The Ecophysiology of Microcystis aeruginosa in response to IAA and Tryptophan
Faculty Advisor Name
Dr. Morgan Steffen
Department
Department of Biology
Description
Microcystis aeruginosa is a freshwater cyanobacterial species that degrades freshwater and brackish ecosystems due to its capacity to form toxic cyanobacterial harmful algal blooms (cyanoHABs). There are both abiotic and the biotic factors that exacerbate the presence of cyanoHABs. Anthropogenic input of nitrogen and phosphorus through agricultural and urban runoff has been shown to impact bloom production. There are also microbial interactions that occur within these blooms that can be beneficial to phytoplankton growth as well. Current research is looking at the microbial interactions that occur between microbes and phytoplankton. Microbes interact with cyanobacteria in the phycosphere, where nutrients are exchanged between the two. Understanding the chemical currencies exchanged can help to show interactions that are beneficial for cyanoHAB formation. A key player in the growth promotion of cyanoHABs is hypothesized to be auxins, which are synthesized by bacterial symbionts, though this has yet to be tested. Previous research has shown that auxins have growth-promoting effects on several marine and freshwater algae, but this has yet to be tested on Microcystis aeruginosa. To understand the mechanism behind this interaction, M. aeruginosa-dominated cHABs in Alabama were exposed to both the auxin Indole-3-acetic acid (IAA) and tryptophan, a precursor for bacterial production of IAA. Metatranscriptomes generated across a time series were paired with growth data (i.e., cell counts, Fv/Fm) to determine the impact of IAA on Microcystis cell physiology and the constituents of its phycosphere microbiome. Field experiments were paired with lab experiments using non-axenic M. aeruginosa strains as well as a field experiment within a JMU retention pond. Community and functional analysis showed that bacteria within the Microcystis phycosphere were able to produce genes related to IAA synthesis from tryptophan, cobalamin synthesis, and metabolism of algal derived carbon. These interactions indicate that there is a bidirectional exchange of nutrients in the phycosphere during the field experiment. Microbial synthesis of IAA from tryptophan was determined to be produced from an alternate pathway within the indoleacetamide pathway. Differential expression of Microcystis in response to exogenous IAA and tryptophan input showed that there was an increase in expression for several unique metabolic genes for Microcystis at each time point compared to the control. A network analysis for each treatment showed that that there was a more complex microbial network interacting with Microcystis for the control compared to the tryptophan and the IAA treatments. This result could potentially be due to the exogenous input of IAA and tryptophan, decreasing the need for microbial-derived nutrients.
The Ecophysiology of Microcystis aeruginosa in response to IAA and Tryptophan
Microcystis aeruginosa is a freshwater cyanobacterial species that degrades freshwater and brackish ecosystems due to its capacity to form toxic cyanobacterial harmful algal blooms (cyanoHABs). There are both abiotic and the biotic factors that exacerbate the presence of cyanoHABs. Anthropogenic input of nitrogen and phosphorus through agricultural and urban runoff has been shown to impact bloom production. There are also microbial interactions that occur within these blooms that can be beneficial to phytoplankton growth as well. Current research is looking at the microbial interactions that occur between microbes and phytoplankton. Microbes interact with cyanobacteria in the phycosphere, where nutrients are exchanged between the two. Understanding the chemical currencies exchanged can help to show interactions that are beneficial for cyanoHAB formation. A key player in the growth promotion of cyanoHABs is hypothesized to be auxins, which are synthesized by bacterial symbionts, though this has yet to be tested. Previous research has shown that auxins have growth-promoting effects on several marine and freshwater algae, but this has yet to be tested on Microcystis aeruginosa. To understand the mechanism behind this interaction, M. aeruginosa-dominated cHABs in Alabama were exposed to both the auxin Indole-3-acetic acid (IAA) and tryptophan, a precursor for bacterial production of IAA. Metatranscriptomes generated across a time series were paired with growth data (i.e., cell counts, Fv/Fm) to determine the impact of IAA on Microcystis cell physiology and the constituents of its phycosphere microbiome. Field experiments were paired with lab experiments using non-axenic M. aeruginosa strains as well as a field experiment within a JMU retention pond. Community and functional analysis showed that bacteria within the Microcystis phycosphere were able to produce genes related to IAA synthesis from tryptophan, cobalamin synthesis, and metabolism of algal derived carbon. These interactions indicate that there is a bidirectional exchange of nutrients in the phycosphere during the field experiment. Microbial synthesis of IAA from tryptophan was determined to be produced from an alternate pathway within the indoleacetamide pathway. Differential expression of Microcystis in response to exogenous IAA and tryptophan input showed that there was an increase in expression for several unique metabolic genes for Microcystis at each time point compared to the control. A network analysis for each treatment showed that that there was a more complex microbial network interacting with Microcystis for the control compared to the tryptophan and the IAA treatments. This result could potentially be due to the exogenous input of IAA and tryptophan, decreasing the need for microbial-derived nutrients.
