Bacterial World - Microbes That Rule Our World

If two people kissing for ten seconds exchange 700 species of millions of bacteria, can you imagine how many of these microbes live on earth? Bacteria came to existence 3.5 billion years ago and since then have been an intrinsic part of most of the species helping them breath, digest and reproduce. Their indispensability to every organism has led scientists to ask - are bacteria driving life on earth?