Let's use biology in ways that make sense, aka lean on the strengths of biology to accomplish tasks better than would be done through other through.
Things biology is good at: parallel processing, self-regeneration, communication, ...?
Food or Energy
Allergen free foods - custom garden toolbox
Material conversion (to fuel)
Bacteria that absorb toxins in air (sulfur dioxide, etc) or water (?)
Something to detect toxin concentrations in air - wouldn't use e. coli because they need to grow in aqueous environments
Organism that breaks down [something] (for removal of unwanted waste).
Health or Medicine
Invasin-based tumor-seeking bacteria.