Bacteria encode their own post-mortem protein catabolism to enable nutrient recycling

For many organisms, death is a tangible, visible event. In bacteria, death can be a natural or an induced process 1. Death permits genes conferring a survival advantage to be selected in a bacterial population. Furthermore, biomolecule recycling from dead bacteria is crucial under nutrient limitation across ecosystems 2. However, the underlying mechanisms that permit macromolecule recycling after bacterial death are largely unknown. Here, we show that bacteria encode their own post-mortem protein catabolism. We observed that live bacteria cannot recycle the lysates of dead bacteria from which the Lon protease-encoding lon gene is deleted. The nutrient recycling function of the Lon protease manifests itself after the death of the bacteria that produced it and is ATP-independent. We demonstrate that the post-mortem Lon protease is a cooperative trait susceptible to exploitation by cheating 3. However, we propose that, in addition to a kin selected benefit of helping related cells, the fitness benefit of cheating is outweighed by the fitness benefit of producing Lon protease under stress. This finding of an unexpected post-mortem biochemistry fundamentally revises our understanding of the nutrient recycling process. Further, we suggest a solution to an evolutionary puzzle of how a phenotype that manifests after death can exist in a population. Nutrient recycling is a vital aspect of all ecosystems, and our results demonstrate a potential new molecular target for modulating bacterial growth that does not directly target the live bacteria.