Papers by Katherine McMahon
Abstract}The feasibility of codigestion of the organic fraction of municipal solid waste, primary... more Abstract}The feasibility of codigestion of the organic fraction of municipal solid waste, primary sludge, and waste activated sludge was evaluated in mesophilic (378C), laboratory-scale digesters. In a first experiment, different startup strategies were compared using four digesters, operated under continuously mixed conditions. After two weeks, the experiment was continued under minimally mixed conditions. Results demonstrated that reducing the level of
PLOS ONE, 2015
Cyanobacterial harmful algal blooms (cyanoHABs) are a primary source of water quality degradation... more Cyanobacterial harmful algal blooms (cyanoHABs) are a primary source of water quality degradation in eutrophic lakes. The occurrence of cyanoHABs is ubiquitous and expected to increase with current climate and land use change scenarios. However, it is currently unknown what environmental parameters are important for indicating the presence of cyano-HAB toxins making them difficult to predict or even monitor on time-scales relevant to protecting public health. Using qPCR, we aimed to quantify genes within the microcystin operon (mcy) to determine which cyanobacterial taxa, and what percentage of the total cyanobacterial community, were responsible for microcystin production in four eutrophic lakes. We targeted Microcystis-16S, mcyA, and Microcystis, Planktothrix, and Anabaena-specific mcyE genes. We also measured microcystins and several biological, chemical, and physical parameters-such as temperature, lake stability, nutrients, pigments and cyanobacterial community composition (CCC)-to search for possible correlations to gene copy abundance and MC production. All four lakes contained Microcystis-mcyE genes and high percentages of toxic Microcystis, suggesting Microcystis was the dominant microcystin producer. However, all genes were highly variable temporally, and in few cases, correlated with increased temperature and nutrients as the summer progressed. Interestingly, toxin gene abundances (and biomass indicators) were anti-correlated with microcystin in all lakes except the largest lake, Lake Mendota. Similarly, gene abundance and microcystins differentially correlated to CCC in all lakes. Thus, we conclude that the presence of microcystin genes are not a useful tool for eliciting an ecological role for toxins in the environment, nor are microcystin genes (e.g. DNA) a good indicator of toxins in the environment.
Limnology and oceanography, methods
Mixing events in temperate lakes are thought to represent an important ecological reset for verti... more Mixing events in temperate lakes are thought to represent an important ecological reset for vertically stratified variables such as nutrients and dissolved oxygen (Alvarez-Cobelas et al. 2005), while also potentially increasing surface fluxes of mass and energy (e.g., Wuest and Lorke 2003; Eugster et al. 2003). Lake mixing is also important for the ecology of temperate lakes and influences available thermal habitat for aquatic species (Meyer et al. 1999), ice cover duration (Robertson et al. 1992; Jensen et al. 2007), and carbon sequestration (e.g., Cole et al. 2007; Eugster et al. 2003). Mixing events can vary in frequency and magnitude; such as, the controls of diurnal heating and cooling on surface layer dynamics (Imberger 1985), deepening of the seasonal thermo-cline resulting from short-term variations in atmospheric forc-ing (MacIntyre et al. 2009; Gaiser et al. 2009), and seasonal overturns caused by complete thermal destratification (Malm and Zilitinkevich 1994). For tempera...
Proceedings of the Water Environment Federation, 2006
Twenty seven and twenty one partial to complete 16S rRNA gene sequences were identified in the US... more Twenty seven and twenty one partial to complete 16S rRNA gene sequences were identified in the US and OZ metagenomes respectively, together representing 30 phylotypes. In only three cases 82 WEFTEC®.06 Figure 2. Reconstruction of the aerobic metabolism of A. phosphatis based on the genes identified in the metagenome sequence. (2000) Identification of polyphosphate accumulating organisms and the design of 16s rRNAdirected probes for their detection and quantitation. Appl Environ Microbiol, 66(3): 1175-1182. Hesselmann, R. P. X., Werlen, C., Hahn, D., van der Meer, J. R. and Zehnder, A. J. B. (1999) Enrichment, phylogenetic analysis and detection of a bacterium that performs enhanced biological phosphate removal in activated sludge. Syst. Appl. Microbiol., 22(3): 454-465. 2002) Polyphosphate kinase from activated sludge performing enhanced biological phosphorus removal. Appl Environ Microbiol, 68(10): 4971-8. Mino, T., Van Loosdrecht, M. C. M. and Heijnen, J. J. (1998) Microbiology and biochemistry of the enhanced biological phosphate removal process. Water Res., 32(11): 3193-3207. Pereira, H., Lemos, P. C., Reis, M. A. M., Crespo, J. P. S. G., Carrondo, M. J. T. and Santos, H. (1996) Model for carbon metabolism in biological phosphorus removal process based on in vivo 13C-NMR labelling experiments. Water Res., 30(9): 2128-2138. Seviour, R. J., Mino, T. and Onuki, M. (2003) The microbiology of biological phosphorus removal in activated sludge systems. FEMS Microbiol Rev, 27(1): 99-127. 85 WEFTEC®.06
Background/Question/Methods The energy and materials provided by cross-ecosystem subsidies critic... more Background/Question/Methods The energy and materials provided by cross-ecosystem subsidies critically shape food web structure and ecosystem functioning. Despite the acknowledged importance of subsidies, surprisingly little information is available regarding the effects of climate change on the availability and quality of ecological subsidies and the resulting biological response in the recipient system. Leaves from terrestrial vegetation are an important subsidy for aquatic ecosystems, especially during autumn leaf drop. Leaf chemistry is highly variable and depends on many environmental factors, including climate. We hypothesized that climate-mediated alterations in leaf chemistry are biologically meaningful for plankton food webs during autumn leaf drop, including both the photoautotroph-based “green” and detrivivore-based “brown” food webs. To test this hypothesis, we collected leaves from heated and ambient temperature forest plots from a long-term soil warming experiment at th...
Biotechnology and bioengineering, Jan 30, 2004
Microbial population dynamics were investigated during start-up and during periods of overload co... more Microbial population dynamics were investigated during start-up and during periods of overload conditions in anaerobic co-digesters treating municipal solid waste and sewage sludge. Changes in community structure were monitored using ribosomal RNA-based oligonucleotide probe hybridization to measure the abundance of syntrophic propionate-oxidizing bacteria (SPOB), saturated fatty acid-beta-oxidizing syntrophs (SFAS), and methanogens. These changes were linked to traditional performance parameters such as biogas production and volatile fatty acid (VFA) concentrations. Digesters with high levels of Archaea started up successfully. Methanosaeta concilii was the dominant aceticlastic methanogen in these systems. In contrast, digesters that experienced a difficult start-up period had lower levels of Archaea with proportionally more abundant Methanosarcina spp. Syntrophic propionate-oxidizing bacteria and saturated fatty acid-beta-oxidizing syntrophs were present at low levels in all dige...
Water science and technology : a journal of the International Association on Water Pollution Research, 2002
The community structure and metabolic function of activated sludge carrying out enhanced biologic... more The community structure and metabolic function of activated sludge carrying out enhanced biological phosphorus removal have been investigated. Laboratory-scale sequencing batch reactors were operated at several influent COD/P ratios to obtain sludges with a range of phosphorus contents. Molecular microbiological techniques based on small subunit ribosomal RNA were used to characterize the structure of these sludges. The dominant polyphosphate accumulating organism was a close relative of Rhodocyclus tenuis, a member of the beta subclass of the Proteobacteria. Fragments of genes coding for polyphosphate kinase (PPK), thought to be responsible for polyphosphate accumulation, were retrieved from one of the sludges. The relative abundance of PPK gene copies in genomic DNA extracted from sludges was determined to confirm that at least one of the PPK gene sequences was derived from the dominant polyphosphate accumulating organism.
Applied and environmental microbiology, 2002
A novel polyphosphate kinase (PPK) was retrieved from an uncultivated organism in activated sludg... more A novel polyphosphate kinase (PPK) was retrieved from an uncultivated organism in activated sludge carrying out enhanced biological phosphorus removal (EBPR). Acetate-fed laboratory-scale sequencing batch reactors were used to maintain sludge with a high phosphorus content (approximately 11% of the biomass). PCR-based clone libraries of small subunit rRNA genes and fluorescent in situ hybridization (FISH) were used to verify that the sludge was enriched in Rhodocyclus-like beta-Proteobacteria known to be associated with sludges carrying out EBPR. These organisms comprised approximately 80% of total bacteria in the sludge, as assessed by FISH. Degenerate PCR primers were designed to retrieve fragments of putative ppk genes from a pure culture of Rhodocyclus tenuis and from organisms in the sludge. Four novel ppk homologs were found in the sludge, and two of these (types I and II) shared a high degree of amino acid similarity with R. tenuis PPK (86 and 87% similarity, respectively). D...
Biodegradation, 2001
Heavy metal and radionuclide contamination presents a significant environmental problem worldwide... more Heavy metal and radionuclide contamination presents a significant environmental problem worldwide. Precipitation of heavy metals on membranes of cells that secrete phosphate has been shown to be an effective method of reducing the volume of these wastes, thus reducing the cost of disposal. A consortium of organisms, some of which secrete large quantities of phosphate, was enriched in a laboratory-scale
Environmental Microbiology, 2008
Multiple forces structure natural microbial communities, but the relative roles and interactions ... more Multiple forces structure natural microbial communities, but the relative roles and interactions of these drivers are poorly understood. Gradients of physical and chemical parameters can be especially influential. In traditional ecological theory, variability in environmental conditions across space and time represents habitat heterogeneity, which may shape communities. Here we used aquatic microbial communities as a model to investigate the relationship between habitat heterogeneity and community composition and dynamics. We defined spatial habitat heterogeneity as vertical temperature and dissolved oxygen (DO) gradients in the water column, and temporal habitat heterogeneity as variation throughout the open-water season in these environmental parameters. Seasonal lake mixing events contribute to temporal habitat heterogeneity by destroying and re-creating these gradients. Because of this, we selected three lakes along a range of annual mixing frequency (polymictic, dimictic, meromictic) for our study. We found that bacterial community composition (BCC) was distinct between the epilimnion and hypolimnion within stratified lakes, and also more variable within the epilimnia through time. We found stark differences in patterns of epilimnion and hypolimnion dynamics over time and across lakes, suggesting that specific drivers have distinct relative importance for each community.
We explored patterns of change in bacterioplankton and phytoplankton community composition in res... more We explored patterns of change in bacterioplankton and phytoplankton community composition in response to typhoons in a subtropical, subalpine freshwater humic lake in Taiwan. Thermal profiles with depth, near- surface dissolved oxygen, and meteorological conditions were measured at high temporal resolution using an instrumented buoy. We collected samples across a time series spanning two typhoon seasons and assessed bacterial community
Water research, 2014
For eutrophic lakes, patterns of phosphorus (P) measured by standard methods are well documented ... more For eutrophic lakes, patterns of phosphorus (P) measured by standard methods are well documented but provide little information about the components comprising standard operational definitions. Dissolved P (DP) and particulate P (PP) represents important but rarely characterized nutrient pools. Samples from Lake Mendota, Wisconsin, USA were characterized using 31-phosphorus nuclear magnetic resonance spectroscopy ((31)P NMR) during the open water season of 2011 in this unmatched temporal study of aquatic P dynamics. A suite of organic and inorganic P forms was detected in both dissolved and particulate fractions: orthophosphate, orthophosphate monoesters, orthophosphate diesters, pyrophosphate, polyphosphate, and phosphonates. Through time, phytoplankton biomass, temperature, dissolved oxygen, and water clarity were correlated with changes in the relative proportion of P fractions. Particulate P can be used as a proxy for phytoplankton-bound P, and in this study, a high proportion o...
2008 38th Annual Frontiers in Education Conference, 2008
A new cross-disciplinary first-year course, "Introduction to Society's Engineering Grand Challeng... more A new cross-disciplinary first-year course, "Introduction to Society's Engineering Grand Challenges," has been developed as part of a collegewide initiative at the University of Wisconsin-Madison to transform undergraduate engineering education for 2010 and beyond. The inspiration for developing this new course was the National Academy of Engineering's "Engineering Grand Challenges" project. By emphasizing humanitarian applications in an introductory engineering course, we expect to not only inspire future generations of engineers and show students how the skills they will be learning can have a positive impact on quality of life, but also encourage more women to pursue engineering degrees. The course consists of an introductory module followed by two theme-based modules of the student's choosing, selected from the following themes: "Engineering challenges that impact our lives on a personal scale," "Engineering for the developing world," "Engineering the megacity," "Global engineering challenges," and "Engineering beyond Planet Earth." The team-taught course is being offered for the first time in the spring of 2008. This paper presents an overview of the course, the expected outcomes, and the preliminary results from a surveybased assessment tool.
Proceedings of the Water Environment Federation, 2013
Frontiers in Microbiology, 2012
Understanding characteristic variation in aquatic bacterial community composition (BCC) across sp... more Understanding characteristic variation in aquatic bacterial community composition (BCC) across space and time can inform us about processes driving community assembly and the ability of bacterial communities to respond to perturbations. In this study, we synthesize BCC data from north temperate lakes to evaluate our current understanding of how BCC varies across multiple scales in time and space. A hierarchy of average similarity emerged with the highest similarity found among samples collected within the same lake, especially within the same basin, followed by similarity among samples collected through time within the same lake, and finally similarity among samples collected from different lakes. Using decay of similarity across time and space, we identified equivalent temporal (1 day) and spatial (10 m) scales of BCC variation. Finally, we identify an intriguing pattern of contrasting patterns of intra-and inter-annual BCC variation in two lakes. We argue our synthesis of spatio-temporal variation of aquatic BCC informs expectations for the response of aquatic bacterial communities to perturbation and environmental change. However, further long-term temporal observations will be needed to develop a general understanding of inter-annual BCC variation and our ability to use aquatic BCC as a sensitive metric of environmental change.
Limnology and Oceanography, 2007
We investigated patterns of intra-and interannual change in pelagic bacterial community compositi... more We investigated patterns of intra-and interannual change in pelagic bacterial community composition (BCC, assessed using automated ribosomal intergenic spacer analysis) over six years in eutrophic Lake Mendota, Wisconsin. A regular phenology was repeated across years, implying that freshwater bacterial communities are more predictable in their dynamics than previously thought. Seasonal events, such as water column mixing and trends in water temperature, were most strongly related to BCC variation. Communities became progressively less similar across years between the months of May and September, when the lake was thermally stratified. Dissolved oxygen and nitrate + nitrite concentrations were highly correlated to BCC change within and across seasons. The relationship between BCC and seasonal drivers suggests that trajectories of community change observed over long time series will reflect large-scale climate variation.
The ISME Journal, 2014
Members of the acI lineage of Actinobacteria are the most abundant microorganisms in most freshwa... more Members of the acI lineage of Actinobacteria are the most abundant microorganisms in most freshwater lakes; however, our understanding of the keys to their success and their role in carbon and nutrient cycling in freshwater systems has been hampered by the lack of pure cultures and genomes. We obtained draft genome assemblies from 11 single cells representing three acI tribes (acI-A1, acI-A7, acI-B1) from four temperate lakes in the United States and Europe. Comparative analysis of acI SAGs and other available freshwater bacterial genomes showed that acI has more gene content directed toward carbohydrate acquisition as compared to Polynucleobacter and LD12 Alphaproteobacteria, which seem to specialize more on carboxylic acids. The acI genomes contain actinorhodopsin as well as some genes involved in anaplerotic carbon fixation indicating the capacity to supplement their known heterotrophic lifestyle. Genome-level differences between the acI-A and acI-B clades suggest specialization at the clade level for carbon substrate acquisition. Overall, the acI genomes appear to be highly streamlined versions of Actinobacteria that include some genes allowing it to take advantage of sunlight and N-rich organic compounds such as polyamines, di-and oligopeptides, branched-chain amino acids and cyanophycin. This work significantly expands the known metabolic potential of the cosmopolitan freshwater acI lineage and its ecological and genetic traits.
Fertility and Sterility, 2003
ObjectiveTo examine the relationship between physical violence, controlling behavior, and spontan... more ObjectiveTo examine the relationship between physical violence, controlling behavior, and spontaneous abortion (SAB).
Australasian Radiology - AUSTRALAS RADIOL, 2005
The aim of this retrospective case series was to assess the role of breast MRI in the investigati... more The aim of this retrospective case series was to assess the role of breast MRI in the investigation of 'occult' malignancy, and the associated potential to influence patient management. Between January 2000 and March 2004, 18 patients, who presented with axillary lymphadenopathy, most likely due to 'occult' breast cancer, were examined with MRI of the breast. The results showed 12 true positives, four true negatives, and two false positives. This gave an overall sensitivity of 85.7% and an overall accuracy of 86.7%. In those in whom malignancy was identified on MRI and subsequently proven histologically, 78% of these cancers were identified, and localized by preoperative MRI-guided sonography. In addition, 55% of these patients were eligible for conservative surgery. As such, MRI of the breast is highly sensitive for the detection of mammographically and clinically occult breast cancer. The use of MRI enables a preoperative diagnosis to be made in a high percentage of patients and may allow retrospective targeted ultrasound localization. Definitive surgical planning, including the option of breast conservation, is made possible with the result of the MRI examination.
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Papers by Katherine McMahon