Methanogens: Man's Good Friend

On a sunny afternoon, the editor took the children to a farm in the nearby mountains. The beautiful scenery, the rustic countryside, the delicious meals, and the occasional quacking, cooing and mooing sounds of ducks, hens, cows and other livestock, created a three-dimensional picture that was intriguing to the audience. The father and daughter were so happy at this moment.

Suddenly, my daughter frowned and said to me: "What's that stinky smell?" The editor looked around and replied: "It's the feces and urine of the farmers' animals." My daughter continued: "It smells so bad. It will ruin the scenery and pollute the environment if it is piled there." The editor replied: "Yes, in fact, in addition to what you said, this is also a waste of resources. After all, these feces can be used as organic fertilizer..."

Methane molecule

In fact, with some technologies and measures, these feces can not only be digested, but also produce methane (a high-quality energy fuel) in the process. The process of turning organic waste into treasure is really exciting, but how many people know that the main contributor is actually invisible microorganisms? Next, the editor will focus on the introduction of methanogens, hoping that readers can understand it.

1. What are methanogens?

Methanogens are a general term for archaea that can metabolize organic or inorganic compounds into carbon dioxide and methane. Methanogens are widely distributed and can be found in almost every environment that is isolated from oxygen, such as water (sea) bottom sediments, wetland soil, plants, and animal digestive tracts.

Methanogens

Methanogens are strictly anaerobic (cannot grow and reproduce in the presence of oxygen, and may even die) prokaryotes. They are a type of environmental microorganism with important functions and significance, and are closely related to the natural carbon cycle (a series of mutual transformation processes of organic and inorganic carbon-containing compounds under biological and non-biological effects).

Due to the limitation of research methods, people’s knowledge of methanogens is less than 170 years old. However, after the invention of strict anaerobic operation technology (most notably the Hungate anaerobic roller tube technology invented by American microbiologist Hungate in 1950), research on methanogens has gradually exploded and is now a well-deserved research hotspot and focus.

Methanosarcina barkeri and Methanobacterium formicium were the first methanogens isolated by researchers. Later, with the improvement of anaerobic separation technology and the continuous updating of analysis and identification methods, more and more new methanogens were discovered. More than five types of methanogens have completed whole genome sequencing, and people have a deeper understanding of their cell structure, metabolic pathways, and suitable environment.

2. Characteristics of Methanogens

1. Slow growth

Different types of methanogens have different cell wall structures and components, some are gram-positive bacteria, and some are gram-negative bacteria. But their common characteristics, in addition to being strictly anaerobic, are that they grow and reproduce very slowly.

It is not an exaggeration to describe their growth speed as "turtle speed", or even much slower. Other types of microorganisms can reproduce a generation in as little as ten minutes or as long as a few days, while methanogens need more than ten days or even dozens of days. This is the "excellent result" achieved under artificial cultivation conditions. If it returns to natural conditions, this time will be longer.

2. Picky eating

Methanogen colonies (cell communities visible to the naked eye formed by a single cell or a group of cells of the same species on the surface or inside a solid culture medium) are notoriously small in the microbial world, and if you don't observe carefully, you may really miss them. The reason why methanogens grow so slowly is closely related to their "picky eating".

The "food" that methanogens like to eat most is mostly simple substances, such as hydrogen, carbon dioxide, formic acid and acetic acid. However, where can there be enough simple organic matter in nature for them to "eat and drink well"? You know, most of the organic matter in the natural environment is relatively complex. Methanogens can only hope that other microorganisms will grow and reproduce, and then decompose the complex organic matter into simple organic matter for them to "fill their stomachs". Alas, it is really frustrating to watch others eat and drink, and then "pick up their ideas" after they are full of food and drink.

3. Friend of Mankind and Helper of Nature

Methanogens can convert organic matter in garbage into methane because they can combine carbon in organic matter with hydrogen in the environment through metabolism. At present, there are three main recognized pathways for methane microbial synthesis, namely, the synthesis pathway with acetic acid (salt) as substrate, hydrogen and carbon dioxide as substrate, and methyl compounds as substrate. Among them, the first synthesis pathway produces the most methane (more than 60% of the methane produced in nature), followed by the second pathway.

It is precisely because of this function of methanogens that acidic substances in the environment do not accumulate in large quantities. Otherwise, after so many other types of microorganisms decompose complex organic substances, the acid content in the environment will increase, and when it reaches a certain level, even the beautiful planet Earth may be corroded.

Finally, it is important to emphasize that methanogenesis also occurs in the intestines of humans and animals. Although methanogenesis is not required for human digestion, methanogens are essential for cattle and sheep, as they convert cellulose in forage into nutrients that are beneficial for cattle and sheep to absorb.

The tiny methanogens are very useful and are inseparable friends of humans, animals and nature.

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