Bacterial Armor Imaged, Down To The Details

Reporting in Nature, an international team of scientists say they've visualized the structure of a protective protein coat that surrounds many bacteria, down to the scale of a single atom. Structural microbiologist Han Remaut, co-author of the study, discusses potential applications of the research.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. Now for the naked truth about bacteria. Well, not exactly the naked truth, because in fact many bacteria wear a suit of armor, an outer layer or coat of many proteins. What exactly that armor looked like has been a mystery, but in a study in Nature this week, researchers say they have imaged the armor down to the level of single atoms, and it looks like chainmail, just what you'd expect armor to look like, no? Dr. Han Remaut is a structural microbiologist at Flanders Institute of Biotechnology and the Free University of Brussels. He was co-author of the paper in Nature and joins us from Brussels. Welcome to SCIENCE FRIDAY.

HAN REMAUT: Hi, Ira. It's a pleasure to be here.

FLATOW: What was the purpose of looking and, you know, under the microscope and looking for that coat on the bacteria?

REMAUT: So scientists have known about the existence of these protein coats for quite a while. They've actually known about them for half a century. So they started seeing them when they started looking at bacteria with electron microbes(ph), and they saw these very regular structures which were, you know, patterned structures which turned out to be protein. But that was the vision that they had. It was a low-magnification view and so we really wanted the more atomic view, a higher resolution view of these structures.

FLATOW: We don't normally think of - I think generally that bacteria wear a suit of armor.

REMAUT: So all bacteria, they need - they do wear kind of a protective coat, so not all bacteria wear this S-layer or surface layer which is this protein coat. Others will wear, you know, a slime coat, if you want a buildup of sugar. So - but, you know, very many bacteria use a protein coat, and this is what we've been looking at here.

FLATOW: Were you surprised to see what it looked like when you got to see it down there?

REMAUT: Well, as I said, these things have been observed before, and we had a low-resolution view. So we knew that it looked like - that you could compare it a way like chainmail. It's individual proteins that assemble themselves. The bacteria secrete about a few thousand - a few 10,000 copies of these, and these are all assemble in this nice ordered monomolecular layer. It's really understanding how the protein units are able to do that. So they self-assemble into this S-layer and we - for that you need higher resolution structure, and that's what we looked at in this study.

FLATOW: What's the next step in this study? What else would you like to know using this technique?

REMAUT: So we've now been looking at harmless bacteria, so - and we've been using that as a model system. So there's, I think, two major interests. One is a biological one, a microbiological one, is understanding bacteria better. And so it turns out there's also a number of pathogens that wear these coats, and so we would really like to look at what they look like and how they're able to interact with the host. And another interest is that because they are these highly ordered structures - and really the proteins, they assemble themselves, and that's a property that material sciences are interested in. So it's those -both those aspects that are interesting.

FLATOW: If the bacteria have this chainmail that surrounds them, how do nutrients and things get in and out of them?

REMAUT: So it - there you can really compare it like a chainmail. A chainmail is also not just like the armor that we probably know. It is little rings sitting next to each other, and they have holes. The nutrients get across those holes.

FLATOW: And does - do - does the chainmail look the same on all different kinds of bacteria, or are there distinctive patterns on some? Could you say, oh, I recognize that one?

REMAUT: Yes. I mean, there are very distinctive patterns, so some of them will just have all the units next to each other, and others will have more regular patterns like hexagonal patterns and trigonal patterns. So it is very different, and also the kind of proteins that they use, even though they all form this nice ordered monolayer, that the kind of protein that they use for it is very different from one bacterium to another.

FLATOW: How come when we see - when we see microscopic pictures of bacteria, we don't see anything coating them?

REMAUT: I mean one thing is the resolution. So when we look at - when we see microscopic images, we don't have enough magnification to really see those individuals, then you really need a high magnification electron microscope. Another thing is that not all bacteria have them, so, you know, E. coli, for example, which is one of the bacteria that is really a model bacterium, doesn't have one. So there you won't even see it. And another thing is that bacteria wear these coats when they're out in the environment, which is a hostile environment. When you do grow them in the lab, they often shed these structures. They lose these structures.

FLATOW: Is that right? They have a home? They feel safe? They don't need their suit of armor?

REMAUT: That's right. That's exactly right.

FLATOW: Wow.

REMAUT: You probably don't realize that bacteria, out in the environment, that they're under all sorts of stresses. There's other bacteria attacking them. There are viruses attacking them. So, you know, that's where they need their armor.

FLATOW: And is it effective armor? Does it really help?

REMAUT: Well, we think, though. The bacteria, they really put a lot of energy in producing this. It's about - you know, it can be up to 20 percent of the entire protein that the cells produce. So it's really a big effort in wearing these coats. And so that's when we see, when we do bring them in a less hostile environment for many - very many bacteria, they don't put the effort in producing this surface layer.

FLATOW: You can hear them go, whew, I'm getting rid of this, when they come inside.

REMAUT: Right.

(LAUGHTER)

FLATOW: What happens when they age? Does the armor change as they get older?

REMAUT: It doesn't change as they get older, but they can dress up for different parties, if you like. I mean, some bacteria have more than one kind of protein that they can put in this surface layer. So they can exchange it depending on the environmental condition.

FLATOW: Wow. I want to see them on New Year's Eve. Thank you very much, Dr. Remaut, for taking time to be with us today.

REMAUT: It's a pleasure.

FLATOW: Dr. Han Remaut is a structural microbiologist at Flanders Institute of Biotechnology and the Free University of Brussels. He was co-author of the paper in Nature.

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