Vertical transmission of tissue microbiota in Caenorhabditis elegans

The past forty-five years has witnessed Caenorhabditis elegans as the most significant model animal in life science since its discovery seventy years ago ^1,2 , as it introduced principles of gene regulated organ development, and RNA interference into biology ^3-5 . Meanwhile, it has become one of the lab animals in gut microbiota studies as these symbionts contribute significantly to many aspects in host biology ^6,7 . Meanwhile, the origin of gut microbiota remains debatable in human ^{8- 11} , and has not been investigated in other model animals. Here we show that the symbiont bacteria in C. elegans not only vertically transmit from the parent generation to the next, but also distributes in the worm tissues parallel with its development. We found that bacteria can enter into the embryos of C. elegans , a step associated with vitellogenin, and passed to the next generation. These vertically transmitted bacteria share global similarity, and bacterial distribution in worm tissues changes as they grow at different life stages. Antibiotic treatment of worms increased their vulnerability against pathogenic bacteria, and replenishment of tissue microbiota restored their immunity. These results not only offered a molecular basis of vertical transmission of bacteria in C. elegans , but also signal a new era for the mixed tissue cell-bacteria multi-species organism study.