As another example of probably fine GMO, I've just come across a review highlighting the urgency of engineering microbes able to assimilate lactose (to use whey and other wastes of dairy industry as substrates for exopolysaccharide synthesis). They also argue for creating (more) efficient EPS-producers culturable on cellulose-containing wastes, although that does seem to me rather more dangerous, on technical glycerole after biodiesel production, etc.