Parallel evolution of alternate morphotypes of Chryseobacterium gleum during experimental evolution with Caenorhabditis elegans Open Access

Duckett, Marissa (Summer 2023)

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Microbial communities shape every organism and environment, and shifts in these communities can cause systemic change within a host that can ultimately affect host health. Understanding how multiple species evolve under the influence of each other in contrast to independently is important for acquiring insight into evolution of community composition, and vice versa. Evolution of community composition is not well understood, but previous research has revealed that community composition converges over evolutionary time. In this investigation, twelve slightly variable communities were created and followed over ten passages in Caenorhabditis elegans hosts. Upon the sixth passage, variable morphotypes were observed and maintained as the experiment progressed. We aim to understand what selective pressures could have contributed to this differentiation and maintenance of variable morphotypes. Chryseobacterium gleum had the greatest relative abundance in these host associated communities and developed alternate morphologies in two of the twelve communities. Common phenotypes, growth rate, carrying capacity, and motility were measured in hopes of revealing causes for this morphotype differentiation. Growth rate and carrying capacity suggest adaptation to the environment rather than evolution to the inside of the host. Motility was a more useful gauge for variability in these morphotypes, revealing consistently less spread in alternate morphs than original morphs. Gliding motility was confirmed through genomics, but no variability was observed in genetic elements responsible for gliding motility, the Gld proteins and T9SS genes, between alternate, original, and ancestral isolates. Previous research observed an increase in motility as nutrient concentration decreased. Our results did not show this trend, indicating that there are differences in how motility is regulated in Chryseobacterium. Although community composition converges over time, microbial lineages evolve differently, likely due to adaptation to environment and regulatory differences in response to unknown selective pressures.

Table of Contents



C. gleum is a worm pathogen 9

There is variability within community and passage and between isolates 10

Growth rate is lower and carrying capacity is greater in alternate morphs than ancestor 11

Pairwise competition in vitro 14

Alternate morphs are less motile than original morphs 18

There is no observable trend in motility of original morphotypes during adaptation 20

Genomic analysis reveals no variability in gliding genes 22

Regulation of motility by nutrient concentration 26



Strains and culture conditions 40

Community-based experimental evolution 41

Pairwise bacterial interactions in vitro 43

Chryseobacterium gleum Mortality Assays 44

Surface motility 45

Data availability 47



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