1The MainThemes ofMicrobiologyThis is a colorized view ofbacterial planktontakenPeering through themicroscopeinto a drop offromtheSargasso Seaseawateris like looking at stars witha telescopeOn a clear night."-DrVictor Gallardo,ocean researcherMicrobesRuletheEarthCASE FILEn2003,a100-foot sailboatcalled theDNA using state-of-the-art moleculardifferent microscopic creatures, each ofSorcerer ll embarked on a highlyun-techniques and computers.**Their stun-them having unique characteristics andusual fishing expedition in the Sar-ning and somewhat unexpected discov-roles in the ocean environment. Accord-gasso Sea.What was most striking aboutery wasthat thevariety and numbers ofing to Dr. David Thomassen, Chief Scientist,U.S.Department of Energy,"Microbesthis voyage was that it did not involvemicrobeslivingintheoceanexceededbyactually catching fish withhooks or nets.farthelevelsfound inanypreviousoceanrule the earth.Scientists estimatethat therestudies.Instead, thetargets were tinyfloating mi-are more microbes on earth than therecrobes"hooked by an exceedinglyThis ambitious undertaking was justare stars in the universe-an estimatedsophisticated and specific technologythe beginning.It was followed by severalnonillion (onefollowed by 30 zeros)This project was the brainchild ofadditional voyages byDr.Venter's shipMicrobes andtheir communities makeupDr. Craig Venter, a prominent genetics re-along with marine microbiologists fromthe foundation of the biosphere and sus-the Marine Biological Institute in Woodssearcher,* and its primary goal was totain all life on earth."survey in detail the microbial populationHole, Massachusetts,and is continuingWhich groups of microorganismstodayall over theglobe.Even though mi-ofoceanwater.Scientistsaboardtheveswould likelybefound intheplankton?sel randomly collected surface watercrobiologists had previously describedabout every 200 miles, extracted the tini-around 5,700 different types of bacteria,Whatfields ofmicrobiologycouldbeestformsof microscopicplankton,pri-the evidence from these studies showedinvolved inthe furtherstudyofthesemarilybacteria,and sent samples backtothat this numberrepresented onlythetini-microbesand in uncovering theirbasicVenter's laboratory. It was here that hisest "drop in the ocean." Some of the datacharacteristics?scientific crew engaged in a new anduncovered evidenceofmorethan20,000powerful way of examining the world. In-different kinds ofmicroorganisms in just aTocontinue thecase,go topage9stead ofpainstakinglylocating and identi-single liter of seawater,most of them un-fying the individual microbes in theknown.Realizingthattheoceanisavast*Dr. Venter was one of the main individuals behind thesample, as might have been done in thespacewith endless nooks and crannies formapping of the human genome in 2001.past, they extracted the genetic materialorganisms to hidein, by one estimate, it$*This technique, called metagenomic analysis, will be(DNA)fromthesamplesandanalyzedthecould easilycontain5millionto10milliondiscussed in chapter 10
1 *Dr. Venter was one of the main individuals behind the mapping of the human genome in 2001. **This technique, called metagenomic analysis, will be discussed in chapter 10. This is a colorized view of bacterial plankton taken from the Sargasso Sea The Main Themes of Microbiology CHAPTER “Peering through the microscope into a drop of seawater is like looking at stars with a telescope on a clear night.” –Dr. Victor Gallardo, ocean researcher 1 DNA using state-of-the-art molecular techniques and computers.**Their stunning and somewhat unexpected discovery was that the variety and numbers of microbes living in the ocean exceeded by far the levels found in any previous ocean studies. This ambitious undertaking was just the beginning. It was followed by several additional voyages by Dr. Venter’s ship along with marine microbiologists from the Marine Biological Institute in Woods Hole, Massachusetts, and is continuing today all over the globe. Even though microbiologists had previously described around 5,700 different types of bacteria, the evidence from these studies showed that this number represented only the tiniest “drop in the ocean.” Some of the data uncovered evidence of more than 20,000 different kinds of microorganisms in just a single liter of seawater, most of them unknown. Realizing that the ocean is a vast space with endless nooks and crannies for organisms to hide in, by one estimate, it could easily contain 5 million to 10 million different microscopic creatures, each of them having unique characteristics and roles in the ocean environment. According to Dr. David Thomassen, Chief Scientist, U.S. Department of Energy, “Microbes rule the earth. Scientists estimate that there are more microbes on earth than there are stars in the universe—an estimated nonillion (one followed by 30 zeros). Microbes and their communities make up the foundation of the biosphere and sustain all life on earth.” Which groups of microorganisms would likely be found in the plankton? What fi elds of microbiology could be involved in the further study of these microbes and in uncovering their basic characteristics? To continue the case, go to page 9. I n 2003, a 100-foot sailboat called the Sorcerer II embarked on a highly unusual fi shing expedition in the Sargasso Sea. What was most striking about this voyage was that it did not involve actually catching fi sh with hooks or nets. Instead, the targets were tiny fl oating microbes “hooked” by an exceedingly sophisticated and specifi c technology. This project was the brainchild of Dr. Craig Venter, a prominent genetics researcher, *and its primary goal was to survey in detail the microbial population of ocean water. Scientists aboard the vessel randomly collected surface water about every 200 miles, extracted the tiniest forms of microscopic plankton, primarily bacteria, and sent samples back to Venter’s laboratory. It was here that his scientifi c crew engaged in a new and powerful way of examining the world. Instead of painstakingly locating and identifying the individual microbes in the sample, as might have been done in the past, they extracted the genetic material (DNA) from the samples and analyzed the CASE FILE 1 Microbes Rule the Earth taL75292_ch01_001-026.indd Page 1 11/3/10 5:48 PM user-f468 /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefiles /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefile
2Chapter1 The Main Themes of Microbiologyspecialized that it is not uncommon for a microbiologist to spend an1.1 TheScopeof Microbiologyentire career concentrating on a single group ortype of microbe,biochemical process,or disease.xpected LearningOutcomesAmong the specialty professions of microbiology are:1.Define microbiology and microorganisms, and identify thegeomicrobiologists,whofocus on the rolesofmicrobes in themajor organisms included in the science of microbiology.development of earth's crust;marine microbiologists,who study the oceans and its smallest2. Name and define the primary areas included ininhabitants;microbiological studies.medical technologists, who do the tests that help diagnosepathogenic microbes and their diseases;Asweobservethenaturalworld,teemingwithlife,wecannothelpnurse epidemiologists,who analyze the occurrence of infec-but be struck by its beauty and complexity.But for everyfeaturetious diseasesin hospitals:andthat is visible to the naked eye, there are millions of other featuresastrobiologists,who study the possibilities of organisms inthat are concealed beyond our sight because of their small size.Thisspace (Case file 2).altermate microscopic universe is populated by a vast microbial me-Studies in microbiology have led to greater understanding ofnagerie that is equallybeautiful and complex.To sum up the pres-many general biological principles. For example, the study of mi-ence of microbes in one word, they are ubiquitous.* They arecroorganisms established universal concepts concerning the chem-found in all natural habitats and most of those that have been cre-istry of life (see chapters 2and 8),systems of inheritance (seeated by humans.As scientists continue to explore remote and un-chapter 9), and the global cycles of nutrients, minerals, and gasesusual environments,the one entity they always find is microbes.(see chapter 26).They exist deep beneath the polar icecaps, in the ocean to a depth of7 miles, in hot springs and thermal vents, in toxic waste dumps, andeven in the clouds.1.2GeneralCharacteristicsofMicrobiology is a specialized area of biology that deals withMicroorganisms and Their Rolestiny lifeforms that are not readily observed without magnification.Such microscopic* organisms are collectively referred to as micro-intheEarth's Environmentsorganisms, microbes, or several other terms, depending upon thepurpose. Some people call them“germs"or"bugs"in reference to theirxpected LearningOutcomesroleininfectionanddiseasebutthosetermshaveotherbiologicameanings and perhaps place undue emphasis on the disagreeable3. Describe the basic characteristics of prokaryotic cells andreputation of microorganisms.There are several major groupseukaryotic cells and their evolutionary origins.of microorganisms that we will be studying.They are bacteria,4. State several ways that microbes are involved in the earth'sviruses, fungi, protozoa, algae, and helminths (parasitic worms).ecosystems.As we will see in subsequent chapters, each group exhibits a dis-5.Describe the cellularmakeup of microorganisms and their sizetinct collection of biological characteristics.The nature of microor-range, and indicate how viruses differ from cellular microbes.ganisms makes them both easy and difficult to study.Easy,becausethey reproduce so rapidly and can usually be grown in large num-bers in the laboratory. Difficult, because we can't observe or ana-lyze them without special techniques,especially the use ofTheOrigins of Microorganismsmicroscopes (see chapter 3).Microbiology is one of the largest and most complex of theFor billions of years, microbes have extensively shaped the devel-biological sciences because it integrates subject matter from manyopment of the earth's habitats and the evolution of other life forms.diverse disciplines. Microbiologists study every aspect ofIt is understandable that scientists searching for life on other plan-microbes-their genetics,theirphysiology,characteristics that mayets firstlookfor signs of microorganisms.be harmful or beneficial, the ways they interact with the environ-The fossil record dating from ancient rocks and sedimentsment, the ways they interact with other organisms, and their uses inpoints to bacterialike cells thatexisted at least 3.5billion yearsagoindustry and agriculture.(figure 1.1).These simple cells were the dominant cells on earthSee table 1.1 for an overview of several areas of basic and ap-for about2billion years.Theywerevery small and lacked com-plied microbiology.plex internal structures. One of these structures was a nucleus. TheEach major discipline in microbiology contains numerous sub-term that is used to define these types of cells is prokaryotic,*divisions or specialties that deal with a specific subject area or fieldreferring to the lack of a nucleus (karyon).About 1.8 billion years(table 1.1).Infact,manyareasofthis sciencehavebecome soago,there appeared in thefossil record a more complex cell, which* ubiquitous (yoo-bik'-wih-tis) L ubique, everywhere and ous, having. Beingar seeming to be, everywhere at the same time.* prokaryotic (proh"-kar-ee-ah'-tik) Gr. pro, before, and karyon, nucleus.microscppic (my-kroh-skaw'-pik) Gr. mikros, small, and scopein, to se.*microbe (my'-krohb) Gr. mikros, small, and bios, life.Sometimes spelled procaryotic and eucaryotic
2 Chapter 1 The Main Themes of Microbiology 1.1 The Scope of Microbiology Expected Learning Outcomes 1. Defi ne microbiology and microorganisms, and identify the major organisms included in the science of microbiology. 2. Name and defi ne the primary areas included in microbiological studies. As we observe the natural world, teeming with life, we cannot help but be struck by its beauty and complexity. But for every feature that is visible to the naked eye, there are millions of other features that are concealed beyond our sight because of their small size. This alternate microscopic universe is populated by a vast microbial menagerie that is equally beautiful and complex. To sum up the presence of microbes in one word, they are ubiquitous.* They are found in all natural habitats and most of those that have been created by humans. As scientists continue to explore remote and unusual environments, the one entity they always fi nd is microbes. They exist deep beneath the polar icecaps, in the ocean to a depth of 7 miles, in hot springs and thermal vents, in toxic waste dumps, and even in the clouds. Microbiology is a specialized area of biology that deals with tiny life forms that are not readily observed without magnifi cation. Such microscopic* organisms are collectively referred to as microorganisms, microbes,* or several other terms, depending upon the purpose. Some people call them “germs” or “bugs” in reference to their role in infection and disease, but those terms have other biological meanings and perhaps place undue emphasis on the disagreeable reputation of microorganisms. There are several major groups of microorganisms that we will be studying. They are bacteria, viruses, fungi, protozoa, algae, and helminths (parasitic worms). As we will see in subsequent chapters, each group exhibits a distinct collection of biological characteristics. The nature of microorganisms makes them both easy and diffi cult to study. Easy, because they reproduce so rapidly and can usually be grown in large numbers in the laboratory. Diffi cult, because we can’t observe or analyze them without special techniques, especially the use of microscopes (see chapter 3). Microbiology is one of the largest and most complex of the biological sciences because it integrates subject matter from many diverse disciplines. Microbiologists study every aspect of microbes—their genetics, their physiology, characteristics that may be harmful or benefi cial, the ways they interact with the environment, the ways they interact with other organisms, and their uses in industry and agriculture. See table 1.1 for an overview of several areas of basic and applied microbiology. Each major discipline in microbiology contains numerous subdivisions or specialties that deal with a specifi c subject area or fi eld (table 1.1). In fact, many areas of this science have become so * ubiquitous (yoo-bik9-wih-tis) L. ubique, everywhere and ous, having. Being, or seeming to be, everywhere at the same time. * microscopic (my0-kroh-skaw9-pik) Gr. mikros, small, and scopein, to see. * microbe (my9-krohb) Gr. mikros, small, and bios, life. specialized that it is not uncommon for a microbiologist to spend an entire career concentrating on a single group or type of microbe, biochemical process, or disease. Among the specialty professions of microbiology are: geomicrobiologists, who focus on the roles of microbes in the development of earth’s crust; marine microbiologists, who study the oceans and its smallest inhabitants; medical technologists, who do the tests that help diagnose pathogenic microbes and their diseases; nurse epidemiologists, who analyze the occurrence of infectious diseases in hospitals; and astrobiologists, who study the possibilities of organisms in space (Case fi le 2). Studies in microbiology have led to greater understanding of many general biological principles. For example, the study of microorganisms established universal concepts concerning the chemistry of life (see chapters 2 and 8), systems of inheritance (see chapter 9), and the global cycles of nutrients, minerals, and gases (see chapter 26). 1.2 General Characteristics of Microorganisms and Their Roles in the Earth’s Environments Expected Learning Outcomes 3. Describe the basic characteristics of prokaryotic cells and eukaryotic cells and their evolutionary origins. 4. State several ways that microbes are involved in the earth’s ecosystems. 5. Describe the cellular makeup of microorganisms and their size range, and indicate how viruses differ from cellular microbes. The Origins of Microorganisms For billions of years, microbes have extensively shaped the development of the earth’s habitats and the evolution of other life forms. It is understandable that scientists searching for life on other planets fi rst look for signs of microorganisms. The fossil record dating from ancient rocks and sediments points to bacterialike cells that existed at least 3.5 billion years ago (fi gure 1.1). These simple cells were the dominant cells on earth for about 2 billion years. They were very small and lacked complex internal structures. One of these structures was a nucleus. The term that is used to defi ne these types of cells is prokaryotic,* referring to the lack of a nucleus (karyon). About 1.8 billion years ago, there appeared in the fossil record a more complex cell, which * prokaryotic (proh0-kar-ee-ah9-tik) Gr. pro, before, and karyon, nucleus. Sometimes spelled procaryotic and eucaryotic. taL75292_ch01_001-026.indd Page 2 11/3/10 5:48 PM user-f468 /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefiles /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefile
31.2GeneralCharacteristicsofMicroorganismsandTheirRolesintheEarth'sEnvironmentsTABLE 1.1ASamplingof Fields andOccupations in MicrobiologyA.ImmunologyC.BiotechnologyThisbranch studiesthecomplexweb ofprotective substancesandThis branch is defined by any process that harnesses the actions ofreactions caused by invading microbes and other harmful entities. Itliving things to arrive at a desired product, ranging from beer to stemincludes such diverse areas as blood testing, vaccination, and allergycells. It includes industrial microbiology, which uses microbes to(seechapters15.16.and17)produce and harvest large quantities of such substances as vaccines,vitamins, drugs, and enzymes (see chapters 10 and 27).FigureA A specialist in the CDC special pathogensunit reads a microscopic test to screen for infection thatis based on an immune reaction.FigureCAbiotechnologytechnicianprepares a bioreactor forvaccineproduction.B.PublicHealth Microbiologyand EpidemiologyThese branches monitor and control the spread of diseases inD.Genetic Engineering and Recombinant DNA Technologycommunities.Someof theinstitutions charged with this taskaretheThese interrelated fields involve deliberate alterations of the geneticU.S.Public Health Service (USPHS) and the Centers for Diseasemakeupoforganismstocreatenovelmicrobes,plants,andanimalsControl andPrevention(CDC).TheCDCcollectsinformation andwith unique behavior and physiology.This is a rapidly expanding fieldstatisticsondiseasesfromaroundtheUnitedStatesandpublishesitinathat often complements biotechnology (see chapter 10).newsletter, The Morbidity and Mortality Weekly Report (see chapter 13).Figure DAgeneticist at the USFigureB Public healthmicrobiologistsDepartment of Agriculture examinesa wheatexamine miceand take samples to determine ifthey carry the hantavirus, one of the emergingplant that has been genetically engineered toresista fungalpathogen.pathogensthatconcernstheCDC
1.2 General Characteristics of Microorganisms and Their Roles in the Earth’s Environments 3 Figure C A biotechnology technician prepares a bioreactor for vaccine production. Figure D A geneticist at the US Department of Agriculture examines a wheat plant that has been genetically engineered to resist a fungal pathogen. TABLE 1.1 A Sampling of Fields and Occupations in Microbiology A. Immunology This branch studies the complex web of protective substances and reactions caused by invading microbes and other harmful entities. It includes such diverse areas as blood testing, vaccination, and allergy (see chapters 15, 16, and 17). C. Biotechnology This branch is defi ned by any process that harnesses the actions of living things to arrive at a desired product, ranging from beer to stem cells. It includes industrial microbiology, which uses microbes to produce and harvest large quantities of such substances as vaccines, vitamins, drugs, and enzymes (see chapters 10 and 27). Figure A A specialist in the CDC special pathogens unit reads a microscopic test to screen for infection that is based on an immune reaction. Figure B Public health microbiologists examine mice and take samples to determine if they carry the hantavirus, one of the emerging pathogens that concerns the CDC. B. Public Health Microbiology and Epidemiology These branches monitor and control the spread of diseases in communities. Some of the institutions charged with this task are the U.S. Public Health Service (USPHS) and the Centers for Disease Control and Prevention (CDC). The CDC collects information and statistics on diseases from around the United States and publishes it in a newsletter, The Morbidity and Mortality Weekly Report (see chapter 13). D. Genetic Engineering and Recombinant DNA Technology These interrelated fi elds involve deliberate alterations of the genetic makeup of organisms to create novel microbes, plants, and animals with unique behavior and physiology. This is a rapidly expanding fi eld that often complements biotechnology (see chapter 10). taL75292_ch01_001-026.indd Page 3 11/3/10 5:48 PM user-f468 /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefiles /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefile
4Chapter1 The Main Themes of MicrobiologyTABLE 1.1(continued)E.FoodMicrobiology,DairyMicrobiology,andAquaticF.AgriculturalMicrobiologyMicrobiologyThis branch is concerned with the relationships between microbes andThese branches examine the ecological and practical roles of microbesdomesticated plants and animals.in food and water.Plant specialists focus on plant diseases, soil fertility, and nutritional...Foodmicrobiologistsareconcermedwiththeeffectsofmicrobesinteractions.including such areas as food spoilage, food-borne diseases, and:Animal specialists work with infectious diseases and otherproduction.associations animals have with microorganismsAquatic microbiologists explore the ecology of natural waters aswell as the impact of microbes on water purity and treatment.G.Branchesof MicrobiologyBranchChapterInvolved in theStudy of:4BacteriologyThe bacteria--small single-celled prokaryotic organisms5,22MycologyThe fungi,a group of eukaryotes that includes both microscopiceukaryotes (molds and yeasts) and larger organisms(mushrooms,puffballs)Protozoology5,23The protozoa-animal-like and mostly single-celled eukaryotesVirology6,24,25Viruses-minute,noncellular particles that parasitize cells5,23ParasitologyParasitism and parasitic organisms-traditionally includingpathogenic protozoa, helminth worms, and certain insects5PhycologyorSimple photosynthetic eukaryotes,the algae,ranging fromsingle-celled forms to large seaweedsAlgologyMorphology4,5,6The detailed structure of microorganismsPhysiology7.8Microbial function (metabolism) at the cellular andmolecular levels1,4,5TaxonomyClassification,naming,and identification of microorganismsMicrobial Genetics,9,10The function of genetic material and biochemical reactions thatMolecularBiologymakeupacell'smetabolism7.26Microbial EcologyInterrelationships between microbes and theenvironment;theroles of microorganisms in the nutrient cycles and naturalecosystemscontained a nucleus and other complex internal structuresinternal compartments called organelles. Organelles are structures(figure 1.2a). These types of cells and organisms are defined asincellsthatareboundbyoneormoremembranesExamplessucheukaryotic* in reference to their"true"nucleus. The early eukary-as mitochondria and Golgicomplexperform specificfunctions inotes,probably similarto algae and protozoa,started lines ofeukaryotic cells.Prokaryotes also perform specific functions,butevolution that eventually gave rise to fungi,plants, and multicellu-they lack the dedicated organelles to carry them out.lar animals such as worms and insects.You can see from figure 1.1The bodyplan of most microorganismsconsists ofa singlehow long that took!The bacteria preceded even the earliest animalscellorclustersofcells(figure1.3).Allprokaryotesaremicroor-by about 3 billion years.This is a good indication that humans areganisms and include the bacteria and archaeons (see figurenot likely to, nor should we try to, eliminate microorganisms from1.14).Only some of the eukaryotes are microorganisms: primar-our environment. They are the ultimate survivors.ily algae,protozoa,molds and yeasts (types of fungi),and cer-tain animals such as arthropods and worms.These last twoTheCellularOrganizationgroups may not be microscopic,but they are still included in thestudy because worms can be involved in infections and may re-ofMicroorganismsquire a microscope to identify them. Some arthropods such asAs ageneral rule,prokaryotic cells are smallerthan eukaryoticfleas and ticks may also be carriers of infectious diseases. Ad-cells, and in addition to lacking a nucleus, they lack other complexditional coverageon celltypes andmicroorganisms appears inchapters 4 and 5.* eukanvotic (yoo'-kar-ee-ah'-tik) Gr. eu, true or good, and karyon, nucleus
4 Chapter 1 The Main Themes of Microbiology E. Food Microbiology, Dairy Microbiology, and Aquatic Microbiology These branches examine the ecological and practical roles of microbes in food and water. • Food microbiologists are concerned with the effects of microbes, including such areas as food spoilage, food-borne diseases, and production. • Aquatic microbiologists explore the ecology of natural waters as well as the impact of microbes on water purity and treatment. TABLE 1.1 (continued) G. Branches of Microbiology Branch Chapter Involved in the Study of: Bacteriology 4 The bacteria—small single-celled prokaryotic organisms Mycology 5, 22 The fungi, a group of eukaryotes that includes both microscopic eukaryotes (molds and yeasts) and larger organisms (mushrooms, puffballs) Protozoology 5, 23 The protozoa—animal-like and mostly single-celled eukaryotes Virology 6, 24, 25 Viruses—minute, noncellular particles that parasitize cells Parasitology 5, 23 Parasitism and parasitic organisms—traditionally including pathogenic protozoa, helminth worms, and certain insects Phycology or Algology 5 Simple photosynthetic eukaryotes, the algae, ranging from single-celled forms to large seaweeds Morphology 4, 5, 6 The detailed structure of microorganisms Physiology 7, 8 Microbial function (metabolism) at the cellular and molecular levels Taxonomy 1, 4, 5 Classifi cation, naming, and identifi cation of microorganisms Microbial Genetics, Molecular Biology 9, 10 The function of genetic material and biochemical reactions that make up a cell’s metabolism Microbial Ecology 7, 26 Interrelationships between microbes and the environment; the roles of microorganisms in the nutrient cycles and natural ecosystems F. Agricultural Microbiology This branch is concerned with the relationships between microbes and domesticated plants and animals. • Plant specialists focus on plant diseases, soil fertility, and nutritional interactions. • Animal specialists work with infectious diseases and other associations animals have with microorganisms. Mycology 5, 22 The fungi, a group of eukaryotes that includes both microscopic eukaryotes (molds and yeasts) and larger organisms (mushrooms, puffballs) Virology 6, 24, 25 Viruses—minute, noncellular particles that parasitize cells Physiology 7, 8 Microbial function (metabolism) at the cellular and molecular levels Phycology or Algology 5 Simple photosynthetic eukaryotes, the algae, ranging from single-celled forms to large seaweeds Microbial Genetics, Molecular Biology 9, 10 The function of genetic material and biochemical reactions that make up a cell’s metabolism contained a nucleus and other complex internal structures ( figure 1.2a ). These types of cells and organisms are defi ned as eukaryotic* in reference to their “true” nucleus. The early eukaryotes, probably similar to algae and protozoa, started lines of evolution that eventually gave rise to fungi, plants, and multicellular animals such as worms and insects. You can see from fi gure 1.1 how long that took! The bacteria preceded even the earliest animals by about 3 billion years. This is a good indication that humans are not likely to, nor should we try to, eliminate microorganisms from our environment. They are the ultimate survivors. The Cellular Organization of Microorganisms As a general rule, prokaryotic cells are smaller than eukaryotic cells, and in addition to lacking a nucleus, they lack other complex internal compartments called organelles. Organelles are structures in cells that are bound by one or more membranes. Examples such as mitochondria and Golgi complex perform specifi c functions in eukaryotic cells. Prokaryotes also perform specifi c functions, but they lack the dedicated organelles to carry them out. The body plan of most microorganisms consists of a single cell or clusters of cells ( fi gure 1.3 ). All prokaryotes are microorganisms and include the bacteria and archaeons (see fi gure 1.14). Only some of the eukaryotes are microorganisms: primarily algae, protozoa, molds and yeasts (types of fungi), and certain animals such as arthropods and worms. These last two groups may not be microscopic, but they are still included in the study because worms can be involved in infections and may require a microscope to identify them. Some arthropods such as fl eas and ticks may also be carriers of infectious diseases. Additional coverage on cell types and microorganisms appears in chapters 4 and 5. * eukaryotic (yoo0-kar-ee-ah9-tik) Gr. eu, true or good, and karyon, nucleus. taL75292_ch01_001-026.indd Page 4 11/3/10 5:48 PM user-f468 /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefiles /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefile
51.2General Characteristics of Microorganisms and Their Roles in the Earth's EnvironmentsHumansappeared.Mammalsappeared.Cockroachestermitesappeared.Probableorigin ofProkaryotesEukaryotesReptilesearthappeared.appeared.appeared.15billion4billion3billion2billion1billionPresenttimeyearsagoyearsagoyearsagoyearsagoyearsagoFigure 1.1Evolutionary time line. The first simple prokaryotes appeared approximately 3.5 billion years ago. They were the only formof lifeforhalf oftheearth'shistory(b) Virus Types(a) Cell TypesProkaryoticEukaryoticNucleus MitochondriaEnvelopeChromosomeRibosomesCapsidRibosomesNucleicacidAIDS virusCellCellwallmembraneFlagellumFlagellumCellmembraneBacterial virusFigure1.2Basic structure of cells and viruses. (a) Comparison of a prokaryotic celland a eukaryotic cell. (b) Two examples ofviruses. These cell types and viruses are discussed in more detail in chapters 4, 5, and 6.TAKENOTE:VIRUSESMicrobialDimensions:HowSmall IsSmall?When we say that microbes are too small to be seen with the un-Viruses are considered one type of microbe because theyaided eye,what sorts of dimensions are we talking about? Thisare microscopic and can cause infections and disease, butconcept is best visualized by comparing microbial groups withthey are not cells.They are small particles that exist at asome organisms ofthe macroscopic world and also with the mole-level of complexitysomewhere between large moleculescules and atoms of the molecular world (figure 1.4). The dimen-and cells(figure 1.4).Viruses aremuch simplerthan cells;theyarecomposedessentiallyofasmall amountofheredi-sions of macroscopic organisms are usuallygiven in centimeters (cm)and meters (m), whereas those of most microorganisms fall withintarymaterialwrappedupinaproteincovering.Somebiolothe range of micrometers (μm) and, sometimes, nanometers (nm)gists referto viruses as parasitic particles; others considerandmillimeters(mm).Thesizerangeofmostmicrobesextendsthem to be very primitive organisms.One thing is certain:from the smallestviruses,measuringaround10 nmand actually notTheyare highlydependent on a host cell'smachinery formuch bigger than a large molecule, to protozoans measuring 3totheiractivities.4mmand visiblewiththe naked eye
1.2 General Characteristics of Microorganisms and Their Roles in the Earth’s Environments 5 Microbial Dimensions: How Small Is Small? When we say that microbes are too small to be seen with the unaided eye, what sorts of dimensions are we talking about? This concept is best visualized by comparing microbial groups with some organisms of the macroscopic world and also with the molecules and atoms of the molecular world (fi gure 1.4). The dimensions of macroscopic organisms are usually given in centimeters (cm) and meters (m), whereas those of most microorganisms fall within the range of micrometers (μm) and, sometimes, nanometers (nm) and millimeters (mm). The size range of most microbes extends from the smallest viruses, measuring around 10 nm and actually not much bigger than a large molecule, to protozoans measuring 3 to 4 mm and visible with the naked eye. Figure 1.1 Evolutionary time line. The fi rst simple prokaryotes appeared approximately 3.5 billion years ago. They were the only form of life for half of the earth’s history. Eukaryotes appeared. Reptiles appeared. Cockroaches, termites appeared. Mammals appeared. Humans appeared. Probable origin of earth 4 billion years ago 15 billion years ago 3 billion years ago 2 billion years ago 1 billion years ago Present time Prokaryotes appeared. TAKE NOTE: VIRUSES Viruses are considered one type of microbe because they are microscopic and can cause infections and disease, but they are not cells. They are small particles that exist at a level of complexity somewhere between large molecules and cells ( fi gure 1.4). Viruses are much simpler than cells; they are composed essentially of a small amount of hereditary material wrapped up in a protein covering. Some biologists refer to viruses as parasitic particles; others consider them to be very primitive organisms. One thing is certain: They are highly dependent on a host cell’s machinery for their activities. Figure 1.2 Basic structure of cells and viruses. (a) Comparison of a prokaryotic cell and a eukaryotic cell. (b) Two examples of viruses. These cell types and viruses are discussed in more detail in chapters 4, 5, and 6. Cell membrane Nucleus Mitochondria Ribosomes Cell membrane Cell wall Flagellum Flagellum Chromosome Prokaryotic Eukaryotic Capsid Envelope AIDS virus Bacterial virus Nucleic acid Ribosomes (a) Cell Types (b) Virus Types taL75292_ch01_001-026.indd Page 5 11/3/10 5:49 PM user-f468 /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefiles /Volume/201/MHDQ245/taL75292_disk1of1/0073375292/taL75292_pagefile