nowhow team explains: Soil bacteria and fungi live by digesting and recycling dead plant material such as leaves and seed cases. Obviously it is impossible for the bacteria to hide their food supply and therefore it is believed that they lace surrounding food with compounds that are toxic to those of other species.

A second explanation is that antibiotic production is rooted in the plant material that is the food source. This material is typically carbon-rich and nitrogen-poor.

Most common antibiotics are carbon-rich polymers made by enzymes that strongly resemble those that normally make saturated fats.

The building blocks of these polymers are often exactly the same as those used to make saturated fats. So perhaps we are seeing a form of clever bacterial bulimia: faced with a situation in which the bacteria literally swim in a soup of fat-producing carbon compounds, the bacteria turn these compounds not into fatty lipids but into their structurally close relations, the antibiotics.

These are then excreted and, should they prove to have a useful, coincidental effect, the bacteria thrive. According to this theory, the myriad useful antibiotics, anti-cancer agents and anti-parasitic agents that soil organisms produce is just a by-product of a bad diet.

The question was sent by Rajarshi Biswas from Calcutta 64