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Electricity-Conducting Bacteria May Inspire Next-Gen Medical Devices

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Nanowires
Credit: Edward H. Egelman

Technological advances with potential for improving human health sometimes come from the most unexpected places. An intriguing example is an electricity-conducting biological nanowire that holds promise for powering miniaturized pacemakers and other implantable electronic devices.

The nanowires come from a bacterium called Geobacter sulfurreducens, shown in the electron micrograph above. This rod-shaped microbe (white) was discovered two decades ago in soil collected from an unlikely place: a ditch outside of Norman, Oklahoma. The bug can conduct electricity along its arm-like appendages, and, in the hydrocarbon-contaminated, oxygen-depleted soil in which it lives, such electrical inputs and outputs are essentially the equivalent of breathing.

Scientists fascinated with G. sulfurreducens thought that its electricity had to be flowing through well-studied microbial appendages called pili. But, as the atomic structure of these nanowires (multi-colors, foreground) now reveals, these nanowires aren’t pili at all! Instead, the bacteria have manufactured unique submicroscopic arm-like structures. These arms consist of long, repetitive chains of a unique protein, each surrounding a core of iron-containing molecules.

The surprising discovery, published in the journal Cell, was made by an NIH-funded team involving Edward Egelman, University of Virginia Health System, Charlottesville. Egelman’s lab has had a long interest in what’s called a type 4 pili. These strong, adhering appendages help certain infectious bacteria enter tissues and make people sick. In fact, they enable bugs like Neisseria meningitidis to cross the blood-brain barrier and cause potentially deadly bacterial meningitis. While other researchers had proposed that those same type 4 pili allowed G. sulfurreducens to conduct electricity, Egelman wasn’t so sure.

So, he took advantage of recent advances in cryo-electron microscopy, which involves flash-freezing molecules at extremely low temperatures before bombarding them with electrons to capture their images with a special camera. The cryo-EM images allowed his team to nail down the atomic structure of the nanowires, now called OmcS filaments.

Using those images and sophisticated bioinformatics, Egelman and team determined that OmcS proteins uniquely fit into the nanowires’ long repetitive chains, spacing their iron-bearing cores at regular intervals to transfer electrons and convey electricity. In fact, bacteria unable to produce OmcS proteins make filaments that conduct electricity 100 times less efficiently.

With these cryo-EM structures in hand, Egelman says his team will continue to explore their conductive properties. Such knowledge might someday be used to build biologically-inspired nanowires, measuring 1/100,000th the width of a human hair, to connect miniature electronic devices directly to living tissues. This is one more example of how nature’s ability to invent is pretty breathtaking—surely one wouldn’t have predicted the discovery of nanowires in a bacterium that lives in contaminated ditches.

Reference:

[1] Structure of Microbial Nanowires Reveals Stacked Hemes that Transport Electrons over Micrometers. Wang F, Gu Y, O’Brien JP, Yi SM, Yalcin SE, Srikanth V, Shen C, Vu D, Ing NL, Hochbaum AI, Egelman EH, Malvankar NS. Cell. 2019 Apr 4;177(2):361-369.

Links:

Electroactive microorganisms in bioelectrochemical systems. Logan BE, Rossi R, Ragab A, Saikaly PE. Nat Rev Microbiol. 2019 May;17(5):307-319.

High Resolution Electron Microscopy (National Cancer Institute/NIH)

Egelman Lab (University of Virginia, Charlottesville)

NIH Support: National Institute of General Medical Sciences; National Institute of Allergy and Infectious Diseases; Common Fund


Fundamental Knowledge of Microbes Shedding New Light on Human Health

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A laboratory researching the human microbiome
Caption: Human microbiome research requires teamwork. Kimberly Jefferson (second from left), a leader of the Multi-Omic Microbiome Study—Pregnancy Initiative, joins some of the team at Virginia Commonwealth University, Richmond. Credit: Courtesy of Kimberly Jefferson

Basic research in biology generates fundamental knowledge about the nature and behavior of living systems. It is generally impossible to predict exactly where this line of scientific inquiry might lead, but history shows that basic science almost always serves as the foundation for dramatic breakthroughs that advance human health. Indeed, many important medical advances can be traced back to basic research that, at least at the outset, had no clear link at all to human health.

One exciting example of NIH-supported basic research is the Human Microbiome Project (HMP), which began 12 years ago as a quest to use DNA sequencing to identify and characterize the diverse collection of microbes—including trillions of bacteria, fungi, and viruses—that live on and in the healthy human body.

The HMP researchers have subsequently been using those vast troves of fundamental data as a tool to explore how microbial communities interact with human cells to influence health and disease. Today, these explorers are reporting their latest findings in a landmark set of papers in the Nature family of journals. Among other things, these findings shed new light on the microbiome’s role in prediabetes, inflammatory bowel disease, and preterm birth. The studies are part of the Integrative Human Microbiome Project.

If you’d like to keep up on the microbiome and other basic research journeys, here’s a good way to do so. Consider signing up for basic research updates from the NIH Director’s Blog and NIH Research Matters. Here’s how to do it: Go to Email Updates, type in your email address, and enter. That’s it. If you’d like to see other update possibilities, including clinical and translational research, hit the “Finish” button to access Subscriber Preferences.

As for the recent microbiome findings, let’s start with the prediabetes study [1]. An estimated 1 in 3 American adults has prediabetes, detected by the presence of higher than normal fasting blood glucose levels. If uncontrolled and untreated, prediabetes can lead to the more-severe type 2 diabetes (T2D) and its many potentially serious side effects [2].

George Weinstock, The Jackson Laboratory for Genomic Medicine, Farmington, CT, Michael Snyder, Stanford University, Palo Alto, CA, and colleagues report that they have assembled a rich new data set covering the complex biology of prediabetes. That includes a comprehensive analysis of the human microbiome in prediabetes.

The data come from monitoring the health of 106 people with and without prediabetes for nearly four years. The researchers met with participants every three months, drawing blood, assessing the gut microbiome, and performing 51 laboratory tests. All this work generated millions of molecular and microbial measurements that provided a unique biological picture of prediabetes.

The picture showed specific interactions between cells and microbes that were different for people who are sensitive to insulin and those whose cells are resistant to it (as is true of many of those with prediabetes). The data also pointed to extensive changes in the microbiome during respiratory viral infections. Those changes showed clear differences in people with and without prediabetes. Some aspects of the immune response also appeared abnormal in people who were prediabetic.

As demonstrated in a landmark NIH study several years ago [2], people with prediabetes can do a lot to reduce their chances of developing T2D, such as exercising, eating healthy, and losing a modest amount of body weight. But this study offers some new leads to define the biological underpinnings of T2D in its earliest stages. These insights potentially point to high value targets for slowing or perhaps stopping the systemic changes that drive the transition from prediabetes to T2D.

The second study features the work of the Inflammatory Bowel Disease Multi’omics Data team. It’s led by Ramnik Xavier and Curtis Huttenhower, Broad Institute of MIT and Harvard, Cambridge, MA. [4]

Inflammatory bowel disease (IBD) is an umbrella term for chronic inflammations of the body’s digestive tract, such as Crohn’s disease and ulcerative colitis. These disorders are characterized by remissions and relapses, and the most severe flares can be life-threatening. Xavier, Huttenhower, and team followed 132 people with and without IBD for a year, collecting samples of their gut microbiomes every other week along with biopsies and blood samples for a total of nearly 3,000 samples.

By integrating DNA, RNA, protein, and metabolic analyses, they followed precisely which microbial species were present. They could also track which biochemical functions those microbes were capable of performing, and which functions they actually were performing over the course of the study.

These data now offer the most comprehensive view yet of functional imbalances associated with changes in the microbiome during IBD flares. These data also show how those imbalances may be altered when a person with IBD goes into remission. It’s also noteworthy that participants completed questionnaires on their diet. This dataset is the first to capture associations between diet and the gut microbiome in a relatively large group of people over time.

The evidence showed that the gut microbiomes of people with IBD were significantly less stable than the microbiomes of those without IBD. During IBD activity, the researchers observed increases in certain groups of microbes at the expense of others. Those changes in the microbiome also came with other telltale metabolic and biochemical disruptions along with shifts in the functioning of an individual’s immune system. The shifts, however, were not significantly associated with people taking medications or their social status.

By presenting this comprehensive, “multi-omic” view on the microbiome in IBD, the researchers were able to single out a variety of new host and microbial features that now warrant further study. For example, people with IBD had dramatically lower levels of an unclassified Subdoligranulum species of bacteria compared to people without the condition.

The third study features the work of The Vaginal Microbiome Consortium (VMC). The study represents a collaboration between Virginia Commonwealth University, Richmond, and Global Alliance to Prevent Prematurity and Stillbirth (GAPPS). The VMC study is led by Gregory Buck, Jennifer Fettweis, Jerome Strauss,and Kimberly Jefferson of Virginia Commonwealth and colleagues.

In this study, part of the Multi-Omic Microbiome Study: Pregnancy Initiative, the team followed up on previous research that suggested a potential link between the composition of the vaginal microbiome and the risk of preterm birth [5]. The team collected various samples from more than 1,500 pregnant women at multiple time points in their pregnancies. The researchers sequenced the complete microbiomes from the vaginal samples of 45 study participants, who gave birth prematurely and 90 case-matched controls who gave birth to full-term babies. Both cases and controls were primarily of African ancestry.

Those data reveal unique microbial signatures early in pregnancy in women who went on to experience a preterm birth. Specifically, women who delivered their babies earlier showed lower levels of Lactobacillus crispatus, a bacterium long associated with health in the female reproductive tract. Those women also had higher levels of several other microbes. The preterm birth-associated signatures also were associated with other inflammatory molecules.

The findings suggest a link between the vaginal microbiome and preterm birth, and raise the possibility that a microbiome test, conducted early in pregnancy, might help to predict a woman’s risk for preterm birth. Even more exciting, this might suggest a possible way to modify the vaginal microbiome to reduce the risk of prematurity in susceptible individuals.

Overall, these landmark HMP studies add to evidence that our microbial inhabitants have important implications for many aspects of our health. We are truly a “superorganism.” In terms of the implications for biomedicine, this is still just the beginning of what is sure to be a very exciting journey.

References:

[1] Longitudinal multi-omics of host-microbe dynamics in prediabetes. Zhou W, Sailani MR, Contrepois K, Sodergren E, Weinstock GM, Snyder M, et. al. Nature. 2019 May 29.

[2] National Diabetes Statistics Report, 2017, Center for Disease Control and Prevention (Atlanta, GA)

[3] Long-term effects of lifestyle intervention or metformin on diabetes development and microvascular complications over 15-year follow-up: the Diabetes Prevention Program Outcomes Study. Diabetes Prevention Program Research Group.Lancet Diabetes Endocrinol.2015 Nov;3(11):866-875.

[4] Multi-omics of the gut microbial ecosystem in inflammatory bowel disease. Lloyd-Price J, Arze C. Ananthakrishnan AN, Vlamakis H, Xavier RJ, Huttenhower C, et. al. Nature. 2019 May 29.

[5] The vaginal microbiome and preterm birth. Fettweis JM, Serrano MG, Brooks, JP, Jefferson KK, Strauss JF, Buck GA, et al. Nature Med. 2019 May 29.

Links:

Insulin Resistance & Prediabetes (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)

Crohn’s Disease (NIDDK/NIH)

Ulcerative colitis (NIDDK/NIH)

Preterm Labor and Birth: Condition Information (Eunice Kennedy Shriver National Institute of Child Health and Human Development/NIH)

Global Alliance to Prevent Prematurity and Stillbirth (Seattle, WA)

NIH Integrative Human Microbiome Project

NIH Human Microbiome Project

NIH Support:

Prediabetes Study: Common Fund; National Institute of Dental and Craniofacial Research; National Institute of Diabetes and Digestive and Kidney Diseases; National Institute of Human Genome Research; National Center for Advancing Translational Sciences

Inflammatory Bowel Disease Study: Common Fund; National Institute of Diabetes and Digestive and Kidney Diseases; National Center for Advancing Translational Sciences; National Institute of Human Genome Research; National Institute of Dental and Craniofacial Research

Preterm Birth Study: Common Fund; National Institute of Allergy and Infectious Diseases; Eunice Kennedy Shriver National Institute of Child Health and Human Development


Mood-Altering Messenger Goes Nuclear

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Serotonin

Serotonin is best known for its role as a chemical messenger in the brain, helping to regulate mood, appetite, sleep, and many other functions. It exerts these influences by binding to its receptor on the surface of neural cells. But startling new work suggests the impact of serotonin does not end there: the molecule also can enter a cell’s nucleus and directly switch on genes.

While much more study is needed, this is a potentially groundbreaking discovery. Not only could it have implications for managing depression and other mood disorders, it may also open new avenues for treating substance abuse and neurodegenerative diseases.

To understand how serotonin contributes to switching genes on and off, a lesson on epigenetics is helpful. Keep in mind that the DNA instruction book of all cells is essentially the same, yet the chapters of the book are read in very different ways by cells in different parts of the body. Epigenetics refers to chemical marks on DNA itself or on the protein “spools” called histones that package DNA. These marks influence the activity of genes in a particular cell without changing the underlying DNA sequence, switching them on and off or acting as “volume knobs” to turn the activity of particular genes up or down.

The marks include various chemical groups—including acetyl, phosphate, or methyl—which are added at precise locations to those spool-like proteins called histones. The addition of such groups alters the accessibility of the DNA for copying into messenger RNA and producing needed proteins.

In the study reported in Nature, researchers led by Ian Maze and postdoctoral researcher Lorna Farrelly, Icahn School of Medicine at Mount Sinai, New York, followed a hunch that serotonin molecules might also get added to histones [1]. There had been hints that it might be possible. For instance, earlier evidence suggested that inside cells, serotonin could enter the nucleus. There also was evidence that serotonin could attach to proteins outside the nucleus in a process called serotonylation.

These data begged the question: Is serotonylation important in the brain and/or other living tissues that produce serotonin in vivo? After a lot of hard work, the answer now appears to be yes.

These NIH-supported researchers found that serotonylation does indeed occur in the cell nucleus. They also identified a particular enzyme that directly attaches serotonin molecules to histone proteins. With serotonin attached, DNA loosens on its spool, allowing for increased gene expression.

The team found that histone serotonylation takes place in serotonin-producing human neurons derived from induced pluripotent stem cells (iPSCs). They also observed this process occurring in the brains of developing mice.

In fact, the researchers found evidence of those serotonin marks in many parts of the body. They are especially prevalent in the brain and gut, where serotonin also is produced in significant amounts. Those marks consistently correlate with areas of active gene expression.

The serotonin mark often occurs on histones in combination with a second methyl mark. The researchers suggest that this double marking of histones might help to further reinforce an active state of gene expression.

This work demonstrates that serotonin can directly influence gene expression in a manner that’s wholly separate from its previously known role in transmitting chemical messages from one neuron to the next. And, there are likely other surprises in store.

The newly discovered role of serotonin in modifying gene expression may contribute significantly to our understanding of mood disorders and other psychiatric conditions with known links to serotonin signals, suggesting potentially new targets for therapeutic intervention. But for now, this fundamental discovery raises many more intriguing questions than it answers.

Science is full of surprises, and this paper is definitely one of them. Will this kind of histone marking occur with other chemical messengers, such as dopamine and acetylcholine? This unexpected discovery now allows us to track serotonin and perhaps some of the brain’s other chemical messengers to see what they might be doing in the cell nucleus and whether this information might one day help in treating the millions of Americans with mood and behavioral disorders.

Reference:

[1] Histone serotonylation is a permissive modification that enhances TFIID binding to H3K4me3. Farrelly LA, Thompson RE, Zhao S, Lepack AE, Lyu Y, Bhanu NV, Zhang B, Loh YE, Ramakrishnan A, Vadodaria KC, Heard KJ, Erikson G, Nakadai T, Bastle RM, Lukasak BJ, Zebroski H 3rd, Alenina N, Bader M, Berton O, Roeder RG, Molina H, Gage FH, Shen L, Garcia BA, Li H, Muir TW, Maze I. Nature. 2019 Mar 13. [Epub ahead of print]

Links:

Any Mood Disorder (National Institute of Mental Health/NIH)

Drugs, Brains, and Behavior: The Science of Addiction (National Institute on Drug Abuse/NIH)

Epigenomics (National Human Genome Research Institute/NIH)

Maze Lab (Icahn School of Medicine at Mount Sinai, New York, NY)

NIH Support: National Institute on Drug Abuse; National Institute of Mental Health; National Institute of General Medical Sciences; National Cancer Institute


LabTV: Curious about Computer Modeling of Proteins

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Josh Carter

In many ways, Josh Carter is a typical college student, with a hectic schedule packed with classes and social activities. But when he enters a structural biology lab at Montana State University in Bozeman, Carter encounters an even faster paced world in which molecular interactions can be measured in femtoseconds—that is, 1 millionth of 1 billionth of 1 second.

Working under the expert eye of principal investigator Blake Wiedenheft, Carter is applying his computational skills to X-ray crystallography data to model the structures of various proteins, as well as to chart their evolution over time and map their highly dynamic interactions with other proteins and molecules. This basic science work is part of this NIH-funded lab’s larger mission to understand how bacteria defend themselves from the viruses that try to infect them. It’s a fascinating area of science with a wide range of potential applications, from treating diseases that arise from imbalances in the microbiome (the communities of microbes that live in and on our bodies) to developing new methods for gene editing and programmable control of gene expression.


LabTV: Curious About the Nervous System

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Maja PetkovicAs a child growing up in Croatia, Maja Petkovic dreamed of a future in archeology, medicine, law, and then architecture. But, as she explains in today’s LabTV video, after taking a class in molecular biology, it was love at first sight.

Her passion for biological research landed her in Paris at the Université Denis Diderot, where she pursued a Ph.D. in neuroscience. Now she’s continuing her studies in the United States, working as a Howard Hughes Medical Institute postdoctoral researcher in the NIH-supported lab of Lily and Yuh Nung Jan at the University of California, San Francisco.

Petkovic’s work in the Jan Lab is focused on the basic mechanisms underlying the formation of neural connections and on understanding what happens when those connections go awry. A thorough understanding of neural circuitry has important medical implications, of course, but Petkovic is equally driven by the desire to understand “how stuff works.”


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