Home > Articles

Why the World Needs Bacteria

Anne Maczulak explains how bacteria can stretch the limits of our imagination with small size and massive numbers. Learn why both of these attributes help bacteria, and by the biological processes they carry out, bacteria also ensure that humans survive.
This chapter is from the book

What is a bacterium? Bacteria belong to a universe of single-celled creatures too small, with rare exceptions, to be seen by the unaided eye, but exist everywhere on Earth. Being small, simple, and many confers on bacteria advantages that allow them to not only survive but also to affect every mechanism by which the planet works. Bacteria influence chemical reactions from miles above the Earth's surface to activities deep within the Earth's mantle.

Bacteria range in size from Thiomargarita namibiensis, which reaches 750 micrometers (μm) end to end and is visible to the naked eye, to Francisella tularensis measuring only 0.2 μm in diameter. Since 1988, microbiologists have explored a new area involving "nanobacteria." These microbes measure 0.05 μm in diameter or one-thousandth the volume of a typical bacterial cell. Excluding these unusual giants and dwarfs, most bacteria are between 0.5 and 1.5 μm in diameter and 1 to 2 μm long, or less than one-twentieth the size of the period at the end of this sentence. The volume of bacterial cells ranges from 0.02 to 400 μm3. One of many advantages in being small involves the ability to sense environmental changes with an immediacy that large multicellular organisms lack.

Bacterial simplicity can deceive. The uncomplicated structure actually carries out every important biochemical reaction in Earth's ecosystems. Bacteria have an outer cell wall that gives them their distinctive shapes (see Figure 1.1) and overlays a membrane, which holds in the watery cytoplasm interior and selectively takes in nutrients, restricts the entry of harmful substances, and excretes wastes. This membrane resembles the membranes of all other living things. That is, it is consists of a bi-layer of proteins and fats that communicates with the aqueous environment and confines the cell contents to the cell interior. Inside the membrane bi-layer proteins and fats line up in a way that hydrophilic or water-attracting portions of the compounds face out or into the cytoplasm, and hydrophobic compounds point into the membrane. The character of membrane fats enables them to assemble spontaneously if put into a beaker of water. The ease with which membranes assemble likely helped the first cells to develop on Earth.

Figure 1.1

Figure 1.1 Bacteria shapes. Cell shape is hardwired into bacteria genetics. No animal life adheres as strictly to a standard shape as bacteria and algae called diatoms.

The bacterial cytoplasm and membrane hold various enzymes that keep the cell alive. Bacterial deoxyribonucleic acid (DNA), the depository of information formed over the millennia, appears in the cytoplasm as a disorganized mass (seen only with an electron microscope), but it actually contains precise folds and loops that decrease the chances of damage and facilitate repair. Tiny protein-manufacturing particles called ribosomes dot much of the remainder of the cytoplasm.

Bacteria require few other structures. Motile bacteria have whiplike tails called flagella for swimming, photosynthetic cyanobacteria contain light-absorbing pigments, and magnetotactic species, such as Aquaspirillum magnetotacticum, contain a chain of iron magnetite particles that enable the cells to orient toward Earth's poles. These micro-compasses help Aquaspirillum migrate downward in aqueous habitats toward nutrient-rich sediments.

Though tiny, bacteria occupy the Earth in enormous numbers. Microbiologists estimate total numbers by sampling soil, air, and water and determining the bacterial numbers in each sample, and then extrapolating to the size of the planet with the aid of algorithms. Guesswork plays a part in these estimates. Bacteria exist 40 miles above the Earth and 7 miles deep in the ocean, and most of these places have so far been inaccessible. The total numbers of bacteria reach 1030. Scientists struggle to find a meaningful comparison; the stars visible from Earth have been estimated at "only" 7 x 1022. The mass of these cells approaches 2 x 1015 pounds, or more than 2,000 times the mass of all 6.5 billion people on Earth. Of these, the overwhelming majority lives in the soil.

Bacteria can stretch the limits of our imagination with small size and massive numbers. Both of these attributes help bacteria, and by the biological processes they carry out, bacteria also ensure that humans survive.

Tricks in bacterial survival

Bacteria and bacterialike archaea survive challenging conditions through the benefit of adaptations accrued in evolution. Survival techniques might be physical or biochemical. For example, motility in bacteria serves as an excellent way to escape danger. In addition to flagella that help bacteria swim through aqueous environments, some bacteria can glide over surfaces, and others start twitching frantically to propel themselves. Certain bacterial species develop impregnable shells called endospores. Others use biochemical aids to survival to counter the effects of acids, bases, salt, high or low temperature, and pressure.

A large number of bacteria use a modified version of a capsule for protection. The cells build long, stringy lipopolysaccharides, which are polysaccharides (sugar chains) with a fatty compound attached and which extend into the cell's surroundings. The bacteria that make these appendages, called O antigens, construct them out of sugars rarely found in nature. As a consequence, protozoa that prey on bacteria do not recognize the potential meal and swim past in search of "real" bacteria.

Archaea seem to be Earth's ultimate survivors because of the extreme environments they inhabit. Archaea and bacteria both belong to the prokaryotes, one of two major types of cells in biology, the other being more complex eukaryotic cells of algae, protozoa, plants, and animals. Because archaea inhabit extreme environments that would kill most terrestrial animal and plant life, the archaea are sometimes thought of as synonymous with "extremophile." The outer membrane of archaea living in boiling hot springs contain lipid (fatlike) molecules of 30 carbons or more, larger than most natural fatty compounds. These lipids and the ether bonds that connect them stabilize the membrane at extremely high temperatures. News stories often tell of new bacteria found at intense pressures 12,000 feet deep on the ocean floor at vents called black smokers. These hydrothermal vents spew gases at 480°F, release acids, and reside at extreme pressures, so any organisms living there would truly be a news item. The organisms living near black smokers are usually archaea, not bacteria. Archaea also dominate habitats of high salt concentration, such as salt lakes, or places completely devoid of oxygen, such as subsurface sediments. Because of the difficulty of getting at many archaea and their aversion to growing in laboratory conditions, studies on archaea trail those completed on bacteria.

Some bacteria also survive in the same extreme conditions favored by archaea. The aptly named Polaromonas inhabits Antarctic Sea ice where temperatures range from 10°F to –40°F by slowing its metabolism until it reproduces only once every seven days. By comparison, E. coli grown in a laboratory divides every 20 minutes. Polaromonas is a psychrophile or cold-loving microbe. Thermus aquaticus is the opposite, a thermophile that thrives in hot springs reaching 170°F by synthesizing heat-stabile enzymes to run its metabolism. Enzymes of mesophiles, which live in a comfortable temperature range of 40°F to 130°F, unfold when heated and thus lose all activity. Mesophiles include the bacteria that live on or in animals, plants, most soils, shallow waters, and foods. The bacteria that live in harsh conditions that mesophiles cannot endure are the Earth's extremophiles.

The genus Halococcus, a halophile, possesses a membrane-bound pump that constantly expels salt so the cells can survive in places like the Great Salt Lake or in salt mines. Barophilic bacteria that hold up under intense hydrostatic pressures from the water above are inexorably corroding the RMS Titanic 12,467 feet beneath the Atlantic. These barophiles contain unsaturated fats inside their membranes that make the membrane interior more fluid than the fats in other bacterial membranes. Unsaturated fats contain double bonds between some of the carbon atoms in the chainlike fat rather than single bonds that predominate saturated fats. At pressures of the deep ocean, normal membrane liquids change into the consistency of refrigerated butter, but the special membrane composition of barophiles prevents such an outcome that would render the membrane useless. A later chapter discusses why red-meat animals store mainly saturated fats and pork and chicken store more unsaturated fats.

The acidophile Helicobacter pylori that lives in the stomach withstands conditions equivalent to battery acid of pH 1 or lower by secreting compounds that neutralize the acid in their immediate surroundings. Even though an acidophile lives in strong acids that would burn human skin, it remains protected inside a microscopic cocoon of about pH 7. Additional extremophiles include alkaliphiles that live in highly basic habitats such as ammonia and soda lakes; xerophiles occupy habitats without water; and radiation-resistant bacteria survive gamma-rays at doses that would kill a human within minutes. Deinococcus, for instance, uses an efficient repair system that fixes the damage caused to the DNA molecule by radiation at doses that would kill a human. This system must be quick enough to complete the repair before Deinococcus's next cell division.

All bacteria owe their ruggedness to the rigid cell wall and its main component, peptidoglycan. This large polymer made of repeating sugars and peptides (chains of amino acids shorter than proteins and lacking the functions of proteins) occurs nowhere else in nature. Peptidoglycan forms a lattice that gives species their characteristic shape and protects against physical damage. A suspension of bacteria can be put in a blender, whipped, and come out unharmed.

Archaea construct a cell wall out of polymers other than peptidoglycan, but their cell wall plays the same protective role. Furthermore, because archaea have a different cell wall composition than bacteria, they resist all the antibiotics and enzymes that attack bacterial cell walls. This quirk would seem to make archaea especially dangerous pathogens to humans, but on the contrary, no human disease has ever been attributed to an archaean.

In a microscope, bacteria present an uninspiring collection of gray shapes: spheres, rods, ovals, bowling pins, corkscrews, and boomerangs. Microbiologists stain bacteria with dyes to make them more pronounced in a light microscope or use advanced types of microscopy such as dark field or phase contrast. Both of these latter methods create a stunning view of bacteria illuminated against a dark background.

When bacteria grow, the cell wall prevents any increase in size so that bacterial growth differs from growth in multicellular organisms. Bacteria grow by splitting into two new cells by binary fission. As cell numbers increase, certain species align like a strand of pearls or form clusters resembling grapes. Some bacteria form thin, flat sheets and swarm over moist surfaces. The swarming phenomenon suggests bacteria do not always live as free-floating, or planktonic, beings but can form communities. In fact, bacterial communities represent more than a pile of cells. Communities contain a messaging system in which identical cells or unrelated cells respond to each other and change their behavior. This adaptation is called quorum sensing.

Quorum sensing begins when cells excrete a steady stream of signal molecules resembling amino acids. The excreted signal travels about 1 μm so that neighboring cells can detect it with specific proteins on their surface. When the receptors clog with signal molecules, a cell gets the message that other cells have nudged too close; the population has grown too dense. The proteins then turn on a set of genes that induce the bacteria to change their behavior. Different types of bacterial communities alter behavior in their own way, yet throughout bacteriology communities offer bacteria a superb survival mechanism. Some communities swarm, others cling to surfaces, and yet others can cover a pond's surface and control the entire pond ecosystem.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020