The Science of Science Fiction: Microbe Nation

I was reading the July issue of Scientific American earlier when I came across this article on microscopic giants. Microbes make up at least half of the oceans' total biomass; it may even be as high as ninety percent. A single liter (about one-fifth of a gallon) of ocean water can contain over a billion microbes--I guess this is the real reason you're not supposed to drink seawater! But the point I found most inspiring from a science fiction perspective was the discovery of a mat of microbes off the coast of South America. The mat is estimated to be the size of Greece. What could you do with so many microbes? Could you create a mat solid enough to indeed form a new nation? How about a floating farm or a natural sponge to digest spilled oil? What if that mat was really a single enormous feature? What ideas can you come up with?