Abstract
Although the microbiota is known to affect host development, metabolism, and immunity, its impact on host behavior is only beginning to be understood. In order to better characterize behavior modulation by host-associated microorganisms, we investigated how bacteria modulate complex behaviors in the nematode model organism Pristionchus pacificus. This nematode is a predator that feeds on the larvae of other nematodes, including Caenorhabditis elegans. By growing P. pacificus on different bacteria and testing their ability to kill C. elegans, we reveal large differences in killing efficiencies, with a Novosphingobium species showing the strongest enhancement. This enhanced killing was not accompanied by an increase in feeding, which is a phenomenon known as surplus killing, whereby predators kill more prey than necessary for sustenance. Our RNA-seq data demonstrate widespread metabolic rewiring upon exposure to Novosphingobium, which facilitated screening of bacterial mutants with altered transcriptional responses. We identified bacterial production of vitamin B12 as an important cause of such enhanced predatory behavior. Although vitamin B12 is an essential cofactor for detoxification and metabolite biosynthesis, shown previously to accelerate development in C. elegans, supplementation with this enzyme cofactor amplified surplus killing in P. pacificus, whereas mutants in vitamin B12-dependent pathways reduced surplus killing. By demonstrating that production of vitamin B12 by host-associated microbiota can affect complex host behaviors, we reveal new connections between animal diet, microbiota, and nervous system.
Highlights
Organisms harbor and interact with diverse microbial communities depending on their own ecology and environment
Using Novosphingobium L76, we found that the number of P. pacificus bites and successful biting events doubled relative to E. coli OP50 grown predators (Fig. 1d)
The greatest enhancement in predatory behaviors was observed when P. pacificus was fed upon Novosphingobium with the increase in killing influenced by bacterial derived vitamin B12
Summary
Organisms harbor and interact with diverse microbial communities depending on their own ecology and environment. Another well-characterized nematode species in addition to C. elegans is Pristionchus pacificus, which shows novel ecological, morphological, and behavioral traits not observed in C. elegans. P. pacificus predation under laboratory conditions is an example of a phenomenon known as surplus-killing behavior [12]. Utilizing previously isolated bacteria from soil, scarab beetles, and figs that are found naturally associated with Pristionchus nematodes [28], we investigate their influence on its predatory behavior and predatory associated traits. We analyze 25 different bacterial species and establish their ability to modulate the predatory feeding behaviors including surplus killing. Ecologically relevant bacteria found naturally associated with P. pacificus influence behavioral traits
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