WEBVTT 00:00:00.000 --> 00:00:03.600 Have you ever stopped to consider who's actually 00:00:03.600 --> 00:00:06.360 running the planet? Most people definitely don't 00:00:06.360 --> 00:00:08.500 think it's microbes. Right, exactly. I mean, 00:00:08.519 --> 00:00:11.039 we tend to focus on macroeconomic forces or, 00:00:11.119 --> 00:00:14.000 you know, top -tier predators, human technological 00:00:14.000 --> 00:00:17.390 advancements. But if we want to talk about the 00:00:17.390 --> 00:00:19.789 true architects of life as we know it, we have 00:00:19.789 --> 00:00:23.109 to scale way, way down. Way down to the microscopic 00:00:23.109 --> 00:00:25.929 level. Yeah. So today we are taking a deep dive 00:00:25.929 --> 00:00:29.510 into a comprehensive Wikipedia source on a class 00:00:29.510 --> 00:00:32.869 of bacteria known as alpha proteobacteria. Which 00:00:32.869 --> 00:00:35.950 is quite a mouthful. It is. It definitely sounds 00:00:35.950 --> 00:00:40.000 like dense microbiology jargon. Pacific class 00:00:40.000 --> 00:00:43.079 of bacteria is secretly functioning as the operational 00:00:43.079 --> 00:00:45.820 back end of the entire global ecosystem. It really 00:00:45.820 --> 00:00:47.579 is. They're everywhere. They are. I mean, they're 00:00:47.579 --> 00:00:49.539 driving the carbon cycle in the oceans. They're 00:00:49.539 --> 00:00:51.740 editing the genomes of the crops we eat. And 00:00:51.740 --> 00:00:54.460 crucially, they are quite literally generating 00:00:54.460 --> 00:00:57.000 the energy required for your brain to process 00:00:57.000 --> 00:00:58.979 the words we are saying right now. Yeah, exactly. 00:00:59.320 --> 00:01:02.240 OK, let's unpack this. We're looking at a massive, 00:01:02.399 --> 00:01:05.599 wildly diverse class of bacteria within the phylum 00:01:05.599 --> 00:01:08.069 Pseudomonadota. Right. Which many of you might 00:01:08.069 --> 00:01:10.250 also know by their older designation, which is 00:01:10.250 --> 00:01:13.629 the alpha purple bacteria. Alpha purple bacteria. 00:01:13.750 --> 00:01:17.129 Right. So what exactly are we dealing with here 00:01:17.129 --> 00:01:20.609 structurally? Well, it's a vast phylogenetic 00:01:20.609 --> 00:01:23.689 umbrella. And what makes alpha proteobacteria 00:01:23.689 --> 00:01:26.450 so compelling to study is that they just defy 00:01:26.450 --> 00:01:29.049 simple morphological categorization. Because 00:01:29.049 --> 00:01:31.569 they're so diverse. Exactly. you're dealing with 00:01:31.569 --> 00:01:34.230 an incredibly broad spectrum of metabolic strategies 00:01:34.230 --> 00:01:36.709 different life cycles all tied together primarily 00:01:36.709 --> 00:01:40.170 by a shared ancient evolutionary lineage but 00:01:40.170 --> 00:01:42.390 structurally we're largely talking about gram 00:01:42.390 --> 00:01:44.890 -negative organisms right now mostly yes gram 00:01:44.890 --> 00:01:47.090 -negative meaning they possess that characteristic 00:01:47.090 --> 00:01:51.709 uh thin peptidoglycan cell wall and that's situated 00:01:51.709 --> 00:01:54.290 right between an inner cytoplasmic cell membrane 00:01:54.290 --> 00:01:56.730 and a bacterial outer membrane but even that 00:01:56.730 --> 00:01:58.769 structural baseline has exceptions doesn't it 00:01:58.769 --> 00:02:00.420 oh absolutely especially when you look at the 00:02:00.420 --> 00:02:03.099 intracellular parasites within the class because 00:02:03.099 --> 00:02:05.819 those specific members live entirely inside the 00:02:05.819 --> 00:02:08.259 protected environment of a host cell. Like completely 00:02:08.259 --> 00:02:11.879 sheltered. Right, completely sheltered. So they've 00:02:11.879 --> 00:02:14.240 experienced this immense evolutionary pressure. 00:02:14.960 --> 00:02:17.919 to shed unnecessary biological baggage. They've 00:02:17.919 --> 00:02:20.919 actually lost the peptidog -like component entirely. 00:02:21.379 --> 00:02:23.460 Which means they don't even test as gram -negative 00:02:23.460 --> 00:02:25.580 anymore. Right. It makes them test as gram -variable. 00:02:25.599 --> 00:02:28.060 They just don't conform to the standard laboratory 00:02:28.060 --> 00:02:31.219 binaries. Which is wild. And I think that structural 00:02:31.219 --> 00:02:34.240 plasticity is really our first hint at their 00:02:34.240 --> 00:02:36.719 adaptability. Definitely. And that adaptability 00:02:36.719 --> 00:02:39.479 translates into a staggering ecological footprint. 00:02:39.840 --> 00:02:41.719 I like to ask you to imagine it like an evolutionary 00:02:41.719 --> 00:02:45.520 Swiss army knife. Or, you know, a highly specialized 00:02:45.520 --> 00:02:48.020 family where every sibling took a radically different 00:02:48.020 --> 00:02:49.860 path in life. That's a great way to look at it. 00:02:49.960 --> 00:02:51.979 Right. You have the agricultural symbionts, the 00:02:51.979 --> 00:02:55.680 ocean navigators, and the deadly obligate intracellular 00:02:55.680 --> 00:02:58.020 assassins. Let's look at the metabolic specialists 00:02:58.020 --> 00:03:01.439 first, like the genus methylobacterium. Ah, the 00:03:01.439 --> 00:03:04.000 C1 compound metabolizers. Yeah. They survive 00:03:04.000 --> 00:03:06.520 on simple single carbon molecules. Which is a 00:03:06.520 --> 00:03:08.759 highly specialized metabolic pathway. It is. 00:03:08.860 --> 00:03:10.860 And then on the other end of that symbiotic spectrum, 00:03:11.039 --> 00:03:13.439 you have the rhizobium species. The farmers of 00:03:13.439 --> 00:03:16.379 the family. Exactly. The rhizobium genera are 00:03:16.379 --> 00:03:19.419 foundational to terrestrial agriculture. These 00:03:19.419 --> 00:03:22.180 are the plant symbionts that colonize the root 00:03:22.180 --> 00:03:24.740 nodules of legumes. Doing biological nitrogen 00:03:24.740 --> 00:03:27.680 fixation. Right. They convert atmospheric nitrogen 00:03:27.680 --> 00:03:30.759 into a bioavailable form that the plant can actually 00:03:30.759 --> 00:03:34.000 use to synthesize proteins. And in return, the 00:03:34.000 --> 00:03:36.439 plant provides the bacteria with carbon and a 00:03:36.439 --> 00:03:38.659 perfectly protected environment. It's basically 00:03:38.659 --> 00:03:41.180 a highly synchronized chemical dialogue between 00:03:41.180 --> 00:03:44.340 plant and microbe. It really is. And that symbiotic 00:03:44.340 --> 00:03:47.379 tendency doesn't stop at plants. It extends right 00:03:47.379 --> 00:03:49.580 into the animal kingdom. with endosymbionts like 00:03:49.580 --> 00:03:52.840 Wolbachia. Wolbachia is fascinating because these 00:03:52.840 --> 00:03:55.360 bacteria reside entirely within the cells of 00:03:55.360 --> 00:03:58.419 arthropods. They infect this massive percentage 00:03:58.419 --> 00:04:01.400 of the world's insects, spiders, crustaceans. 00:04:01.539 --> 00:04:03.919 And what's remarkable about Wolbachia is that 00:04:03.919 --> 00:04:06.500 it has evolved mechanisms to directly manipulate 00:04:06.500 --> 00:04:09.159 the reproductive biology of its hosts. Just to 00:04:09.159 --> 00:04:11.599 ensure its own survival. Yes, to ensure its own 00:04:11.599 --> 00:04:13.159 maternal transmission to the next generation. 00:04:13.460 --> 00:04:15.740 They are fundamentally altering the evolutionary 00:04:15.740 --> 00:04:18.480 trajectory of millions of species. of arthropods. 00:04:18.639 --> 00:04:21.100 Which is an enormous ecological impact on its 00:04:21.100 --> 00:04:23.759 own. But if we're discussing sheer scale... We 00:04:23.759 --> 00:04:26.060 have to shift to the ocean. Yes. We have to look 00:04:26.060 --> 00:04:28.100 at marine environments and talk about Pelagibacter 00:04:28.100 --> 00:04:31.339 ubique. The ocean explorer of the family. Pelagibacter 00:04:31.339 --> 00:04:34.899 ubique is an aerobic, anoxygenic, phototrophic 00:04:34.899 --> 00:04:37.100 bacterium. Right. And that metabolic classification 00:04:37.100 --> 00:04:39.600 is critical. Because it means they can harvest 00:04:39.600 --> 00:04:42.860 light energy to generate ATP, but they don't 00:04:42.860 --> 00:04:46.519 fix carbon dioxide or produce oxygen. like traditional 00:04:46.519 --> 00:04:49.100 photosynthetic organisms do. Exactly. They rely 00:04:49.100 --> 00:04:51.779 on dissolved organic carbon just floating in 00:04:51.779 --> 00:04:54.120 the water. And that metabolic efficiency allows 00:04:54.120 --> 00:04:57.180 them to thrive in the open ocean. In what we 00:04:57.180 --> 00:04:59.899 call oligrophic environments, where nutrients 00:04:59.899 --> 00:05:03.500 are exceptionally scarce. Because of that streamlined 00:05:03.500 --> 00:05:06.279 survival strategy, Pelagibacter ubique is arguably 00:05:06.279 --> 00:05:08.759 one of the most successful organisms on the planet. 00:05:08.899 --> 00:05:10.970 The numbers are staggering. Current estimates 00:05:10.970 --> 00:05:12.829 from the source material suggest they make up 00:05:12.829 --> 00:05:16.149 more than 10 % of the entire open ocean microbial 00:05:16.149 --> 00:05:20.990 community. 10%. That translates to an unfathomable 00:05:20.990 --> 00:05:24.910 number of individual cells. We're talking about 00:05:24.910 --> 00:05:28.149 billions of these organisms in every single liter 00:05:28.149 --> 00:05:31.329 of seawater. Constantly cycling carbon and energy 00:05:31.329 --> 00:05:34.350 on a planetary scale. You simply cannot model 00:05:34.350 --> 00:05:37.350 the Earth's climate or the marine food web without 00:05:37.350 --> 00:05:40.459 factoring in this massive metabolic engine. It 00:05:40.459 --> 00:05:43.040 really forces a recalibration of how we view 00:05:43.040 --> 00:05:45.500 global infrastructure. We are entirely dependent 00:05:45.500 --> 00:05:48.300 on these invisible ocean drifters. But, you know, 00:05:48.300 --> 00:05:50.139 the influence of this class of bacteria gets 00:05:50.139 --> 00:05:52.240 infinitely more personal than the ocean's carbon 00:05:52.240 --> 00:05:54.579 cycle. Here's where it gets really interesting. 00:05:54.819 --> 00:05:57.399 Because this bacterial lineage didn't just remain 00:05:57.399 --> 00:06:00.139 in the soil or the sea. It crossed the ultimate 00:06:00.139 --> 00:06:03.139 biological threshold. Becoming a permanent structural 00:06:03.139 --> 00:06:06.279 component of complex eukaryotic life. We're talking 00:06:06.279 --> 00:06:08.759 about the endosymbiotic theory, the origin of 00:06:08.759 --> 00:06:11.009 mitochondria. If we connect this to the bigger 00:06:11.009 --> 00:06:13.649 picture, every eukaryotic cell, which includes 00:06:13.649 --> 00:06:15.730 the cells making up your tissues, your heart, 00:06:15.810 --> 00:06:17.990 your nervous system contains organelles. And 00:06:17.990 --> 00:06:19.889 the mitochondrion is the organelle responsible 00:06:19.889 --> 00:06:22.829 for generating cellular energy in the form of 00:06:22.829 --> 00:06:25.720 ATP. Right. And what phylogenomics has revealed 00:06:25.720 --> 00:06:28.660 is that the entire class of alpha proteobacteria 00:06:28.660 --> 00:06:31.540 is a sister lineage to the protomytochondria. 00:06:31.660 --> 00:06:35.480 So millions of years ago, an ancient single -celled 00:06:35.480 --> 00:06:38.879 eukaryotic ancestor managed to engulf a free 00:06:38.879 --> 00:06:41.379 -living alpha proteobacterium. But instead of 00:06:41.379 --> 00:06:43.860 digesting it... Or the bacterium parasitizing 00:06:43.860 --> 00:06:46.259 the host... A stable endosymbiosis was established. 00:06:46.889 --> 00:06:49.569 The host cell provided a steady supply of nutrients 00:06:49.569 --> 00:06:53.110 and a safe harbor. And in exchange, that engulfed 00:06:53.110 --> 00:06:56.170 bacterium utilized its highly efficient aerobic 00:06:56.170 --> 00:06:58.970 metabolism to supply the host with a massive 00:06:58.970 --> 00:07:01.879 surplus of energy. That surplus energy was the 00:07:01.879 --> 00:07:04.680 evolutionary spark. It's what allowed eukaryotic 00:07:04.680 --> 00:07:07.000 cells to grow larger, become more complex, and 00:07:07.000 --> 00:07:09.439 eventually form multicellular organisms. Like 00:07:09.439 --> 00:07:13.060 us. Like us. Over eons of co -evolution, that 00:07:13.060 --> 00:07:15.420 engulfed bacterium transferred the majority of 00:07:15.420 --> 00:07:17.540 its own genome right into the host cell's nucleus, 00:07:17.899 --> 00:07:20.500 essentially domesticating itself into the mitochondrion 00:07:20.500 --> 00:07:22.600 we map today. So for you listening right now, 00:07:22.680 --> 00:07:24.899 every single time you move a muscle, every beat 00:07:24.899 --> 00:07:26.680 of your heart, every cognitive leap you make 00:07:26.680 --> 00:07:29.300 while listening to us? You are relying on an 00:07:29.300 --> 00:07:31.720 energy. energy -producing architecture that evolved 00:07:31.720 --> 00:07:34.120 directly from this specific bacterial class. 00:07:35.839 --> 00:07:39.000 complex biological scaffolding built around an 00:07:39.000 --> 00:07:42.060 ancient internalized alpha proteobacterium. It 00:07:42.060 --> 00:07:44.639 is a sobering realization. We carry their genetic 00:07:44.639 --> 00:07:47.860 legacy in every single one of our cells. And 00:07:47.860 --> 00:07:50.560 that innate ability of these bacteria to interact 00:07:50.560 --> 00:07:54.060 with and alter the genetics of their hosts hasn't 00:07:54.060 --> 00:07:56.360 just been confined to ancient evolutionary history. 00:07:56.560 --> 00:07:59.199 No, not at all. It is happening right now and 00:07:59.199 --> 00:08:02.079 modern science is actively exploiting it. Which 00:08:02.079 --> 00:08:04.139 brings us to the bioengineers of the family. 00:08:04.569 --> 00:08:06.769 When researchers want to create genetically modified 00:08:06.769 --> 00:08:09.790 crops, they frequently turn to a naturally occurring 00:08:09.790 --> 00:08:13.550 alpha proteobacterium called Agrobacterium tumefaciens. 00:08:13.670 --> 00:08:16.129 Also documented in the literature as Rhizobium 00:08:16.129 --> 00:08:19.149 radiobacter. Right. And scientists use this specific 00:08:19.149 --> 00:08:21.629 bacteria as a tool. Because this species has 00:08:21.629 --> 00:08:23.689 evolved an incredibly sophisticated mechanism 00:08:23.689 --> 00:08:26.389 for transferring foreign DNA directly into the 00:08:26.389 --> 00:08:29.899 genome of a host plant. In nature, Agrobacterium 00:08:29.899 --> 00:08:33.139 tumefaciens uses this ability to insert genes 00:08:33.139 --> 00:08:35.440 that force the plant to produce specific nutrients 00:08:35.440 --> 00:08:38.480 that only the bacteria can metabolize. It's a 00:08:38.480 --> 00:08:41.179 literal form of molecular hijacking. But plant 00:08:41.179 --> 00:08:43.460 geneticists realized they could utilize this 00:08:43.460 --> 00:08:46.750 exact same delivery mechanism. By removing the 00:08:46.750 --> 00:08:49.049 bacteria's original payload and replacing it 00:08:49.049 --> 00:08:52.049 with desired genetic sequences, like traits for 00:08:52.049 --> 00:08:54.809 drought tolerance or pest resistance, they use 00:08:54.809 --> 00:08:58.309 the bacterium as a microscopic syringe. It physically 00:08:58.309 --> 00:09:01.649 infiltrates the plant cells and keenly integrates 00:09:01.649 --> 00:09:03.629 the new genetic code into the plant's existing 00:09:03.629 --> 00:09:06.049 DNA. What's fascinating here is that this capacity 00:09:06.049 --> 00:09:08.750 for genetic manipulation isn't just a lab trick 00:09:08.750 --> 00:09:11.210 or an aggressive tactic used against plants. 00:09:11.509 --> 00:09:14.070 It is a fundamental part of how these bacteria 00:09:14.070 --> 00:09:16.350 interact with each other. other in nature. You're 00:09:16.350 --> 00:09:17.690 talking about natural genetic transformation. 00:09:18.070 --> 00:09:20.610 Exactly. It's effectively a parasexual mechanism 00:09:20.610 --> 00:09:23.250 for bacteria. Natural genetic transformation 00:09:23.250 --> 00:09:26.690 involves a bacterial cell taking up free exogenous 00:09:26.690 --> 00:09:29.129 DNA from its surrounding medium, whether that's 00:09:29.129 --> 00:09:32.110 soil, water, or host tissue. But simply grabbing 00:09:32.110 --> 00:09:34.250 the DNA isn't enough, right? It has to be integrated. 00:09:34.909 --> 00:09:38.250 Right. And that integration happens via homologous 00:09:38.250 --> 00:09:41.750 recombination. The bacteria actively align the 00:09:41.750 --> 00:09:44.830 imported DNA strands with similar sequences in 00:09:44.830 --> 00:09:47.590 their own chromosome, cut their own DNA, and 00:09:47.590 --> 00:09:50.169 splice the new sequence in. So it's an active, 00:09:50.230 --> 00:09:52.590 ongoing process of horizontal gene transfer. 00:09:52.789 --> 00:09:55.470 Yes, which allows them to rapidly adapt to environmental 00:09:55.470 --> 00:09:58.490 stressors. And this has been definitively documented 00:09:58.490 --> 00:10:01.429 not just in Agrobacterium tumefaciens, but also 00:10:01.429 --> 00:10:04.210 in other members like Methylobacterium organ... 00:10:04.269 --> 00:10:07.970 and bradyrhizobium japonica. Basically, they've 00:10:07.970 --> 00:10:10.470 been practicing genetic engineering long before 00:10:10.470 --> 00:10:13.070 humans figured it out, continuously updating 00:10:13.070 --> 00:10:15.509 their own genetic software. That constant genomic 00:10:15.509 --> 00:10:17.970 iteration is part of what makes them so incredibly 00:10:17.970 --> 00:10:20.730 successful. However, that same evolutionary drive 00:10:20.730 --> 00:10:23.149 to exploit new niches has also produced some 00:10:23.149 --> 00:10:25.309 of the most formidable human pathogens in existence. 00:10:26.029 --> 00:10:27.690 We have to talk about the dark side of the family. 00:10:27.789 --> 00:10:29.970 The villains. The members of this class that 00:10:29.970 --> 00:10:32.789 utilize their intracellular expertise for destruction. 00:10:33.090 --> 00:10:35.570 They've perfected the art of invading host cells, 00:10:35.730 --> 00:10:38.470 not to form a mutually beneficial symbiosis, 00:10:38.629 --> 00:10:42.049 but to parasitize and destroy. Specifically within 00:10:42.049 --> 00:10:45.429 the alpha proteobacteria, the order Rickettsiales 00:10:45.429 --> 00:10:48.669 contains a terrifying roster of these obligate 00:10:48.669 --> 00:10:51.629 intracellular pathogens. The Rickettsia genus 00:10:51.629 --> 00:10:55.190 alone has shaped human history. through severe 00:10:55.190 --> 00:10:58.289 widespread disease. You have Rickettsia proizeki, 00:10:58.509 --> 00:11:01.889 the causative agent of epidemic typhus. Transmitted 00:11:01.889 --> 00:11:04.169 by the human body louse, it thrives in conditions 00:11:04.169 --> 00:11:06.809 of overcrowding and poor sanitation. Epidemic 00:11:06.809 --> 00:11:09.649 typhus has routinely collapsed military campaigns 00:11:09.649 --> 00:11:12.590 and decimated civilian populations during times 00:11:12.590 --> 00:11:14.649 of war and famine throughout history. And then 00:11:14.649 --> 00:11:16.850 you have Rickettsia typhi, which causes murine 00:11:16.850 --> 00:11:19.690 typhus, typically transmitted by fleas. Beyond 00:11:19.690 --> 00:11:21.710 the typhus group, the order is also responsible 00:11:21.710 --> 00:11:24.889 for devastating spotted fevers. In the Americas, 00:11:25.049 --> 00:11:27.230 rickettsia rickettsii is the pathogen behind 00:11:27.230 --> 00:11:29.590 Rocky Mountain spotted fever. A severe tick -borne 00:11:29.590 --> 00:11:31.850 illness that can easily be fatal if not treated 00:11:31.850 --> 00:11:34.029 promptly. And in the Asia -Pacific region, a 00:11:34.029 --> 00:11:36.830 related organism, Orientia tsutsugimushi, causes 00:11:36.830 --> 00:11:39.470 scrub typhus, utilizing mites as its vector. 00:11:39.649 --> 00:11:41.190 And those are just the heavy hitters from the 00:11:41.190 --> 00:11:43.850 sources disease list. The Bronner class also 00:11:43.850 --> 00:11:46.450 includes Buschella abortus, the organism responsible 00:11:46.450 --> 00:11:49.720 for brucellosis. Right, which causes severe undulating 00:11:49.720 --> 00:11:52.519 fevers and joint pain, often transmitted through 00:11:52.519 --> 00:11:55.240 unpasteurized dairy. We also have the Bartonella 00:11:55.240 --> 00:11:57.940 species. Yeah. Responsible for cat scratch disease, 00:11:58.360 --> 00:12:01.230 carrion's disease, and trench fever. Trench fever 00:12:01.230 --> 00:12:04.149 famously incapacitated hundreds of thousands 00:12:04.149 --> 00:12:07.149 of soldiers in the trenches of World War I, again 00:12:07.149 --> 00:12:10.409 transmitted by the human body louse. It's a profound 00:12:10.409 --> 00:12:13.830 paradox. The exact same overarching phylogenetic 00:12:13.830 --> 00:12:17.490 branch that gave complex eukaryotic life the 00:12:17.490 --> 00:12:20.809 ability to thrive by providing the protomytochondria. 00:12:21.049 --> 00:12:23.009 also contains the machinery to systematically 00:12:23.009 --> 00:12:26.129 dismantle human cellular biology. It's terrifying. 00:12:26.450 --> 00:12:29.090 So what does this all mean? How do scientists 00:12:29.090 --> 00:12:31.649 even make sense of such a chaotic and diverse 00:12:31.649 --> 00:12:34.210 group of organisms? You have some fixing nitrogen, 00:12:34.490 --> 00:12:36.769 some harvesting light, editing plant genomes, 00:12:36.789 --> 00:12:39.389 powering human neurons, and causing hemorrhagic 00:12:39.389 --> 00:12:42.090 fevers. The taxonomy is famously a massive mess. 00:12:42.269 --> 00:12:44.529 A total nightmare for microbiologists. Exactly. 00:12:45.070 --> 00:12:47.450 Reconstructing a definitive evolutionary family 00:12:47.450 --> 00:12:49.929 tree for alpha proteobacteria has been a subject 00:12:49.929 --> 00:12:52.450 of tense, ongoing debate in the scientific community. 00:12:52.769 --> 00:12:55.250 The genomic data is just riddled with contradictions. 00:12:55.450 --> 00:12:57.970 One of the primary sources of this taxonomy drama 00:12:57.970 --> 00:13:00.730 is what's called the GC content problem, right? 00:13:00.809 --> 00:13:03.820 Yes. To map relatedness, scientists analyzed 00:13:03.820 --> 00:13:06.960 the nucleotide composition of a genome, specifically 00:13:06.960 --> 00:13:10.220 the ratio of guanine cytosine pairs to adenine 00:13:10.220 --> 00:13:13.159 thymine pairs. And when we sequence the genomes 00:13:13.159 --> 00:13:15.299 of species within the orders Palladibacterales, 00:13:15.580 --> 00:13:18.320 Rickettsiales, and Holosporales, we find they 00:13:18.320 --> 00:13:22.320 all possess highly AT -rich genomes. More adenine 00:13:22.320 --> 00:13:25.399 thymine pairs than guanine cytosine pairs. In 00:13:25.399 --> 00:13:28.200 classical phylogenetics, sharing such a distinct 00:13:28.200 --> 00:13:31.500 genomic trait strongly implies a close... evolutionary 00:13:31.500 --> 00:13:33.919 relationship you'd naturally group them on adjacent 00:13:33.919 --> 00:13:36.480 branches of the family tree Assuming they inherited 00:13:36.480 --> 00:13:38.879 this A .T. richness from a recent common ancestor, 00:13:39.120 --> 00:13:41.120 but the debate centers on whether that shared 00:13:41.120 --> 00:13:43.899 trait is actually an artifact of convergent evolution. 00:13:44.360 --> 00:13:46.840 Convergent evolution meaning unrelated organisms 00:13:46.840 --> 00:13:49.240 independently acquire similar traits because 00:13:49.240 --> 00:13:51.639 they face similar evolutionary pressures. Exactly. 00:13:51.840 --> 00:13:54.519 Both intracellular parasites like Rickettsialis 00:13:54.519 --> 00:13:57.600 and oligotrophic ocean specialists like Pelagibacteralis 00:13:57.600 --> 00:14:00.200 experience intense evolutionary pressure for 00:14:00.200 --> 00:14:02.500 genome streamlining. Because adenine -cyamine 00:14:02.500 --> 00:14:05.340 base pairs are metabolically cheaper to synthesize 00:14:05.340 --> 00:14:08.480 than guanine -cytosine pairs. Right. If an organism 00:14:08.480 --> 00:14:11.720 is trying to minimize metabolic overhead, either 00:14:11.720 --> 00:14:13.919 because it lives in a nutrient -starved ocean 00:14:13.919 --> 00:14:17.240 or relies entirely on a host cell, it will gradually 00:14:17.240 --> 00:14:20.620 accumulate an AT -rich genome. Therefore, clustering 00:14:20.620 --> 00:14:22.919 them together purely based on their AT -rich 00:14:22.919 --> 00:14:25.600 genomes might create a completely artificial 00:14:25.600 --> 00:14:28.139 phylogenetic tree. They might not be closely 00:14:28.139 --> 00:14:30.500 related at all. And the source notes there is 00:14:30.500 --> 00:14:33.519 no consensus here. Furthermore, the data from 00:14:33.519 --> 00:14:36.679 ribosomal RNA only deepens the confusion. Because 00:14:36.679 --> 00:14:39.419 ribosomal RNA sequences are the traditional marker 00:14:39.419 --> 00:14:42.409 for prokaryotes. Yes, but in this case, the GC 00:14:42.409 --> 00:14:45.149 content of the ribosomal RNA directly conflicts 00:14:45.149 --> 00:14:47.690 with the GC content of the whole genome. For 00:14:47.690 --> 00:14:49.309 example, if we look at the Holospiralis order, 00:14:49.549 --> 00:14:52.409 their ribosomal RNA exhibits a high GC content. 00:14:52.669 --> 00:14:54.590 Which typically indicates a relationship with 00:14:54.590 --> 00:14:57.450 other high GC content species. Yet their overall 00:14:57.450 --> 00:15:00.429 genome is highly AT -rich. The markers are contradicting 00:15:00.429 --> 00:15:02.470 each other. This raises an important question. 00:15:02.970 --> 00:15:05.350 How do we achieve an accurate reconstruction 00:15:05.350 --> 00:15:09.070 of evolutionary history? when our primary molecular 00:15:09.070 --> 00:15:11.970 markers are compromised by immense compositional 00:15:11.970 --> 00:15:14.590 bias. It's incredibly difficult, and we see this 00:15:14.590 --> 00:15:17.350 exact tension when analyzing the basal group, 00:15:17.549 --> 00:15:20.690 Magnetococciidae. Organisms like Magnetococcus 00:15:20.690 --> 00:15:24.350 marinus, they exhibit magnetotaxis, synthesizing 00:15:24.350 --> 00:15:27.049 intracellular magnetic crystals to align with 00:15:27.049 --> 00:15:29.470 the Earth's magnetic field. Using it as a compass. 00:15:29.710 --> 00:15:32.090 But morphologically and genetically, they sit 00:15:32.090 --> 00:15:35.009 at the extreme edge of the alpha proteobacteria 00:15:35.009 --> 00:15:37.620 class. The debate is whether they should be included 00:15:37.620 --> 00:15:40.440 in alpha proteobacteria at all, or if they deserve 00:15:40.440 --> 00:15:42.519 their own independent class, like the proposed 00:15:42.519 --> 00:15:45.440 candidatus ediproteobacteria. And this structural 00:15:45.440 --> 00:15:47.799 ambiguity directly impacts our understanding 00:15:47.799 --> 00:15:50.240 of the protomytochondrion's placement. To bring 00:15:50.240 --> 00:15:52.500 it full circle, for a long time, people thought 00:15:52.500 --> 00:15:54.519 the protomytochondrion was closely related to 00:15:54.519 --> 00:15:56.879 the rickettsidae, the deadly intracellular pathogens. 00:15:57.259 --> 00:16:00.159 Because both invade and survive inside eukaryotic 00:16:00.159 --> 00:16:03.539 cells. But recent analyses suggest that protomytochondrial 00:16:03.539 --> 00:16:06.179 lineage might have diverged extremely early in 00:16:06.179 --> 00:16:08.779 the evolutionary timeline. Placing it right between 00:16:08.779 --> 00:16:12.039 Magnetococidae and all other alpha proteobacteria. 00:16:12.080 --> 00:16:14.539 Meaning it might not be as closely related to 00:16:14.539 --> 00:16:16.399 the rickettsial's pathogens as once thought. 00:16:16.519 --> 00:16:19.519 It represents a deeply ancient, entirely distinct 00:16:19.519 --> 00:16:22.360 trajectory. It is a dizzying scale to comprehend. 00:16:22.919 --> 00:16:25.220 We began this deep dive by establishing that 00:16:25.220 --> 00:16:28.240 alpha proteobacteria are a ubiquitous, highly 00:16:28.240 --> 00:16:31.919 varied class bound by a common ancestor. From 00:16:31.919 --> 00:16:34.480 the carbon -cycling populations of Pelagibacter 00:16:34.480 --> 00:16:37.159 ubique in the open ocean. To the intricate genomic 00:16:37.159 --> 00:16:40.679 engineering by Agrobacterium tumefaciens. We 00:16:40.679 --> 00:16:42.759 looked at the historical devastation wrought 00:16:42.759 --> 00:16:45.720 by the Rickettsiel's order and traced the ancient 00:16:45.720 --> 00:16:49.129 protomedocondrion powering your own body. It 00:16:49.129 --> 00:16:51.970 is an unparalleled biological resume. But given 00:16:51.970 --> 00:16:53.750 the immense difficulties we discussed regarding 00:16:53.750 --> 00:16:56.690 their taxonomy, the mismatched ribosomal RNA, 00:16:56.990 --> 00:16:59.870 the convergent evolution of AT -rich genomes. 00:16:59.950 --> 00:17:01.409 I think it leaves us with a lingering thought. 00:17:01.649 --> 00:17:04.410 Exactly. If genomic streamlining and contradictory 00:17:04.410 --> 00:17:06.869 genetic markers make it this difficult for top 00:17:06.869 --> 00:17:09.130 scientists to agree on the alpha proteobacteria 00:17:09.130 --> 00:17:11.549 family tree. How much of our broader understanding 00:17:11.549 --> 00:17:13.970 of the microbial world might just be an illusion 00:17:13.970 --> 00:17:16.589 created by convergent evolution? If horizontal 00:17:16.589 --> 00:17:19.789 gene transfer and extreme environmental pressures 00:17:19.789 --> 00:17:22.630 can blur an organism's evolutionary history this 00:17:22.630 --> 00:17:25.430 completely, we have to wonder what they are actively 00:17:25.430 --> 00:17:27.910 achieving right now that we simply haven't detected 00:17:27.910 --> 00:17:30.890 yet. That is a staggering concept for you to 00:17:30.890 --> 00:17:33.450 ponder as you go about your day. You are not 00:17:33.450 --> 00:17:36.250 just a static organism. You are part of an ongoing 00:17:36.250 --> 00:17:39.529 microbial continuum. Truly fascinating. Thank 00:17:39.529 --> 00:17:41.670 you for joining us as we explored the profound 00:17:41.670 --> 00:17:44.369 intricacies of the unseen world. We look forward 00:17:44.369 --> 00:17:45.950 to having you back for our next deep dive.