An important part of terraforming is the use of organisms, capable of reproduction. As long as they survive, they will multiply and affect the environment. In order for them to survive though, and affect the environment in a useful way, cutting edge bioengineering is needed.
The corporations who wish to apply biological means for terraforming are not alone either. The Greens party in the Terraforming Committee has the exact same focus and will do anything to make Mars green as soon as possible. If allowed to dominate the Committee, the Greens may even grant you a GMO Contract, compensating every biological project you launch!
The power struggle in the Terraforming Committee is sure to give the Greens some competition, not the least from the Reds, the true environmentalist party that wants to preserve Mars as the red planet. The Greens can gain strength from public support though, if the tides of time turn in their favor, such as a bioengineering boom where bio technology rapidly develops and new possibilities open up. Even so, there can be backlashes. Experimental lifeforms sponsored by the Greens may seem like a good idea, but may ultimately cause people to develop a disgust towards reckless terraforming.
The corporations are not alone on Mars. There are politicians, populations, and independent factions to take into account as well. And a big red planet that will not always cooperate.
Welcome to the turmoil of the human colonization of the solar system!