🔬 Phage Takes

Bacteriophage Ecology Group News, or BEG News, was published mostly quarterly as an online newsletter for a total of 26 issues, starting July 1, 1999 and continuing through December 31, 2007. As follows is a reprint of an article from the newsletter. Also included in issues were lists of new members to the Bacteriophage Ecology Group, an introduction to new website features, a list of upcoming meetings, phage images found on the web (remember, this was 2001, so effectively pre-Google), etc., but most of all, a listing of new phage ecology-related publications. The newsletter was modelled after T4 News, which was a printed newsletter distributed earlier in the 1990s. The newsletter's successors are the ongoing Phage.org website, phage-therapy.org, and the Bacteriophage Ecology Group Facebook page.

[Note: This article has been lightly updated on April 18, 2026. The solar mass figure, originally given in pounds, has been corrected to kilograms per the Wikipedia article on solar mass; the solar volume figure has been updated to liters accordingly. A bracketed note on current estimates of 10³¹ has also been added. Original text is preserved in HTML comments.]

Whitman et al. (1998) argue that there are between 10³⁰ and 10³¹ prokaryotic cells on our planet. If we assume numerically one virus for every prokaryote host, then we conservatively (e.g., Bergh et al., 1989) reach a total worldwide abundance of 10³⁰ virus-like particles. Is 10³⁰ virus-like particles a reasonable estimation? What does a number like that mean? Astronomers, for instance, can account for "only" about 10²² stars in the entire universe (Turner, 2000). The size of the universe is something on the order of 1.5 × 10¹⁰ light years across (depending on whose estimation of the age of the universe you choose to believe), while a light year is about 10¹³ kilometers (9,460,800,000,000, actually). That means that the universe is something like 10²⁹ mm wide (10¹⁰ × 10¹³ × 10⁶ mm/kilometer). If phages were one mm wide, then 10³⁰ phages placed end to end would form a single line that would stretch ten-times across the entire universe! Of course, phages (and bacteria) are something less than one mm wide.

From a now defunct website called About Big Numbers (ABN), 10³⁰ is approximately the mass of the sun in kilograms (2 × 10³⁰) and about the volume of the sun in liters (1.41 × 10³⁰), and that there are over 10⁴⁷ atoms of water on Earth's surface. Of greater relevance to our subject, ABN claimed that 10³⁶ is the "Maximum number of living things the Earth can accommodate." Therefore 10³⁰ would only be claiming that the Earth's smallest "organisms" would numerically represent only one-millionth of the Earth's total organismal capacity. From that perspective, 10³⁰ phages strike me as quite reasonable, perhaps even on the low side [indeed, current estimates are closer to 10³¹ (Mushegian, 2020)].

The chemist in me wants to know how many moles 10³⁰ represents. Avogadro's number is 6.022 × 10²³ atoms, molecules, or particles per mole. 10³⁰ / 6.022 × 10²³ = 1.66 × 10⁶ or over one million moles of bacteriophage! Given the examples in the above paragraph, my first impulse would be to compare this number with the number of moles that make up the Sun. Since the sun consists mostly of hydrogen gas (with a molecular weight of 2) then there are approximately 10³³ moles of hydrogen making up the sun! This would mean that the sun has nearly 10²⁷ molecules for every phage on Earth. However, far more humbling, the volume of the sun would accommodate approximately one million earth-size balls. That would be a lot of heat-inactivated phages!

Dubin et al. (1970) provide an estimation of the molecular weights of phages T4, T5, and T7 of 192, 109, and 50 × 10⁶ dalton, which we'll assume on average is something like 10⁸ grams per mole of phage. This is approximately the mass of a single blue whale, i.e., 100 short tons. 10⁸ grams per mole translates to about 10¹⁴ grams of phages (10⁶ moles) found on the Earth. That's about equal to the total mass of humanity (6 × 10⁹ people at 50 kilograms per person), and is slightly more than the total mass of the approximately 10⁸ cows in the U.S., where 10⁶ grams is one metric ton and a good-sized cow is about half a metric ton. The mass of the whole Earth is approximately 5 × 10²⁸ grams, so we need not worry about running out of planet to make our phages. In fact, a single mole of an average-sized bacterium weighs approximately 5 × 10¹¹ grams (30 × 10¹² "average-sized" bacteria per ounce) which means that 10³⁰ phages is equivalent in mass to 200 moles of bacteria (10¹⁴ / 5 × 10¹¹), or about 10²⁶ individual cells. Numerically, 10²⁶ is 10 orders of magnitude less than the above-noted guestimate for Earth's total organismal capacity.

So if there may be 10³⁰ phages then there are ~10⁶ moles of phages or something like 10¹⁴ grams in total. What phage density would be necessary to account for such numbers? Estimations of the surface area of the Earth can vary depending upon whether Earth is truly a sphere (in fact, the poles are flattened) or whether one insists on taking into account the degree to which that surface is rough (which can dramatically increase the Earth's surface area). For our purposes we will assume that Earth is a perfectly smooth sphere with a diameter of 1.28 × 10⁷ meters at the equator. The surface area of a sphere is 4πr² and 4 × 3.14 × (1.28 × 10⁷ / 2)² = 5 × 10¹⁴ square meters or 5 × 10¹⁸ square centimeters. The density of phages therefore is 10³⁰ / 5 × 10¹⁸ = 2 × 10¹¹ which, to be conservative, we'll call 5 × 10¹¹. To account for 10³⁰ total phages this is the number that would have to be present per ml to a depth of 1 cm over the surface of the entire world's oceans. A more reasonable density is 10⁶ phages per ml (or, at least, of virus-like particles), total count (Wommack & Colwell, 2000). Diluting 5 × 10¹¹ phages per ml to 10⁶ phages per ml requires a depth of 500,000 cm which is 5,000 meters of 10⁶ phages per ml to account for 10³⁰ phages worldwide. 5,000 meters is within the range of the average depth of the world's oceans, which is about 4 kilometers. So 10³⁰ represents an assumption of approximately 10⁶ virus particles per ml over (and under) the entire world's oceans.

More precisely, assuming 10⁶ virus-like particles per ml:

Thus, a total of 10³⁰ phages is, in fact, a reasonable and entirely plausible worldwide estimation of total virus particles.

References

1.  Bergh, O., K.Y. Børsheim, G. Bratbak, and M. Heldal. 1989. High abundance of viruses found in aquatic environments. Nature 340:467-468. 10.1038/340467a0
2.  Dubin, S.B., G.B. Benedek, F.C. Bancroft, and D. Freifelder. 1970. Molecular weights of coliphages and coliphage DNA. II. Measurement of diffusion coefficients using optical mixing spectroscopy, and measurement of sedimentation coefficients. Journal of Molecular Biology 54:547-556.
3.  Mushegian, A.R. 2020. Are there 10³¹ virus particles on Earth, or more, or fewer? Journal of Bacteriology 202:e00052-20. 10.1128/JB.00052-20
4.  Turner, M.S. 2000. More than meets the eye. The Sciences November/December:32-37.
5.  Whitman, W.B., D.C. Coleman, and W.J. Wiebe. 1998. Prokaryotes: The unseen majority. Proceedings of the National Academy of Sciences, USA 95:6578-6583. 10.1073/pnas.95.12.6578
6.  Wommack, K.E. and R.R. Colwell. 2000. Virioplankton: viruses in aquatic ecosystems. Microbiology and Molecular Biology Reviews 64:69-114. 10.1128/MMBR.64.1.69-114.2000