...why your breath stinks? (with Batbileg Bor)

Ever Wonder? / February 16, 2022
Bat_photo in lab
Image attribution
Courtesy of Batbileg Bor
Bacteria TM7
Image attribution
Courtesy of Bor & Dewhirst Lab

The bacteria TM7 (in blue) lives on a host bacteria (in pink), as seen in this image from an electron microscope.

One of the first things you might notice when you wake up is a weird taste in your mouth, followed by the realization that your breath smells… bad. So, you grab your mouthwash and get on with your day, hoping no one feels the need to offer you a breath mint. 

Ever wonder why your breath stinks? 

To find out, we asked Dr. Batbileg Bor (@BatbilegBor), a scientist who studies the bacteria that live in our mouths with his lab at the Forsyth Institute

It turns out that there are a bunch of microbes, including bacteria and other microscopic critters, that live in our mouth. Collectively, scientists call this the “oral microbiome”. And going beyond our breath, they can affect our health in ways that we are just beginning to understand. Bat takes us on a tour of this crazy small world and the one corner of it that he studies, a super tiny bacteria called TM7

Have a question you've been wondering about? Send an email or voice recording to the podcast team to tell us what you'd like to hear in future episodes. 

Subscribe to our show on Apple Podcasts, Spotify, or Google Podcasts. To see a full list of episodes, visit our show’s webpage


Perry Roth-Johnson (00:06):

Hello! This is Ever Wonder? from the California Science Center. I'm Perry Roth-Johnson. If you're like me, one of the first things you notice when you wake up is a weird taste in your mouth, followed by the realization that your breath smells... bad. So, you grab your mouthwash and get on with your day, hoping no one feels the need to offer you a breath mint. Ever wonder why your breath stinks?

Perry Roth-Johnson (00:30):

To find out, we asked Dr. Batbileg Bor, a scientist who studies the bacteria that live in our mouths with his lab at the Foresyth Institute. It turns out there are a bunch of microbes, including bacteria and other microscopic critters, that live in our mouth. Collectively, scientists call this the "oral microbiome" and going beyond our breath, they can affect our health in ways that we are just beginning to understand. Bat takes us on a tour of this crazy small world and the one corner of it that he studies, a super tiny bacteria called TM7. Lets get into it. Dr. Batbileg Bor, you are an Assistant Member of Staff and you're the leader of the Bor Lab at the Forsyth Institute—Bat, welcome to the show!

Batbileg Bor (01:14):

Thank you. Thank you for having me.

Perry Roth-Johnson (01:15):

Yeah. And Jenny Aguirre, producer and now co-host of the show is also here with us. Hi Jenny!

Jennifer Aguirre (01:20):

Hey Perry, and hi Bat.

Perry Roth-Johnson (01:21):

So, Bat, we're thrilled to talk to a scientist like you, because there's so much buzz and marketing lately around, you know, "gut health" and the "microbiome". And I know you study bacteria, not the ones that actually live in your gut, but that live in your mouth. Uh, if I can just tell you a funny little story, we got the idea for this episode from one of our Science Center staff members who was asking the question, "Why does my breath stink?" And we were like, "Huh, I kind of wonder about that sometimes too!" So why don't we start there? Um, what makes my breath smell bad?

Batbileg Bor (01:53):

Our breath smells because of, uh, certain bacteria that we have in our, uh, oral cavity. So the actual proper term for, uh, smelly breath is halitosis. It, it could be a, a, a symptom and these bacteria actually can be, uh, sulfur producing bacteria most of the time. And that sulfur compound that released from these bacteria, that's what makes the breath smell.

Perry Roth-Johnson (02:18):

They, they produce sulfur, which is like the same kind of thing. I don't know. I, I remember I took this trip up to, uh, I think it was Mount Fuji and they have like sulfur coming out of the volcano. Sometimes they like cook hard boiled eggs in the sulfur. So that same stuff is like, what's coming out of these bacteria in my mouth.

Batbileg Bor (02:37):

Yep, exactly. A lot of the times these bacteria eat a lot of the sugars and things like that we eat. Right. And then what the byproduct of that, their, their metabolism is a sulfur. And then you smell that sulfur compound.

Perry Roth-Johnson (02:52):

Gross. Okay, cool.

Jennifer Aguirre (02:56):

So, Bat you run your own lab, studying the oral microbiome. What exactly is the oral microbiome?

Batbileg Bor (03:02):

Oral microbiome is actually combination of community of bacteria in our oral cavities. So many bacteria microorganisms together. Um, and that includes not only bacteria, but oral microbiome actually contains bacteria, archaea, viruses and, uh, fungi.

Jennifer Aguirre (03:23):

How many microbes are in our mouth?

Batbileg Bor (03:25):

If you, if we take a look at the actual numbers, they're about 10 to the 8th, to 10 to the ninth. So that's one with eight zeros behind it, that many bacteria usually found per mill. Wow. So there's actually a lot of bacteria. Um, and then, and then there are actually about, uh, seven more than 700 species of bacteria have been detected in the human oral cavity, but per person, it's about 200 to 250 species per person.

Jennifer Aguirre (03:58):

Wow. So it's, uh, a huge diversity of microbes inside my mouth.

Batbileg Bor (04:03):

Absolutely. Just to, just to give you an example, you know, each person has about 2 to 250 species of bacteria. On earth there's only one species of human.

Perry Roth-Johnson (04:14):


Jennifer Aguirre (04:15):

And it, so I, I have a question. How does that compare to the rest of the microbiome in other parts of our body? Like let's say the gut.

Batbileg Bor (04:25):

So, they're different of course, gut is much more, uh, um, I guess, place where microbes actually can live longer because it's more, uh, enclosed environment, oral cavities, a lot of the times food and liquid going through. So it's more a transient environment. So in, in human oral cavity, you know, it's 200 to, to 250 species of bacteria and the gut is about thousand species. Um, so there's much more in the gut, but if you go to other places like skin or, uh, stomach, or, you know, um, there's a eye microbiome as well. You know, things like that, the number of species goes down. Uh, it's less than oral cavity.

Perry Roth-Johnson (05:08):

I see. Okay. So we have all of these microbes, lot of numbers, lot of diversity of species, um, what are they doing? Are there good microbes? Are there bad microbes?

Batbileg Bor (05:23):

Uh, it's a combination of both. Um, it also depends on the situation as well. Um, lot of the times in a healthy human there's a healthy microbiome. We think those micro microbiome or all the bacteria, let's say they're actually good for you. They're they're for you to help you. For example, um, a lot of the gut microbes, right? All, we cannot digest many food if they were not there without those bacteria, we won't be able to digest those food. Um, I mean, lettuce or vegetable will be one, for example, uh, our stomach cannot break those down. Bacteria breaks them down to smaller components and then our gut absorbs them. Right?

Perry Roth-Johnson (06:08):


Batbileg Bor (06:09):

So that's a good aspect of it. But what happens is a lot of these bacteria, depending, sometimes the immune or the environment can change. And a lot of these bacteria could turn into what's called opportunistic pathogens. So now they were your, you know, bacteria that used to live in you now suddenly because there's a lot of amount of nutrition or the environment is right. They start to overgrow and that will stimulate the immune system even more and then now it becomes bad for you.

Perry Roth-Johnson (06:39):

You. So it sounds like it's really dependent on the environment, like the bacteria, how we perceive the bacteria as being good or bad is like how it makes our body feel. Not so much that like the bacteria has an agenda, you know, and it's like, it's automatically bad or good by default. Did I get that right?

Batbileg Bor (06:57):

Exactly. Exactly. Absolutely. So, you know, there's, uh, um, it there's, you know, microbiologists are people who study bacteria, right. And they're thought process is actually, you know, these microbes, not, you know, they're not good or they're not bad. They're try to, is just simply try to live, right. Just like us, they're trying to survive. So if there's food they're going to grow, if there is no food, they're going to starve and go into dormant state, et cetera, et cetera. So those kind of situation then leads to, you know, uh, whether it's disease, health, or just kind of stay neutral.

Perry Roth-Johnson (07:37):

Okay. But I do want to focus on, uh, one common, bad thing that might happen. Like when I go to the dentist and the dentist is looking for cavities, uh, are these microbes in my mouth the things that give me the cavities, these bacteria?

Batbileg Bor (07:52):

Yes. So the overall hypothesis is actually, um, your oral bacteria. They're, you know, couple that are more, uh, people think more pathogenic than the others, right? Bacteria like s mutans or, uh, uh prevotella or, you know, their acid producing bacteria. Right? And what happens is these bacteria actually eat sugar and then produce acid. And the acid actually shown to break down your enamel, which is the surface, the co you know, the coding of your teeth. And that once that surface enamel breaks down, then that is what's called cavities, you know, uh, start to form these cavities in your oral cavity. And, um, but more and more studies have been showing that it's not maybe specific bacteria. It's actually a community of bacteria form these biofilms called plaques. And these plaques actually sit on a specific area and producing acid. And then that's where it gets a lot of the acid gets, or the enamel gets eaten up.

Perry Roth-Johnson (08:55):

Oh, okay. I didn't realize that. I always thought that just like having sugar itself, like was rotting out my teeth, but I guess there's this middle man, you know, the bacteria gang that's converting the sugar into acid. That's what's drilling a hole into. Yep. Okay. Okay. I got it.

Batbileg Bor (09:11):

What's really interesting is actually a lot of the, these cavities, you know, problem with cavities started after people start to actually eat sugar, right after learning how to, uh, process sugar. And then suddenly people start to have cavities. And this is actually a huge, you know, uh, transition in our diet as a humanity that we see, you know, a lot of these diseases occur because we were able to, um, process sugar and have a lot more sugar in our diet.

Perry Roth-Johnson (09:43):


Jennifer Aguirre (09:45):

Let's talk about TM7. That's what you're studying , right? That's right. Like, what does it do to us? How does it help us in our mouth? And just anything about it? I mean, it's, it's fairly new.

Batbileg Bor (09:59):

That's right. So TM7 is a bacteria, first of all. And it's a new area of study because these kind of bacteria hasn't really been studied for a long time. So we, as a human society, we've been studying bacteria for a long time, about 366 years give or take right. Since the first time we actually saw bacteria under a microscope. And during this 366 years of studying bacteria, people saw, you know, see a lot of different kind of interaction. So bacteria, one bacteria interacting with another bacteria or bacteria interacting with humans or different animals or different insects or different plants. So there's all kinds of these interactions, but these TM7 bacteria actually interacts with other bacteria, such a way that it's different from anything we have ever seen before these TM7s grow on the surface of another bacteria and those kind of interaction haven't really been seen between two bacteria. It's been seen between different other organisms, but not like between two bacteria. And that's kind of why TM7 is really interesting is that why these very small bacteria growing on another bacteria and is it bad to them? Is it okay to them? You know, we don't know anything about this right now. And that's why it's so interesting.

Perry Roth-Johnson (11:26):

I know we're on radio, but like paint a picture for us. Like what, what does this thing look like? The host bacteria in the TM7.

Batbileg Bor (11:33):

Yeah. It's actually, um, they, they look like a little blob and they're just living on another blob that are little bigger in size. Okay. So, so yeah, they're most of the bacteria, TM7 bacteria that we looked at, the, the ship looked like, uh, submarines, let's say.

Perry Roth-Johnson (11:56):

Okay. And so the host bacteria is like this big submarine that has a bunch of little submarines stuck on the side of it. And those little submarines are TM7?

Batbileg Bor (12:05):


Perry Roth-Johnson (12:06):

Okay. Okay. So,

Batbileg Bor (12:07):

And, and we're talking about, this is at the micron scale we're talking about.

Perry Roth-Johnson (12:10):

Yeah. I want to get into some of, of the skills because bacteria already are confusing to me because they're so small. And I like to think about big things cuz I'm an engineer. So, um, how small is TM7 compared to, you know, the host bacteria or like more common bacteria that we might be familiar with. And then how does that relate to other things like, you know, a grain of sand, for example?

Batbileg Bor (12:36):

So TM7 bacteria is about 200 to 500 nanometer in size. Uh, and then typical bacteria or in this is case the host bacteria is about one micron or that's equal to 1000 nanometers, right. One to five micron in size. Okay. So TM7 is about, depending on the size of the bacteria could be about 1/5th of the host bacteria. Um, now taking that, you know, into a bigger picture. So typical bacteria that the host bacteria in this case, uh, is about one to five micron. How, how big or large is that? Um, so if you take a grain of sand from a beach, let's say, um, in Cancun, uh, about a hundred thousand bacteria can live on a single grain of sand.

Perry Roth-Johnson (13:28):


Batbileg Bor (13:28):

Okay. Now if we translate that to little bigger, let's say, uh, if there's a tea, uh, teaspoon full of sand, uh there's about 6 to 7 billion bacteria can live on that.

Perry Roth-Johnson (13:42):


Batbileg Bor (13:42):

Okay. So that's about world population of human right. Now if we scale up even larger on earth, how many bacteria live on earth? Uh, there's about 10 to the 30th power. So one with 30 zeros in the back. Number of bacteria on earth. And that I believe is, uh, more than, uh, number of stars in our galaxy.

Perry Roth-Johnson (14:06):

That's what I was going to ask. Like that seems like the same order of magnitude as stars you might find in space.

Batbileg Bor (14:12):

Yep. So that's the number of bacteria live on earth.

Perry Roth-Johnson (14:16):

Wow. Wow. Okay. So you have these smaller, I think the technical term I've seen in, in you and your colleagues, papers like ultra-small bacteria that live on other bacteria, is that like a common thing for one bacteria to live on another bacteria?

Batbileg Bor (14:37):

You know, in the past we have seen bacteria that actually invade into other bacteria. So there is a bacteria called predatory bacteria that actually goes and attaches, uh, in this case, a host, bacteria, something larger. And then it actually goes inside the bacteria grows inside the bacteria, almost like a virus and then just bursts out and kills the host. So they call predatory bacteria.

Perry Roth-Johnson (15:01):

Oh my gosh.

Batbileg Bor (15:02):

Whereas TM7 bacteria actually goes and binds to the host and it lives on the surface. It never goes invades. Uh, the host bacteria, it just lives on the surface, divides on the surface. And as far as we can tell, they also seem to, um, let the host live as well. They don't completely just kill off the host bacteria. They actually let the host live. So they're all more in a symbiotic relationship.

Perry Roth-Johnson (15:28):

So they're kind of like barnacles on a ship. Like the barns aren't drilling through the ship's hole. They're just like happy there. They're happy that the ship takes 'em around and they can get food. Okay.

Batbileg Bor (15:39):

Yeah. And, and, and a lot of the times, you know, it's advantages, right? So if you want, think about in the symbiosis these TM7 don't want to kill off their host bacteria because they want to have a host that they want to keep living it on. So they want to keep them alive to a certain level.

Jennifer Aguirre (15:56):

So not a lot is known yet about ultra-small bacteria, but what has been the most exciting to you in your work? What, what gets you excited about going into the lab every day and studying microbes?

Batbileg Bor (16:09):

I think I want to answer that at two levels. I want to go in the lab and study bacteria. Um, first and foremost, I wanted to study these TM7 bacteria because they actually, you know, this is not just some small bacteria living in, you know, uh, human oral cavity, but TM7 bacteria or TM7 like bacteria actually is a very large in diversity, uh, at the current estimate. So these TM7 and their cousins, they call right family of bacteria. They actually take about 26% of roughly 26% of all bacterial diversity. Wow. Um, that actually tells you how much of the bacteria out there actually may have these small bacteria that live on them symbiontly are called episymbiontly on the surface, uh, living on the surface of other microorganisms. So by studying TM7, we're actually also kind of looking into these, all these other, uh, small bacteria that live out there. And we have very limited understanding. Currently only these TM7 bacteria has been cultured in the lab and has been studied very rigorously. Whereas these all other bacteria that share very similar, uh, traits, we don't know nothing really about them. So that really makes me gets excited and, you know, want to learn more about these TM7s and how they actually contribute to our, you know, not only human, uh, health and disease and things like that, but also to our environment, what are they doing to our environment? How are they shaping our, uh, environment, right? Because they, because they grow on other bacteria, they have such a close relationship with these other bacterial communities as well. And on a higher, uh, level, I think, you know, studying bacteria in general is very interesting because of their size, because of their, uh, uh, number, their so many bacteria. There's so many different bacteria, there's so many different microbiomes human microbiome, you know, you can take different human body sites and there's so many different human microbiome we can study. And then beyond that, there's, you know, every surface your table, you know, there's actually a lot of studies on, uh, our work environment, like in the, in the office or in the building or in, in our house, you know, where are the microbes? Where do they locate it? How do they live, et cetera, et cetera. A lot of those have been studied. And I, that really gets me excited about, you know, why microbes, you know, such a common yet we know so little about. Um, I think one of the biggest examples, you know, there's, uh, uh, on Twitter actually, you know, I'm going shout out to the micronauts, uh, who loves to study microbes. And, you know, we kind of think of the opposite. You know, a lot of, uh, astronomers wants to, you know, use the big telescopes to look out and look, look for all the stars and, you know, different planets, et cetera, cetera, a lot of the microbiologists are, you know, we wanted to take the microscope and look down, you know, into small things that we cannot see. And want, we want to, you know, understand their world and how they behave. Right?

Perry Roth-Johnson (19:24):

I think that's a great point you just made by, because so much of the science world was obsessed with the James Webb space telescope that recently just, uh, you know, made it into, um, its parking spot in space. Uh, and, and you guys are kind of like turning James Webb around and shrinking the world down and trying to figure out what the heck is happening on these tiny little things growing on, on, on other tiny little things.

Batbileg Bor (19:51):

That's right.

Jennifer Aguirre (19:52):

Okay. So we're going to change gears a little bit for a minute. And I wanted to ask, how did you get interested in studying the oral microbiome? Did you want to become a dentist perhaps?

Batbileg Bor (20:07):

Actually not quiet. So I did my, uh, PhD or doctorate studying, um, human cells and how they move and, uh, how they're, you know, what are the tools that they use to move around. And while that I was studying that I actually run into, you know, studies of these bacteria, where they are looking at these, uh, bacteria called listeria monocytogenes, which actually invades human cells. And then within the human cells, they move around, they zip around really fast, and then whenever they're ready, they will, you know, zip around so fast that it will actually move through the cell membrane, puncture them and move into the next human cell. Right. So that's how they infect cells. And after studying this bacteria, I, I really wanted to study bacteria and, and, you know, wanted to get in this field.

Jennifer Aguirre (21:02):

And if we take it back a little bit more, what about science in general, um, caught your attention maybe as a kid, something maybe started that spark.

Batbileg Bor (21:15):

Yeah. So I would say, I would say my high school biology teacher, uh, Angie Feather, her name is, she actually was probably inspire me in studying, uh, biology because in our biology class, I actually took, you know, regular biology class and I, I did really bad. Um, my English was back then, not so good either. I'm originally from Mongolia, so my English was not so good and I did pretty bad. I think I got like B- or something in the regular biology class, but she, my biology teacher said, oh, you should take the AP biology. You might like it better. So I took the AP biology class. I remember studying, you know, all these different concepts, chloroplast, you know, electron transfer chain or, you know, different biochemistry, uh, uh, uh, metabolism or different stages of these processes. And I just fell in love with it. And I remember reading these AP biology books and my English again was not so good. So I translated almost every book, um, to actually...

Perry Roth-Johnson (22:21):

Into Mongolian?

Batbileg Bor (22:22):

every word into Mongolian to actually try to understand that. Wow.

Jennifer Aguirre (22:26):

Yeah, no, I, I can definitely relate to that I was horrible in biology and then fell in love with microbiology in college. Um, but, Bat do you have any advice you'd like to share with kids that are in high school who might be thinking or considering a career in science?

Batbileg Bor (22:46):

Absolutely. My biggest at advice will be to follow your interest and commit to it. If you are doing something that brings out passion and your effort and your hard work, and you know, if something brings that out of you, that's the, that's the thing you want to follow. And for me, that's, that's what biology did when I started studying these concepts and, you know, ideas. I started to realize that I can be a scientist and I can come up with these kind of ideas and do research and, you know, really push the boundaries of science, you know, small, but still, you know, push the boundaries of science, um, in my own way. And that's what I wanted to do.

Jennifer Aguirre (23:36):

Yeah. Even if it's small, it's a step forward. So it's, that's great.

Batbileg Bor (23:41):


Perry Roth-Johnson (23:42):

That's a great message Bat. And where can people follow you online and find your work? I know you're on Twitter.

Batbileg Bor (23:49):

Yes. You can always follow me on Twitter. And, uh, also on our Twitter, you'll see our, uh, lab website. You can go on there and read about our research and as well as the board lab members.

Perry Roth-Johnson (24:00):

What's your Twitter handle, Bat?

Batbileg Bor (24:02):

Uh, my Twitter handle is, uh, @BatbilegBor.

Perry Roth-Johnson (24:05):

All right. It's been wonderful talking to you, Bat. Thanks for giving us a peek inside our mouths and the tiny things living in there. Appreciate you joining the show!

Batbileg Bor (24:14):

Thank you. Thank you for having me.

Jennifer Aguirre (24:15):

Thanks Bat!

Perry Roth-Johnson (24:16):

That's our show, and thanks for listening. Until next time, keep wondering. Ever Wonder? from the California Science Center is produced by me, Perry Roth-Johnson, along with Devin Stewart and Jennifer Aguirre. Liz Roth-Johnson is our editor. Theme music provided by Michael Nickolas and Pond5. We'll drop new episodes every other Wednesday. If you're a fan of the show, be sure to subscribe and leave us a rating or review on Apple Podcasts. It really helps other people discover our show. Have a question you've been wondering about? Send an email or voice recording to [email protected] to tell us what you'd like to hear in future episodes.