Preferred Name

Bryan Puma

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Graduation

5-11-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Biology

Advisor(s)

Morgan Steffen

Louie Wurch

Raymond Enke

Abstract

Microcystis spp. produce prolific annual blooms in freshwater systems worldwide. The success of these blooms depends heavily on the Microcystis spp. overcoming environmental factors such as oxidative stress caused by reactive oxygen species (ROS) like hydrogen peroxide. Most Microcystis genomes do not contain many genes for responding to oxidative stress, including those that encode the enzyme catalase. Other cyanobacteria such as Prochlorococcus that also lack hydrogen peroxide degrading enzymes have been shown to benefit from partnerships with heterotrophic bacteria. Microcystis spp. may also receive similar benefits from heterotrophic bacteria in the phycosphere. To test this hypothesis, we examined the effect of bloom stage and how both Microcystis and its phycosphere microbiome respond to being treated with a low (1 µM) and high (10 µM) concentrations of hydrogen peroxide during different stages of bloom development. Additional treatments were also supplemented with a nonnative consortium of catalase positive bacteria isolated from a Microcystis bloom in Lake Tai (Taihu) to test the impact of these bacteria on the oxidative stress response of Microcystis. Significant changes in growth occurred in the late bloom period between the control and the high treatment, indicating that the elevated concentration of hydrogen peroxide had an effect on fitness. Metatranscriptomic analysis was used to evaluate the changes in gene expression and community composition to determine the functional response to ROS stress. Differential expression was greatest between the high treatment and the high treatment inoculated with the nonnative bacterial consortium, indicating the nonnative bacteria influenced Microcystis expression under conditions of elevated oxidative stress. When the bloom community was incubated with the high concentration of hydrogen peroxide and inoculated with the nonnative catalase positive consortium of bacteria, Microcystis upregulated expression of photosystem genes, as well as genes in the oxidative pentose phosphate pathway. These incubation experiments provide evidence that the response by Microcystis to stress is influenced by its microbiome.

Available for download on Thursday, April 11, 2024

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