Dr Chris Smith and the Naked Scientist team present the latest science news, analysis and breakthroughs. This week: how scientists are getting to grips with the UK's E. coli outbreak. Lettuce leaves look likely to be the source, but how? We find out how atomic bomb tests have helped us to build a better picture of how much carbon plants can actually lock away. And why are scientists near Norwich sniffing the air for DNA? Plus we get to the root of how our changing climate is affecting trees.