Chemosynthetic bacteria
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Chemosynthetic bacteria are chemolithotrophs that live under the extreme conditions of hydrothermal vents, thriving in temperatures that can reach up to 150°C, and with pressures reaching 250 Atmosphere.
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They use sulfur compounds, such as hydrogen sulfide and elemental sulfur, produced by geological activity, as an energy source to create organic material, instead of using sunlight to generate energy. Chemosynthetic microorganisms help to support the biogeochemical cycle of sulfur. They form the base of the food chain in deep-sea ecosystems, sustaining diverse organisms such as tubeworms, clams, and shrimp with unique symbiotic and commensal relationships.
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Tubeworms, for instance, which may grow to over 2 m, lack a mouth and gut but house billions of sulfur-oxidizing bacteria in their trophosome. Tubeworms transfer haemoglobin from their red plumes to the bacteria living inside their tissues, through the use of hydrogen sulfide, and in return, the sulfur-oxidizing bacteria facilitate the tubeworms in the absorption of carbon nutrients.
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From your oldest ancestors, Chemosynthetic Bacteria:
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Chemosynthetic bacteria - Sulfur-reducing and sulfur-oxidizing bacteria - live symbiotically, complementing and sustaining each other's respiration, and energy conservation in anaerobic conditions, and they form microbial mats with various colours, contributing to the vibrant hues seen on seamounts.
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Let me start by reminding you of who we are. Around 4 billion years ago, in the darkens of the deep sea, we were once born, just after the oceans were formed. We are chemosynthetic bacteria, believed to be one of the first forms of life on this planet, and we have specialised sensors which allow us to perceive our environment under the sea. If you can breathe and smell now is because your sense of smell evolved from our primordial sensors, enabling you to perceive molecules in the air, just like we can perceive molecules inside the water.
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It was in the deep sea, that rocks and fumes self-organised to became alive and form what we are now today, tiny bacteria living inside hydrothermal vents, the unsettling undersea ridge, where extreme temperatures coming from the centre of the earth meet the freezing deep sea. You can find us inside the rocks, in complete darkness, withstanding the pressure of entire oceans while living surrounded by sulfur compounds and other substances extremely toxic for most organisms. With our chemosensors, we were able to detect sulfur compounds from the sea, which we used to generate energy. This complex mechanism allowed us to create symbiotic relationships and support the biodiversity of the hydrothermal vents.
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With time, our chemoreceptors took different paths and evolved to form more complex systems, such as your olfactory receptor, which helped you in the flitting moments even before you were one being. In the form of sperm, you used your olfactory receptors to help you navigate and find your egg cell, which was sending signals in the form of hormones. These olfactory receptors would later evolve into your olfactory system, during the first weeks of pregnancy. This means that inside the womb, you could smell the nutrients from your mother’s diet so that after you were born you would be familiar with them and recognize both your mother and maternal milk just by using your sense of smell.​
The ability to detect molecules and smell them has played a relevant role throughout the history of life. From ancient chemosensors to novel olfactory systems, the ability to perceive chemical signals has been fundamental. This journey highlights the importance of chemosensing and smelling the world around us. We believe that your olfactory system is rooted in our distant past. When you breathe in, remember our complex and beautiful interconnectivity, that weaves our ancient origins to your present existence.​​