[
International Worm Meeting,
2021]
Aging in C. elegans is unusual in terms of the severity and early onset of senescent pathology, particularly affecting organs involved in reproduction (1-3). For example, in post-reproductive hermaphrodites, intestinal biomass is converted into yolk leading to intestinal atrophy and yolk steatosis (3). While such post-reproductive yolk production has long been viewed as futile (1,4), we wondered if it could somehow promotes fitness. We report that sperm-depleted hermaphrodites vent copious amounts of yolk through the vulva. This yolk can be consumed by larvae and promote their growth. This implies that post-reproductive mothers can continue to contibute to reproductive fitness by converting their biomass into a substance that serves a similar function to milk. This suggests that gut atrophy is a cost of a form of primitive lactation (also seen in certain insects). Moreover, unfertilized oocytes function as vectors carrying yolk to larvae. This type of massive reproductive effort involving biomass repurposing that causes organ degeneration is characteristic of semelparous organisms (i.e. that exhibit only a single reproductive episode) ranging from monocarpic plants to Pacific salmon, where it frequently leads to rapid death (reproductive death). We also observed yolk venting in hermaphrodites of other Caenorhabditis species and in Pristionchus pacificus hermaphrodites, but not in females of either genus. Moreover, females do not exhibit gut atrophy or steatosis and are longer lived, suggesting absence of reproductive death. Furthermore, across species germline ablation strongly increases lifespan in nematode hermaphrodites but not females; similarly, in diverse animal and plant species blocking sexual maturation e.g. by gonadectomy frequently causes large increases in lifespan in organisms that undergo reproductive death, but not in those that don't. Insulin/IGF-1 signaling, which accelerates C. elegans aging, also promotes yolk production and gut atrophy (1,3). These results suggest that C. elegans hermaphrodites exhibit reproductive death, suppression of which increases lifespan. If correct, this has significant implications in terms of what one can learn about human aging from C. elegans. (1) Nature 2002 419: 808. (2) Genetics 2002 161: 1101. (3) Curr. Biol. 2018 28: 2544. (4) BMC Physiol. 2011 11: 11.
[
International Worm Meeting,
2007]
A wide variety of bacterial and fungal pathogens have been shown to cause lethal intestinal infections in C. elegans. However, relatively little is known about the relevant pathogens that C. elegans encounters in the wild, and no bacterial pathogens have yet been shown to invade C. elegans intestinal cells. Antoine Barriere and Marie-Anne Felix recently identified a strain of C. elegans that harbors intracellular bacteria during a sampling of French compost pits (1) and they generously sent us this strain for characterization. The intracellular bacteria in this strain are only found in the intestine, and they can be transmitted from one C. elegans animal to another by co-incubating infected and uninfected animals on the same plate. The infection can be cured in the next generation by bleaching, or by removing adults from the plate immediately after egg-laying, indicating that it is not transmitted vertically. We have found that the infection can be transmitted by taking a streak of bacteria from a plate of infected worms, transferring it to a new plate, and then adding recipient worms immediately. However, if the streak of bacteria is incubated for 24 hours or more before adding recipient worms, worms will not become infected, indicating that the bacteria lose infectivity outside of their hosts. Through 16S rDNA cloning and sequencing we have identified the infecting intracellular bacteria as a species in the Ochrobactrum genus. Ochrobactrum are Gram negative bacteria commonly found in the soil, and are generally considered harmless, as they are only rarely associated with infection in humans. However, the closest relative of Ochrobactrum is Brucella, which is an intracellular pathogen of mammals that can infect and kill humans. Brucella is considered a potential bioterrorism weapon and is a BSL3 (biosafety level 3) organism. Perhaps because of the difficulties in working with Brucella, little is known about how it infects its host, and its genome contains few classical virulence factors. Thus, the C.elegans/Ochrobactrum model may provide a safer alternative for understanding how this clade of intracellular bacteria infect and kill their hosts.
1) Barriere and Felix (05) Current Biology
Subsequent experiments have indicated that the intracellular pathogen is not the bacterium Ochrobactrum, but instead corresponds to a new species of microsporidia, which are eukaryotic pathogens.