Animals cannot digest Cellulose

Most plants synthesize cellulose which they use to give strength to their bodies and make them withstand the vagaries of storms. It gives the shape to the trees and branches then expand the tree. Cellulose becomes the wood when trees become mature. Furniture is made of this material. It is obvious that cellulose is insoluble in water otherwise no one will use it in construction and furniture.

Cellulose and starch and other carbohydrates consist of glucose molecules which are arranged in chains of different styles. In starch, two chains are intertwined. These chains get separated on boiling the starch in water. This caused the chains to disperse in the water increasing its viscosity. Such starch is called pre-gelatinized starch.

On the other hand, cellulose structure is such that chains are not dispersed and wood remains unaffected in water. Glucose is the basic unit of sugar which is used by animals like humans for obtaining energy to keep the body running.

How do then we assimilate higher sugars like starch. They have to broken down to glucose units. The enzymes found in humans and other animals allow them to digest and metabolize many, but not all, biomolecules. Cellulose is one example of a molecule that defies digestion in many animals.

But the slight difference in the way the glucose molecules are hooked together in starch compared with how they are hooked together in cellulose makes a big difference in their digestibility.

Humans and many other higher animals have the enzyme required to break the bonds in starch, releasing glucose. The particular enzyme is called alpha-amylase.But because the shape of the linkage is different in cellulose, the same enzyme will not work. In fact, where cellulose is concerned, humans do not have an enzyme that will work.

As it turns out, most humans eat a fair amount of cellulose in the form of fruits and vegetables. Although we cannot digest it, the cellulose serves as roughage or fiber that gives food bulk and keeps it moving through the digestive system. In the end, all of the undigested material ends up being eliminated as feces.

Maybe you are wondering how animals such as cattle, sheep, deer, and goats thrive on a diet of grass or other cellulose-rich food. Can they digest cellulose when humans cannot? The answer is no. None of these animals have the enzymes required to digest cellulose. Instead they rely on colonies of microorganisms living in their digestive systems.

These simple microorganisms have the correct enzymes to digest the cellulose and to reassemble the products into starches and proteins. From these products, grazing animals acquire their nutrients. The special relationship between these animals and their resident microbes is called symbiosis—two organisms living with each other to the benefit of both.

Is there life on Mars? Again Microbes hold the key

Earliest life of single cell evolved into 3 branches having distinct traits. The branches further subdivide into more branches on the evolutionary tree of life called Phylogenetic tree of life. The first three branches are called Bacteria, archaea and Eucaryota.


As we can see in this tree, there is a member of archaea family with the name Methanogen. This microbe holds the answer for presence of vast quantities of methane which is trapped inside the ice cages called methane hydrates. These hydrates are found on Earth in the permafrost regions having very low temperatures or under the deep sea floor. Water molecules arrange themselves into octahedral cubes in which molecules of many compounds can fit into them. These are called clathrate compounds. These structures are very fragile and as soon as the overhead pressure is reduced or temperature increases, the structure crumbles and gas is released. So special technology is required to produce the methane from hydrates. In US, carbon dioxide was pumped into the hydrate layer. It substituted into the cages releasing the methane free. It served two important purposes. First the production of fuel gas methane and sequestration of unwanted carbon dioxide. These microbes use carbon dioxide and hydrogen to make their food and also generate methane and water. These microbes are very enterprising. They can use alternative sources of carbon like acetates which are the products formed by another kind of bacteria by breaking the macro-molecules present in the buried organic matter, for their food. One thing these tiny beings hate is oxygen. They work in anaerobic environments like deep buried locations.

Now this microbe is being held responsible for the methane gas found on Mars indicating that there is life on the planet. It means Mars is not a dead planet. Professor James Kasting said if there is anything alive on Mars at this time in its history, it would probably be some form of microbial life living deep beneath the planet’s surface. Perhaps the most likely form of microbial life is a type of bacteria known as methanogenic bacteria, or methanogens for short. The CO2 needed by the methanogens could presumably come from the atmosphere. The H2 could come from chemical reactions between water and certain types of rocks, specifically magnesium- and iron-rich basalts. Such rocks are found on certain parts of the seafloor today on Earth. When they react with water, they form minerals called serpentine minerals. In the process, hydrogen is produced. The reaction that produces methane is thermodynamically favorable, so Methanogens could use the energy released by this reaction to drive their metabolism. Microbes can make many reactions happen at much lower temperature by changing the path of reactions through enzyme catalysts which these microbes synthesize.

Microbes Rule Our World

There are trillions of microbes which inhabit an adult body. Looking at the sheer numbers, one may think that all these microbes are responsible for the ailments only. But this is not true. On the contrary, microbes are much more our friends than our enemies. Microbes run this world despite their infinitely small size. Their success lies in the sheer numbers and ability to adapt to the changing conditions. Following is the list of some species of the microbes that make our lives better:

Bacillus thuringiensis: A common soil bacterium that is a natural pest-killer in gardens and on crops.

Arbuscular mycorrhizas: It is a fungus living in the soil that helps crops take up nutrients from the soil.

Saccharomyces cerevisiae: Baker’s yeast that makes bread rise by generating carbon dioxide.

Escherichia coli It is one of many kinds of microbes that live in your digestive system to help you digest your food every day.

Streptomyces: Bacteria in soil that makes an antibiotic used to treat infections.

Pseudomonas putida:  It is one of many microbes that clean wastes from sewage water at water treatment plants.

Lactobacillus acidophilus: One of the bacteria that turn milk into yogurt.

There are many other important jobs microbes do. They are used to make medicine. They break down the oil from oil spills which otherwise can pollute the sea and cause havoc to the aquatic life . They make about half of the oxygen we breathe by breaking the water molecules into respective components hydrogen and oxygen. They are the foundation of the food chain that feeds all living things on earth.

We’ve been using microbes for thousands of years to make products we need and enjoy. For example, you can thank fungi for the cheese on your cheeseburger and yeast for your bun. Cheese and bread are two microbe-made foods people have been enjoying since time began.

Over the past 50 years, we’ve begun using microbes to do all kinds of new work for us. Here are some examples of microbes at work in pollution control and medicine.

In pollution control, researchers are using bacteria that eat methane gas to clean up hazardous waste dumps and landfills. These methane-eating bacteria make an enzyme that can break down more than 250 pollutants into harmless cells. By piping methane into the soil, researchers can increase growth of the bacteria that normally live in the polluted soil. More bacteria means faster pollution break up. Also, bacteria is being used as one of the tools to clean up oil spills. These bacteria eat the oil, turning it into carbon dioxide and other harmless by-products.

Fungi and bacteria produce antibiotics such as penicillin and tetracycline . These are medicines we use to fight off harmful bacteria that cause sore throats, ear infections, diarrhea and other discomforts. Scientists have changed the genetic material of bacteria and yeasts to turn them into medicine. They inject genes for medicines they want to make into the microbe cells, as if adding new building information to the microbe’s cell DNA. The scientists then grow the microbes in huge containers called fermenters where they reproduce into billions, all making new medicines.

The Mighty Microbes

Microbes may be very small in size but their sheer numbers and remarkable adaptability to the existing climates is astounding. The word microbe is derived from micro-organisms meaning they are so small that they can be seen with the help of a microscope. But these tiny organisms are so active that they can bring about mammoth changes into the environment in which they live.

When the earth first formed, the atmosphere consisted of carbon dioxide and water. Due to this iron existed in the soluble ionic forms in the water. And also there was organic matter. But in the water lived the earliest bacteria called cyanobacteria which were the first photo synthesizers. They combined carbon dioxide and water using sunlight and turned it into their food. Oxygen was the byproduct of this process. Then why did we said there was no free oxygen in the atmosphere and anaerobic conditions existed. Sure oxygen was produced but hungry sinks for it readily available. Iron in the ionic form immediately captured the produced oxygen and got precipitated and iron ore. Similarly organic matter acquired its share of oxygen.Thus all the iron ore we see on the earth is the handiwork of microbes.

Slowly and slowly, all the available iron was precipitated. Now nothing was there to capture the free oxygen and over the period of time, atmosphere was enriched with oxygen. This free oxygen was poison to many microbes which were adapted to conditions devoid of oxygen. Thus they were exterminated. But as we said in the beginning, some of them got buried deep along with organic matter and survived.

It has been reported that amongst these microbe consortia exist a class which uses carbon dioxide and hydrogen to synthesize methane gas. So far it was thought that methane was produced under aerobic conditions but evidence now indicates to the anaerobic bacteria. These bacteria are the terminal stage actors. Before them are a variety of other bacteria which breakdown the organic matter and provide carbondioxide and hydrogen to these bacteria.

The methane in the gas hydrates which hold the promise to solve the energy requirements of the ever hungry industrial world is formed by these microbes and has been trapped in the ice lattices in the form of clathrate compounds which are nothing but cages formed by the water molecule and methane is trapped inside. These bacteria are thought to be starved for food and are ready to pounce on the reactants as soon as they are available.

Microbes are thus omnipresent and affect the life on our planet since the life began with them.