“The Human Placenta,” or “Why I Love Science Writing”

Have you read last week’s breaking story about the microbiome of the human placenta? Wait, stop, don’t run away to Google it! I’ll tell you all about it – this is a science blog, remember?

I’m asking because as I started reading about the topic in preparation for writing this blog post, I noticed two things. First, as a science writer who tries to stay well-connected with what’s going on in the world of biology research, it would have been nearly impossible for me to avoid this story. I get eight or nine daily digest emails from scientific publications every day, and I think over the course of last week, every single one came with a headline related to the placenta study. (Of course, I read them all. And the Nature study they were based on.)

Second, I noticed that each story I read had a slightly different angle on covering the research. As scientists, we like to believe that science is, well, just science. It’s factual. We pore over the data and reach a conclusion. If we aren’t sure of something, we search the journals. The story, if there is one, is about methods and controls, protocols and reagent quality. However, when information about that research is communicated broadly, outside of the journals, we can get a different impression based on how the author frames their article.

For example, I started with Science News. I love this site for its quick, high-level overviews of research that I wouldn’t otherwise dive into. Their article gave me the highlights of the study in just a few paragraphs. I learned that a group led by Stephen Charnock-Jones at the University of Cambridge published a study in Nature that concluded that the human placenta is microbe-free. The paper includes data from over 500 samples, and though they did find traces of bacteria in their analysis, all of it was shown to be contamination from a few different sources.

The Science News article also mentioned that this field of research has seen conflict in the past 5 years. Dr. Kjersti Aagaard of Baylor College of Medicine, who published a 2014 study concluding that the placenta does have a microbiome, believes that the Cambridge team attributed too much to contamination, especially those that were classified as vaginal bacteria transferred when the placenta was expelled through the birth canal. However, the thesis of the story seemed to be that despite some remaining skeptics, the recent Nature article delivered decisive proof that the placenta was sterile. Simple enough.

The next article I read was in The Scientist magazine. This story, titled “Placental Microbiome’s Existence Challenged,” focused almost exclusively on the controversy around the research. The article began with a paragraph introducing the recently published Nature study, but quickly brought in quotes from other researchers who disagree with Charnock-Jones’s conclusions. Microbiologist Andrew Onderdonk, of Brigham and Women’s Hospital and Harvard Medical School, is quoted saying, “What they have done is extremely good, I just don’t accept their conclusions.”

The Scientist dives into the methods of the study more than Science News. In this article, I learned that the Cambridge team used 16S rRNA gene sequencing and metagenomic analysis. They used two different kits for nucleic acid extraction (neither from Promega) and according to Charnock-Jones, the reagents of each kit were contaminated with trace amounts of bacterial DNA that showed up in their analysis. The methods, though, are a point of contention for Dr. Onderdonk. He says that the 16S signal is hard to detect, and questions whether broad conclusions can be drawn from this data.

After two articles, I had the general highlights of the story, a few details about the methods, and some information about the controversy surrounding it. At this point, I decided to jump into The Atlantic writer Ed Yong’s article, “Why the Placental Microbiome Should Be A Cautionary Tale.” (It wasn’t a tough decision – Ed’s one of my favorite writers.)

Ed sets the scene with a brief history of the field, and mentions the conflicting conclusions of Aagaard and the Cambridge team. However, his story goes in a different direction by drilling into the problem presented by Stephen Charnock-Jones: reagent contamination. He describes the concept of the “kit-ome,” which refers to contaminants that lead to “spurious discoveries.” In the 2019 paper, the Cambridge group used cross-referencing and extensive controls to ensure they could eliminate bacterial signatures from contaminants. They also noticed patterns in their data, such as a fungus that showed up in batches of samples that were processed together. Aagaard is quoted again, listing more of her perceived flaws in the methods, including the methods used to clean the placentas post-delivery and pre-processing.

Ed Yong’s article ends with thoughts from Washington University researcher Indira Mysorekar. Dr. Mysorekar says that while we’re spending so much time arguing over the methods and conclusions, we’re missing the more interesting biological points. A sterile placenta is a fascinating possibility, but how does the fetus’s immune system develop without exposure to bacteria? When does the fetus develop a microbiome of its own, and what are all the ways microflora is transferred between mother and child? In other words, as we argue about the methods and analysis, we’re forgetting why this was a compelling research question to begin with.

Now, I’m not here to pit all of these publications against each other and declare a “best article.” They all serve a specific purpose, and that’s what makes the field of science writing so beautiful. Science writers have the opportunity to put a frame around the science, and to lead the reader to a specific set of conclusions. As readers, we’re free to choose which story we want to engage with. In three articles, I read a broad overview of the research, an exposition on how the community is dealing with conflicting studies, and a dive into how this study is illustrative of a specific larger issue in scientific research. In a way, without misrepresenting the science at all, these three writers both helped me understand the research, and crafted how I thought about it in the bigger picture of science.

And that’s why I love science writing. Science doesn’t happen in a vacuum, it’s subject to personal perception just like everything else. As science writers, we’re tasked with communicating that science to all types of audiences, from experts within the field to non-scientists with no prior knowledge of the subject. The way we craft our narrative can influence how research is perceived by any of those groups. At our worst, we misrepresent conclusions, sensationalize and lead astray. At our best, we give readers an accurate understanding, guide them to captivating nuances and connect everything to broad themes.

I don’t take that responsibility lightly.

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Jordan Villanueva studied writing and biology at Northwestern University before joining Promega in 2017. As a science writer, he's most interested in the human side of science - the stories and people behind the journal articles. Research interests include immunology and neuroscience, as well as the COVID-19 pandemic. When he isn't working, Jordan loves turning sourdough baking into a science. It's just a symbiotic culture of yeast and lactic acid bacteria, right?

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