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Nutrition and Growth of Bacteria (page 1)
(This chapter has 6 pages)
© Kenneth Todar, PhD
Nutritional Requirements of Cells
Every organism must find in its environment all of the substances
for energy generation and cellular biosynthesis. The chemicals and
of this environment that are utilized for bacterial growth are referred
to as nutrients or nutritional requirements. Many
bacteria can be grown the laboratory in culture media which are
designed to provide
all the essential nutrients in solution for bacterial growth. Bacteria
that are symbionts or obligate intracellular parasites of other cells,
usually eucaryotic cells, are (not unexpectedly) difficult to grow
outside of their natural host cells. Whether the microbe is a mutualist
or parasite, the host cell must ultimately provide the nutritional
requirements of its resident.
Many bacteria can be identified in the environment by inspection or
using genetic techniques, but attempts to isolate and grow them in
artificial culture has been unsuccessful. This, in part, is the basis
of the estimate that we may know less than one percent of all
procaryotes that exist.
The Major Elements
At an elementary level, the nutritional requirements of a bacterium
such as E. coli are revealed by the cell's elemental
which consists of C, H, O, N, S. P, K, Mg, Fe, Ca, Mn, and traces of
Co, Cu, and Mo. These elements are found in the form of water,
ions, small molecules, and macromolecules which serve either a
or functional role in the cells. The general physiological functions of
the elements are outlined in Table 1.
Table 1. Major elements,
sources and functions in bacterial cells.
||% of dry weight
||organic compounds or CO2
||Main constituent of cellular material
||H2O, organic compounds, CO2,
||Constituent of cell material and cell water; O2
acceptor in aerobic respiration
||NH3, NO3, organic
||Constituent of amino acids, nucleic acids
||H2O, organic compounds, H2
||Main constituent of organic compounds and
||inorganic phosphates (PO4)
||Constituent of nucleic acids, nucleotides,
||SO4, H2S, So,
||Constituent of cysteine, methionine,
||Main cellular inorganic cation and cofactor
||Inorganic cellular cation, cofactor for
||Inorganic cellular cation, cofactor for
certain enzymes and a
||Component of cytochromes and certain nonheme
and a cofactor
for some enzymatic reactions
Table 1 ignores the occurrence of trace elements in bacterial
elements are metal ions required by certain cells in such small
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
or other media components. As metal ions, the trace elements usually
as cofactors for essential enzymatic reactions in the cell. One
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.
Carbon and Energy Sources for Bacterial
In order to grow in nature or in the laboratory, a bacterium must
an energy source, a source of carbon and other required nutrients, and
a permissive range of physical conditions such as O2
temperature, and pH. Sometimes bacteria are referred to as individuals
or groups based on their patterns of growth under various chemical
or physical conditions. For example, phototrophs are organisms that use
light as an energy source; anaerobes are organisms that grow without
thermophiles are organisms that grow at high temperatures.
All living organisms require a source of energy. Organisms that use
radiant energy (light) are called phototrophs. Organisms that
(oxidize) an organic form of carbon are called heterotrophs or (chemo)heterotrophs.
Organisms that oxidize inorganic compounds are called lithotrophs.
The carbon requirements of organisms must be met by organic carbon
chemical compound with a carbon-hydrogen bond) or by CO2.
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
nutritional types of procaryotes may be defined (Table 2).
Table 2. Major nutritional
||Cyanobacteria, some Purple and Green Bacteria
||Some Purple and Green Bacteria
|Chemoautotrophs or Lithotrophs
||Inorganic compounds, e.g. H2, NH3,
||A few Bacteria and many Archaea
|Chemoheterotrophs or Heterotrophs
||Most Bacteria, some Archaea
Almost all eucaryotes 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
Bacteria, occurs only in a very few eucaryotic algae. Phototrophy has
been found in the Archaea, except for nonphotosynthetic light-driven
synthesis in the extreme halophiles.