Obligate laboratory culture, specifically in liquid medium, aerobic

Obligate aerobes are organisms that need oxygen to survive and multiply. There are some interesting examples of obligate aerobes in the microbial world. Some are useful, some are dangerous, and others are part of our healthy body.

Obligate Aerobes

Have you ever traveled somewhere really high up? Maybe you’ve driven through some mountains or even stayed there for awhile. It’s not uncommon in those circumstances to suffer from symptoms such as breathlessness and headaches. This can happen because we are obligate aerobes.

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What does that mean?An obligate aerobe is an organism that needs at least 20% oxygen in its surroundings to grow. The term obligate, as in ‘obligatory’ or ‘required,’ suggests that oxygen is absolutely essential for the survival and multiplication of obligate aerobes.Almost all eukaryotic organisms, those that have a nucleus in their cells, are obligate aerobes. This includes plants, animals, and fungi. Thus, most of the organisms that we encounter in our day-to-day to life are obligate aerobes. However, in the microbial world there are organisms like yeast or bacteria such as Lactobacilli that can survive in presence or absence of oxygen. Therefore, it is essential to understand the features of obligate aerobic microbes that differ from other microbes.

Characteristics

Obligate aerobes come in a wide range of different shapes and sizes, but they have some defining characteristics. Let’s go over them now:1. Obligate aerobes use oxygen to break down complex carbon compounds with a goal of producing energy. Theses carbon compounds can be simple carbohydrates like glucose and lactose, complex polymers like cellulose (which is found in plants), or even hydrocarbons like phthalate.2. Obligate aerobes use oxygen as final electron acceptor in the electron transport chain to produce energy in the form of ATP (adenosine triphosphate).

This gives them the advantage of producing more energy than other organisms that are not obligate aerobes.3. In a laboratory culture, specifically in liquid medium, aerobic bacteria always grow very close to the surface of liquid medium so that the culture appears like a thick film on the surface, leaving the medium below it transparent and almost sterile.4. While growing obligate aerobes in the laboratory, it is very important to maintain the appropriate percentage of oxygen in the incubator.

Examples

Let’s look at some examples of microbes that are considered obligate aerobes:Micrococcus luteus is a gram-positive spherical bacteria often found in the groups of four, also known as a tetrad. As it needs oxygen for survival, it is found in the areas where oxygen is easily accessible such as soil, dust, air and water. It can tolerate metals and is even claimed to degrade some of the metallic compounds. It is a member of the normal flora of our skin and is involved in decomposing proteins found in our sweat, which causes body odor.

Micrococcus luteus has the ability to degrade highly toxic organic compounds, which makes it is an asset in bioremediation of our environment, as it is used to decompose oil spills and clear organic wastes. In laboratory cultures, it forms beautiful yellow-colored colonies, and it is susceptible to bacitracin.Mycobacterium tuberculosis, or MTB, is an acid-fast bacilli, and as you may have guessed by its name, it causes tuberculosis.

It belongs to the group of acid-fast bacteria, as it is neither gram-positive nor gram-negative. It acquires the pink stain and retains it even after the cells are exposed to highly acidic solutions. After staining, they appear as dark-pink colored rods.MTB is an obligate aerobe and a human pathogen, meaning it can grow and multiply only in human cells, and it does not infect plants or other animals.

Since MTB is an obligate aerobe, it is most commonly found in the well-aerated upper lobes of human lungs. It has a tendency to become dormant, meaning it can remain alive but not multiply. It is a very slow-growing bacteria, and it takes about 15 to 20 hours to complete one cell division. In laboratory cultures, the colonies appear after 4 to 6 weeks.All fungi except unicellular yeast are obligate aerobes. Fungi are the scavengers of our ecosystem, and they break down highly complex organic compounds found in dead and decaying matter into simpler organic compounds that can be returned back in to the food chain.

They are present everywhere around us: on plants, on the soil surface, in the air, and on any decaying food.They are also widely used in food industry. For example, Aspergillus oryzae is used in production of soy sauce and tempeh, a soy meat substitute. Various types of mushrooms are consumed as rich protein sources, including Agaricus bisporous, which is more commonly known as the portobello mushroom.

Other fungal species, such as Beauveria bassiana and Metarhizium anisopliae, are used as biopesticides.

Lesson Summary

Obligate aerobes are organisms that need oxygen for their survival and multiplication example plants, animals, and fungi. Not all microbes are obligate aerobes; some have the ability to survive in the absence of oxygen.

There are various examples of obligate aerobic microbes; some are not so harmful like Micrococcus luteus, some cause dangerous infections like Mycobacterium tuberculosis, and there are others like fungi that are an important part of our ecosystem and have significant industrial applications.

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