Steven Wilhelm

Steven Wilhelm
University of Tennessee | UTK · Department of Microbiology

PhD

About

278
Publications
87,400
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15,134
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Introduction
Steven Wilhelm is the Kenneth and Blaire Mossman Professor of the Department of Microbiology. In 2016 he became a fellow of the American Academy of Microbiology as well as a Sustaining Fellow of ASLO. In 2018 he was also named a James R. Cox Professor at the University of Tennessee. His group studies viruses, bacteria, cyanobacteria and algae in lakes and oceans using biomolecular tools - DNA and RNA sequencing, metabolomics, and PCR-based quantitative analyses.

Publications

Publications (278)
Article
Full-text available
Freshwater cyanobacterial blooms are regularly formed by Microcystis spp., which are well-known producers of the hepatotoxin microcystin. The environmental factors that regulate microcystin synthesis remain unclear. We used reverse transcription-quantitative PCR (RT-qPCR), metabolomics, and toxin profiling (both by LC-MS) to measure the response of...
Article
Full-text available
The use of urea as a nitrogenous fertilizer has increased over the past two decades, with urea itself being readily detected at high concentrations in many lakes. Urea has been linked to cyanobacterial blooms as it is a readily assimilated nitrogen (N) - source for cyanobacteria that possess the enzyme urease. We tested the hypothesis that urea may...
Article
Full-text available
Drivers of algal bloom dynamics remain poorly understood, but viruses have been implicated as important players. Research addressing bloom dynamics has generally been restricted to the virus-infection of the numerically dominant (i.e. bloom forming) taxa. Yet this approach neglects a broad diversity of viral groups, limiting our knowledge of viral...
Article
Full-text available
Blooms of the toxin-producing cyanobacterium Microcystis are increasing globally, leading to the loss of ecosystem services, threats to human health, as well as the deaths of pets and husbandry animals. While nutrient availability is a well-known driver of algal biomass, the factors controlling “who” is present in fresh waters are more complicated....
Article
Full-text available
Aseptic technique has historically served as a fundamental practice in microbiology, helping to maintain culture purity and integrity. This technique has been widely encouraged and employed for use with cultures of heterotrophic bacteria as well as freshwater and marine algae. Yet, recent observations have suggested that these approaches may bring...
Article
Billions of years ago, the Earth's waters were dominated by cyanobacteria. These microbes amassed to such formidable numbers, they ushered in a new era—starting with the Great Oxidation Event—fuelled by oxygenic photosynthesis. Throughout the following eon, cyanobacteria ceded portions of their global aerobic power to new photoautotrophs with the r...
Preprint
Full-text available
Climate change is affecting how energy and matter flow within ecosystems, altering global carbon and nutrient cycles. Microorganisms play a fundamental role in carbon and nutrient cycling and are thus an integral link between ecosystems and climate. Here, we highlight a major black box hindering our ability to anticipate ecosystem climate responses...
Article
Here, we report the assembled and annotated genome of the freshwater diatom Fragilaria crotonensis SAG 28.96. The 61.85-Mb nuclear genome was assembled into 879 contigs, has a GC content of 47.40%, contains 26,015 predicted genes, and shows completeness of 81%.
Article
Pseudanabaena spp. are filamentous cyanobacteria widely distributed in temperate lakes. Though infrequent, they can form harmful algal blooms. Here, we present a high-quality metagenome-assembled genome of a Pseudanabaena sp. from a toxic, crimson cyanobacterial bloom in Lake Salubria, NY.
Article
Full-text available
The trace metal iron (Fe) controls the diversity and activity of phytoplankton across the surface oceans, a paradigm established through decades of in situ and mesocosm experimental studies. Despite widespread Fe-limitation within high-nutrient, low chlorophyll (HNLC) waters, significant contributions of the cyanobacterium Synechococcus to the phyt...
Article
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Here, we report the genomic sequence of Aureococcus anophagefferens virus, assembled into one circular contig from both Nanopore and Illumina reads. The genome is 381,717 bp long with a GC content of 29.1%, which includes an additional 5-kb region between the previously predicted polar ends of the reference genome.
Article
Previous reports suggest planktonic and under-ice winter microbial communities in Lake Erie are dominated by diatoms. Here, we report the assembled metatranscriptomes of 79 Lake Erie surface water microbial communities spanning both the winter (28 samples) and spring (51 samples) months over spatial, temporal, and climatic gradients in 2019 through...
Article
Harmful cyanobacteria are a global environmental problem, yet we lack actionable understanding of toxigenic versus nontoxigenic strain ecology and toxin production. We performed a large-scale meta-analysis including 103 papers and used it to develop a mechanistic, agent-based model of Microcystis growth and microcystin production. Simulations for L...
Article
Full-text available
Nano‐ and picophytoplankton are a major component of open‐ocean ecosystems and one of the main plankton functional types in biogeochemical models, yet little is known about their trace metal contents. In cultures of the picoeukaryote Ostreococcus lucimarinus, iron limitation reduced iron quotas by 68%, a fraction of the plasticity known in diatoms....
Article
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The environmental conditions experienced by microbial communities are rarely fully simulated in the laboratory. Researchers use experimental containers (“bottles”), where natural samples can be manipulated and evaluated. However, container-based methods are subject to “bottle effects”: changes that occur when enclosing the plankton community that a...
Article
Full-text available
Harmful algal blooms are increasing in duration and severity globally, resulting in increased research interest. The use of genetic sequencing technologies has provided a wealth of opportunity to advance knowledge, but also poses a risk to that knowledge if handled incorrectly. The vast numbers of sequence processing tools and protocols provide a m...
Article
The pelagophyte Aureococcus anophagefferens causes harmful brown tide blooms in marine embayments on three continents. Aureococcus anophagefferens was the first harmful algal bloom species to have its genome sequenced, an advance that evidenced genes important for adaptation to environmental conditions that prevail during brown tides. To expand the...
Preprint
This protocol is designed/used for extraction of total cellular lipids from cyanobacteria samples (either lab cultures or field samples) collected on polycarbonate filters for use in lipid analysis and quantification via mass spectrometry. Please contact Dr. Steven Wilhelm (wilhelm@utk.edu) or Robbie M. Martin (rmarti49@vols.utk.edu) for additional...
Preprint
Full-text available
Climate warming will likely disrupt the flow of matter and energy within ecosystems, threatening the global carbon balance. Microorganisms are fundamental components of carbon cycling and are thus integral to ecosystem climate responses. However, ecosystem responses to warming are uncertain due to the functional and trophic complexity of microbial...
Article
Full-text available
Among early adopters of wastewater monitoring for SARS-CoV-2 have been colleges and universities throughout North America, many of whom are using this approach to monitor congregate living facilities for early evidence of COVID-19 infection as an integral component of campus screening programs. Yet, while there have been numerous examples where was...
Article
Full-text available
Microbial interactions in harmful algal bloom (HAB) communities have been examined in marine systems, but are poorly studied in fresh waters. To investigate HAB-microbe interactions, we isolated bacteria with close associations to bloom-forming cyanobacteria, Microcystis spp., during a 2017 bloom in the western basin of Lake Erie. The genomes of fi...
Preprint
Full-text available
A wastewater surveillance program targeting a university residence hall was implemented during the spring semester 2021 as a proactive measure to avoid an outbreak of COVID-19 on campus. Over a period of 7 weeks from early February through late March 2021, wastewater originating from the residence hall was collected as grab samples 3 times per week...
Article
Full-text available
There is growing interest in the use of metatranscriptomics to study virus community dynamics. We used RNA samples collected from harmful brown tides caused by the eukaryotic alga Aureococcus anophagefferens within New York (United States) estuaries and in the process observed how preprocessing of libraries by either selection for polyadenylation o...
Article
Full-text available
Pelagophytes are abundant picophytoplankton within open ocean ecosystems and the causative algae of harmful brown tide blooms in estuaries. The physiological capabilities facilitating the ecological success of pelagophytes in these diverse ecosystems remains poorly understood. Here, we investigated the transcriptional response of two coastal pelago...
Article
Full-text available
Cyanobacterial Harmful Algal Blooms (CyanoHABs) commonly increase water column pH to alkaline levels ≥9.2, and to as high as 11. This elevated pH has been suggested to confer a competitive advantage to cyanobacteria such as Microcystis aeruginosa. Yet, there is limited information regarding the restrictive effects bloom-induced pH levels may impose...
Article
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Raphidiopsis raciborskii and Planktothrix agardhii are filamentous, potentially toxin-producing cyanobacteria that form nuisance blooms in fresh waters. Here, we report high-quality metagenome-assembled genome sequences of R. raciborskii and P. agardhii collected from a bloom in Kissena Lake, New York.
Article
Full-text available
Cyanobacterial harmful algal bloom (CyanoHAB) proliferation is a global problem impacting ecosystem and human health. Western Lake Erie (WLE) typically endures two highly toxic CyanoHABs during summer: a Microcystis spp. bloom in Maumee Bay that extends throughout the western basin, and a Planktothrix spp. bloom in Sandusky Bay. Recently, the USA a...
Article
Full-text available
Harmful algal blooms are commonly thought to be dominated by a single genus, but they are not homogenous communities. Current approaches, both molecular and culture-based, often overlook fine-scale variations in community composition that can influence bloom dynamics. We combined homology-based searches (BLASTX) and phylogenetics to distinguish and...
Article
Full-text available
Microcystins produced during harmful cyanobacterial blooms are a public health concern. Although patterns are emerging, the environmental cues that stimulate production of microcystin remain confusing, hindering our ability to predict fluctuations in bloom toxicity. In earlier work, growth at cool temperatures relative to optimum (18°C vs. 26°C) wa...
Article
Wind-driven wave disturbance is one of the environmental factors that shapes the formation of Microcystis blooms. Here we present data on the effect of different disturbance modes (continuous vs intermittent disturbances) on colony size, biomass and dominance of Microcystis in Lake Taihu under field conditions. Small submersible pumps were used to...
Article
Full-text available
Viruses modulate the function(s) of environmentally relevant microbial populations, yet considerations of the metabolic capabilities of individual virus particles themselves are rare. We used shotgun proteomics to quantitatively identify 43 virus-encoded proteins packaged within purified Aureococcus anophagefferens Virus (AaV) particles, normalizin...
Article
Full-text available
Chloroviruses (family Phycodnaviridae) infect eukaryotic, freshwater, unicellular green algae. A unique feature of these viruses is an abundance of DNA methyltransferases, with isolates dedicating up to 4.5% of their protein coding potential to these genes. This diversity highlights just one of the long-standing values of the chlorovirus model syst...
Article
Full-text available
Large lakes of the world are habitats for diverse species, including endemic taxa, and are valuable resources that provide humanity with many ecosystem services. They are also sentinels of global and local change, and recent studies in limnology and paleolimnology have demonstrated disturbing evidence of their collective degradation in terms of dep...
Article
The over‐enrichment of nitrogen (N) in the environment has contributed to severe and recurring harmful cyanobacterial blooms, especially by the non‐N2‐fixing Microcystis spp. N chemical speciation influences cyanobacterial growth, persistence and the production of the hepatotoxin microcystin, but the physiological mechanisms to explain these observ...
Article
Full-text available
The pelagophyte Aureococcus anophagefferens blooms annually in shallow bays around the world, where it is hypothesized to outcompete other phytoplankton in part by using alternative nitrogen sources. The high proportion of natural populations that are infected during the late stages of the bloom suggest viruses cause bloom collapse. We hypothesized...
Article
Full-text available
The pelagophyte Aureococcus anophagefferens has caused recurrent brown tide blooms along the northeast coast of the United States since the mid-1980’s, and more recently spread to other regions of the globe. These blooms, due to the high cell densities, are associated with severe light attenuation that destroys the sea grass beds which provide the...
Article
Full-text available
Microcystins are potent hepatotoxins that are frequently detected in fresh water lakes plagued by toxic cyanobacteria. Microbial biodegradation has been referred to as the most important avenue for removal of microcystin from aquatic environments. The biochemical pathway most commonly associated with the degradation of microcystin is encoded by the...
Poster
One major threat to freshwater systems is the proliferation of toxic cyanobacterial harmful algal blooms (cyanoHABs). A prolific group of cyanotoxins, the microcystins, is enriched in nitrogen (N), and their synthesis is thought to be linked to N availability. There is a need to investigate the potential roles a major watershed N source; N fertiliz...
Preprint
Aseptic technique has historically served as a fundamental practice in microbiology, helping maintain culture purity and integrity. This technique has been widely encouraged and employed for use with cultures of heterotrophic bacteria as well as freshwater and marine algae. Yet, recent observations have suggested these approaches may bring their ow...
Article
Full-text available
This study examined diel shifts in metabolic functions of Microcystis spp. during a 48-h Lagrangian survey of a toxin-producing cyanobacterial bloom in western Lake Erie in the aftermath of the 2014 Toledo Water Crisis. Transcripts mapped to the genomes of recently sequenced lower Great Lakes Microcystis isolates showed distinct patterns of gene ex...
Article
Viruses shape microbial communities and associated processes across ecosystems. However, soil viral ecology remains poorly understood, and in particular, the vertical distribution and diversity of viruses and virus-host interactions in soils remain underexplored. In this study, 16S rRNA gene amplicon and virome sequencing were applied to investigat...
Article
Full-text available
An adequate in vivo analysis of HCMV’s viral chemokine vCXCL-1 has been lacking. Here we generate recombinant MCMVs expressing vCXCL-1 to study vCXCL-1 function in vivo using MCMV as a surrogate. We demonstrate that vCXCL-1 increases MCMV dissemination kinetics for both primary and secondary dissemination. Additionally, we provide evidence, that th...
Article
Full-text available
Soil microbiome responses to short-term nitrogen (N) inputs remain uncertain when compared with previous research that has focused on long-term fertilization responses. Here, we examined soil bacterial/archaeal and fungal communities pre- and post-N fertilization in an 8 year-old switchgrass field, in which twenty-four plots received N fertilizatio...
Article
Full-text available
Coevolution is a force contributing to the generation and maintenance of biodiversity. It is influenced by environmental conditions including the scarcity of essential resources, which can drive the evolution of defence and virulence traits. We conducted a long‐term chemostat experiment where the marine cyanobacterium Synechococcus was challenged w...
Article
Full-text available
Some giant viruses are ecological agents that are predicted to be involved in the top-down control of single-celled eukaryotic algae populations in aquatic ecosystems. Despite an increased interest in giant viruses since the discovery and characterization of Mimivirus and other viral giants, little is known about their physiology and ecology. In th...
Article
Full-text available
Best practices in laboratory culture management often include cryopreservation of microbiota, but this can be challenging with some virus particles. By preserving viral isolates researchers can mitigate genetic drift and laboratory-induced selection, thereby maintaining genetically consistent strains between experiments. To this end, we developed a...
Preprint
Coevolution is a force contributing to the generation and maintenance of biodiversity. It is influenced by environmental conditions including the scarcity of essential resources, which can drive the evolution of defense and virulence traits. We conducted a long-term chemostat experiment where the marine cyanobacterium Synechococcus was challenged w...
Article
Full-text available
The delivery of fermentable substrate(s) to subsurface environments stimulates Fe(III)‐bioreduction and achieves detoxification of organic/inorganic contaminants. Though much research has been conducted on the microbiology of such engineered systems at lab and field scales, little attention has been given to the phage‐host interactions and virus co...
Preprint
Full-text available
Best practices in laboratory culture management often include cryopreservation of microbiota, but this can be challenging with some virus particles. By preserving viral isolates researchers can mitigate genetic drift and laboratory-induced selection, thereby maintaining genetically consistent strains between experiments. To this end, we developed a...
Article
Full-text available
Butterfield Lake is a mesotrophic lake in New York State where residents and pets have experienced unexplained health issues. Microseira wollei (basionym Lyngbya wollei) was found at two of 15 sites in Butterfield Lake and analyzed for microcystins, anatoxins, cylindrospermopsins, and paralytic shellfish poisoning toxins (PSTs). Only PSTs and trace...
Preprint
Full-text available
Soil microbiome responses to short-term nitrogen (N) inputs within the context of existing spatio-temporal variability remain uncertain. Here, we examined soil bacterial and fungal communities pre/post-N fertilization in an 8 year-old switchgrass field, in which twenty-four plots received N fertilization at three levels (0, 100, and 200 kg N ha-1 a...
Article
Full-text available
We present an extension of the Minimum Information about any (x) Sequence (MIxS) standard for reporting sequences of uncultivated virus genomes. Minimum Information about an Uncultivated Virus Genome (MIUViG) standards were developed within the Genomic Standards Consortium framework and include virus origin, genome quality, genome annotation, taxon...
Article
Full-text available
Mixing is an integral environmental factor that affects lake ecosystems. For the cyanobacterium Microcystis , colony size is important with respects to migration velocity, how cells respond to grazing pressure, light attenuation, nutrient uptake and growth. To understand how mixing shapes colony size and the growth of Microcystis , we measured the...
Article
Algal viruses and cyanophages infect primary producers and have wide-ranging effects upon the food web and biogeochemical cycles. However, little is known about the diversity and distribution of these viruses in freshwater sediments. To address this information gap, sediment core samples were collected from Lake Erie at 4 distinct sites across its...