THE UNIVERSITY OF TENNESSEE

AQUATIC MICROBIAL ECOLOGY RESEARCH GROUP

 

 

Steven W. Wilhelm -  Professor OF Microbiology 

 

Office: 865-974-0665    Labs: 865-974-0682  or  865-974-4014

CURRENTLY FUNDED RESEARCH PROJECTS

 

 

Development of a tractable genetic system for Aureococcus anophagefferens.

Funding Source: The Gordon & Betty Moore Foundation

PI.  SW Wilhelm.  coPIs ER Zinser, T Sparer, T Reynolds and WH Wilson.

Aureococcus anophagefferens, the cause of Brown Tides, persists in coastal regions globally in what many considered hostile environments (i.e., turbid, enriched in nutrient and trace metal waste, etc.) at densities of greater than 109 cells L-1. This organism has a highly mosaic genome, indicative of frequent genomic modifications.  Along with suggestions that Aureococcus undergoes natural transformation, members of these populations are regularly infected by a giant virus (AaV) that is enriched with repeats believed to be active in genomic shuffling and frequent gene exchange between the virus and its host. Indeed, exchange has also occurred between AaV and other non-host organisms (i.e., bacteria and other algae) and implies a natural recombination mechanism with A. anophagefferens as the intermediate. We will develop a genetic system for Aureococcus that can serve to further our understanding of this algae’s ecology and evolution as well provide potential for biotechnological advances.  A series of approaches, including the use of the AaV and putative repeat regions that may encode promoters, will be employed in the transformation of Aureococcus. Along with direct transduction using modified AaV, we propose to take advantage of tools developed for the transformation of other algae (e.g., Chlorella, Nannochloropsis, Emiliania huxleyi) and other single-celled eukaryotes.

Award Abstract #1451528.  Collaborative Research: an integrated approach to understanding the function of the potent hepatotoxin microcystin in the growth & ecology of Microcystis

Funding source: NSF Division of Integrative Organismal Systems

PI  SW Wilhelm.  coPIs ER Zinser, SR Campagna, JM DeBruyn, EM Fozo and GL Boyer

Blooms of toxic photosynthetic bacteria (cyanobacteria) are occurring globally with expanding frequency, duration and intensity in lakes, reservoirs and river systems. Most recently blooms of the toxic cyanobacterium Microcystis shut down the water supply of the city of Toledo, OH for a weekend in August of 2014. While the scientific community has developed a solid understanding of the factors that contribute to the blooms of Microcystis, previous research has not explained why cells make the hepato- (liver) toxin microcystin. As a potent inhibitor of a key class of enzymes - protein phosphatases - microcystin might play important roles inside Microcystis cells, and once released, inside the cells of other (target) organisms. This project will use advanced tools in molecular biology (RNA sequencing), microbial genetics, the quantification of small metabolites (metabolomics) and enzyme analyses to understand how the presence of microcystin shapes the activity of both the cells that make the compound and the community of microorganisms around them. Experiments in the laboratory will be complemented by field surveys of bloom events across naturally occurring toxin gradients - areas of historically high and low concentrations of toxin during the summer bloom season. State-of-the-art statistical analyses combined with these advanced scientific approaches will transform the understanding of why these cyanobacteria make this toxic compound. Understanding of the biological functions of the microcystin, will lead to better stewardship of a valuable natural resource: potable water. The total research effort will train students, including those from underrepresented groups, and broadly disseminate information to the public, systems managers and the scientific community. A significant component will feed into state-associated, in-class 4H training that will expose as many as 200,000 students to cyanobacteria as a model system to examine complex biochemical questions.

The goal of this project is to develop a deeper understanding of the biochemical role of microcystins, a potent protein phosphatase inhibitor, within cells and communities, and address both ecological and evolutionary questions concerning the maintenance of this and other expensive biosynthetic pathways for non-ribosomally encoded secondary metabolites within a (sub)population of cells. To determine how microcystin shapes cellular biochemistry and physiology, controlled lab experiments with Microcystis isolates that make microcystin, engineered strains where the biosynthetic gene has been knocked out, and wild-type Microcystis cells that lack the biosynthetic pathway will be conducted. Other cyanobacterial pairs (Planktothrix and Anabaena spp.) that make or do not make the toxin, engineered bacteria that produce this compound and a set of microorganisms isolated from Lake Erie that co-occur with Microcystis and may be influenced by toxin will also be tested. Experiments in the presence and absence of exogenous toxin will be conducted with both producers and non-toxin producers. State-of-the-art techniques in metabolic (LC-MS and LC-MS/MS metabolomics and lipidomics), transcriptional (Illumina mRNA-sequencing), enzymatic (4:3:3-regulated processes) and physiological analyses (e.g., cellular growth rates, primary production, and photosynthetic efficiency) for these defined lab strains will be employed to develop "fingerprints" of cellular function and elucidate how microcystin shapes these biochemical pathways and the physiological ecology of these cells. Lab experiments will be complemented by field surveys of bloom events across naturally occurring and well documented toxin gradients. Relationships will be identified using univariate and multivariate techniques. This novel integration of sequencing, small molecule chemistry, physiological and enzymatic approaches will permit the mapping of the physiological biochemistry of cells and identify both isolated as well as synergistic effects: indeed this work may transform the study of secondary metabolites in complex microbial systems and provide insights into microbial evolutionary ecology.

Award Abstract #1240870.  Dimensions: Collaborative Research: Anthropogenic nutrient input drives genetic, functional and taxonomic biodiversity in hypereutrophic Lake Taihu, China.

Funding Source: NSF DEB (Dimensions of Biodiversity program).

PI HW Paerl. coPIs SW Wilhelm, W Gardner, F Hellweger.  Collaborator GL Boyer.

Human activities have dramatically increased nitrogen inputs into many rivers and lakes, causing algal blooms that threaten economic and recreational uses of those waters. Lake Taihu, the third largest lake in China, experiences damaging blooms of toxic cyanobacteria as a result of excessive nutrient inputs. The identities, nitrogen processing capabilities, and activities of microbial communities in Lake Taihu will be examined to determine if nitrogen processing can be predicted from knowledge of the identity and genetic makeup of those communities. Various components of the nitrogen cycle will be measured and linked to representative molecular markers which, coupled with high throughput genetic sequencing, will provide a genetic database of nitrogen-cycling processes in freshwater ecosystems. A goal of the project will be to link microbial taxonomic, genetic, and functional data in a model that can predict how reduction of nutrient inputs will affect toxic cyanobacterial blooms.

This project will have broad applicability to the management of aquatic systems that are threatened by excessive nutrient inputs, a problem that is increasing worldwide. Additional broader impacts will include training of high school, undergraduate, and graduate students, international student exchanges, training of a postdoctoral researcher, and incorporation of science journalism students into field studies to promote adult scientific literacy.


                                                     
updated 09/21/2017