Releasing the spores

The object being removed by David in the early trailer is clear in a appearance, but the goo in the official trailer is dark. It is different from the substance that has infected grimacing crew member, and the substance flowing through the Engineer's body. Are we seeing a seed, a symbiotic being, or just a pathogen. Has the Engineers galactic labs been a way to isolate a cure for very potent virus, while pursuing new avenues of bio-mechanical development. And while laying dormant in a temporary suspended animation, we arrive at their current base of operation with said virus and our inquisitive and greedy nature.