Almost all the DNA came from edible plants.
Apparently, there are many well preserved documents from that time and place that discuss food, so the scientists have been able to match up the DNA with what plants were being cultivated and consumed, by animals and humans, in that time period.
The most exciting part - when we start to isolate human DNA from the bricks, we will be able to trace human and animal migration going back almost 10,000 years.
It will be interesting if they can pull human dna from the bricks because the ancient sumerians were an isolate people. They were not of the prevailing semetic stock of the time—as were the Akkadians to their north. From what I’ve read, its unclear just what kind of people the sumerians were or where they were from. Modern marsh arabs who inhabit the same area as the ancient sumerians —and even built their boats in the same way as ancient sumerians— have a similar mix of genetics as surrounding areas. So they don’t seem to be of the same stock as the original sumerians....anyhow that’s my understanding of what I’ve read so far on the subject. Maybe you have a different take?