Unlike my earlier post, the two things in the title are actually quite tightly linked.
Read a paper about the genome sequence of Bifidobacterium longum infantis. Basically this is a bacterial species that dominates the gastrointestinal tract of breast-fed infants. By cracking the genome sequence, the scientists found that it has a whole battery of genes for utilizing human milk oligosaccharides that lack a nutritive value to human infants. In other words, this little critter is specialized in growing on breast milk (oh boy do the infants consume a lot of that, just ask my wife, a proud mother of 3 breast-fed babies) and thus out-compete other potentially harmful bacteria in infants' gut, all the while without taking up the nutrients that infants need.
Very cool science story about human-bacteria co-evolution indeed.