BACTERIA vs HUMAN CELLS: 1 to 1 (FINAL) PT1/3

by @sciencemug

The ratio between bacteria and human cells in the human body is 1 to 1 and not, as commonly thought till now, 10 to 1.
The updated estimate has been provided by three scientists from Israeli and Canadian universities in a study published on the science journal Cell.
(A pre-print version of the paper is avaiable also on bioRxiv, a free online archive for unpublished research papers in the field of life sciences).

PART 1/3

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Ooooh, hallo dear English speaking-reading-hearing visitor, welcome back to me, @sciencemug, the blog/podcast/twitter account which tells science stories, masters the ancient art of napping en plein air, breeds race sloths (for adrenaline addicted betters who like to stretch as much as possible the adrenaline-producing suspense of the races) aaand which sometimes (but not this time) talks to you thanks to the voice that is kidnapped, via a voodoo-wireless trick, from a veeery very very dumb dude.
Aaand which does all of this in Eng?ish, a language that is to proper English what a sneeze is to an authentic expression of free will and a student loan is to a cascade of donuts+pizza which plunges into a pool full of prosecco, gold and diamonds (and beautiful shoes if you’re a lady) and that is surrounded by sexy half naked women/men holding signs that say: “all of this is for you [YOUR NAME], for free. Come and get it!”

Today I’m gonna tell you the story of the death of a semi-scientific almost urban legend about numbers, bacteria and human cells!

by @sciencemug

Soo, the story goes like this: a biology student, Ron Sender, a medical doctor, Shai Fuchs and a biology professor, Ron Milo (aka the SFMs) join their efforts to debunk the myth that, in the human body, bacteria outnumber human cells by 10 to 1.
Well, in the human body… Let’s say in the human body of an healthy adult male between 20-30 years of age, weighing 70 kg (oooooh for your brain’s sake, get over all this “I don’t know the Metric System-SI gnè gnè gnè”… Look, it’s more rational, efficient and simple than yours, besides being used worldwide. Stop whining and learn it!) and 170 cm in height that scientists use as the reference human being (aka Mr. Ref) since 1975 [when The International Commission on Radiological  Protection (alias ICRP) publishes the 480 pages long “Report of the Task Group on Reference Man, ICRP Publication 23” which addresses the need to define a reference individual for the studies regarding humans and the risks and consequences of radiations exposition (1)].
 
Ok, let’s say that it’s true that a looot of bacteria (belonging to more than “10,000 microbial species (2))” -at least in the healthy Western population- live in and on you, and that they “inhabit just about every part of the human body (2)” (skin, up the nose, mouth, guts and so on). But the news is that the number of these microorganisms, the SFMs say, is smaller than thought.
 
First of all the science trio gets to the roots of the 10:1 myth, digging deep into the science literature and finding out that all the recent papers that report the 10 to 1 ratio refer to just one study published in 1977 by Savage (aaand good luck if you want to read it for free… By the way, in case you find it, please send me a copy of it).
Now, this study, the SFMs say, is a solid piece of science work, but, although “referenced over 1000 times in the literature often in the context of the estimate for the vast overabundance of bacteria over human cells” (Sanders et al, 2016; (P)) its 10 to 1 estimate is just a rough calculation. Above all, Sender and lab coat pals precise, it isn’t meant at all to become “the cornerstone of an entire field” (P), being this one the human microbiome field, namely the research area which sees human beings as ecosystems formed by human cells and a plethora of other life forms, mostly bacteria (i.e. the microbiota).
Moreover, our three science myth-busters add, ironically the very same 1977 Savage study refers to another paper by Luckey dated 1972 (again, good luck if you wanna read it) for the total amount of bacteria harbored by humans (FIG1).
 

The chain of citations (adaptation of a figure of Sander et al, 2016 paper by @sciencemug)

 FIG 1

This 1972 Luckey’s paper says that you human beings live with 10¹⁴ bacteria, assuming that your alimentary tract have a capacity of about 1liter (and thus of roughly 1kilogram) and that it contain 10¹¹ bugs per gram (gram: see above, you “gné gné gné”) (FIG2).
 

by @sciencemug

[Hamlet's image is a Public Domain pic adapted by @sciencemug (source: Wikimedia Commons)]

FIG2

Soooo, dear listener, being you the smart ecosystem you are, I guess you’re probably wondering why the ‘70s science guys and all the science community after ‘em focus only on the bacterial population of the alimentary tract to determine how many microbes inhabit your whole body, right? I mean, I can feel you thinking “hey, wait a min dude – sorry, pal, but technically I’m not a dude (and also non technically, I’ve to say)…- I’m much more than my mouth stomach and bowels, c’mon, I’ve a couple of lungs (just to mention something) eyes, a lot of skin, those funny thingies I can’t figure out why be there, yeah, those… I mean, really, I’ve got a lot of stuff of me other than mouth stomach and bowels!”.
Aaand yeah, you’re right dear visitor, you’re the proud owner of lungs, eyes, skin and the non-bowel rest, but, science at hand, the ‘70s lab guys were right to focus on the alimentary tract to quantify the microbiota members of the human body, and even our science myth-busters SFMs back ‘em up on this. Well, more or less.
Actually our science trio specifies that, of the whole human alimentary tract, the relevant part is only