[Previous] | [Next]

Culture Media
Physical Limits
More Physical

Search | Send us your comments

Nutrition and Growth of Bacteria

©2000 Kenneth Todar, University of Wisconins-Madison

Every organism must find in its environment all of the substances required for energy generation and cellular biosynthesis. The chemicals and elements of this environment that are utilized for bacterial growth are referred to as nutrients or nutritional requirements. In the laboratory, bacteria are grown in culture media which are designed to provide all the essential nutrients in solution for bacterial growth.

At an elementary level, the nutritional requirements of a bacterium such as E. coli are revealed by the cell's elemental composition, which consists of C, H, O, N, S. P, K, Mg, Fe, Ca, Mn, and traces of Zn, Co, Cu, and Mo. These elements are found in the form of water, inorganic ions, small molecules, and macromolecules which serve either a structural or functional role in the cells. The general physiological functions of the elements are outlined in the Table below.

Table 1. Major elements, their sources and functions in bacterial cells.

Element% of dry weight Source Function
Carbon50organic compounds or CO2Main constituent of cellular material
Oxygen20H2O, organic compounds, CO2, and O2Constituent of cell material and cell water; O2 is electron acceptor in aerobic respiration
Nitrogen14NH3, NO3, organic compounds, N2Constituent of amino acids, nucleic acids nucleotides, and coenzymes
Hydrogen8H2O, organic compounds, H2Main constituent of organic compounds and cell water
Phosphorus3inorganic phosphates (PO4)Constituent of nucleic acids, nucleotides, phospholipids, LPS, teichoic acids
Sulfur1SO4, H2S, So, organic sulfur compoundsConstituent of cysteine, methionine, glutathione, several coenzymes
Potassium1Potassium saltsMain cellular inorganic cation and cofactor for certain enzymes
Magnesium0.5Magnesium saltsInorganic cellular cation, cofactor for certain enzymatic reactions
Calcium0.5Calcium saltsInorganic cellular cation, cofactor for certain enzymes and a component of endospores
Iron0.2Iron saltsComponent of cytochromes and certain nonheme iron-proteins and a cofactor for some enzymatic reactions

The above table ignores the occurrence of trace elements in bacterial nutrition. Trace elements are metal ions required by certain cells in such small amounts that it is difficult to detect (measure) them, and it is not necessary to add them to culture media as nutrients. Trace elements are required in such small amounts that they are present as "contaminants" of the water or other media components. As metal ions, the trace elements usually act as cofactors for essential enzymatic reactions in the cell. One organism's trace element may be another's required element and vice-versa, but the usual cations that qualify as trace elements in bacterial nutrition are Mn, Co, Zn, Cu, and Mo.

In order to grow in nature or in the laboratory, a bacterium must have an energy source, a source of carbon and other required nutrients, and a permissive range of physical conditions such as O2 concentration, temperature, and pH. Sometimes bacteria are referred to as individuals or groups based on their patterns of growth under various chemical (nutritional) or physical conditions. For example, phototrophs are organisms that use light as an energy source; anaerobes are organisms that grow without oxygen; thermophiles are organisms that grow at high temperatures.

Carbon and Energy Sources for Bacterial Growth

All living organisms require a source of energy.

Organisms that use radiant energy (light) are called phototrophs.

Organisms that use (oxidize) an organic form of carbon are called heterotrophs or chemo(hetero)trophs.

Organisms that oxidize inorganic compounds are called lithotrophs.

The carbon requirements of organisms must be met by organic carbon (a chemical compound with a carbon-hydrogen bond) or by CO2. Organisms that use organic carbon are heterotrophs and organisms that use CO2 as a sole source of carbon for growth are called autotrophs.

Thus, on the basis of carbon and energy sources for growth four major nutritional types of procaryotes may be defined (Table 2)

Table 2. Major nutritional types of procaryotes.

Nutritional TypeEnergy SourceCarbon SourceExamples
PhotoautotrophsLightCO2Cyanobacteria, some Purple and Green Bacteria
PhotoheterotrophsLightOrganic compoundsSome Purple and Green Bacteria
Chemoautotrophs or Lithotrophs (Lithoautotrophs)Inorganic compounds, e.g. H2, NH3, NO2, H2SCO2A few Bacteria and many Archaea
Chemoheterotrophs or HeterotrophsOrganic compoundsOrganic compoundsMost Bacteria, some Archaea

Almost all eukaryotes are either photoautotrophic (e.g. plants and algae) or heterotrophic (e.g. animals, protozoa, fungi). Lithotrophy is unique to procaryotes and photoheterotrophy, common in the purple and green Bacteria, occurs only in a very few eukaryotic algae. Phototrophy has not been found in the Archaea.

This simplified scheme for use of carbon, either organic carbon or CO2, ignores the possibility that an organism, whether it is an autotroph or a heterotroph, may require small amounts of certain organic compounds for growth because they are essential substances that the organism is unable to synthesize from available nutrients. Such compounds are called growth factors.

Growth factors are required in small amounts by cells because they fulfill specific roles in metabolism. The need for a growth factor results from either a blocked or missing metabolic pathway in the cells. Growth factors are organized into three categories.

  1. purines and pyrimidines: required for synthesis of nucleic acids (DNA and RNA)

  2. amino acids: required for the synthesis of proteins

  3. vitamins: needed as coenzymes and functional groups of certain enzymes

Some bacteria (e.g E. coli) do not require any growth factors: they can synthesize all essential purines, pyrimidines, amino acids and vitamins, starting with their carbon source, as part of their own intermediary metabolism. Certain other bacteria (e.g. Lactobacillus) require purines, pyrimidines, vitamins and several amino acids in order to grow. These compounds must be added in advance to culture media that are used to grow these bacteria. The growth factors are not metabolized directly as sources of carbon or energy, rather they are assimilated by cells to fulfill their specific role in metabolism. Mutant strains of bacteria that require some growth factor not needed by the wild type (parent) strain are referred to as auxotrophs. Thus, a strain of E. coli that requires the amino acid tryptophan in order to grow would be called a tryptophan auxotroph and would be designated E. coli Trp-.

Some vitamins that are frequently required by certain bacteria as growth factors are listed in Table 3. The function(s) of these vitamins in essential enzymatic reactions gives a clue why, if the cell cannot make the vitamin, it must be provided exogenously in order for growth to occur.

Table 3. Common vitamins required in the nutrition of certain procaryotes.

VitaminCoenzyme formFunction
p-Aminobenzoic acid (PABA) - Precursor for the biosynthesis of folic acid
Folic acidTetrahydrofolateTransfer of one-carbon units and required for synthesis of thymine, purine bases, serine, methionine and pantothenate
BiotinBiotinBiosynthetic reactions that require CO2 fixation
Lipoic acidLipoamideTransfer of acyl groups in oxidation of keto acids
Mercaptoethane-sulfonic acidCoenzyme MCH4 production by methanogens
Nicotinic acidNAD (nicotinamide adenine dinucleotide) and NADPElectron carrier in dehydrogenation reactions
Pantothenic acidCoenzyme A and the Acyl Carrier Protein (ACP)Oxidation of keto acids and acyl group carriers in metabolism
Pyridoxine (B6)Pyridoxal phosphateTransamination, deamination, decarboxylation and racemation of amino acids
Riboflavin (B2)FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide)Oxidoreduction reactions
Thiamine (B1)Thiamine pyrophosphate (TPP)Decarboxylation of keto acids and transaminase reactions
Vitamin B12Cobalamine coupled to adenine nucleosideTransfer of methyl groups
Vitamin KQuinones and napthoquinonesElectron transport processes

[Previous] | [Next]

frontierlogo picture This page was last built with Frontier on a Macintosh on Fri, Oct 6, 2000 at 3:22:56 PM.