Day 1- Energetics

Hey guys! Welcome to the first day of our gut microbiome adventure. Today, we’re diving into the world of energy and exploring how our gut bacteria help power up our bodies through an incredible process called glycolysis.

Now, you might be wondering, what does glycolysis have to do with our gut microbiome? Well, our gut bacteria play a huge role in breaking down food and producing energy, which is crucial for their survival and our overall health. But it’s not just about glycolysis—there are many other processes like fermentation, the link reaction, the Krebs cycle, and the electron transport chain. Understanding these processes helps us see how these tiny microbes keep our gut balanced and energized.

Glycolosis

Glycolysis is an essential metabolic activity that breaks down glucose in the cytosol of cells to produce energy. There are two main phases in this process: phases that require energy and phases that release energy. Fructose-1,6-bisphosphate is first created when two phosphate groups from ATP are linked to glucose. This molecule then splits into two three-carbon sugars, one of which becomes glyceraldehyde-3-phosphate (G3P) very quickly. In the second phase, each G3P does through a sequence of steps that turn it into pyruvate, resulting in the production of two NADH molecules and four ATP molecules overall However, because two ATPs were used in the initial phase, the net gain is two ATPs. A key enzyme in this process, phosphofructokinase, regulates the speed of glycolysis based on the cell’s energy needs. Ultimately, glycolysis transforms one glucose molecule into two pyruvate molecules, yielding a net production of two ATP and two NADH molecules, which are essential for cellular energy and metabolic processes.

This image shows glycolysis which is the first step of cellular respiration. If no oxygen is present, the bacteria will use the pyruvate in anaerobic cellular respiration and produce ethanol or lactic acid depending on the type of bacteria.

Fermentation

Anaerobic Respiration and Fermentation

When oxygen is not present, cells can undergo anaerobic respiration, which includes processes like lactic acid fermentation and alcoholic fermentation. These processes allow cells to create energy in the absence of oxygen, though less efficiently than aerobic respiration. So we have two types and i will explain them to you right now, it may get confusing but the visuals will help.

This image depicts lactic acid fermentation, Let me explain to you what it does. Lactic acid fermentation occurs in muscle cells and certain bacteria. During this process, glucose is first broken down into pyruvate through glycolysis, producing two ATP molecules. In the absence of oxygen, pyruvate is then converted into lactic acid. This conversion regenerates NAD+ from NADH, allowing glycolysis to continue. Certain gut bacteria also use lactic acid fermentation, contributing to the balance and health of the gut microbiome.

This image depicts Alchoholic fermentation: Alcoholic fermentation is carried out by yeast and some types of gut bacteria. Similar to lactic acid fermentation, glucose is first broken down into pyruvate during glycolysis, yielding two ATP molecules. The pyruvate is then converted into ethanol and carbon dioxide, regenerating NAD+ from NADH. In the gut, some microorganisms can perform alcoholic fermentation, influencing the gut environment and the energy availability within the microbiome.

How does the gut microbiome connect?:

Energy production through fermentation allows for ATP generation in the absence of oxygen, although it yields less energy compared to aerobic respiration. The gut microbiome has many diverse microorganisms, including those that can perform lactic acid and alcoholic fermentation. These processes help keep a healthy balance of the microbiome and play apart in the overall energy homeostasis within the gut. Fermentation by gut bacteria produces short-chain fatty acids (SCFAs) like butyrate, which are important for gut health, energy supply to colon cells, and overall metabolic health. The ability of different organisms and cells to switch to anaerobic respiration and fermentation shows us the evolutionary adaptations to varying oxygen levels and other environmental pressures.

Link Reaction

In eukaryotic cells link reaction takes place in mitochondria however in the bacteria it takes place in the cytoplasm. Once its converted to acetyl CoA the kreb cycle will also occur in the cytoplasm instead of the mitochondria lastly the ETC takes place in the bacterial cell membranes (Mesosomes). 

This image depicts the link reaction in the cytoplasm as bacteria don’t have mitochondria. Link reaction converts pyruvate into Acetyl CoA.

 Link reaction, is a super important part of how bacteria in our gut turn food into energy. Let’s break it down in a way that will be easy to understand. So, bacteria don’t have mitochondria like our cells do. Instead, they do all their energy-making in the cytoplasm. Here’s how it works:When bacteria munch on glucose, it gets broken down into pyruvate. In the link reaction, pyruvate gets transformed into Acetyl CoA. Think of Acetyl CoA as a special pass that lets pyruvate enter the citric acid cycle .

During this transformation, pyruvate loses a carbon atom as CO2 , and what’s left is a two-carbon molecule. This molecule hooks up with a helper called Coenzyme A to become Acetyl CoA. Oh, and NAD+ also joins , grabbing two electrons to become NADH. This NADH will later help make even more energy. Why does all this matter? Acetyl CoA entering the citric acid cycle produces ATP (the cell’s energy currency), NADH, and FADH2. These molecules are crucial for bacteria to survive and thrive in your gut. When these bacteria are happy and energised, they help keep your whole gut microbiome balanced and healthy.

Krebs Cycle

This image above is an image i have drawn that describes the processes of the Krebs Cycle. Let me go in detail and explain the steps and processes that are presented in this image i have drawn.

Krebs Cycle:

In bacterial cells, the Krebs cycle takes place in the cytoplasm since bacteria lack mitochondria. This crucial step in cellular respiration generates carbon dioxide, NADH, FADH2, and ATP, essential for energy production.

The Krebs cycle begins with Acetyl CoA, produced from the link reaction, combining with oxaloacetate to form citrate. Through a series of reactions, citrate is converted back to oxaloacetate, releasing two molecules of carbon dioxide. During these reactions, high-energy molecules are produced: NADH and FADH2, which carry electrons to the electron transport chain, and ATP, which provides direct energy for cellular activities.

The Krebs cycle takes place in the mitochondrial matrix of eukaryotic cells. Nonetheless, in bacteria, this whole mechanism occurs within the cytoplasm. The generation of NADH and FADH2 is essential because these molecules power the electron transport chain, resulting in additional ATP production. Effective energy generation is crucial for the survival and operation of bacteria, promoting the well-being and equilibrium of the gut microbiome.

Electron Transport Chain

Finally, we have reached the last step of this complex energetic process, the electron transport chain… This is the seal, the cherry on the top and the end game.

This image depicts, the process of the ETC which i will now explain below:

In bacterial cells, the electron transport chain (ETC) occurs in the cytoplasmic membrane since bacteria lack mitochondria. This final step in cellular respiration uses high-energy electrons from NADH and FADH2, generated in the Krebs cycle, to produce ATP.

The ETC consists of protein complexes in the cytoplasmic membrane. As electrons pass through these complexes, they release energy to pump protons across the membrane, creating a proton gradient. This gradient powers ATP synthase, which synthesizes ATP from ADP and inorganic phosphate. Oxygen, or another terminal electron acceptor, combines with electrons and protons to form water.

The ETC is crucial for efficient energy production in bacteria, enabling them to thrive in various environments, including the gut. The ATP generated supports bacterial growth, maintenance, and reproduction. This energy production plays a significant role in maintaining a balanced gut microbiome and influencing the host’s metabolic health. Understanding the ETC in bacterial energetics highlights the importance of microbial processes in supporting a healthy digestive system and optimal energy utilization.