Understanding Caenorhabditis elegans Decision-Making in Complex Foraging Environments Restricted; Files Only

Abstract

Decisions made by the nematode Caenorhabditis elegans when foraging for bacterial food sources have been thoroughly studied in 2D environments using canonical choice assays; however, interactions between C. elegans and microbes in structured 3D environments such as soil matrices are currently unclear. Additionally, the scales at which C. elegans are able to make foraging decisions in patchy environments are not well understood, and the consequences for microbial ecology are currently unknown. This project seeks to better understand the spatial scales of decision making and worm-microbe interactions by creating patterned bacterial lawns with various strain combinations and performing choice assays using these mixtures. By pairing three bacterial test strains (Pseudomonas alcaligenes, Pseudomonas veronii, Salmonella enterica) with one reference strain (Pseudomonas citronellolis) in various assay layouts, we were able to determine that C. elegans foraging behavior changes based on the spatial scale of the decision they must make. Additionally, we found that mixing and plating one diluted fluorescent bacterial strain with a separate diluted non-fluorescent bacterial strain at a 1:1 volume ratio produced lattices with small patches of bacteria that can be differentiated using a fluorescent microscope, and that worms behaved differently towards food spots containing two bacterial species than towards food spots with one bacterial species. These results expand our awareness of the decisions made by C. elegans in complex foraging environments and serve as foundational data to further investigate the consequences of spatially structured environments on microbial populations.

Table of Contents

Chapter 1: Introduction ………………………..……………………….……………………….……………………………............ 1

           1.1: Microbial community ecology ..………………………………….....………………………………………............... 1

           1.2: Spatial effects on microbial communities ..……………………………………..………………………................. 2

           1.3: Effects of Caenorhabditis elegans decision-making on microbial communities ………........................... 3

           1.4: Project summary ..……………………………………..………………………………………..…………………........... 4

Chapter 2: Methods ……………………..……………………….……………………….……………………………..................... 5

           2.1: Bacterial strains and growth media ..……………………………………..…………………………….................... 5

           2.2: C. elegans propagation and synchronization ..……………………………………..………………….................. 6

           2.3: Microscopy ..……………………………………..………………………..……………………………………..…........... 7

           2.4: Traditional choice assays ..……………………………………..………………………..…………………................. 7

           2.5: Conjugation ..……………………………………..………………………...…………………………………….............. 9

           2.6: Electroporation ..……………………………………..………………………..……………………………...........…… 10

           2.7: Mixture preparation ..……………………………………..………………………...………………….............……… 11

           2.8: Mixture attraction assays ..……………………………………..………………………..…………..............………. 11

Chapter 3: Results ……………………..……………………….……………………….……………………………...................... 12

           3.1: C. elegans strain preferences under traditional conditions ................................................................ 12

           3.2: Lattice preparation ........................................................................................................................ 21

           3.3: C. elegans strain preferences under complex conditions ................................................................... 22

Chapter 4: Discussion ................................................................................................................................... 27

           4.1: C. elegans make distinct feeding and leaving choices based on bacterial species ................................. 27

           4.2: C. elegans behavior is altered in different spatial environments ........................................................ 28

                       4.2.1: Pseudomonas veronii case study ........................................................................................ 29

           4.3: Study limitations and future directions ........................................................................................... 31

           4.4: Conclusion .................................................................................................................................... 33

Chapter 5: References ................................................................................................................................... 34

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Ecology
Keyword	microbial community ecology spatial structure C. elegans
Committee Chair / Thesis Advisor	Vega, Nic, Emory University
Committee Members	Morran, Levi, Emory University Benian, Guy, Emory University

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