What elements are necessary for life?

Living cells rely on a small but somewhat variable subset of the periodic table for life. The elements of life can be divided into macronutrients (C, H, N, O, P, S), major cations (K, Mg, Ca), and micronutrients (including many metal ions).

 

The macronutrients are necessary for life in all organisms. Life is fundamentally based on aqueous chemistry, and therefore H and O are readily available to cells. The chemistry of proteins, nucleic acids, carbohydrates, and lipids accounts for the major requirements for C, H, N, O, P, and S. 

 

The requirements for metal ions and other elements are more variable. All organisms require K, Zn, and Mg, and almost all require Fe and Cu. There are other elements, such as Mn, Co, Ni, Ca, Na, Mo, and Se, that are commonly employed in biology, but are not thought to be universally required.

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As we learn more about life’s vast diversity and expand our scope to include the Bacteria and Archaea, our assessment of those elements that are universally essential for all life becomes more restricted. In contrast with the shrinking list of universally essential elements, the list of elements with a known beneficial function in biology- including Cd and the lanthanides- has expanded significantly in recent years. This website presents a current perspective on the biological roles of each chemical element that is currently thought to be utilized by living cells and will be updated as new research sheds light on novel uses for elements. 

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Elemental Economy

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What happens when cells are limited for certain elements?

There are two levels at which we examine responses to elemental limitation: adaption and acclimation.

Adaptation is used here to refer a fixed change in DNA that alters the atomic constituents, and it is an important response for organisms in environments with relatively stable composition. Acclimation is a change in cellular physiology, such as conditional expression of alternative enzymes or pathways, in response to element availability, and is important for organisms in more variable environments. 

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Adaptation:

Organisms adapt to elemental limitation by altering the atomic composition of their constituents in a process called elemental optimization. Adaptations occur through the process of natural selection (evolution) on a timescale of many generations. For example, cells may express proteins necessary for the acquisition of S, and these may be  selectively depleted of Cys and Met (S-containing amino acids) in their amino acid sequence. Other examples include elimination of an Fe requirement in organisms that grow in Fe-limited environments, and a reduction in phospholipid content in cells that have adapted to persistent P limitation.

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Acclimation:

Acclimation occurs within cells within the time span of a cell's life cycle. Acclimation requires regulators that sense cellular elemental status and control expression of transporters, storage proteins, chaperones, and other proteins involves in maintaining homeostasis.

  There are four common responses during acclimation: elemental acquisition, mobilization, sparing, and recycling. Acquisition and mobilization from stores are both typically activated when nutrients first start to become limiting for growth, a state that can be defined as elemental deficiency. If the acquisition and mobilization strategies are ineffective, and the deficiency is not relieved, the lack of the specific required element will ultimately lead to a cessation of growth or of key metabolic activities, a state that can be defined as elemental limitation, when sparing and recycling may be employed. 

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1. Acquisition- One major cellular response during acclimation to nutrient limitation is an increased expression of import pathways. Import pathways are dominated by transporters for the limiting element or compounds that are rich in the limiting element.

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2. Mobilization- Along with acquisition, organisms may mobilize elements from a source whose primary function is elemental storage. Examples of mobilization include release of Fe from ferritin, degradation of polyphosphates to release inorganic P, and mobilization of excess C stored in lipid bodies.

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3. Sparing- Sparing responses reduce cellular demand for limiting nutrients by selectively repressing synthesis of nonessential proteins and macromolecules. This is a prioritization mechanism by which the cell distinguishes between high priority and often essential functions and those that are of lower priority for survival. A common feature of many elemental-sparing responses is functional substitution.

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4. Recycling- When sparing is ineffective, cells may additionally implement an elemental recycling program. Recycling is the degradation of key cellular components for the purpose of recovering the constituent elements to supply new biosynthetic processes.

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Goals of this Website

  This website serves as an updatable database of information on how cells across all three domains of life utilize elements and how they respond to elemental limitation. On the home page, when you click on a bolded element, you will be directed to a page dedicated to information about that specific element. At the top of this page, you will find a summary section that provides an overview of that element's biological function in cells, its environmental and health impacts, and mechanisms the cell uses to reduce and recycle that element when it is limited in the environment. To gain more insight into the specifics of these mechanisms, scroll down the page to find a deeper explanation of the relevant mechanisms. 

  You will also see links to papers for even more information on these topics for further research. If you know of a relevant paper that is not included in this website, please go to the "Submissions" page and enter in your contact information and the paper's information so that we can update our database and continue to provide the most recent and relevant information. Other feedback and suggestions for the website are also encouraged on the "Feedback" page. 

  This website was adapted from the 2012 article Elemental economy: microbial strategies for optimizing growth in the face of nutrient limitation by Sabeeha S. Merchant and John D. Helmann and the 2023 review The elements of life: A biocentric tour of the periodic table by Kaleigh Remick and John D. Helmann.  If you would like a PDF copy of the 2023 review, please contact John Helmann at jdh9@cornell.edu. The goal of this website is to help make information from these review articles accessible and to help engage the broader community in bringing new mechanisms to light.

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CREDITS:  This website was assembled by Kaleigh Remick (Cornell, class of 2021) as an undergraduate research project.  For further inquiries about the database, please contact: Dr. John Helmann, jdh9@cornell.edu. 

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The periodic table image used on the home page was accessed from National Center for Biotechnology Information at https://pubchem.ncbi.nlm.nih.gov/periodic-table/.