This image is not final, it's really just an idea. Acetogenic bacteria can live on carbon dioxide, but in order to do so, a key reaction must take place. It seems simple - a methyl group is transferred from folate to vitamin B12 (the molecule shown here). But a number of proteins must organize themselves and undergo what the authors of this work call "molecular gymnastics". They used X-ray crystallography to obtain a complete picture of this process, and remarkably show that the requisite conformational changes even occur in the protein crystals. To get the photo for this piece, I went to the pedestrian overpass at 5:00pm last Friday expecting the freeway to look like a parking lot. I found myself ambivalent about what I saw. The photo is not as striking, but I suppose I should be happy for the earth?