《环境微生物学与实验》课程教学资源（文献资料）Microbial Nutrition

thoc PART I CHAPTER 5 Microbial Microbial Nutrition Nutrition Growth,and Control Chapter 5 Microbial Nutrition Chapter 6 Microbial Growth Chapter 7 Control of Microorganisms by Physical and Chemical Agents Outline Concepts 5.1 The Comm 1.Mic p 53 54 ts by the 103 104 7 on,waler an .8 108

Prescott−Harley−Klein: Microbiology, Fifth Edition II. Microbial Nutrition, Growth, and Control 5. Microbial Nutrition © The McGraw−Hill Companies, 2002 PART II Microbial Nutrition, Growth, and Control Chapter 5 Microbial Nutrition Chapter 6 Microbial Growth Chapter 7 Control of Microorganisms by Physical and Chemical Agents CHAPTER 5 Microbial Nutrition Staphylococcus aureus forms large, golden colonies when growing on blood agar. This human pathogen causes diseases such as boils, abscesses, bacteremia, endocarditis, food poisoning, pharyngitis, and pneumonia. Outline 5.1 The Common Nutrient Requirements 96 5.2 Requirements for Carbon, Hydrogen, and Oxygen 96 5.3 Nutritional Types of Microorganisms 97 5.4 Requirements for Nitrogen, Phosphorus, and Sulfur 98 5.5 Growth Factors 98 5.6Uptake of Nutrients by the Cell 100 Facilitated Diffusion 100 Active Transport 101 Group Translocation 103 Iron Uptake 104 5.7 Culture Media 104 Synthetic or Defined Media 104 Complex Media 105 Types of Media 105 5.8 Isolation of Pure Cultures 106 The Spread Plate and Streak Plate 106 The Pour Plate 107 Colony Morphology and Growth 108 Concepts 1. Microorganisms require about 10 elements in large quantities, in part because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. Several other elements are needed in very small amounts and are parts of enzymes and cofactors. 2. All microorganisms can be placed in one of a few nutritional categories on the basis of their requirements for carbon, energy, and hydrogen atoms or electrons. 3. Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion. They must be transported by one of three major mechanisms involving the use of membrane carrier proteins. Eucaryotic microorganisms also employ endocytosis for nutrient uptake. 4. Culture media are needed to grow microorganisms in the laboratory and to carry out specialized procedures like microbial identification, water and food analysis, and the isolation of particular microorganisms. Many different media are available for these and other purposes. 5. Pure cultures can be obtained through the use of spread plates, streak plates, or pour plates and are required for the careful study of an individual microbial species

5.Microbial Nutrition 6 Chapter 5 Microbial Nutrition Besides the common macroelements and trace elements,n nvironment.Diatoms (see and oceans (ee pp.2. pendon the presenceo Finally.it must be emphasized that micr rganisms requir wthwill be limited rega rdless of the con on and therefo c a lor micr centrations of other nutrients. ental facte 52 of microorganisms.These cussed in chapter 6 after an introduction to micre ng as carbon sour 5.1 The Common Nutrient Requirements thes nts ced and that they ca Indeed.the more reduced .the bigher their because they nisms in relatively larg yhenthceclecions move fro reduced donor ed electron don't have to. cium (Ca)among other functions.con s to the heat resist CO,is c m送m and F)isa part of cytochromes can use CO,as thei eral otr most cells.Howe ver.cells requir aminants in water.glass reduced.comp nts are tous and prot heterotrophs (these prefor rmed molecules normally come from ociation of regulatory and catalytic subun in E coli as- ergy.For exam ple.the glycolytic pathway produces carbon skel ses energy as ATP and snhat NADH A most remarkable nutrit ristic of microo s and enz

Prescott−Harley−Klein: Microbiology, Fifth Edition II. Microbial Nutrition, Growth, and Control 5. Microbial Nutrition © The McGraw−Hill Companies, 2002 The whole of nature, as has been said, is a conjugation of the verb to eat, in the active and passive. —William Ralph Inge To obtain energy and construct new cellular components, or￾ganisms must have a supply of raw materials or nutrients. Nutrients are substances used in biosynthesis and energy production and therefore are required for microbial growth. This chapter describes the nutritional requirements of microorganisms, how nutrients are acquired, and the cultivation of microorganisms. Environmental factors such as temperature, oxygen levels, and the osmotic concentration of the medium are critical in the successful cultivation of microorganisms. These topics are dis￾cussed in chapter 6 after an introduction to microbial growth. 5.1 The Common Nutrient Requirements Analysis of microbial cell composition shows that over 95% of cell dry weight is made up of a few major elements: carbon, oxygen, hy￾drogen, nitrogen, sulfur, phosphorus, potassium, calcium, magne￾sium, and iron. These are called macroelements or macronutrients because they are required by microorganisms in relatively large amounts. The first six (C, O, H, N, S, and P) are components of car￾bohydrates, lipids, proteins, and nucleic acids. The remaining four macroelements exist in the cell as cations and play a variety of roles. For example, potassium (K
) is required for activity by a number of enzymes, including some of those involved in protein synthesis. Cal￾cium (Ca2
), among other functions, contributes to the heat resist￾ance of bacterial endospores. Magnesium (Mg2
) serves as a cofac￾tor for many enzymes, complexes with ATP, and stabilizes ribosomes and cell membranes. Iron (Fe2
and Fe3
) is a part of cytochromes and a cofactor for enzymes and electron-carrying proteins. All organisms, including microorganisms, require several micronutrients or trace elements besides macroelements. The micronutrients—manganese, zinc, cobalt, molybdenum, nickel, and copper—are needed by most cells. However, cells require such small amounts that contaminants in water, glassware, and regular media components often are adequate for growth. There￾fore it is very difficult to demonstrate a micronutrient require￾ment. In nature, micronutrients are ubiquitous and probably do not usually limit growth. Micronutrients are normally a part of enzymes and cofactors, and they aid in the catalysis of reactions and maintenance of protein structure. For example, zinc (Zn2
) is present at the active site of some enzymes but is also involved in the association of regulatory and catalytic subunits in E. coli as￾partate carbamoyltransferase (see section 8.9). Manganese (Mn2
) aids many enzymes catalyzing the transfer of phosphate groups. Molybdenum (Mo2
) is required for nitrogen fixation, and cobalt (Co2
) is a component of vitamin B12. Electron carri￾ers and enzymes (pp. 157–64) 96 Chapter 5 Microbial Nutrition Besides the common macroelements and trace elements, mi￾croorganisms may have particular requirements that reflect the special nature of their morphology or environment. Diatoms (see figure 26.6c,d) need silicic acid (H4SiO4) to construct their beau￾tiful cell walls of silica [(SiO2)n]. Although most bacteria do not require large amounts of sodium, many bacteria growing in saline lakes and oceans (see pp. 123, 461) depend on the presence of high concentrations of sodium ion (Na
). Finally, it must be emphasized that microorganisms require a balanced mixture of nutrients. If an essential nutrient is in short supply, microbial growth will be limited regardless of the con￾centrations of other nutrients. 5.2 Requirements for Carbon, Hydrogen, and Oxygen The requirements for carbon, hydrogen, and oxygen often are sat￾isfied together. Carbon is needed for the skeleton or backbone of all organic molecules, and molecules serving as carbon sources normally also contribute both oxygen and hydrogen atoms. They are the source of all three elements. Because these organic nutri￾ents are almost always reduced and have electrons that they can donate to other molecules, they also can serve as energy sources. Indeed, the more reduced organic molecules are, the higher their energy content (e.g., lipids have a higher energy content than car￾bohydrates). This is because, as we shall see later, electron trans￾fers release energy when the electrons move from reduced donors with more negative reduction potentials to oxidized electron ac￾ceptors with more positive potentials. Thus carbon sources fre￾quently also serve as energy sources, although they don’t have to. Oxidation-reduction reactions and energy (pp. 157–59) One important carbon source that does not supply hydrogen or energy is carbon dioxide (CO2). This is because CO2 is oxi￾dized and lacks hydrogen. Probably all microorganisms can fix CO2—that is, reduce it and incorporate it into organic molecules. However, by definition, only autotrophs can use CO2 as their sole or principal source of carbon. Many microorganisms are au￾totrophic, and most of these carry out photosynthesis and use light as their energy source. Some autotrophs oxidize inorganic molecules and derive energy from electron transfers. Photosyn￾thetic carbon dioxide fixation (pp. 207–8) The reduction of CO2 is a very energy-expensive process. Thus many microorganisms cannot use CO2 as their sole carbon source but must rely on the presence of more reduced, complex molecules such as glucose for a supply of carbon. Organisms that use reduced, preformed organic molecules as carbon sources are heterotrophs (these preformed molecules normally come from other organisms). As mentioned previously, most heterotrophs use reduced organic compounds as sources of both carbon and en￾ergy. For example, the glycolytic pathway produces carbon skele￾tons for use in biosynthesis and also releases energy as ATP and NADH. The glycolytic pathway (pp. 176–77) A most remarkable nutritional characteristic of microorgan￾isms is their extraordinary flexibility with respect to carbon sources. Laboratory experiments indicate that there is no natu-

tena see electrons from organic compounds. use over 100 different carbon con unds.In contrast to thes pite the great metabolic diversity ria are exc ingy fastid ost may be placed in one of fou lotrophic m The pr ority of micro isms thus far studi ed are eithe nc- only long-chain fatty trophs)use light energy and have CO as thei Table 5.1 1010-14) 5.3 Nutritional Types of Microorganisms In addition to the peed for carbon.hvdroee .and oxygen,all or e（m1s-20 n长7GhTg o sources of energy available to organisms:(1)light energy e molecules ganic or inorganic).Microorganisms also have only two sources for Table 5.2 Major Nutritional Types of Microorganisms Major Nutritional Type Repre opaotoRtroop lectron (H/e)donor ce (inorganic) ulfur-oxidizing bacteri urce(organic

Prescott−Harley−Klein: Microbiology, Fifth Edition II. Microbial Nutrition, Growth, and Control 5. Microbial Nutrition © The McGraw−Hill Companies, 2002 rally occurring organic molecule that cannot be used by some mi￾croorganism. Actinomycetes will degrade amyl alcohol, paraffin, and even rubber. Some bacteria seem able to employ almost any￾thing as a carbon source; for example, Burkholderia cepacia can use over 100 different carbon compounds. In contrast to these bacterial omnivores, some bacteria are exceedingly fastidious and catabolize only a few carbon compounds. Cultures of meth￾ylotrophic bacteria metabolize methane, methanol, carbon monoxide, formic acid, and related one-carbon molecules. Para￾sitic members of the genus Leptospira use only long-chain fatty acids as their major source of carbon and energy. It appears that in natural environments complex populations of microorganisms often will metabolize even relatively indigestible human-made substances such as pesticides. Indigestible molecules sometimes are oxidized and degraded in the presence of a growth￾promoting nutrient that is metabolized at the same time, a process called cometabolism. The products of this breakdown process can then be used as nutrients by other microorganisms. Degradation and microorganisms (pp. 1010–14) 5.3 Nutritional Types of Microorganisms In addition to the need for carbon, hydrogen, and oxygen, all organ￾isms require sources of energy and electrons for growth to take place. Microorganisms can be grouped into nutritional classes based on how they satisfy all these requirements (table 5.1). We have already seen that microorganisms can be classified as either heterotrophs or autotrophs with respect to their preferred source of carbon. There are only two sources of energy available to organisms: (1) light energy, and (2) the energy derived from oxidizing organic or inorganic mol￾ecules. Phototrophs use light as their energy source; chemotrophs obtain energy from the oxidation of chemical compounds (either or￾ganic or inorganic). Microorganisms also have only two sources for electrons. Lithotrophs (i.e., “rock-eaters”) use reduced inorganic substances as their electron source, whereas organotrophs extract electrons from organic compounds. Photosynthesis light reactions (pp. 195–201); Oxidation of organic and inorganic molecules (pp. 176–95) Despite the great metabolic diversity seen in microorganisms, most may be placed in one of four nutritional classes based on their primary sources of carbon, energy, and electrons (table 5.2). The large majority of microorganisms thus far studied are either photolithotrophic autotrophs or chemoorganotrophic heterotrophs. Photolithotrophic autotrophs (often called photoautotrophs or photolithoautotrophs) use light energy and have CO2 as their car￾bon source. Eucaryotic algae and cyanobacteria employ water as the electron donor and release oxygen. Purple and green sulfur 5.3 Nutritional Types of Microorganisms 97 Table 5.1 Sources of Carbon, Energy, and Electrons Carbon Sources Autotrophs CO2 sole or principal biosynthetic carbon source ( pp. 207–8) a Heterotrophs Reduced, preformed, organic molecules from other organisms (chapters 9 and 10) Energy Sources Phototrophs Light ( pp. 195–201) Chemotrophs Oxidation of organic or inorganic compounds (chapter 9) Electron Sources Lithotrophs Reduced inorganic molecules ( pp. 193–94) Organotrophs Organic molecules (chapter 9) a For each category, the location of material describing the participating metabolic pathways is given within the parentheses. Table 5.2 Major Nutritional Types of Microorganisms Major Nutritional Typesa Sources of Energy, Hydrogen/Electrons, and Carbon Representative Microorganisms Photolithotrophic autotrophy Light energy Algae (Photolithoautotrophy) Inorganic hydrogen/electron (H/e– ) donor Purple and green sulfur bacteria CO2 carbon source Cyanobacteria Photoorganotrophic heterotrophy Light energy Purple nonsulfur bacteria (Photoorganoheterotrophy) Organic H/e– donor Green nonsulfur bacteria Organic carbon source (CO2 may also be used) Chemolithotrophic autotrophy Chemical energy source (inorganic) Sulfur-oxidizing bacteria (Chemolithoautotrophy) Inorganic H/e– donor Hydrogen bacteria CO2 carbon source Nitrifying bacteria Iron-oxidizing bacteria Chemoorganotrophic heterotrophy Chemical energy source (organic) Protozoa (Chemoorganoheterotrophy) Organic H/e– donor Fungi Organic carbon source Most nonphotosynthetic bacteria (including most pathogens) a Bacteria in other nutritional categories have been found. The categories are defined in terms of energy, electron, and carbon sources. Condensed versions of these names are given in parentheses

5.Microbial Nutrition Chapter 5 Microbial Nutrition ena ns from in 5orrogen,Phmporu chemo. rotrophs,chemoorganoneterotr ohs,or ev Togrow.a microorganism must be able to large quanti- all th lly all croorganisms usually employ inorganic sources as well.Bioch The have fewermi sms Nitrogen is needed for the synthesis of amino acids purne some ca ohydrates and lipids.enzyme co donor The photoorgan het in amino acids.and amn monia ofen is directly incorporate nic o rogen,or h energy and elec eria many cyanobacteria and the symbiotic bacte ospheric nitrogen usin c the the y e monia to nitrate or sulfur to sulfate)that continally occur in the nents. Almost all microorgan ms use inorg pho phosphorus s cies ually belongs ino ents.Phosphate uptake by coli ha ty and alter their meta sively n can use lic nmen 0n220 example.many purp the enzyr which then is the plasma membrane example is provided by bac cria such as Beg the outer membrane by the use of a porin protein channel.One ccause they probably is due to the Pit system.When phosphate ons are low,th This sort of flexibility seems co mplex and confusing.vet it give mpecycatrnieadaniaeifcmioamendcomdioas for phosphate:it isan ABC transporter (see pp.101)anduse P amino acids cysteir and methionine,some carbohydrates,bi- tion 10.4):a few require a reduced form of sulfur such as cysteine. otrophand he roph tremsotcergyndcecton d o 5.5 Growth Factors Microorganisms often grow and reproduce when minerals and

Prescott−Harley−Klein: Microbiology, Fifth Edition II. Microbial Nutrition, Growth, and Control 5. Microbial Nutrition © The McGraw−Hill Companies, 2002 bacteria cannot oxidize water but extract electrons from inorganic donors like hydrogen, hydrogen sulfide, and elemental sulfur. Chemoorganotrophic heterotrophs (often called chemo￾heterotrophs, chemoorganoheterotrophs, or even heterotrophs) use organic compounds as sources of energy, hydrogen, elec￾trons, and carbon. Frequently the same organic nutrient will sat￾isfy all these requirements. It should be noted that essentially all pathogenic microorganisms are chemoheterotrophs. The other two nutritional classes have fewer microorganisms but often are very important ecologically. Some purple and green bacteria are photosynthetic and use organic matter as their electron donor and carbon source. These photoorganotrophic het￾erotrophs (photoorganoheterotrophs) are common inhabitants of polluted lakes and streams. Some of these bacteria also can grow as photoautotrophs with molecular hydrogen as an electron donor. The fourth group, the chemolithotrophic autotrophs (chemolithoau￾totrophs), oxidizes reduced inorganic compounds such as iron, ni￾trogen, or sulfur molecules to derive both energy and electrons for biosynthesis. Carbon dioxide is the carbon source. A few chemolithotrophs can derive their carbon from organic sources and thus are heterotrophic. Chemolithotrophs contribute greatly to the chemical transformations of elements (e.g., the conversion of am￾monia to nitrate or sulfur to sulfate) that continually occur in the ecosystem. Photosynthetic and chemolithotrophic bacteria (sections 21.3, 22.1, and 22.3) Although a particular species usually belongs in only one of the four nutritional classes, some show great metabolic flexibil￾ity and alter their metabolic patterns in response to environmen￾tal changes. For example, many purple nonsulfur bacteria (see section 22.1) act as photoorganotrophic heterotrophs in the ab￾sence of oxygen but oxidize organic molecules and function chemotrophically at normal oxygen levels. When oxygen is low, photosynthesis and oxidative metabolism may function simulta￾neously. Another example is provided by bacteria such as Beg￾giatoa (see p. 501) that rely on inorganic energy sources and or￾ganic (or sometimes CO2) carbon sources. These microbes are sometimes called mixotrophic because they combine chemolithoautotrophic and heterotrophic metabolic processes. This sort of flexibility seems complex and confusing, yet it gives its possessor a definite advantage if environmental conditions frequently change. 1. What are nutrients, and on what basis are they divided into macroelements and micronutrients or trace elements? Describe some ways in which macroelements and micronutrients are used by an organism. 2. Define autotroph and heterotroph. 3. Discuss the ways in which microorganisms are classified based on their requirements for energy and electrons. 4. Describe the nutritional requirements of the four major nutritional groups and give some microbial examples of each. What is a mixotroph? 5.4 Requirements for Nitrogen, Phosphorus, and Sulfur To grow, a microorganism must be able to incorporate large quanti￾ties of nitrogen, phosphorus, and sulfur. Although these elements may be acquired from the same nutrients that supply carbon, mi￾croorganisms usually employ inorganic sources as well. Biochemical mechanisms for the incorporation of nitrogen, phosphorus, and sulfur (pp. 210–14) Nitrogen is needed for the synthesis of amino acids, purines, pyrimidines, some carbohydrates and lipids, enzyme cofactors, and other substances. Many microorganisms can use the nitrogen in amino acids, and ammonia often is directly incorporated through the action of such enzymes as glutamate dehydrogenase or glutamine synthetase and glutamate synthase (see section 10.4). Most phototrophs and many nonphotosynthetic microor￾ganisms reduce nitrate to ammonia and incorporate the ammonia in assimilatory nitrate reduction (see pp. 210–11). A variety of bacteria (e.g., many cyanobacteria and the symbiotic bacterium Rhizobium) can reduce and assimilate atmospheric nitrogen using the nitrogenase system (see section 10.4). Phosphorus is present in nucleic acids, phospholipids, nu￾cleotides like ATP, several cofactors, some proteins, and other cell components. Almost all microorganisms use inorganic phosphate as their phosphorus source and incorporate it di￾rectly. Low phosphate levels actually limit microbial growth in many aquatic environments. Phosphate uptake by E. coli has been intensively studied. This bacterium can use both organic and inorganic phosphate. Some organophosphates such as hex￾ose 6-phosphates can be taken up directly by transport proteins. Other organophosphates are often hydrolyzed in the periplasm by the enzyme alkaline phosphatase to produce inorganic phos￾phate, which then is transported across the plasma membrane. When inorganic phosphate is outside the bacterium, it crosses the outer membrane by the use of a porin protein channel. One of two transport systems subsequently moves the phosphate across the plasma membrane. At high phosphate concentrations, transport probably is due to the Pit system. When phosphate concentrations are low, the PST, (phosphate-specific transport) system is more important. The PST system has higher affinity for phosphate; it is an ABC transporter (see pp. 101–2) and uses a periplasmic binding protein. Sulfur is needed for the synthesis of substances like the amino acids cysteine and methionine, some carbohydrates, bi￾otin, and thiamine. Most microorganisms use sulfate as a source of sulfur and reduce it by assimilatory sulfate reduction (see sec￾tion 10.4); a few require a reduced form of sulfur such as cysteine. 5.5 Growth Factors Microorganisms often grow and reproduce when minerals and sources of energy, carbon, nitrogen, phosphorus, and sulfur are supplied. These organisms have the enzymes and pathways nec- 98 Chapter 5 Microbial Nutrition

8e Table 5.3 Functions of Some Common Vitamins in Microorganisms Vitamin Functions Examples of Microorganisms Requiring Vitamin' B Folic acid is (B Lipoic acid Transfer of acyl groups (P spp(P (B) Niacin (ncn) neaaaadNbR-terydkaem (B) Riboflavin (B.) Nryero (B) is (B) ctera (B).fanp (algae (A)and pe ssary to synthesize all cell comnonents required for their well- used in microbiological assays of most vitamins and amino acids componentsex cept the wth factor to beass aved.A differen amount of grow factor is added to e ach vessel.The standard re are thre sses th Ta th resulting i ynthesis purines and pyrimidinesfor mins are mo tity of t vi large au le and a '0r many microorganisms nakes the microor that synth For example,spec

Prescott−Harley−Klein: Microbiology, Fifth Edition II. Microbial Nutrition, Growth, and Control 5. Microbial Nutrition © The McGraw−Hill Companies, 2002 essary to synthesize all cell components required for their well￾being. Many microorganisms, on the other hand, lack one or more essential enzymes. Therefore they cannot manufacture all indis￾pensable constituents but must obtain them or their precursors from the environment. Organic compounds required because they are essential cell components or precursors of such components and cannot be synthesized by the organism are called growth fac￾tors. There are three major classes of growth factors: (1) amino acids, (2) purines and pyrimidines, and (3) vitamins. Amino acids are needed for protein synthesis, purines and pyrimidines for nu￾cleic acid synthesis. Vitamins are small organic molecules that usually make up all or part of enzyme cofactors (see section 8.6), and only very small amounts sustain growth. The functions of se￾lected vitamins, and examples of microorganisms requiring them, are given in table 5.3. Some microorganisms require many vita￾mins; for example, Enterococcus faecalis needs eight different vi￾tamins for growth. Other growth factors are also seen; heme (from hemoglobin or cytochromes) is required by Haemophilus influenzae, and some mycoplasmas need cholesterol. Knowledge of the specific growth factor requirements of many microorganisms makes possible quantitative growth￾response assays for a variety of substances. For example, species from the bacterial genera Lactobacillus and Streptococcus can be used in microbiological assays of most vitamins and amino acids. The appropriate bacterium is grown in a series of culture vessels, each containing medium with an excess amount of all required components except the growth factor to be assayed. A different amount of growth factor is added to each vessel. The standard curve is prepared by plotting the growth factor quantity or con￾centration against the total extent of bacterial growth. Ideally the amount of growth resulting is directly proportional to the quan￾tity of growth factor present; if the growth factor concentration doubles, the final extent of bacterial growth doubles. The quan￾tity of the growth factor in a test sample is determined by com￾paring the extent of growth caused by the unknown sample with that resulting from the standards. Microbiological assays are spe￾cific, sensitive, and simple. They still are used in the assay of sub￾stances like vitamin B12 and biotin, despite advances in chemical assay techniques. The observation that many microorganisms can synthesize large quantities of vitamins has led to their use in industry. Several water-soluble and fat-soluble vitamins are produced partly or com￾pletely using industrial fermentations. Good examples of such vi￾tamins and the microorganisms that synthesize them are riboflavin (Clostridium, Candida, Ashbya, Eremothecium), coenzyme A (Brevibacterium), vitamin B12 (Streptomyces, Propionibacterium, 5.5 Growth Factors 99 Table 5.3 Functions of Some Common Vitamins in Microorganisms Vitamin Functions Examples of Microorganisms Requiring Vitamina Biotin Carboxylation (CO2 fixation) Leuconostoc mesenteroides (B) One-carbon metabolism Saccharomyces cerevisiae (F) Ochromonas malhamensis (A) Acanthamoeba castellanii (P) Cyanocobalamin (B12) Molecular rearrangements Lactobacillus spp. (B) One-carbon metabolism—carries methyl groups Euglena gracilis (A) Diatoms and many other algae (A) Acanthamoeba castellanii (P) Folic acid One-carbon metabolism Enterococcus faecalis (B) Tetrahymena pyriformis (P) Lipoic acid Transfer of acyl groups Lactobacillus casei (B) Tetrahymena spp. (P) Pantothenic acid Precursor of coenzyme A—carries acyl groups Proteus morganii (B) (pyruvate oxidation, fatty acid metabolism) Hanseniaspora spp. (F) Paramecium spp. (P) Pyridoxine (B6) Amino acid metabolism (e.g., transamination) Lactobacillus spp. (B) Tetrahymena pyriformis (P) Niacin (nicotinic acid) Precursor of NAD and NADP—carry electrons Brucella abortus, Haemophilus influenzae (B) and hydrogen atoms Blastocladia pringsheimii (F) Crithidia fasciculata (P) Riboflavin (B2) Precursor of FAD and FMN—carry electrons Caulobacter vibrioides (B) or hydrogen atoms Dictyostelium spp. (F) Tetrahymena pyriformis (P) Thiamine (B1) Aldehyde group transfer Bacillus anthracis (B) (pyruvate decarboxylation, α-keto acid oxidation) Phycomyces blakesleeanus (F) Ochromonas malhamensis (A) Colpidium campylum (P) a The representative microorganisms are members of the following groups: bacteria (B), fungi (F), algae (A), and protozoa (P)