Wednesday, January 18, 2017

UM scientists integrate microbial genomics, environmental chemistry, and ecosystem processes to understand harmful algal blooms

UM scientists integrate microbial genomics, environmental chemistry, and ecosystem processes to understand harmful algal blooms. One of the key processes at the nexus of these three fields is hydrogen peroxide production and interaction with bacterial communities. Hydrogen peroxide is known to suppress certain strains of bacteria and could play a pivotal role in the rise of toxic cyanobacterial communities.

Scientists continue to tease apart the causes of harmful algal bloom (HAB) appearances and toxic effects in the Great Lakes and beyond. While much attention has been paid to the role excess nutrients play in bloom formation, the role and interaction of microbiology, ecology, and chemistry in HAB formation remains unknown. One of the key processes at the nexus of these three fields is hydrogen peroxide production and interaction with bacterial communities. Hydrogen peroxide is known to suppress certain strains of bacteria and could play a pivotal role in the rise of toxic cyanobacterial communities called Microcystis.

 

To explore this question, a research team of microbiologists, environmental chemists, phytoplankton ecologists, molecular biologists, ecosystem ecologists, and a natural products chemist collaborated on a project to uncover the interrelationships between microbial community composition, genomic content, gene expression, toxin concentrations, dissolved organic carbon (DOC), reactive oxygen species, nutrients, and bacterial activity. Specifically, the team sought to understand the potential effect of hydrogen peroxide on the toxicity of harmful algal blooms and the environmental and biological controls on hydrogen peroxide concentrations. They established four sample collection stations in Lake Erie’s western basin, where HABs occur each summer, and collected nearly weekly samples from June to November throughout the 2014 field season. They characterized all samples for microbial community structure, nutrients, and DOC chemistry. Key samples representing contrasting conditions of interest, for example high vs. low concentrations of toxins and hydrogen peroxide, received a more detailed analysis, including metagenomic and metatranscriptomic sequencing, bacterial process rates, and DOC character. For the dominant microbial populations, the team reconstructed whole genomes to uncover their gene content and expression.

 

Two publications from 2016 help to describe the work done by this team:

  1. Cyanobacterial harmful algal blooms are a biological disturbance to western Lake Erie bacterial communities
  2. Seasonal Dynamics in Dissolved Organic Matter, Hydrogen Peroxide, and Cyanobacterial Blooms in Lake Erie

 

The project resulted in four major findings about Lake Erie cyanobacterial harmful algal blooms with regard to the source and character of dissolved organic matter; concentrations, sources, and sinks of hydrogen peroxide; the composition of bacterial communities; and bloom toxicity.

 

  • The team found that DOC composition in Lake Erie is largely due to inflow from rivers. DOC flows from the surrounding watershed to Lake Erie in late spring and early summer. In late summer and fall, more DOC is produced within the lake itself. This finding is important because light reacts with DOC to produce a substantial source of hydrogen peroxide, meaning DOC originating from rivers may be a source of hydrogen peroxide present during HABs. In addition, DOC may serve as a source for bacterial metabolism and growth, which is key for understanding microbial community dynamics.
  • Researchers observed a seasonal pattern of hydrogen peroxide for both 2014 and 2015. Hydrogen peroxide peaked during late July and early August. This timing correlates with the development of the HABs. Two possibilities emerge. The bloom itself may be the source of the hydrogen peroxide, or, because hydrogen peroxide has been shown to favor toxic over non-toxic strains of Microcystis, the hydrogen peroxide may influence bloom toxicity.
  • The team found that the overall bacterial community composition changes systematically during the season, in part due to normal seasonal succession driven by temperature, and in part as a specific response to the HAB. This established that HABs are biotic disturbances that elicit a specific response from the rest of the microbial community and highlighted a potential role for bacteria other than Microcystis in bloom development. Further studies will need to uncover if and how this changing bacterial community relates to ecosystem functions and bloom toxicity.
  • The team discovered that the toxicity of the bloom changes dramatically from June to November. This change in toxin concentration correlates with a shift in the portion of Microcystis cells containing genes for toxin production. This means that there is a shift in the Microcystis community from predominantly toxic cells early in the season to predominantly non-toxic cells later in the season. These results encourage further research on the environmental and biological factors that favor toxic or non-toxic strains of Microcystis.

Given the coincidence of the hydrogen peroxide peak with high toxicity and previous lab results indicating that the toxin provides protection against hydrogen peroxide, a key avenue of research will be to test how hydrogen peroxide influences the growth of – and competition between – toxic versus non-toxic Microcystis.

The data collected during this project has been made publicly available by the team for other researchers to utilize. The team produced longitudinal omics datasets and a Great Lake Microbial Database during the course of their research. Data collection for the datasets and database began in 2014, and includes a weekly/bi-weekly survey of microbial community composition and environmental chemistry. The massive new omics datasets include over fifty reconstructed genome sequences from cyanobacteria, bacteria, and viruses. The Great Lakes Microbial Database provides access to raw and processed omic, chemical, and environmental data in a curated and searchable format. It can be accessed through http://cyanohub.earth.lsa.umich.edu.

About the Water Center

The U-M Water Center addresses critical and emerging water resource challenges through collaborative research projects. We believe that diversity is key to individual empowerment, and the advancement of sustainability knowledge, learning and leadership. The Center is part of the Graham Sustainability Institute, which integrates faculty and student talent across U-M, and partners with external stakeholders to foster collaborative sustainability solutions at all scales. See: www.graham.umich.edu/water

Click here to see additional information on the project to track the toxicity of lake Erie algal blooms.

Click here to listen to Michigan Radio coverage of the 2015 cyanobacteria bloom.