INTRODUCTION TO MICROORGANISMS

Microorganisms are microscopic organisms that cannot be seen by the naked eye. These organisms are usually unicellular in nature.

the guys who are everywhere, BACTERIA;

the guys that love death, FUNGI;

the creepy PROTOZOANS; and

from computers to life, VIRUSES.

Bacteria are unicellular prokaryotic microorganisms.They are mostly multicellular and not microscopic.However, yeast is a unicellular and microscopic organism. Bacteria may be spherical, rod-shaped, and spiral.

WHAT ARE BACTERIA AND WHAT DO THEY DO?

Bacteria are microscopic, single-celled organisms that exist almost everywhere. They are thought to have been the first organisms on earth. The oldest known fossils are bacteria-like organisms. While there may be harmful bacteria that cause diseases, there are also bacteria that provide useful purposes, particularly in industrial and medicinal processes.

Bacteria are micrometers in length and exist together in communities of millions. For example, a gram of soil contains about 40 million bacterial cells, and a milliliter of freshwater contains about one million bacterial cells.

In total, the earth holds at least five nonillion bacteria.

BACTERIAL STRUCTURE:

The basic structure of a bacterial cell includes the capsule, cell wall, plasma membrane, cytoplasm, DNA, ribosomes, flagellum, and pili.

Capsule: The capsule is the bacterial cell’s outermost protective layer which is composed of complex carbohydrates. Its functions include protecting the bacteria from phagocytosis attack of other organisms and keeping the bacteria from drying out.

Cell wall: The cell wall is another protective layer of the bacterial cell. It is made up of polysaccharide, particularly the peptidoglycan. Its functions include protecting the cell from the outside environment and providing it with shape and structure.

Plasma membrane: The plasma membrane is a phospholipid bilayer found within the cell wall. Its functions include providing permeability to molecules that need to enter the system of the cell, generating energy, and transporting chemicals.

Cytoplasm: The cytoplasm is a gel-like substance within the plasma membrane. It is the site where cellular functions for growth, metabolism, and replication occur. It also contains the genetic material and ribosomes of the bacterial cell.

DNA: The DNA contains all the genetic instructions used in the development and function of the bacterium. It is found in the cytoplasm of the cell.

Ribosomes: The ribosome is the site for protein synthesis.

Flagellum: The flagellum is a lash-like structure which protrudes from the cell body. It is used for movement and propulsion of certain types of bacteria. Some bacteria, like the lophotrichous, contain multiple flagella.

Pili: The pili is a hair-like appendage found on the outside of the cell. It allows the cell to stick to surfaces and transfer genetic material to other cells. This contributes to the spread of illness in humans.

FEEDING:

Bacteria feed in different ways.

Heterotrophic bacteria, or heterotrophs, get their energy through consuming organic carbon. Most absorb dead organic material, such as decomposing flesh. Some of these parasitic bacteria kill their host, while others help them.

Autotrophic bacteria (or just autotrophs) make their own food, either through either: photosynthesis, using sunlight, water, and carbon dioxide, or chemosynthesis, using carbon dioxide, water, and chemicals such as ammonia, nitrogen, sulfur, and others

Bacteria that use photosynthesis are called photoautotrophs. Some types, for example, cyanobacteria, produce oxygen. These probably played a vital role in creating oxygen in the earth’s atmosphere. Others, such as heliobacteria, do not produce oxygen.

Those that use chemosynthesis are known as chemoautotrophs. These bacteria are commonly found in ocean vents and in the roots of legumes, such as alfalfa, clover, peas, beans, lentils, and peanuts.

WHERE DO THEY LIVE?

Bacteria can be found in soil, water, plants, animals, radioactive waste, deep in the earth’s crust, arctic ice and glaciers, and hot springs. There are bacteria in the stratosphere, between 6 and 30 miles up in the atmosphere, and in the ocean depths, down to 32,800 feet or 10,000 meters deep.

Aerobes, or aerobic bacteria, can only grow where there is oxygen. Some types can cause problems for the human environment, such as corrosion, fouling, problems with water clarity, and bad smells.

Anaerobes, or anaerobic bacteria, can only grow where there is no oxygen. In humans, this is mostly in the gastrointestinal tract. They can also cause gas, gangrene, tetanus, botulism, and most dental infections.

Facultative anaerobes, or facultative anaerobic bacteria, can live either with or without oxygen, but they prefer environments where there is oxygen. They are mostly found in soil, water, vegetation, and some normal flora of humans and animals. Examples include Salmonella.

Mesophiles, or mesophilic bacteria, are the bacteria responsible for most human infections. They thrive in moderate temperatures, around 37°C. This is the temperature of the human body.

Examples include Listeria monocytogenes, Pseudomonas maltophilia, Thiobacillus novellus, Staphylococcus aureus, Streptococcus pyrogenes, Streptococcus pneumoniae, Escherichia coli, and Clostridium kluyveri. The human intestinal flora, or gut microbiome, contains beneficial mesophilic bacteria, such as dietary Lactobacillus acidophilus.

Extremophiles, or extremophilic bacteria, can withstand conditions considered too extreme for most life forms.

Thermophiles can live in high temperatures, up to 75 to 80°C, and hyperthermophiles can survive in temperatures up to 113°C. Deep in the ocean, bacteria live in total darkness by thermal vents, where both temperature and pressure are high. They make their own food by oxidizing sulfur that comes from deep inside the earth.

Other extremophiles include:

halophiles, found only in a salty environment

acidophiles, some of which live in environments as acidic as pH 0

alkaliphiles, living in alkaline environments up to pH 10.5

psychrophiles, found in cold temperatures, for example, in glaciers

Extremophiles can survive where no other organism can.

REPRODUCTION AND TRANSFORMATION:

Bacteria may reproduce and change using the following methods:

Binary fission: An asexual form of reproduction, in which a cell continues to grow until a new cell wall grows through the center, forming two cells. These separate, making two cells with the same genetic material.

Transfer of genetic material: Cells acquire new genetic material through processes known as conjugation, transformation, or transduction. These processes can make bacteria stronger and more able to resist threats, such as antibiotic medication.

Spores: When some types of bacteria are low on resources, they can form spores. Spores hold the organism’s DNA material and contain the enzymes needed for germination. They are very resistant to environmental stresses. The spores can remain inactive for centuries until the right conditions occur. Then they can reactivate and become bacteria. Spores can survive through periods of environmental stress, including ultraviolet (UV) and gamma radiation, desiccation, starvation, chemical exposure, and extremes of temperature. Some bacteria produce endospores, or internal spores, while others produce exospores, which are released outside. These are known as cysts.

Clostridium is an example of an endospore-forming bacterium. There are about 100 species of Clostridium, including Clostridium botulinum (C. botulinum) or botulism, responsible for a potentially fatal kind of food poisoning, and Clostridium difficile (C. Difficile), which causes colitis and other intestinal problems. [2]

FUNGI:

The three major groups of fungi are:

Multicellular filamentous molds

  • Macroscopic filamentous fungi that form large fruiting bodies. Sometimes the group is referred to as ‘mushrooms’, but the mushroom is just the part of the fungus we see above ground which is also known as the fruiting body.

  • Single-celled microscopic yeasts.

MULTICELLULAR FILAMENTOUS MOLDS

Molds are made up of very fine threads (hyphae). Hyphae grow at the tip and divide repeatedly along their length creating long and branching chains. The hyphae keep growing and intertwining until they form a network of threads called a mycelium. Digestive enzymes are secreted from the hyphal tip. These enzymes break down the organic matter found in the soil into smaller molecules that are used by the fungus as food.

Some of the hyphal branches grow into the air and spores form on these aerial branches. Spores are specialized structures with a protective coat that shields them from harsh environmental conditions such as drying out and high temperatures. They are so small that between 500 – 1000 could fit on a pinhead.

Spores are similar to seeds as they enable the fungus to reproduce. Wind, rain, or insects spread spores. They eventually land in new habitats and if conditions are right, they start to grow and produce new hyphae. As fungi can’t move they use spores to find a new environment where there are fewer competing organisms.

MACROSCOPIC FILAMENTOUS FUNGI

Macroscopic filamentous fungi also grow by producing a mycelium below ground. They differ from molds because they produce visible fruiting bodies (commonly known as mushrooms or toadstools) that hold the spores. The fruiting body is made up of tightly packed hyphae which divide to produce the different parts of the fungal structure, for example, the cap and the stem. Gills underneath the cap are covered with spores and a 10-cm diameter cap can produce up to 100 million spores per hour.

YEASTS

Yeasts are small, lemon-shaped single cells that are about the same size as red blood cells. They multiply by budding a daughter cell off from the original parent cell. Scars can be seen on the surface of the yeast cell where buds have broken off. Yeasts, such as Saccharomyces, play an important role in the production of bread and in brewing. Yeasts are also one of the most widely used model organisms for genetic studies, for example in cancer research. Other species of yeast such as Candida are opportunistic pathogens and cause infections in individuals who do not have a healthy immune system.

PROTOZOANS

Protozoa are single-celled microscopic animals which include flagellates, ciliates, sporozoans, and many other forms.

Few examples are: amoeba, paramecium, euglena, plasmodium, etc.

Protozoans 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 freshwater, marine environments, and the soil. Some are parasitic, which means they live in other plants and animals including humans, where they cause disease. Plasmodium, for example, causes malaria. They are motile and can move by:

Cilia - tiny hair-like structures that cover the outside of the microbe. They beat in a regular continuous pattern like flexible oars.

Flagella - long thread-like structures that extend from the cell surface. The flagella move in a whip-like motion that produces waves that propel the microbe around.

Amoeboid movement - the organism moves by sending out pseudopodia, temporary protrusions that fill with cytoplasm that flows from the body of the cell

Stentor is a trumpet-shaped protozoan, with a ring of cilia around the mouth of the trumpet 'funnel'. The cilia waft bacteria and prey, like small crustaceans, into this opening and down into the digestive system.

VIRUSES

  • Viruses are organisms that possess nucleic acid but lack the replicating machinery. Thus, a virus cannot survive without a living cell.

  • Viruses are also considered to be on the borderline between living and nonliving entities.

  • Few examples are: influenza virus, HIV, Rabies virus, poliovirus, tobacco mosaic virus etc.

WHAT IS A VIRUS?

A virus is a type of parasite the size of which mostly ranges from 0.02 to 0.3μm. It contains a single nucleic acid (RNA or DNA) core which is surrounded by a protein coat. Its ability to duplicate is made possible by the enzymes surrounding the RNA or DNA. Furthermore, the replication of virus only occurs in the cells of animals, plants, and bacteria. Thus, it needs a living host to proliferate.

The classification of viruses depends on the number of its nucleic acid (whether single- or double-stranded), presence of viral envelope, and its mode of replication.

Rabies is a deadly viral disease of the nervous system.

Single-stranded RNA viruses are further classified into a DNA or RNA virus. DNA viruses replicate in the nucleus of host cells while RNA viruses replicate in the cytoplasm.

ARE VIRUSES ALIVE?

Initially, the similar behavior of viruses with bacteria led to the former’s classification as a living organism. However, this changed in the 1930s when it was shown that viruses are not capable of sustaining metabolic functions that are essential to life. Although it contains a DNA or RNA, viruses need a living host to propagate. Until then, a virus only exists as a biochemical mechanism.

VIRUS STRUCTURE:

The protein that surrounds a virus is referred to as the capsid. Capsids vary in shape, from simple helical forms to more complicated structures with tails. It protects the viral genome from the external environment and plays a role in receptor recognition which then enables the virus to bind to susceptible hosts and cells.

Once the virus attaches to a host cell, the capsid is further contained in a phospholipid envelope made up of the membranes of the given host cells. This phospholipid envelope contains the so-called “spike projections”, which are usually glycoproteins. These spike projections aid the movement of the virus towards target cells through receptor recognition.

The largest and most complex viruses can be viewed using a high-resolution light microscope.

Viruses may come in the shape of rods (or filaments), where the nucleic protein subunits are arranged in a linear fashion, and spheres, which are icosahedral polygons. Most of the plant and bacterial viruses have the shape of small filaments or polygoins.

HOW DO VIRUSES INFECT?

As mentioned, a virus is not capable of performing metabolic functions for it to survive independently and increase in number. Rather, it needs to infect a host to replicate. But how does a virus enter the internal system of a host?

The virus enters the hosts through horizontal or vertical transmission. Examples of horizontal transmission include the following:

Direct contact transmission: The transmission via physical contact between an infected and uninfected subject through kissing, biting, or sexual intercourse.

Indirect transmission: The transmission via contact with contaminated objects or materials such as medical equipment or eating utensils.

Common vehicle transmission: This transmission mode refers to when individuals pick up the virus from food and water supplies that are contaminated with feces. This often causes epidemic disease.

Airborne transmission: The transmission that refers to the respiratory infection that occurs when the virus is inhaled.

Once a virus has accessed its host, it recognizes and binds to a specific receptor on the surface of a target cell. One well-studied example is the interaction that occurs between the CCR5 receptor on human T lymphocytes and the gp41 protein present on the surface of the human immunodeficiency virus (HIV).

LIFE CYCLE OF VIRUS?

The replication of a virus begins when it enters the host. This process of replication occurs through the lytic cycle.

In the lytic cycle, the virus replicates its DNA and protein coats, which are then assembled into new virus particles. This causes the host cell to burst or "lyse," which is why the cycle is so-called. The new virus particles that are released once the cell has burst then infect surrounding host cells.

  • The process can take as little as twelve hours, as is the case with the norovirus, or as long as several days, as is the case with the Ebola virus.

Some complex viruses called phages bind their DNA to that of their host cell or deposit small pieces of their DNA in the cytoplasm. When the cell then divides, the viral DNA is copied into the daughter cells. This cycle, which is called the lysogenic cycle, is less common than the lytic cycle.

OTHER MICROORGANISM RELATED INFORMATION-

VACCINES:

  • A vaccine is a biological preparation that provides active acquired immunity to a disease.

  • Vaccines are usually made for viral diseases.

  • Few examples are the Salk vaccine for Polio, Influenza vaccine, Rabies vaccine, etc.

ANTIBIOTICS:

  • Antibiotics are an inorganic or organic compound that inhibits and kills microorganisms.

  • Antibiotics usually target bacteria.

  • Thus most of the bacterial diseases are treated with antibiotics.

PATHOGENS:

  • A pathogen is any organism that causes disease.

  • In this context, pathogens are microorganisms.

  • Bacteria, protozoa, and viruses can be pathogenic.

CARRIER:

  • Carrier is a person or organism infected with an infectious disease agent but displays no symptoms of it.

  • They can spread the infection since they already have the pathogen in their bodies.

VECTOR:

  • A vector is an organism, which is a biting insect or tick, that can transmit disease or parasite from one animal or plant to another.

  • Common examples are mosquitoes.

  • Aedes mosquito spreads dengue virus, Anopheles mosquito spreads the malarial parasite.

AIRBORNE DISEASES:

  • Certain diseases can spread by air.

  • These diseases are called airborne diseases.

  • Influenza is the best example of this type of disease.

WATERBORNE DISEASE:

  • The diseases that spread through water are called waterborne diseases.

  • Contaminated water is host to several pathogens. Typhoid is the best example of waterborne disease.