I’ve done at lot to promote the better side of the Earth’s microorganisms and bacteria in particular. Are they grateful? I have to say no! In September 2011, I became seriously ill, only to find out that the cause of the illness was a species of bacterium called Streptococcus mitis that had set up home on my aortic heart valve. The disease is called endocarditis and is fatal unless treated but fortunately for me, it was sensitive to penicillin (a disturbingly rare vulnerability in bacteria these days). I spent a month in hospital, and after a month’s intensive antibiotic therapy the unwanted bacterial guest had disappeared. I found out after the infection, that the same bacterium had also survived for over two years on the Surveyor 3 probe on the moon , so that a little lunar outpost of earthly biology and my heart are intimately linked over many hundreds of thousands miles of space. These are photographs of the bacteria in my blood, taken by an obliging hospital microbiologist. The bacteria are the small purple chains amongst the larger red objects which are my blood cells.