Martin Blaser isn’t just worried that some people are short of important microbes. He is deeply concerned that some of these species may be disappearing altogether. Take Helicobacter pylori, his favourite bacterium. Blaser was partly responsible for ruining its reputation in the 1990s. Scientists already knew that it caused stomach ulcers, but he and others confirmed that it increases the risk of stomach cancer, too. Only later did he realise the microbe’s beneficial side: it reduces the risk of reflux (a condition where stomach acid gurgles back into the throat), oesophageal cancer, and
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