What Is Bacteria?



Bacteria differ from viruses very much. First of all, they are bigger, second of all, they represent quite self-sufficient live organisms capable of self-reproducing if corresponding feeding is available. Penetrating to a human body, certain bacteria find food and suitable conditions for reproduction, and diseases are appeared this way.

Before the XX century, the doctors’ fight against bacterial infections has not differed from fighting against infection virus: all their efforts were directed at help to an organism to cope with a disease. Fortunately, the possibilities of modern medicine are significantly increased. It was due to creation of several groups of medications able to kill microbes without any significant harm to an individual. You, for sure, heard about these medications: antibiotics (Penicillin, Tetracycline, Gentamycin), sulfanilamides (Streptocide, Aethazolum, Biseptol) and etc.

Reading these words, the readers may think that bacterial infections are treated much easier, comparing to infection virus. But unfortunately, this is not like this. First of all, because bacteria show incredible adaptability and as the doctors discover new medications, new species of known bacteria refractory to these antibiotics are appeared (or probably the drugs affect bacteria for a short period of time or not very effectively.) Second of all, the same bacterial diseases, for example, pneumonia or meningitis, may be caused by hundreds different microbes and the doctors, sometimes, are not able to answer a question: “What is the reason?” and, accordingly, prescribe the correct antibiotic.

The world of bacteria is diverse, as well as the diseases caused by bacteria are various and numerous. Bacteria differ from each other in the sizes, structure, reproductive abilities. The conditions suitable for their normal existing are various. Some bacteria are round, they are named cocci (staphylococcus, pneumococcus, streptococcus, meningococcus, gonococcus,) others are oblong, they are named rods (dysenteric bacillus, pertussis and colon bacillus). Bacteria have outgrowth, flagellum, and cilium. In contrast to viruses, bacteria are not characterized by selective lesion of certain human body parts.

However, each microbe has own “preferences.” So, dysenteric bacillus is developed in the large intestine, pertussis agent is developed in the epithelium cells of the respiratory tracts, meningococcus agent is developed in the arachnoid membrane. Staphylococcus may cause an inflammatory process anywhere on the skin, in bones, in lungs, and in intestines, and etc.

The word bacteria is the plural of bacterium. Grammatically the headline should just say “What are bacteria?” The incorrect usage has been included in the headline to remind readers that it is wrong – and hopefully help correct an increasingly common mistake in the English language.

Bacteria are tiny living beings (microorganisms) 

they are neither plants nor animals – they belong to a group all by themselves. Bacteria are tiny single-cell microorganisms, usually a few micrometers in length that normally exist together in millions.

A gram of soil typically contains about 40 million bacterial cells. A milliliter of fresh water usually holds about one million bacterial cells.

Planet Earth is estimated to hold at least 5 nonillion bacteria. Scientists say that much of Earth’s biomass is made up of bacteria.

5 nonillion = 5,000,000,000,000,000,000,000,000,000,000 (or 5×1030)

(Nonillion = 30 zeros in USA English. In British English it equals 54 zeros. This text uses the American meaning)

Bacteria come in three main shapes:

1) Spherical (like a ball)

These are usually the simplest ones. Bacteria shaped like this are called cocci (singular coccus).

2) Rod shaped

These are known as bacilli (singular bacillus).

Some of the rod-shaped bacteria are curved; these are known as vibrio.

3) Spiral

These known are as spirilla (singular spirillus).

If their coil is very tight they are known as spirochetes.

There are many variations within each shape group.

Bacteria morphology. Image by Vojtěch Dostál

Bacteria are found everywhere

Bacteria can be found in:

  • Soil
  • Radioactive waste
  • Water
  • Plants
  • Animals
  • Deep in the earth’s crust
  • Organic material
  • Arctic ice
  • Glaciers
  • Hot springs
  • The stratosphere (between 6 to 30 miles up in the atmosphere)
  • Ocean depths – they have been found deep in ocean canyons and trenches over 32,800 feet (10,000 meters) deep. They live in total darkness by thermal vents at incredible pressure. They make their own food by oxidizing sulfur that oozes from deep inside the earth.

Scientists who specialize in bacteria – bacteriologists – say bacteria are found absolutely everywhere except for places that humans have sterilized. Even the most unlikely places where temperatures may be extreme, or where there may be a high concentration of toxic chemicals, have bacteria. These bacteria are known as extremophiles (an extremophile is any organism adapted to living in conditions of extreme temperature, pressure, or/and chemical concentrations) and can survive where no other organism can.

Bacteria cells

A bacterial cell differs somewhat from the cell of a plant or animal. Bacterial cells have no nucleus and other organelles (sub-units within a cell with a specific function) bound by a membrane, except for ribosomes. Bacteria have pili, flagella and a cell capsule (most of them), unlike animal or plant cells. An organism without a nucleus is called a prokaryote.

A diagram of a bacterial cell.

A bacterial cell includes:

  • Basal body – this anchors the base of the flagellum, allowing it to rotate.
  • Capsule – a layer on the outside of the cell wall. Some bacteria don’t have a capsule.
  • Cell wall – a thin layer (membrane) outside the plasma membrane, and within the capsule.
  • DNA (Deoxyribonucleic acid) – contains all the genetic instructions used in the development and functioning of the bacterium. It is inside the cytoplasm.
  • Cytoplasm – a gelatinous substance inside the plasma membrane. Genetic material and ribosomes lie inside.
  • Flagellum – this is used for movement; to propel the cell. Some bacterial cells have more than one.
  • Pili (singular: pilus) – these spikes allow the cell to stick to surfaces and transfer genetic material to other cells. A study revealed that pili are involved in causing traveler’s diarrhea.
  • Plasma membrane – it generates energy and transports chemicals. Substances can pass through the membrane (permeable). It is located within the cell wall.
  • Ribosomes – this is where protein is made (synthesized). Ribosomes are small organelles made up of RNA-rich granules.

The origins and evolution of bacteria

Modern bacteria’s ancestors – single-celled microorganisms – appeared on earth about 4 billion years ago. Scientists say they were the first life forms on Earth. For the following 3 billion years all life forms on Earth were microscopic in size, and included two dominant ones: 1. Bacteria, and 2. Archaea (classified as bacteria, but genetically and metabolically different from all other known bacteria).

There are fossils of bacteria. However, because their form and structure (morphology) are not distinctive it is virtually impossible to date them, making it extremely hard to study the process of bacterial evolution with any degree of accuracy. However, with the help of gene sequences, it is now possible to know that bacteria diverged from their original archaeal/eukaryotic ancestry (Eukaryotic = pertaining to an eukaryotice; a single-celled or multicellular organism whose cells contain a distinct membrane-bound nucleus).

Archaea is bacteria’s most recent common ancestor – it was most likely hyperthermophile, an organism that thrived in extremely hot environments, approximately 2.5 – 3.2 billion years ago. Bacteria were also involved in the divergence of archaea and eukaryotes. Eukaryotes came from a very early bacteria which had an endosymbiotic association (when an organism lives within the body or cells of another organism) with the predecessors of eukaryotes cells, which were probably related to the Archaea. Biologists say that some algae probably originated from later endosymbiotic relationships.

Put simply 

bacteria were the first organisms to appear on earth, about 4 billion years ago. Our oldest known fossils are of bacteria-like organisms.

On the next page 

we look at a short history of bacteriology, how bacteria feed themselves and what kinds of environments bacteria inhabit. On the final page we discuss how bacteria reproduce and the effects of bacteria

Bacteria are microscopic single-celled organisms that thrive in diverse environments. They can live within soil, in the ocean and inside the human gut. Humans’ relationship with bacteria is complex. Sometimes they lend a helping hand, by curdling milk into yogurt, or helping with our digestion. At other times they are destructive, causing diseases like pneumonia and MRSA.


Based on the relative complexity of their cells, all living organisms are broadly classified as either prokaryotes or eukaryotes.

Bacteria are prokaryotes. The entire organism consists of a single cell with a simple internal structure. Unlike eukaryotic DNA, which is neatly packed into a cellular compartment called the nucleus, bacterial DNA floats free, in a twisted thread-like mass called the nucleoid.


Bacterial cells also contain separate, circular pieces of DNA called plasmids. Bacteria lack membrane-bound organelles, specialized cellular structures that are designed to execute a range of cellular functions from energy production to the transport of proteins. However, both bacterial and eukaryotic cells contain ribosomes. These spherical units are where proteins are assembled from individual amino acids, using the information encoded in a strand of messenger RNA.

On the outside, bacterial cells are generally surrounded by two protective coverings: an outer cell wall and an inner cell membrane. However, certain bacteria, like the mycoplasmas do not have a cell wall at all. Some bacteria may even have a third, outermost, protective layer called the capsule. Lastly, bacterial surfaces can be covered by whip-like extensions: flagella or pili. According to the authors of “Mims Medical Microbiology, 5th Ed” (Saunders, 2013), long flagella aid in motility while short pili help bacteria to attach to host surfaces.


A few different criteria are used to classify bacteria. They can be distinguished by the nature of their cell walls, by their shape, or by differences in their genetic makeup.

The Gram stain is a test used to identify bacteria by the composition of their cell walls. It is named for Hans Christian Gram, who developed the technique in 1884. Bacteria are first stained with a purple dye called crystal violet, which specifically binds to peptidoglycan, a complex structure of amino acids and sugars found in the cell wall. This is followed by a series of steps that ultimately remove any unbound or loosely bound crystal violet.

Then the cells are stained with a second red-colored dye called safranin. Gram-positive bacteria stain purple because their cell walls are rich in peptidoglycan. On the other hand, Gram-negative bacteria whose cells walls have two layers take on a red coloring. The outer layer of lipids does not bind strongly to crystal violet and the dye is easily washed away during the staining process. For example, Streptococcus pneumoniae, which causes pneumonia, is a Gram-positive bacterium, while Escherichia coli (E.coli) and Vibrio cholerae, which causes cholera, are Gram-negative bacteria.

There are three basic bacterial shapes, according to “Mims Medical Microbiology.” Round bacteria are referred to as cocci (singular: coccus); cylindrical, capsule-shaped bacteria as bacilli (singular: bacillus); and spiral bacteria are aptly called spirilla (singular: spirillum). Cocci can also associate with one another in different configurations: combinations of two or diplococcus; a linear chain or streptococcus; and a cluster or staphylococcus. The shapes and configurations of bacteria are often reflected in their names. For example, the milk-curdling Lactobacillus acidophilus are bacilli, and pneumonia-causing Streptococcus pneumoniae are a chain of cocci.

The classification criteria mentioned thus far are based on physiological properties and morphology. However, classification of bacteria based on their evolutionary relationships to one another, that is to say, drawing a sort of family tree of all bacterial species, is a relatively new development. This type of phylogeneticclassification became possible with the advent of nucleotide sequencing technology (the ability to read the order of nucleotides in DNA or RNA). Since ribosomes are present in all living organisms, one can look at similarities and differences in the RNA sequences that encode certain ribosomal proteins and determine the degree of relatedness of different organisms.

In his essay, “How We Do, Don’t and Should Look at Bacteria and Bacteriology,” included in “The Prokaryotes, 3rd Ed, Vol. 1” (Springer, 2006) Carl Woese notes that sequencing ribosomal RNA (rRNA) allowed for the development of a “clear concept of a bacterium” by establishing phylogenetic relationships between bacterial species. Using early sequencing technology developed by Frederick Sanger in the mid-1960s, Woese began to characterize bacterial rRNA and discovered a second group of prokaryotic organisms called archaea. Until then, the only known members of this group, the methanogens, had been mistakenly identified as bacteria. In their 1977 paper published in PNAS, authors Woese and George Fox state that methanogens bore “no phylogenetic resemblance” to bacteria.


Most bacteria multiply by a process called binary fission. A single bacterial cell, the “parent,” makes a copy of its DNA and grows large in size by doubling its cellular content. The doubled contents are pushed out to either end of the cell. Then a small fissure emerges at the center of the parent, eventually splitting it into two identical “daughter” cells. Some bacterial species such as cyanobacteria and firmicutes reproduce via budding. During budding, the daughter cell grows as an offshoot of the parent. It starts off as a small nub, grows until it is the same size as its parent, and splits off.

The DNA found in parents and offspring after binary fission or budding is exactly the same. Therefore bacterial cells try to introduce some variation into their genetic material by integrating additional DNA into their genome. This is known as horizontal gene transfer, and the resulting genetic variation ensures that bacteria can adapt and survive as their environment changes. There are three ways by which this occurs: transformation, transduction and conjugation.

During transformation, bacterial cells integrate short fragments of DNA from their surrounding environment. According to the authors of “Mims Medical Microbiology,” these fragments may be released by nearby bacteria that have ruptured. On the other hand, transduction occurs when bacteria are infected by special viruses known as bacteriophages that can carry bacterial DNA.

Conjugation requires physical contact between two bacteria. Genetic material, usually a duplicated plasmid, will transfer from a donor to a recipient. This plasmid copy travels out through a physical extension called the pilus and enters the recipient bacterial cell. Donor bacteria contain a sequence of DNA called the F-factor that enables pilus formation. Conjugation can aid in the spread of antibiotic resistance genes.

Bacteria in human health and disease

Bacteria can be beneficial as well as detrimental to human health. Commensal bacteria, which share space and resources within our bodies, tend to be helpful. In a 2012 article in the journal Nature, titled “Learning About Who We Are,” David A. Relman, a microbiologist at Stanford University, states that there are about 10 times more microbial cells than human cells in the human body. The highest numbers of microbial species are found in the gut.

The human gut is a comfortable setting for bacteria, with plenty of nutrients available for their sustenance. In a 2014 review article, “Analyzing the Human Microbiome: A ‘How To’ Guide for Physicians,” in the American Journal of Gastroenterology, the authors mention that gut bacteria and other microorganisms aid in digestion, stave off colonization by harmful pathogens, and help in the development of the immune system. Moreover, the disruption of gut bacteria has been linked to certain disease conditions. For instance, patients with Crohn’s disease have increased antibodies against their gut bacteria and their T-cells are quite aggressive toward bacterial antigens, according to the authors of “Gut Flora in Health and Disease,” published in The Lancet journal in 2003.

Other bacteria can cause infections. For example, Streptococcus pneumoniae causes pneumonia. Several bacteria ranging from group A StreptococcusClostridiumEscherichia coli and Staphylococcus aureus can cause a rare but severe soft tissue infection called necrotizing fasciitis sometimes called “flesh-eating bacteria.” According to the Centers for Disease Control, this infection affects the tissues surrounding muscles, nerves, fat, and blood vessels but it can be treated, especially when caught early.

Antibiotic-resistant strains of Staphlyococcus aureus bacteria (purple) have become the most common cause of skin infections seen in hospital emergency departments.

Antibiotic resistance

Antibiotics are typically used to treat bacterial infections. However in recent years, the improper or unnecessary use of antibiotics has promoted the spread of several strains of antibiotic-resistant bacteria.

Antibiotic resistance is a phenomenon where infectious bacteria are no longer susceptible to previously effective antibiotics. According to the CDC, each year in the United States, at least 2 million people are infected with antibiotic resistant bacteria, leading to the death of at least 23,000 each year. “Pretty much any infection you can think of now has been identified as being associated with some level of resistance,” said Dr. Christopher Crnich, an infectious disease physician and hospital epidemiologist at the University of Wisconsin Hospitals and Madison Veterans Affairs Hospital. “There’s very few infections that we now treat where infections caused by resistant bacteria is not a clinical concern.”

One of the more notorious antibiotic resistant bacterial strains is methicillin-resistant Staphylococcus aureus (MRSA), which resists methicillin and other antibiotics used to treat Staphylococcus infections. It spreads primarily through skin contact. MRSA infections occur in health care settings such as hospitals and nursing homes, where it can lead to pneumonia or bloodstream infections. MRSA also spreads in the community, especially in situations where there is a lot of skin contact or the use of shared equipment; for example, among athletes, in tattoo parlors, or in day care facilities and schools. Community-acquired MRSA most often causes skin infections.

An important facet of combating antibiotic resistance is to be careful about their use. “It’s so important for us to use antibiotics intelligently,” Crnich told LiveScience. “You only want to use an antibiotic when you have a clear cut bacterial infection.”

A short history of bacteriology

Some people had suggested thousands of years ago that something too small for the naked eye to see may be the cause of disease. Over the hundreds of years that followed various theories were given. It was not until 1676 that bacteria were properly identified as microorganisms. Below is a short synopsis of some of the most famous scientists/microbiologists in history:

Marcus Terentius Varro 

a prolific author. He suggested that disease may be caused by miniscule animals that floated in the air. He is admired by many scientists today for his anticipation of microbiology (the study of microorganisms and their effects on other living organisms) and epidemiology (the study of the causes, distribution, and control of disease in populations). He believed marshy places should be avoided during building work because they might contain insects too small for the eye to see that entered the body through the mouth and nostrils and cause diseases.


a physician, considered one of the most outstanding figures in the history of medicine. He was the first physician to separate medicine from superstition. He said disease was not a punishment meted out by gods, but rather a result of lifestyle, diet and environmental factors. However, Hippocrates’ theories on diseases being an imbalance of the four humors present in the human body, caused by miasmas – vapors from rotting vegetables or bodies, polluted rivers and marshy places – were slightly wider of the mark than we know about today.

Jacobo Forli and Alexandro Benedetti (Italian c. 14th/15th century) 

they said it was not possible to get ill just by breathing in the air. They said particles that floated in the air may cause disease if they were breathed in.

Nevertheless, the Miasma Theory persevered for a long time, right from the first century through to about 1500, when the Germ Theory started to develop:

Antonie van Leeuwenhoek (Dutch 1632-1723)

 he handcrafted single-lens microscopes himself, with which he saw what he called animalcules in 1676 (to be called bacteria 162 years later). In a series of letters to the Royal Society (England) he published his findings. He is commonly known as the father of microbiology and considered to be the first microbiologist.

Christian Gottfried Ehrenberg (German 1795-1876)

 one of the most famous and prolific scientists during the nineteenth century, introduced the term bacterium in 1838.

Louis Pasteur (French – 1822 – 1895)

a remarkable chemist who became famous for many breakthroughs in the causes and preventions of disease. He created the first vaccine for rabies. Pasteur demonstrated in 1859 that the fermentation process is caused by the growth of microorganisms, and not spontaneous generation. He and Robert Koch, said that diseases were caused by germs (The Germ Theory).

Robert Koch (German – 1843-1910) 

a brilliant physician/researcher who was awarded the Nobel Prize in 1905 after he proved The Germ Theory.

Paul Ehrlich (German – 1854-1915)

 a scientist who became a world authority in immunology. He invented the term chemotherapy. He developed the first antibiotic (Salvarsan) and used it to cure syphilis. He was awarded the Nobel Prize in 1908 for his research on immunology. He pioneered the use of stains to detect bacteria.

Carl Woese (American – 1928-)

 currently professor of microbiology at the University of Illinois at Urbana-Champaign. His work recognized that archaea evolved along a separate line from bacteria.

Metabolism – How do bacteria feed themselves?

Bacteria feed themselves in a variety of ways.

Heterotrophic bacteria (or just heterotrophs)

Heterotrophic bacteria eat other organisms.

Most of them are saprobes, they 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)

Autotrophic bacteria make their own food.

This could be done by photosynthesis 

they use sunlight, C02, and water to make their food. Bacteria that use sunlight to synthesize their food are called photoautotrophs. These include the cyanobacteria which probably played a vital role in creating the Earth’s oxygen atmosphere. Other photoautotraphs do not produce oxygen, such as heliobacteria, purple non-sulfur bacteria, purple sulfur bacteria, and green sulfur bacteria.

Others do it by chemosynthesis 

they use C02, water, and such chemicals as ammonia to synthesize their food. We call them nitrogen fixers. They are commonly in legume roots and ocean vents. Examples of legumes are alfalfa, clover, peas, beans, lentils, and peanuts. These bacteria are known as chemoautotrophs. Other chemicals used for nutrition are nitrogen, sulfur, phosphorous, vitamins, and such metallic elements as sodium, potassiumcalcium, magnesium, manganese, iron, zinc, and cobalt.

What kinds of environments do bacteria inhabit?

Aerobes (aerobic bacteria) 

 these can grow only in the presence of oxygen. Some types may cause serious problems to people’s infrastructure as they can cause corrosion, fouling, problems with water clarity, and bad smells.

Anaerobes (anaerobic bacteria) 

 these can only grow if there is no oxygen present. In humans, they are most commonly found in the gastrointestinal tract. They also cause gas gangrenetetanus, and botulism. Most dental infections are caused by this type of bacterium.

Facultative anaerobes (facultative anaerobic bacteria) 

these thrive in environments with or without oxygen. However, when given both options, they prefer to use oxygen for respiration. Most commonly found in soil, water, vegetation and some normal flora of humans and animals. An example of a facultative anaerobic bacterium is salmonella.

Mesophile (mesophilic bacteria)

 these thrive in moderate temperatures. Examples include Listeria monocytogenes, Pesudomonas maltophilia, Thiobacillus novellus, Staphylococcus aureus, Streptococcus pyrogenes, Streptococcus pneumoniae, Escherichia coli, and Clostridium kluyveri. Human bacterial infections are mainly caused by mesophilic bacteria – this is because the body of a human is moderate (37 Celsius). The human intestinal flora contains many beneficial mesophilic bacteria, such as dietary Lactobacillus acidophilus.

Extremophiles (extremophilic bacteria) 

these thrive in conditions considered too extreme for most life forms, including mankind. There are several different types of extremophilic bacteria, depending on what kind of extremes they can tolerate:

  • Thermophiles (thermophilic bacteria) – these thrive in temperatures above 55 Celsius, and can tolerate up to 75-80 Celsius. They take longer to destroy in boiling water than other bacteria. The bacteria Pyrolobus fumarii can tolerate temperatures up to 113 Celsius – it is classed as a hyperthermophile.
  • Halophiles (halophilic bacteria) – these only thrive in a salty environment, such as saltine lakes. An example is Halobacteriacea.
  • Acidophiles (acidophilic bacteria) – these only thrive in acidic environments. Cyanidium caldarium, and Ferroplasma sp can tolerate an environment with an acidity of pH 0.
  • Alkaliphiles (alkiliphilic bacteria) – these only thrive in alkaline environments. Natronobacterium, Bacillus firmus OF4, and Spirulina spp can all tolerate up to pH 10.5.
  • Psychrophiles (psychrophilic bacteria) – these thrive at very low temperatures, such as in glaciers. An example is Psychrobacter.

How bacteria reproduce

Bacteria may reproduce using the following methods:

Binary fission

This is known as an asexual form of reproduction; it does not involve a male and female. The cell continues growing and growing, eventually a new cell wall grows through the center forming two daughter cells, which eventually separate. Each daughter cell has the same genetic material as the parent cell.

Bacterial recombination

The problem with binary fission is that every daughter cell is identical to the cell it came from, as well as all its sisters. This makes it harder for bacteria to prevail, especially if we attack them with antibiotics. To get around this, bacteria use a process called recombination. Bacterial recombination is achieved through:


this simply means passing pieces of genes from one bacterial cell to another one when they come in contact. A bacterium connects itself to another through a tube structure called pilus (there are lots of them, spiky things, plural: pilli), you can see them in the second illustration in this article (scroll up). Genes from one bacterial cell go through this tube into the other cell.


some bacterial cells can grab DNA form the environment around them – often DNA from dead bacterial cells. The bacterial cell binds the DNA and carries it across the bacterial cell membrane. Put simply, it pulls the DNA in from outside through its cell wall.


bacteria get infected by viruses called bacteriophages. The bacteriophage inserts its genome into the bacterium when it attaches itself to the bacterial cell. The genome of this virus, enzymes and components of the virus are replicated and assembled inside the host bacterium. The newly formed bacteriophages then cause the rupture or disintegration of the bacterial cell wall, resulting in the release of the replicated viruses. Sometimes, however, some of the bacterium’s DNA can become encased in the viral capsid (protein shell that surrounds a virus particle) instead of the viral genome during the assembly process. When this bacteriophage goes and infects another bacterium it injects DNA fragments from its previous host (the first bacterium), which then becomes inserted into the DNA of the new bacterium. We call this generalized transduction.

Put simply – transduction is when a virus gets into the bacterium, picks up some of its DNA, and then places it in the next bacterium it gets into.

Researchers at Texas A&M University’s Artie McFerrin Department of Chemical Engineering suggest that genetic material isn’t really captured as much as it is simply utilized after it’s injected into the bacteria by an invading virus.

Another form of transduction is specialized transduction. Fragments of the first bacterium’s DNA become incorporated into the viral genome of the new bacteriophage. These DNA fragments are then transferred to the next bacterium the bacteriophage infects.

Resting stage – spores

This is more a form of hibernation than reproduction. When bacteria do not have enough resources they can reproduce by forming spores, which hold the organism’s DNA material.

These spores are alive but not active. When conditions are appropriate the spores become new bacteria. Spores can remain dormant for centuries before becoming new bacteria. The main function of these spores is to survive through periods of environmental stress. They are resistant to ultraviolet and gamma radiation, desiccation, starvation, chemicals and extremes of temperature. Some bacteria produce endospores (internal spores) while others produce exospores (released outside) or cysts. The spore contains enzymes which are involved in germination.

An example of an endospore-forming bacterium is Clostridium, which consists of about 100 species that include common free-living bacteria as well as important human disease causing bacteria, such as botulism (C. botulinim) and pseudomembranous colitis (C. difficile).

The effects of bacteria

Most people tend to imagine negative things when asked about bacteria. It is important to remember that bacteria are so ubiquitous, and have been around so long – since the beginning of life on earth, in fact – that we would not have existed without them. The air we breathe – specifically the oxygen in the air we breathe – was most probably created millions of years ago by the activity of bacteria.

Nitrogen fixation

Bacteria assimilate atmospheric nitrogen and then release it for plant use when they die. Plants cannot extract nitrogen from the air and place it in the soil – but plants need nitrogen in soil to live – without the bacteria doing this would not be able to carry out a vital part of their metabolism. The relationship between plant and bacteria has become so close in this sense that many plant seeds have a small container of bacteria that will be used when the plant sprouts.

Humans need bacteria to survive

The human body contains huge amounts of friendly bacteria that are either neutral or help us somehow. Bacteria in the digestive system are crucial for the breakdown of certain types of nutrients, such as complex sugars, into forms the body can use. Friendly bacteria also protect us from dangerous ones by occupying places in the body the pathogenic (disease causing) bacteria want attach to. Some friendly bacteria actually come to the rescue and attack the pathogens.

Bacteria and the ‘obesity epidemic’

According to a study released by the International & American Association for Dental Research, bacteria may be a contributory factor in today’s obesity explosion.

Effect of bacteria as pathogens to humans (causes of diseases)

Some of the most deadly diseases and devastating epidemics in human history have been caused by bacteria.

Smallpox and malaria – not caused by bacteria – have killed more humans than bacterial diseases. However, the following bacterial diseases have destroyed hundreds of millions of human lives:

  • Cholera
  • Diphtheria
  • Dysentery
  • Plague
  • Pneumonia
  • Tuberculosis
  • Typhoid
  • Typhus.

In the year 1900 pneumonia, tuberculosis and diarrhea were the three biggest killers in the USA. As water purification improved, vaccines and immunization programs evolved, and antibiotic treatment became more advanced – the human death toll in the USA from bacterial diseases has dropped significantly (as well as in the rest of the developed world). In developing countries, success rates have depended on several factors, such as the strategies implemented by local health authorities, and whether countries enjoyed periods of peacetime (no wars). Countries such as Mexico, Argentina, and Uruguay, to mention but a few, have also seen significant falls in bacterial related deaths over the last 100 years.

Significance of bacteria in food technology

Lactic acid bacteria, such as Lactobacillus and Lactococcus together with yeast and molds (fungi) have been used for the preparation of such foods as cheese, soy sauce, vinegar, yoghurt and pickles. Humans have been using these bacteria for preparing fermented foods for thousands of years.

Significance of bacteria in other technologies

Bacteria can break down organic compounds at remarkable speed and help us in our waste processing and bioremediation activities. Bacteria are frequently used for cleaning up oil spills. They are useful in clearing up toxic waste.

The pharmaceutical and chemical industries use bacteria in the production of certain chemicals. They are used in the molecular biology, biochemistry and genetic research because they can grow quickly and are relative easy to manipulate. Scientists can use bacteria to study the functions of genes and enzymes, as well as bacterial metabolic pathways, and then test out their results on more complex organisms.

Such bacteria as Bacillus thuringiensis (BT) can be used in agriculture instead of pesticides, without the undesirable environmental consequences that pesticide use may cause.

Scientists from University College London created an arsenic biosensor from living bacteria.

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