A Worm Autopsy: What Actually Kills Worms?

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C. elegans appear to die primarily as a result of bacterial invasion

Autopsy studies have contributed a lot to medical knowledge. For example, Alzheimer’s disease was described a century ago by Dr. Alois Alzheimer after he autopsied the brain of one of his patients. More recently, autopsies conducted in supercentenarians, people over the age of 110, have discovered that the majority of them died from a rare disease called senile TTR amyloidosis.    In a new paper published in Nature Communications authors identified two types of death in worms. Worms dying early (around 12 days) with a swollen pharynx (they termed these P deaths) and worms dying at an older age (around 22 days) with an atrophied pharynx (they termed these p deaths). The pharynx is the connection between the mouth and the intestine of the worm (see image).  Next the authors carefully excised the pharynx from the animals. Pharynxes from animals that had died with a swollen pharynx were found to contain more E. coli bacteria. Worms are grown on E.coli as a food source but it is also known that these bacteria can invade the worm and limit its lifespan. Next, the authors added an antibiotic to the culture media or killed the bacteria with UV-light. Under these conditions P deaths were completely eliminated and the lifespan was extended.    The authors discovered that the high pumping rate in early adulthood probably causes wounds in the pharynx which can subsequently be invaded by the dietary bacteria. In some worms, for still unknown reasons, the bacterial infection is contained and the animals have a long lifespan while in others the infection worsens and P death follows. Interestingly, mutants with a reduced pumping rate had a significant lower chance of P death. One of the tested mutants was eat-2, a frequently used ‘genetic version of calorie restriction’. Hence, these results suggest that the longevity of the eat-2 mutant is largely caused by a reduction in bacterial infection and not by a reduced nutrient intake.    Zhao Y et al. (2017). Two forms of death in ageing Caenorhabditis elegans. Nature Commun 8: 15458.