bacteria are as important to Mars as bacteria in our stomachs or in our medicine or even our beer. They played a leading role in the first ecosystem on Earth and will do so again on the red planet. The simple fact is that without bacteria, Mars will never be terraformed.
Bacteria can be supplied with Carbon, Oxygen, Hydrogen, Nitrogen, and Phosphorus, the basic components in biochemistry and all in abundance on Mars. Carbon can be found in the copious supply of carbon dioxide in the atmosphere. Oxygen can be found almost anywhere, mainly in carbon dioxide, aluminum oxide, iron oxide (rust), water, or the very little bit in the present Martian atmosphere. Hydrogen could be found in underground aquifers of water, two miles underground. Nitrogen can be found in the Martian soil and so can phosphorus. These amounts should be sufficient to substance our bacteria and then later, plants and animals.
There are several types of bacteria. There are aerobic bacteria that require oxygen to survive, and anaerobic bacteria that can live with or without oxygen. Obviously on Mars with very little oxygen present, anaerobic bacteria will be the bacteria of choice. Next are heterotrophic bacteria that use other organisms for energy and autotrophs that produce their own food through photosynthesis. With sunlight readily available on the surface, autotrophs will most likely be used. Utilizing the Keener Black Chlorophyll theory, black bacteria would absorb much more energy than green ones. The red planet would become the black planet as billions of bacteria covered the entire surface.
So what would they do on the surface? They could pump water up from underground aquifers by the same way we drink water upside-down. By releasing diatomic Oxygen (O2, the kind we breathe) into the atmosphere, they would be making mars livable. On the other hand, if we would prefer, we could pump Triatomic Oxygen (O3, ozone) to heat the planet, or even a combination of both. Bacteria could also pump other Greenhouse gases into the atmosphere. They could also be used in life support to purify water and air.

Glow-in-the dark chain. Credit: Luxgene They could be used as a building material or could mine deep underground like they already do here on earth. Coral is a good example of a hard covering material manufactured in the depths of the ocean. If we laminated coral-like bacteria together in different layers I think we could build with them, like a growing concrete. They could also mine iron and aluminum for our use. We could use it as a building material or sell it on Earth as Mars' first trading export.
We could manufacture bacteria DNA to accomplish any of these tasks using biological engineering. This is a technique long used that stems back from the days when a horse and donkey were first combined to produce a stronger, more efficient mule. When combining traits from different organisms with bacterial DNA we would be doing the same thing. We would have to make bacteria divide and grow at a set pace, so as not to overrun the planet with our creations. Kim Stanley Robinson suggests manufacturing a "suicide gene" that would kick in whenever a bacteria reproduced x amount of times. In addition, we would have to make them interlock, like moss, and cling to the rocks, ground, and/or something so not to be blown away during a Martian dust storm.
One of the Surveyors sent to the moon was imperfectly sterilized. When we landed on the moon the Apollo astronauts brought back pieces of the craft and found that when fed on Earth, the Bacteria started to grow and thrive. Bacteria are the most adaptive and hardy organism known to man, and I see no reason why we could not make them survive on Mars.