BIO2230-BACTERIAL-METABOLISM.REEDER 10/4/04

BIOL 2230 REEDER

BACTERIAL METABOLISM

I. Nutritional Classification

A. Microorganisms

1. Classification depends upon two factors

a. Carbon source to make precursor metabolites

1) autotrophs, or self feeders: obtains all carbon from atmospheric CO2; CO2 is then fixed (reduced) into

primarily carbohydrate compounds which can be used to provide the majority of compounds needed for

metabolism

2) heterotrophs, or different feeders: obtain carbon from organic compounds in their medium or diet

b. how the organism generates ATP and reducing power

1) phototrophs: gets energy needed from radiant energy; may be aerobic (oxigenic) or anaerobic

(anoxigenic)

2) chemotrophs

: derives energy from the oxidation of preexisting chemicals: fermentative bacteria; those

that use the ETS may be aerobic or anaerobic

a) chemorganotrophs: oxidizes organic molecules

b) chemolithotrophs: oxidizes inorganic molecules; majority are autotrophic (i.e. ammonia-oxidizing

bacteria)

c. Resulting variety of microorganisms:

1) chemoautotrophs: CO2, chemicals for energy; some bacteria

2) chemoheterotrophs: organics, chemicals for energy: most bacteria, protozoa, animals, fungi

3) photoautotrophs: CO2, radiant energy: cyanobacteria, algae, plants

4) photoheterotroph: radiant energy (anoxigenic), organics: purple sulfur and green sulfur bacteria

II. Chemosynthesis and Photosynthesis

A. Chemoautotrophs (Chemolithotrophs): Chemosynthesis

l. Transforms inorganic matter into carbohydrates, fats, proteins, vitamins, and nucleic acids (Biosynthesis) as well

as provides a modest amount of energy

a. Chemoautotrophic bacteria are unable to utilize organic cpds. as well as sunlight

l) CO

2 from the atmosphere is their carbon source: required for organic biosynthesis

b. Photoautotrophs utilize light energy to power photosynthesis, while chemoautotrophs chemically oxidize

inorganic cpds (cpds. of iron, nitrogen, hydrogen, sulfur, etc.) via an electron-transport chain and oxidative

phosphorylation process to obtain their energy; usually O2 is the oxidant.

c. Chemoautotrophic bacteria are categorized and named according to the type of inorganic substance oxidized

(reductants):

l) Nitrifying bacteria: soil bacteria of ecological significance oxidize NH4

+ (ammonia) to NO2

- (nitrite) and

then nitrite to NO3

- (nitrate) in the nitrification process.

a) Energy released in the oxidations of NH4

+ and NO2

- are oxidatively phosphorylated into ATP

b) Nitrosomonas, Nitrobacter

2) Sulfur oxidizing bacteria: oxidizes So, H2S (hydrogen sulfide), S2O3

2- (thiosulfate), and H2SO4 (sulfuric

acid)

a) Thiobacillus

3) Hydrogen bacteria utilize hydrogen gas (H2)

4) Iron bacteria: ferrous iron (Fe2+)

B. Photoautotrophs: oxigenic and anoxigenic types of Photosynthesis

l. Only plants, algae, some protists and a few bacteria carry on photosynthesis

2. Cyanobacterial procaryotes carry out photosynthetic reactions that are essentially identical to that of green plant

photosynthesis: chlorophylls are the chief photosynthetic pigments using the same wavelengths of white light,

CO2 and H2O as reactants and oxygen as a by-product (oxigenic) and PGAL as the immediate product (can be

converted to glucose).

3. Two sets of reactions are involved:

a. Light set of reactions may involve two possible routes of electron flow:

l) Cyclic photophosphorylation: simplest pathway involving only photosystem I and generating ATP only

to supplement the cell's needs with no O2 derived

2) Noncyclic photophosphorylation: most common pathway of oxigenic photosynthesis involving

photosystem II, which generates ATP and releases O2, followed by photosystem I which generates

NADPH

a) ATP and NADPH will be utilized in the dark reactions

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BIOL 2230 REEDER

BACTERIAL METABOLISM

I. Nutritional Classification A. Microorganisms

Classification depends upon two factors a. Carbon source to make precursor metabolites 1) autotrophs, or self feeders: obtains all carbon from atmospheric CO (^) 2; CO 2 is then fixed (reduced) into primarily carbohydrate compounds which can be used to provide the majority of compounds needed for metabolism 2) heterotrophs, or different feeders: obtain carbon from organic compounds in their medium or diet b. how the organism generates ATP and reducing power 1) phototrophs: gets energy needed from radiant energy; may be aerobic (oxigenic) or anaerobic (anoxigenic) 2) chemotrophs: derives energy from the oxidation of preexisting chemicals: fermentative bacteria; those that use the ETS may be aerobic or anaerobic a) chemorganotrophs: oxidizes organic molecules b) chemolithotrophs: oxidizes inorganic molecules; majority are autotrophic (i.e. ammonia-oxidizing bacteria) c. Resulting variety of microorganisms: 1) chemoautotrophs: CO (^) 2, chemicals for energy; some bacteria 2) chemoheterotrophs: organics, chemicals for energy: most bacteria, protozoa, animals, fungi 3) photoautotrophs: CO 2 , radiant energy: cyanobacteria, algae, plants 4) photoheterotroph: radiant energy (anoxigenic), organics: purple sulfur and green sulfur bacteria

II. Chemosynthesis and Photosynthesis A. Chemoautotrophs (Chemolithotrophs): Chemosynthesis l. Transforms inorganic matter into carbohydrates, fats, proteins, vitamins, and nucleic acids (Biosynthesis) as well as provides a modest amount of energy a. Chemoautotrophic bacteria are unable to utilize organic cpds. as well as sunlight l) CO 2 from the atmosphere is their carbon source: required for organic biosynthesis b. Photoautotrophs utilize light energy to power photosynthesis, while chemoautotrophs chemically oxidize inorganic cpds (cpds. of iron, nitrogen, hydrogen, sulfur, etc.) via an electron-transport chain and oxidative phosphorylation process to obtain their energy; usually O 2 is the oxidant. c. Chemoautotrophic bacteria are categorized and named according to the type of inorganic substance oxidized (reductants): l) Nitrifying bacteria: soil bacteria of ecological significance oxidize NH 4 +^ (ammonia) to NO 2 -^ (nitrite) and then nitrite to NO 3 -^ (nitrate) in the nitrification process. a) Energy released in the oxidations of NH 4 +^ and NO 2 -^ are oxidatively phosphorylated into ATP b) Nitrosomonas, Nitrobacter

Sulfur oxidizing bacteria: oxidizes So, H 2 S (hydrogen sulfide), S 2 O 3 2-^ (thiosulfate), and H 2 SO 4 (sulfuric acid) a) Thiobacillus
Hydrogen bacteria utilize hydrogen gas (H 2 )
Iron bacteria: ferrous iron (Fe2+^ ) B. Photoautotrophs: oxigenic and anoxigenic types of Photosynthesis l. Only plants, algae, some protists and a few bacteria carry on photosynthesis

Cyanobacterial procaryotes carry out photosynthetic reactions that are essentially identical to that of green plant photosynthesis: chlorophylls are the chief photosynthetic pigments using the same wavelengths of white light, CO 2 and H2O as reactants and oxygen as a by-product (oxigenic) and PGAL as the immediate product (can be converted to glucose).
Two sets of reactions are involved: a. Light set of reactions may involve two possible routes of electron flow: l) Cyclic photophosphorylation: simplest pathway involving only photosystem I and generating ATP only to supplement the cell's needs with no O 2 derived 2) Noncyclic photophosphorylation: most common pathway of oxigenic photosynthesis involving photosystem II, which generates ATP and releases O 2 , followed by photosystem I which generates NADPH a) ATP and NADPH will be utilized in the dark reactions

b. Dark set of reactions that follow the light l) CO 2 fixation occurs resulting in PGAL

1. Cyanobacteria lack chloroplasts, but utilize chromatophores or photosynthetic lamellae (thylakoids) instead

Noncyanobacterial photosynthesis utilizes an *anaerobic photosynthetic system which does not result in free oxygen liberation (anoxygenic) a. lacks photosystem II; therefore water is not involved as a reductant source: no photolysis with no oxygen by- product (anoxygenic), with similar to different pigmentation utilizing different wavelengths of light; occurs only in the complete absence of oxygen b. overall reaction is the same as that for green plants except that a hydrogen donor other than water is used; only cyclic photophosphorylation occurs, as various sulfur, hydrogen and nitrogen cpds. are utilized. c. three families represented based on their pigmentation and type of reductant l) Chlorobiaceae (green sulfur bacteria): different sulfur-containing cpds. as well as hydrogen gas used as reductants (H 2 S, 2S, Na 2 S 2 O 3 , H 2 ) 2) Chromatiaceae (purple-sulfur bacteria): contain red and purple carotenoid pigments, use same reductants as the green-sulfur types 3) Rhodospirillaceae (non-sulfur purple bacteria): instead of sulfur cpds. as reductants, these organisms use hydrogen or various organics; capability to use atmospheric nitrogen (N 2 ) as their nitrogen source

III. Catabolic Metabolism (Precursor and energy production utilized by both photoautotrophs and chemoheterotrophs) A. Heterotrophs l. Most bacterial forms are heterotrophs: rely on an external source of ready-made organic material for food which serves as the energy source through oxidative reactions to do work: biosynthesis, motility, etc.; inorganic users, also.

Categorized according to the nature of their metabolic end products, which in most cases, represent the final electron acceptors (oxidant). a. fermentation: intermediate organic products serving as the final oxidants results in stable fermentative products such as various alcohols, acids, and gases b. anaerobic respiration: inorganic salts (oxygen containing salts: SO4, NO (^) 3, CO (^) 2) serve as the final oxidants resulting in various sulfur and nitrogenous compounds, including methane c. aerobic respiration: atmospheric oxygen (O 2 ) serves as the final oxidant resulting in CO 2 and H 2 O.
Also categorized as to type of metabolic (catabolic) pathway utilized: a. fermentation: anaerobic process lacking membrane bound electron transport and oxidative phosphorylation (respiratory chain); substrate level phosphorylation occurs with an accumulation of stable fermentative products; represents an incomplete oxidation; may be the principal mechanism used by an organism (i.e., yeast) or is supplemental 1) anaerobic glycolysis with SLP b. respiratory: oxidations are linked to a bacterial membrane-bound electron transport chain coupled to oxidative phosphorylation: aerobic and anaerobic pathway types 1) Anaerobic a) anaerobic glycolysis b) anaerobic respiratory chain (ETS and OP) 2) Aerobic a) anaerobic glycolysis b) TCA cycle c) Aerobic respiratory chain (ETS and OP) B. Fermentation by Microbes l. Catabolism of an organic substrate (principally glucose) forms intermediate organic products (acids, alcohols, and/or gases) that serve as the final electron acceptors due to inefficiency of the anaerobic process (no external inorganic electron acceptor is required); least efficient process, yet the microbes that rely on it gain sufficient energy to survive; incomplete oxidation
The Embden-Meyerhof-Parnes pathway (EMP) is the common mechanism for the conversion of glucose to pyruvic acid in nine reactions regardless of whether organism is anaerobic or aerobic; commonly referred to as glycolysis. a. 2 ATP required as energy of activation b. substrate level phosphorylation nets 2 ATP per glucose (4 ATP grossed) c. 2 pyruvic acids result as the final end product of glycolysis with 2 molecules of NADH left to be oxidized d. Depending on the microorganism type, there is great variation as to which compounds will serve as final acceptors of hydrogen and the final stable fermentative product(s) from the metabolism of pyruvic acid: l) lactic acid: lactococcus (streptococci) and lactobacilli (milk souring)

Microbial Metabolism: Classification of Organisms and Energy Production, Exams of Microbiology

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BIOL 2230 REEDER

BACTERIAL METABOLISM