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Introduction, Stephen G. Krueger, Keahi Adolpho, Krista Mccracken

Dartmouth Library Staff Publications

In the library profession, and in the world as a whole, the experiences of trans and gender diverse people often go unnoticed, hidden, and ignored. But we are here. Trans and Gender Diverse Voices in Libraries is entirely written and edited by trans and gender diverse people involved in the field: its fifty-seven authors include workers from academic and public libraries, special collections and archives, and more; LIS students; and a few people who have left the library profession completely.

This book is not intended to be the definitive guide to trans and gender diverse experiences in libraries, but instead …

The Real Energy Burden: Exploring The Intersection Of Equity And Home Energy Efficiency In Vermont, Nathaniel G. Roe

ENGS 88 Honors Thesis (AB Students)

This thesis quantifies the financial burden induced by a home energy efficiency and electrification project through a new metric, the real energy burden (REB). REB captures the percentage of income allocated to the annualized capital cost and the annual energy expenditure of an energy efficiency project. To characterize and demonstrate the use of REB, I draw data from the National Renewable Energy Laboratory ResStock Housing Stock tool to simulate a 2023 energy efficiency and electrification project for three Vermont household archetypes: low, moderate, and high incomes. I find that the REB for the low income archetype is above the energy …

Product Review Classification Using Machine Learning And Statistical Data Analysis, Kajal Singh

Independent Student Projects and Publications

The aim of the paper is to implement and analyze the machine learning models for product review dataset. The project focuses on binary classification, multi-class classification, and clustering approaches to analyze and categorize product reviews. The performance of the models over each of the five classification tasks is measured by the 5-fold cross-validation scores over the training data.

Interpretable Learning In Multivariate Big Data Analysis For Network Monitoring, José Camacho, Rasmus Bro, David Kotz

Dartmouth Scholarship

There is an increasing interest in the development of new data-driven models useful to assess the performance of communication networks. For many applications, like network monitoring and troubleshooting, a data model is of little use if it cannot be interpreted by a human operator. In this paper, we present an extension of the Multivariate Big Data Analysis (MBDA) methodology, a recently proposed interpretable data analysis tool. In this extension, we propose a solution to the automatic derivation of features, a cornerstone step for the application of MBDA when the amount of data is massive. The resulting network monitoring approach allows …

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Rigorous Care: The Early Warning Syllabus, Michelle Warren, Guadalupe Ortega, Jenny Oh

Open Education Initiative Projects

This document includes a set of policies that are designed to provide efficient ways for instructors to implement pedagogies of care. The principle of “rigorous care” is informed by research on learning, accessibility, and mental health. The idea of “early warnings” is meant to help students identify their needs and seek support before problems become unmanageable. Both ideas respect the fact that both students and instructors work under enormous pressure.

Each policy statement is preceded by a brief framing justification and followed by a selected bibliography of the research and testimonials that have informed the policy.

Reasoning About The Conant Gasket, M. Douglas Mcilroy

Computer Science Technical Reports

Previously conjectured properties of the Conant gasket, a particular non-periodic tiling of the non-negative integer grid, are proved using new recurrences. A slabwise periodicity property is identified and proved. Further fractal properties are conjectured.

The Wennberg Anthology, John E. Wennberg

Dartmouth Scholarship

In 1967, after finishing my postgraduate training at Johns Hopkins in internal medicine and epidemiology, I took a job at the University of Vermont in Burlington as Director of the Northern New England Regional Medical Program (RMP). The Vermont program was one of some fifty RMPs that blanketed the country as part of President Johnson’s Great Society program. The idea behind the RMP was that advances in biomedicine had so improved the outcomes of major killer diseases that it was critical to ensure that all Americans, not just those fortunate enough to live near an academic medical center, had access …

Structural Files For The Etr1 Ethylene-Receptor Dimer Based On Computational Modeling, Beenish J. Azhar, Safdar Abbas, Sitwat Aman, Maria V. Yamburenko, Wei Chen, Lena Muller, Buket Uzun, David A. Jewell, Jian Dong, Samina N. Shakeel, Georg Groth, Brad M. Binder, Gevorg Grigoryan, G. Eric Schaller

Dartmouth Scholarship

Structural models for the ETR1 homodimer were generated with AlphaFold-Multimer. Coppers were modeled under two potential coordinations involving Cys65 and His69 of the ETR1 homodimer, one in which the two coppers are bound independently and do not share an interaction with each other, and another where they are closely bonded.

See the following publication for details: Azhar, B.J., Abbas, S., Aman, S., Yamburenko, M.V., Chen, W., Müller, L., Uzun, B., Jewell, D.A., Dong, J., Shakeel, S.N., Groth, G., Binder, B.M., Grigoryan, G., Schaller, G.E. (2023) Basis for high-affinity ethylene binding by the ethylene receptor ETR1 of Arabidopsis. Proc. Natl. Acad. …

Efficiency Of Primary Spine Care As Compared To Conventional Primary Care: A Retrospective Observational Study At An Academic Medical Center, Serena Bezdjian, James M. Whedon, Robb Russell, Justin M. Goehl, Louis A. Kazal

Dartmouth Scholarship

Background: Primary Spine Care (PSC) is an innovative model for the primary management of patients with spine-related disorders (SRDs), with a focus on the use of non-pharmacological therapies which now constitute the recommended first-line approach to back pain. PSC clinicians serve as the initial or early point of contact for spine patients and utilize evidence-based spine care pathways to improve outcomes and reduce escalation of care (EoC; e.g., spinal injections, diagnostic imaging, hospitalizations, referrals to a specialist). The present study examined 6-month outcomes to evaluate the efficiency of care for patients who received PSC as compared to conventional primary care. …

Missed Opportunities To Improve Food Security For Pregnant People: A Qualitative Study Of Prenatal Care Settings In Northern New England During The Covid-19 Pandemic, Chelsey R. Canavan, Tiffany D’Cruze, Meaghan A. Kennedy, Kayla E. Hatchell, Maureen Boardman, Arvind Suresh, Daisy Goodman, Alka Dev

Dartmouth Scholarship

Background: Food insecurity during pregnancy has important implications for maternal and newborn health. There is increasing commitment to screening for social needs within health care settings. However, little is known about current screening processes or the capacity for prenatal care clinics to address food insecurity among their patients. We aimed to assess barriers and facilitators prenatal care clinics face in addressing food insecurity among pregnant people and to identify opportunities to improve food security among this population. Methods: We conducted a qualitative study among prenatal care clinics in New Hampshire and Vermont. Staff and clinicians engaged in food security screening …

Immune Profiles And Dna Methylation Alterations Related With Non-Muscle-Invasive Bladder Cancer Outcomes, Ji Qing Chen, Lucas A. Salas, John K. Wiencke, Devin C. Koestler, Annette M. Molinaro, Angeline S. Andrew, John D. Seigne, Margaret R. Karagas, Karl T. Kelsey, Brock C. Christensen

Dartmouth Scholarship

Background: Non-muscle-invasive bladder cancer (NMIBC) patients receive frequent monitoring because ≥ 70% will have recurrent disease. However, screening is invasive, expensive, and associated with significant morbidity making bladder cancer the most expensive cancer to treat per capita. There is an urgent need to expand the understanding of markers related to recurrence and survival outcomes of NMIBC. Methods and results: We used the Illumina HumanMethylationEPIC array to measure peripheral blood DNA methylation profiles of NMIBC patients (N = 603) enrolled in a population-based cohort study in New Hampshire and applied cell type deconvolution to estimate immune cell-type proportions. Using Cox proportional …

Lung Function And Atherosclerosis: A Cross-Sectional Study Of Multimorbidity In Rural Uganda, Rebecca F. Gilbert, Cody Cichowitz, Prossy Bibangambah, June Ho Kim, Linda C. Hemphill, Isabelle T. Yang, Ruth N. Sentongo, Bernard Kakuhikire, David C. Christiani, Alexander C. Tsai, Samson Okello, Mark J. Siedner, Crystal M. North

Dartmouth Scholarship

Background: Chronic obstructive pulmonary disease (COPD) is a leading cause of global mortality. In high-income settings, the presence of cardiovascular disease among people with COPD increases mortality and complicates longitudinal disease management. An estimated 26 million people are living with COPD in sub-Saharan Africa, where risk factors for co-occurring pulmonary and cardiovascular disease may differ from high-income settings but remain uncharacterized. As non-communicable diseases have become the leading cause of death in sub-Saharan Africa, defining multimorbidity in this setting is critical to inform the required scale-up of existing healthcare infrastructure. Methods: We measured lung function and carotid intima media thickness …

Diurnal Rnapii-Tethered Chromatin Interactions Are Associated With Rhythmic Gene Expression In Rice, Li Deng, Baibai Gao, Lun Zhao, Ying Zhang, Qing Zhang, Minrong Guo, Yongqing Yang, Shuangqi Wang, Liang Xie, Hao Lou, Meng Ma, Wei Zhang, Zhilin Cao, Qinghua Zhang, C. Robertson Mcclung, Guoliang Li, Xingwang Li

Dartmouth Scholarship

Background: The daily cycling of plant physiological processes is speculated to arise from the coordinated rhythms of gene expression. However, the dynamics of diurnal 3D genome architecture and their potential functions underlying the rhythmic gene expression remain unclear. Results: Here, we reveal the genome-wide rhythmic occupancy of RNA polymerase II (RNAPII), which precedes mRNA accumulation by approximately 2 h. Rhythmic RNAPII binding dynamically correlates with RNAPII-mediated chromatin architecture remodeling at the genomic level of chromatin interactions, spatial clusters, and chromatin connectivity maps, which are associated with the circadian rhythm of gene expression. Rhythmically expressed genes within the same peak phases …

Gene–Gene Interaction Of Ahrwith And Within The Wntcascade Affects Susceptibility To Lung Cancer, Albert Rosenberger, Nils Muttray, Rayjean J. Hung, David C. Christiani, Neil E. Caporaso, Geoffrey Liu, Stig E. Bojesen, Loic Le Marchand, Demetrios Albanes, Melinda C. Aldrich, Adonina Tardon, Guillermo Fernández-Tardón, Gad Rennert, John K. Field, Michael P.A. Davies, Triantafillos Liloglou, Lambertus A. Kiemeney, Philip Lazarus, Bernadette Wendel, Aage Haugen, Shanbeh Zienolddiny, Stephen Lam, Matthew B. Schabath, Angeline S. Andrew, Eric J. Duell, Susanne M. Arnold, Gary E. Goodman, Chu Chen, Jennifer A. Doherty

Dartmouth Scholarship

Background: Aberrant Wnt signalling, regulating cell development and stemness, influences the development of many cancer types. The Aryl hydrocarbon receptor (AhR) mediates tumorigenesis of environmental pollutants. Complex interaction patterns of genes assigned to AhR/Wnt-signalling were recently associated with lung cancer susceptibility. Aim: To assess the association and predictive ability of AhR/Wnt-genes with lung cancer in cases and controls of European descent. Methods: Odds ratios (OR) were estimated for genomic variants assigned to the Wnt agonist and the antagonistic genes DKK2, DKK3, DKK4, FRZB, SFRP4 and Axin2. Logistic regression models with variable selection were trained, validated and tested to predict lung …

Phytolith Evidence For The Pastoral Origins Of Multi-Cropping In Mesopotamia (Ancient Iraq), Elise Jakoby Laugier, Jesse Casana, Dan Cabanes

Dartmouth Scholarship

Multi-cropping was vital for provisioning large population centers across ancient Eurasia. In Southwest Asia, multi-cropping, in which grain, fodder, or forage could be reliably cultivated during dry summer months, only became possible with the translocation of summer grains, like millet, from Africa and East Asia. Despite some textual sources suggesting millet cultivation as early as the third millennium BCE, the absence of robust archaeobotanical evidence for millet in semi-arid Mesopotamia (ancient Iraq) has led most archaeologists to conclude that millet was only grown in the region after the mid-first millennium BCE introduction of massive, state-sponsored irrigation systems. Here, we present …

I Am Hiq—A Novel Pair Of Accuracy Indices For Imputed Genotypes, Albert Rosenberger, Viola Tozzi, Heike Bickeböller, Rayjean J. Hung, David C. Christiani, Neil E. Caporaso, Geoffrey Liu, Stig E. Bojesen, Loic Le Marchand, Demetrios Albanes, Melinda C. Aldrich, Adonina Tardon, Guillermo Fernández-Tardón, Gad Rennert, John K. Field, Mike Davies, Triantafillos Liloglou, Lambertus A. Kiemeney, Philip Lazarus, Aage Haugen, Shanbeh Zienolddiny, Stephen Lam, Matthew B. Schabath, Angeline S. Andrew, Eric J. Duell, Susanne M. Arnold, Hans Brunnström, Olle Melander, Gary E. Goodman

Dartmouth Scholarship

Background: Imputation of untyped markers is a standard tool in genome-wide association studies to close the gap between directly genotyped and other known DNA variants. However, high accuracy with which genotypes are imputed is fundamental. Several accuracy measures have been proposed and some are implemented in imputation software, unfortunately diversely across platforms. In the present paper, we introduce Iam hiQ, an independent pair of accuracy measures that can be applied to dosage files, the output of all imputation software. Iam (imputation accuracy measure) quantifies the average amount of individual-specific versus population-specific genotype information in a linear manner. hiQ (heterogeneity in …

Predicting Clinical Outcomes Of Cancer Patients With A P53 Deficiency Gene Signature, Evelien Schaafsma, Eric M. Takacs, Sandeep Kaur, Chao Cheng, Manabu Kurokawa

Dartmouth Scholarship

The tumor suppressor p53, encoded by the TP53 gene, is mutated or nullified in nearly 50% of human cancers. It has long been debated whether TP53 mutations can be utilized as a biomarker to predict clinical outcomes of cancer patients. In this study, we applied computational methods to calculate p53 deficiency scores (PDSs) that reflect the inactivation of the p53 pathway, instead of TP53 mutation status. Compared to TP53 mutation status, the p53 deficiency gene signature is a powerful predictor of overall survival and drug sensitivity in a variety of cancer types and treatments. Interestingly, the PDSs predicted clinical outcomes …

A Problem At Any Age: A Case Report Of Congenital Malrotation With Bowel Ischemia In An 84-Year-Old, Marisa E. Schwab, Sage P. Kramer, Aya Bashi, Taehyun P. Chung, Claudia M. Mueller

Dartmouth Scholarship

Background: Malrotation with bowel ischemia is classically thought of as a disease of infants. However, the true prevalence of malrotation in both the pediatric and adult population is unknown due to the unclear number of asymptomatic patients. Case presentation: A previously healthy 84-year-old man with no prior abdominal surgeries presented with an acute abdomen and was found on CT to have small bowel located in the right hemiabdomen and an abnormal SMA-SMV relationship suggestive of intestinal malrotation, as well as pneumatosis intestinalis. He underwent an exploratory laparotomy, where he was found to have a paraduodenal space which did not contain …

Evolution Of The Repression Mechanisms In Circadian Clocks, Jonathan Tyler, Yining Lu, Jay Dunlap, Daniel B. Forger

Dartmouth Scholarship

Background: Circadian (daily) timekeeping is essential to the survival of many organisms. An integral part of all circadian timekeeping systems is negative feedback between an activator and repressor. However, the role of this feedback varies widely between lower and higher organisms. Results: Here, we study repression mechanisms in the cyanobacterial and eukaryotic clocks through mathematical modeling and systems analysis. We find a common mathematical model that describes the mechanism by which organisms generate rhythms; however, transcription’s role in this has diverged. In cyanobacteria, protein sequestration and phosphorylation generate and regulate rhythms while transcription regulation keeps proteins in proper stoichiometric balance. …

Phagocytosis By An Hiv Antibody Is Associated With Reduced Viremia Irrespective Of Enhanced Complement Lysis, David A. Spencer, Benjamin S. Goldberg, Shilpi Pandey, Tracy Ordonez, Jérémy Dufloo, Philip Barnette, William F. Sutton, Heidi Henderson, Rebecca Agnor, Lina Gao, Timothée Bruel, Olivier Schwartz, Nancy L. Haigwood, Margaret E. Ackerman, Ann J. Hessell

Dartmouth Scholarship

Increasingly, antibodies are being used to treat and prevent viral infections. In the context of HIV, efficacy is primarily attributed to dose-dependent neutralization potency and to a lesser extent Fc-mediated effector functions. It remains unclear whether augmenting effector functions of broadly neutralizing antibodies (bNAbs) may improve their clinical potential. Here, we use bNAb 10E8v4 targeting the membrane external proximal region (MPER) to examine the role of antibody-mediated effector and complement (C’) activity when administered prophylactically against SHIV challenge in rhesus macaques. With sub-protective dosing, we find a 78–88% reduction in post-acute viremia that is associated with 10E8v4-mediated phagocytosis acting at …

Volatile Organic Compound Profiling To Explore Primary Graft Dysfunction After Lung Transplantation, Pierre Hugues Stefanuto, Rosalba Romano, Christiaan A. Rees, Mavra Nasir, Louit Thakuria, Andre Simon, Anna K. Reed, Nandor Marczin, Jane E. Hill

Dartmouth Scholarship

Primary graft dysfunction (PGD) is a major determinant of morbidity and mortality following lung transplantation. Delineating basic mechanisms and molecular signatures of PGD remain a fundamental challenge. This pilot study examines if the pulmonary volatile organic compound (VOC) spectrum relate to PGD and postoperative outcomes. The VOC profiles of 58 bronchoalveolar lavage fluid (BALF) and blind bronchial aspirate samples from 35 transplant patients were extracted using solid-phase-microextraction and analyzed with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry. The support vector machine algorithm was used to identify VOCs that could differentiate patients with severe from lower grade PGD. Using …

Association Between Chiropractic Care And Use Of Prescription Opioids Among Older Medicare Beneficiaries With Spinal Pain: A Retrospective Observational Study, James M. Whedon, Sarah Uptmor, Andrew W.J. Toler, Serena Bezdjian, Todd A. Mackenzie, Louis A. Kazal

Dartmouth Scholarship

Background: The burden of spinal pain can be aggravated by the hazards of opioid analgesics, which are still widely prescribed for spinal pain despite evidence-based clinical guidelines that identify non-pharmacological therapies as the preferred first-line approach. Previous studies have found that chiropractic care is associated with decreased use of opioids, but have not focused on older Medicare beneficiaries, a vulnerable population with high rates of co-morbidity and polypharmacy. The purpose of this investigation was to evaluate the association between chiropractic utilization and use of prescription opioids among older adults with spinal pain. Methods: We conducted a retrospective observational study in …

Enhanced Cell Deconvolution Of Peripheral Blood Using Dna Methylation For High-Resolution Immune Profiling, Lucas A. Salas, Ze Zhang, Devin C. Koestler, Rondi A. Butler, Helen M. Hansen, Annette M. Molinaro, John K. Wiencke, Karl T. Kelsey, Brock C. Christensen

Dartmouth Scholarship

DNA methylation microarrays can be employed to interrogate cell-type composition in complex tissues. Here, we expand reference-based deconvolution of blood DNA methylation to include 12 leukocyte subtypes (neutrophils, eosinophils, basophils, monocytes, naïve and memory B cells, naïve and memory CD4 + and CD8 + T cells, natural killer, and T regulatory cells). Including derived variables, our method provides 56 immune profile variables. The IDOL (IDentifying Optimal Libraries) algorithm was used to identify libraries for deconvolution of DNA methylation data for current and previous platforms. The accuracy of deconvolution estimates obtained using our enhanced libraries was validated using artificial mixtures and …

National Identity Predicts Public Health Support During A Global Pandemic, Jay J. Van Bavel, Aleksandra Cichocka, Valerio Capraro, Hallgeir Sjåstad, John B. Nezlek, Tomislav Pavlović, Mark Alfano, Michele J. Gelfand, Flavio Azevedo, Michèle D. Birtel, Aleksandra Cislak, Patricia L. Lockwood, Robert Malcolm Ross, Koen Abts, Elena Agadullina, John Jamir Benzon Aruta, Sahba Nomvula Besharati, Alexander Bor, Becky L. Choma, Charles David Crabtree, William A. Cunningham, Koustav De, Waqas Ejaz, Christian T. Elbaek, Andrej Findor, Daniel Flichtentrei, Renata Franc, Biljana Gjoneska, June Gruber

Dartmouth Scholarship

Changing collective behaviour and supporting non-pharmaceutical interventions is an important component in mitigating virus transmission during a pandemic. In a large international collaboration (Study 1, N = 49,968 across 67 countries), we investigated self-reported factors associated with public health behaviours (e.g., spatial distancing and stricter hygiene) and endorsed public policy interventions (e.g., closing bars and restaurants) during the early stage of the COVID-19 pandemic (April-May 2020). Respondents who reported identifying more strongly with their nation consistently reported greater engagement in public health behaviours and support for public health policies. Results were similar for representative and non-representative national samples. Study 2 …

Chesapeake Governance Study: Report Of 2021 Decision Maker Interview Results, D.G. Webster

Dartmouth Scholarship

This report describes the aggregate results from a series of interviews conducted with decision makers involved in governance of the Chesapeake Watershed. Interviews began in June and ended in December of 2021. Information collected will be combined with other data to create and then test a computer model to predict likely policy changes under a range of future scenarios. It is part of a larger project funded by the National Science Foundation called Modeling the Dynamics of Human and Estuarine Systems with Regulatory Feedbacks (Award #2009248). Using the Chesapeake Bay as an example, this project will combine the policy model …

Designing Vr Games To Improve Engagement With At-Home Physical Therapy, Andrada Pantelimon

ENGS 88 Honors Thesis (AB Students)

Musculoskeletal (MSK) conditions are the leading cause of disability worldwide. Every year, 50% of American adults over 18 years-old develop an MSK condition that requires physical therapy (PT). However, only about 35% of patients fully adhere to their plans of treatment. As the population ages and telehealth permeates the PT industry, there is a growing need as well as an opportunity to use new and emerging technologies to create immersive interfaces that increase motivation. This thesis explores the potential VR-based gameful experiences to improve engagement and follow-through with at-home physical therapy for ACL injury, a common acute MSK condition that …

A Smartwatch Step-Counting App For Older Adults: Development And Evaluation Study, George Boateng, Curtis L. Petersen, David Kotz, Karen L. Fortuna, Rebecca Masutani, John A. Batsis

Dartmouth Scholarship

Background: Older adults who engage in physical activity can reduce their risk of mobility impairment and disability. Short amounts of walking can improve quality of life, physical function, and cardiovascular health. Various programs have been implemented to encourage older adults to engage in physical activity, but sustaining their motivation continues to be a challenge. Ubiquitous devices, such as mobile phones and smartwatches, coupled with machine-learning algorithms, can potentially encourage older adults to be more physically active. Current algorithms that are deployed in consumer devices (eg, Fitbit) are proprietary, often are not tailored to the movements of older adults, and have …

The Feasibility And Utility Of Harnessing Digital Health To Understand Clinical Trajectories In Medication Treatment For Opioid Use Disorder: D-Tect Study Design And Methodological Considerations, Lisa A. Marsch, Ching-Hua Chen, Sara R. Adams, Asma Asyyed, Monique B. Does, Saeed Hassanpour, Emily Hichborn, Melanie Jackson-Morris, Nicholas C. Jacobson, Heather K. Jones, David Kotz, Chantal A. Lambert-Harris, Zhiguo Li, Bethany Mcleman, Varun Mishra, Catherine Stanger, Geetha Subramaniam, Weiyi Wu, Cynthia I. Campbell

Dartmouth Scholarship

Introduction: Across the U.S., the prevalence of opioid use disorder (OUD) and the rates of opioid overdoses have risen precipitously in recent years. Several effective medications for OUD (MOUD) exist and have been shown to be life-saving. A large volume of research has identified a confluence of factors that predict attrition and continued substance use during substance use disorder treatment. However, much of this literature has examined a small set of potential moderators or mediators of outcomes in MOUD treatment and may lead to over-simplified accounts of treatment non-adherence. Digital health methodologies offer great promise for capturing intensive, longitudinal ecologically-valid …

Context-Specific Activations Are A Hallmark Of The Neural Basis Of Individual Differences In General Executive Function, Andrew E. Reineberg, Marie T. Banich, Tor D. Wager, Naomi P. Friedman

Dartmouth Scholarship

Common executive functioning (cEF) is a domain-general factor that captures shared variance in performance across diverse executive function tasks. To investigate the neural mechanisms of individual differences in cEF (e.g., goal maintenance, biasing), we conducted the largest fMRI study of multiple executive tasks to date (N = 546). Group average activation during response inhibition (antisaccade task), working memory updating (keep track task), and mental set shifting (number–letter switch task) overlapped in classic cognitive control regions. However, there were no areas across tasks that were consistently correlated with individual differences in cEF ability. Although similar brain areas are recruited when completing …

In Vivo Evolution Of Lactic Acid Hyper-Tolerant Clostridium Thermocellum, Roberto Mazzoli, Daniel G. Olson, Angela Maria Concu, Evert K. Holwerda, Lee R. Lynd

Dartmouth Scholarship

Lactic acid (LA) has several applications in the food, cosmetics and pharmaceutical industries, as well as in the production of biodegradable plastic polymers, namely polylactides. Industrial production of LA is essentially based on microbial fermentation. Recent reports have shown the potential of the cellulolytic bacterium Clostridium thermocellum for direct LA production from inexpensive lignocellulosic biomass. However, C. thermocellum is highly sensitive to acids and does not grow at pH < 6.0. Improvement of LA tolerance of this microorganism is pivotal for its application in cost-efficient production of LA. In the present study, the LA tolerance of C. thermocellum strains LL345 (wild-type fermentation profile) and LL1111 (high LA yield) was increased by adaptive laboratory evolution. At large inoculum size (10 %), the maximum tolerated LA concentration of strain LL1111 was more than doubled, from 15 g/L to 35 g/L, while subcultures evolved from LL345 showed 50–85 % faster growth in medium containing 45 g/L LA. Gene mutations (pyruvate phosphate dikinase, histidine protein kinase/phosphorylase) possibly affecting carbohydrate and/or phosphate metabolism have been detected in most LA-adapted populations. Although improvement of LA tolerance may sometimes also enable higher LA production in microorganisms, C. thermocellum LA-adapted cultures showed a yield of LA, and generally of other organic acids, similar to or lower than parental strains. Based on its improved LA tolerance and LA titer similar to its parent strain (LL1111), mixed adapted culture LL1630 showed the highest performing phenotype and could serve as a framework for improving LA production by further metabolic engineering.