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What are Microorganisms (Bacteria, Viruses, Fungi, Protozoa, Algae and Archaea) ?

news-details Image Source Mar 07, 2021 16:25 IST , Updated: Jun 09, 2021 16:25 IST · 6 min read

Microorganisms or microbes are microscopic organisms that exist as unicellular, multicellular, or cell clusters. Microorganims are widespread in nature and are beneficial to life, but some can cause serious harm. They can be divided into six major types: bacteria, archaea, fungi, protozoa, algae, and viruses.

What are Virus ?

A virus is a submicroscopic infectious agent that cannot replicate alone and replicates only inside the living cells of an organism. Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

A virus is a small collection of genetic code, either DNA or RNA, surrounded by a protein coat.

Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity, outnumber bacteria by 10 to 1.

Viruses don't have the same components as bacteria, they cannot be killed by antibiotics - only antiviral medications or vaccines can eliminate or reduce the severity of viral diseases

Viruses can't be seen in the microscope and have two or three components - A virus is made up of a core of genetic material (single-stranded or double-stranded nucleic acid), either DNA or RNA, surrounded by a protective coat called a capsid which is made up of protein. Sometimes the capsid is surrounded by an additional spikey coat - glycoprotein spikes haemagglutinin (H) and neuraminidase (N) called the envelope.

The simplest viruses contain only enough RNA or DNA to encode four proteins, the most complex can encode 100 0 200 proteins.

The virus particle attaches to the host cell before penetrating it. The virus then uses the host cell's machinery to replicate its own genetic material. Once replication has been completed the virus particles leave the host by either budding or bursting out of the cell (lysis).

What are Bacteria ?

Bacteria constitute a large domain of prokaryotic microorganisms, typically a few micrometres in length. Bacteria have a number of shapes, ranging from spheres to rods and spirals.

Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats - soil, water, acidic hot springs, radioactive waste, and the deep biosphere of the earth's crust.

Nearly all animal life is dependent on bacteria for survival as only bacteria and some archaea possess the genes and enzymes necessary to synthesize vitamin B12, also known as cobalamin, and provide it through the food chain.

Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere.

In humans and most animals, the largest number of bacteria exist in the gut and on the skin. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial.

However, several species of bacteria are pathogenic and cause infectious diseases including cholera, syphilis, anthrax, leprosy, and bubonic plague.

Viruses are not living organisms, whereas bacteria are - Viruses are only "active" within host cells which they need to reproduce, while bacteria are single-celled organisms that produce their own energy and can reproduce on their own.

Bacteria are giants when compared to viruses, the smallest bacteria are about 0.4 micron in diameter while viruses range in size from 0.02 to 0.25 micron. Viruses are typically studied with an electron microscope.

Most bacteria multiply by a process called binary fission, in this process, a single bacterial cell, called the "parent," makes a copy of its DNA and grows larger by doubling its cellular content. The cell then splits apart, pushing the duplicated material out and creating two identical "daughter" cells.

Bacteria are classified as prokaryotes, which are single-celled organisms with a simple internal structure that lacks a nucleus, and contains DNA that either floats freely in a twisted, thread-like mass called the nucleoid, or in separate, circular pieces called plasmids.

A prokaryote is a cellular organism that lacks an envelope-enclosed nucleus.

Bacterial cells are generally surrounded by two protective coverings - an outer cell wall and an inner cell membrane. Certain bacteria, like the mycoplasmas, do not have a cell wall at all, while some bacteria may even have a third, outermost protective layer called the capsule.

What are Fungus ?

A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts, rusts, smuts, mildews, molds, as well as the more familiar mushrooms.

Fungi can be single celled (yeast) or very complex multicellular organisms. They are the principal decomposers in ecological systems.

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

Many fungi are free-living in soil or water; others form parasitic or symbiotic relationships with plants or animals.

Historically, fungi were included in the plant kingdom, however, because fungi lack chlorophyll (do not photosynthesize), and have some distinct structural and physiological features of their cell wall and cell membrane, they have been separated from plants.

The cell walls of fungi contain chitin, which is a hard substance also found in the exoskeletons of insects and arthropods such as crustaceans.

Fungi, like animals, are heterotrophs(cannot produce its own food), they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment.

Fungi reproduce both sexually and asexually, and they also have symbiotic associations with plants and bacteria.

Yeast are single-celled microorganisms that are classified, along with molds and mushrooms, as members of the Kingdom Fungi.

What are Protozoa ?

Protozoa is an informal term for a group of single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris.

They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure.

They live in a wide variety of moist habitats including fresh water, marine environments and the soil.

What are Algae ?

Algae are photosynthetic eukaryotic organisms (neither plants nor animals) that can range from the microscopic (microalgae), to large seaweeds (macroalgae), such as giant kelp more than one hundred feet in length, the largest and most complex marine algae are called seaweeds.

Microalgae include cyanobacteria (bacteria, and formerly called "blue-green algae"), green, brown and red algae etc. By producing and releasing oxygen (as a byproduct of photosynthesis), cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event.

Cyanobacteria are a group of photosynthetic bacteria, some of which are nitrogen-fixing, that live in a wide variety of moist soils and water either freely or in a symbiotic relationship with plants or lichen-forming fungi (as in the lichen genus Peltigera)

Most microalgae grow through photosynthesis - by converting sunlight, CO2 and a few nutrients, including nitrogen and phosphorous, into material known as biomass. Other algae can grow in the dark using sugar or starch, or even combine both growth modes.

What are Archaea ?

Archaea or Archaebacteria differ from true bacteria in their cell wall structure and lack peptidoglycans. They are prokaryotic cells with avidity to extreme environmental conditions.

Archaeans use different energy sources like hydrogen gas, carbon dioxide, and sulphur. Some of them use sunlight to make energy, but not the same way plants do. They absorb sunlight using their membrane pigment, bacteriorhodopsin. This reacts with light, leading to the formation of the energy molecule adenosine triphosphate (ATP).

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