Tag: Cathy Robinson

Effect of Pyomelanin Production on Oxidative Stress in an Aeromonas Zebrafish Gut Isolate

Presenter: Helena Klein

Faculty Mentor: Karen Guillemin, Cathy Robinson

Presentation Type: Poster 72

Primary Research Area: Science

Major: Biology

Bacteria have rapid growth rates, which allow us to study their adaptive evolution in the lab to selected environments. By studying the genetic changes that occur during the evolutionary process, we can learn about selective pressures experienced by bacteria when evolved in selected conditions. Through passaging of a strain of a natural zebrafish gut isolate, Aeromonas ZOR0001, we isolated one strain that has increased pigmentation compared to the wildtype. This pigmentation is a result of accumulation of pyomelanin in the extracellular environment. We confirmed through genetic sequencing a mutation in the isolate’s metabolic pathway known to be involved in pyomelanin production. Pyomelanin production has been shown in other organisms to be linked to increased resilience to oxidative stress. Therefore, we hypothesized this mutation confers a fitness advantage to this evolved isolate compared to the ancestral strain. Therefore we generated a genetic knockout of the mutated gene in the ancestral strain and used hydrogen peroxide to simulate oxidative stress in vitro. We found that the knockout strain did better than the wild type strain. This demonstrates that pyomelanin production confers resistance to oxidative stress in Aeromonas ZOR0001 which suggests an adaptive advantage for in vivo growth. Knowledge of genes that increase fitness in bacterial strains in the gut can ultimately allow for better probiotics to be developed with wide repercussions for human health.

Experimental Evolution of a Bacterial Symbiont to its Host’s Environment

Presenter(s): Helena Klein − Biology

Faculty Mentor(s): Karen Guillemin, Cathy Robinson

Poster 85

Research Area: Natural/Physical Science

Funding: META Grant

The bacteria that live in our guts, and those of other vertebrates, affect our health in a myriad of ways, from aiding in digestion to training our immune system. However, how bacteria first colonize the gut is little-understood. In particular, environment seems to play an important role in host colonization, especially in aquatic organisms. I proposed investigating environmental adaptation to find novel mechanisms for host colonization. I hypothesized that adaptation of a bacterial symbiont to its host’s environment increases host colonization. I tested this hypothesis via experimental evolution by serially passaging a strain of Aeromonas veronii, a zebrafish gut isolate, in fish-conditioned water to quickly and non-specifically find new genes that could affect host colonization. Surprisingly, I found that while the evolved strains grew to higher population densities in the water than the ancestor, these strains had variable gut colonization fitness. In fact, one strain had significantly reduced gut colonization fitness. Genome sequencing revealed that this strain had mutations affecting motility and Type I secretion system membrane protein genes. I recreated the latter mutation in the wildtype bacterial strain and found that it increased Aeromonas fitness in fish water, however gut colonization was comparable to the wildtype. This suggests that other mutations in the evolved isolate, presumably those in the motility genes, are responsible for the reduced host colonization. Future work will further investigate motility mutations among others. This work contributes to our understanding of host colonization dynamics and can lead to the development of probiotics to improve human health.

Investigating amino acid-modulated motility of the zebrafish bacterial isolate, Aeromonas veronii

Presenter(s): Emily Ma

Faculty Mentor(s): Cathy Robinson & Karen Guillemin

Poster 53

Session: Sciences

Animals are colonized by communities of microorganisms that influence the health and development of their host. However, the mechanisms of host colonization are still underexplored. To investigate this, previous work in the lab used experimental evolution to adapt a bacterial symbiont, Aeromonas, to the zebrafish gut. These experiments led to the identification of a novel gene, spdE, which significantly impacts host colonization. We found that evolved isolates with mutations in spdE had faster rates of motility and increased host immigration. Sequence analysis revealed that the protein, SpdE, has a domain for sensing extracellular signals and a diguanylate cyclase domain which produces an intercellular signaling molecule that regulates motility. Further biochemical investigation identified that the signal SpdE senses is hydrophobic amino acids, specifically proline, valine, and isoleucine. To further investigate the relationship between SpdE-dependent Aeromonas motility and environmental amino acids, we developed a new technique (“exploration assay”) which is designed to measure differences in motility between strains or conditions. Using the exploration assay, we compared motility of wild type and spdE knockout strains in different amino acid environments. From our results, we found that the wild type strain is more motile in the presence of these amino acids. However, even in the absence of amino acid signal, the spdE knockout is more motile than the wild type. From these data, we have created a model for how SpdE regulates motility in response to amino acids which offers novel insights into Aeromonas biology and the mechanisms of host colonization.