Pro-longevity bacterial colanic acid regulates host mitochondrial dynamics through the endo-lysosomal system and transcriptional response Guo Hu1,2, Mooncheol Park1, and Meng Wang1,2 1Huffington Center on Aging, Baylor College of Medicine, Houston, TX 77030, USA; 2Department of Genetics and Genomics, Baylor College of Medicine, Houston TX 77030, USA. Irreversible and inevitable, aging occurs in every organism. Confronting soaring number of age-related diseases, to promote healthy aging is more urgent than ever. The gut microbiota effectively impacts the host’s physiological functions and the progression of aging. To detangle the complex network of host-microbiota interaction, we took advantages of the genetic tractability and the short lifespan of Caenorhabditis elegans to dissect the effect of microbial genetics on host longevity. Through systemically screening the Escherichia coli deletion library, our previous findings revealed that host C. elegans live longer when raised on the Lon protease deletion mutant of E. coli (∆lon) that overproduces exopolysaccharide – Colanic Acid (CA). We further discovered that CA is sufficient to promote longevity, and both the ∆lon and CA induce mitochondrial fission in the host. To understand how bacterial CA signals to host mitochondria, we hypothesized endo-lysosomal system facilitates CA uptake to host intestinal cells. We found that genetic knock-down of key regulators in the endocytic pathway fully suppressed the CA-induced mitochondrial fission and lifespan extension. Through profiling lysosomal proteomics, we found that CA increases the interaction of lysosomes with mitochondria. Furthermore, through transcriptome analysis, we identified several candidates of the hsf-1 transcription factor are up-regulated in the host raised on the ∆lon. RNAi inactivation of hsf-1 fully suppresses the lifespan extension and mitochondrial fission in the host caused by ∆lon. Together, our results suggest that the host’s endo-lysosome system may facilitate CA transportation into host’s intestinal cells and mediate the interaction with mitochondria, which consequently induces specific transcriptional responses to promote mitochondrial homeostasis and organism longevity. On-going studies will examine the targets of hsf-1 and the role of lipid metabolism in the CA-mediated longevity mechanism. Understanding the longevity mechanisms of bacterial CA will provide new strategies in probiotic development to combat with age-related diseases.