Reproductive Span of Caenorhabditis Elegans is Extended by Microbacterium Sp

Abstract

The reproductive span (RS) of organisms could be affected by different factors during their lifetime. In the model nematode, Caenorhabditis elegans, RS is affected by both genetic and environmental factors. However, none of the factors identified so far were related to environmental bacteria, which may incidentally appear anywhere in the habitats of C. elegans. We aimed to find environmental bacteria that could affect the RS of C. elegans and related species. We tested 109 bacterial isolates and found that Microbacterium sp. CFBb37 increased the RS and lifespan of C. elegans but reduced its brood size. We studied the effect of M. sp. CFBb37 on the RS of Caenorhabditis briggsae, Caenorhabditis tropicalis, and another Rhabditidae family species, Protorhabditis sp., and found similar trends of RS extension in all three cases, suggesting that this bacterial species may induce the extension of RS broadly among Caenorhabditis species and possibly for many other Rhabditidae. This work will facilitate future research on the mechanism underlying the bacterial extension of RS of nematodes and possibly other animals.

Keywords: Caenorhabditis nematodes; Microbacterium sp.; Protorhabditis sp.; bacteria; brood size; lifespan; physiology; reproductive span.

Figure 1

RS of individual nematodes on Microbacterium sp. CFBb37 and the E. coli OP50 control. (A) C. elegans, (B) C. briggsae, (C) C. tropicalis, and (D) Protorhabditis sp. on CFBb37 had longer RS than on OP50 (P < 0.001, log-rank test). Full RS data in Table 2. RS, reproductive span.

Figure 2

Lifespan assays of C. elegans on Microbacterium sp. CFBb37 and the OP50 control. C. elegans grown on CFBb37 survived longer than OP50 (P < 0.001, log-rank test). Detailed lifespan data are in Tables S4 and S5.

Figure 3

Summary of RS extension in the Caenorhabditis species (orange) and the outgroup Protorhabditis sp. (light blue). Red lines indicate inferred ancestral evolutionary lineages with extended RS. We suggest that other species within the genus Caenorhabditis are likely to have extended RS but this is untested. For simplification, some species are not listed and are grouped together in triangles, with the numbers of known species indicated. Phylogeny is adapted from Kiontke and Fitch (2005) and Felix et al. (2014) with the position of Protorhabditis sp. CFB231 placed next to P. sp. 1 species based on the 18S ribosomal RNA gene sequence (Zhang et al., 2000; Morgulis et al., 2008). Protorhabditis sp. CFB231 is self-fertile but the sexual system, hermaphroditic or parthenogenetic, is unknown (indicated by a question mark). RS, reproductive span.

Figure S1

Size comparison of the four tested nematode species grown on Microbacterium sp. CFBb37 and Escherichia coli OP50. Images are representative samples.

Figure S2

Protorhabditis sp. CFB231 make sperm. (A) DIC image of spermathecal region (outlined). One oocyte is apparently transiting the spermatheca. (B) DAPI staining for nuclei. (C) Merged images of DIC and DAPI. DIC, differential interference contrast.