Project Summary All animals live in environments surrounded by microbes, yet the impact of bacteria on nervous systems has been relatively under-studied. Recent data suggests that commensal gut bacteria may be capable of modulating host behavior. Gut bacteria benefit from nutrients consumed by their host and because these bacteria must be transmitted largely via diet, manipulation of host feeding behavior is a principal mode by which resident microbes can influence the gut microbial community. Due to the dynamic nature of such an interaction, studying feeding manipulation has been either challenging or impossible to date in most systems. First, we must identify systems in which both host and microbe are amenable to genetic manipulation, and which enable high-throughput behavioral screening in response to defined and naturalistic conditions. Here, we propose to comprehensively study this phenomenon for the first time in any experimental system, using the roundworm C. elegans — in combination with its natural associated bacteria — to gain mechanistic insights into inter-organismal signals driving host-microbe interactions and decision making. C. elegans is a bacterial- feeding nematode that is often found in rotting plant material and is commonly colonized by microbes. C. elegans has some of the most extensive molecular, neurobiological and genetic tools of any multicellular eukaryote, and, coupled with the ease of gnotobiotic culture in these worms, represents a highly attractive system in which to study microbial influence on host behavior. I have recently shown that in C. elegans, gut bacteria can influence chemosensory decisions — a proxy for feeding behavior in certain contexts — resulting in increased preference for odors produced by these enteric microbes. In parallel preliminary work, I have found that olfactory plasticity upon gut colonization by diverse microbes correlates with gut colonization patterns in naturalistic settings. Together, these findings suggest that the C. elegans native gut microbiota may be capable of impacting microbiome assembly by influencing feeding behavior. In this proposal, we aim to establish C. elegans as a system to study feeding manipulation by developing tools to identify the behavioral parameters which influence microbiome structure in naturalistic settings. We propose to experimentally isolate ingestion from locomotory behavior through the development of novel microfluidics imaging devices. We will develop new behavioral assays in 2- and 3- dimensional arenas to present microbial communities mimicking the worms’ natural environment. We will then identify the molecular basis of microbial-dependent changes in olfactory behaviors using naturalistic microbial communities. Together, we propose to develop a new field of feeding manipulation by gut microbes, with C. elegans centered as a preeminent model. We anticipate that the principles we identify in this proposal should generalize to multiple systems and th...