6. MICROBIAL NUTRITION
6.1. Elements and energy sources
 Microorganisms require about 10 elements
in large quantities (C, N, H, O, S, P, K, Ca,
Mg, Fe); others as microelements or trace
elements (Mn, Zn, Co, Mo, Cu…..) – part
of enzymes and cofactors
 Nutrients are used in biosynthesis and as a
source of energy (chemotrophs)
 CARBON – the skeleton of organic
substances (often together as source of H
and O)
Carbon source:
Autotrophs – can use CO2, often
phototrophic, some chemotrophic
Heterotrophs – require organic C
molecules (usually as the source
of C and energy)
- Saprotrophs (saprophytes) –
non-living organic matter
- Parasites – living organisms
Mixotrophs – use both forms of
carbon
 Energy source
Phototrophs – light
Chemotrophs – oxidation of organic
or inorganic compounds
 Hydrogen or electron sources
Litotrophs – reduced inorganic
molecules
Organotrophs – organic molecules
 Main nutritional types of microorganisms:
Photolitotrophic autotrophs
Light energy
Inorganic H/e- donor
CO2 as carbon source
Photoorganotrophic heterotrophs
Light energy
Organic H/e- donor
Organic carbon source (CO2 also)
Chemolitotrophic autotrophs
Energy source - inorganic
Inorganic H/e- donor
CO2 as carbon source
Chemoorganotrophic heterotrophs
Energy source - organic
Organic H/e- donor
Organic carbon source
 NITROGEN – needed for synthesis of
amino acids (proteins), purines,
pyrimidines, (nucleic acids), etc.
Sources of nitrogen:
Organic - (mostly amino acids, NA, …)
NH4+ - used for amino acids synthesis
NO3- - (usually the first step is reduction
to NH4+)
N2 - diazotrophic bacteria (usually the
first step is reduction to NH4+)
 PHOSPHORUS (present in nucleic acids,
phospholipids, ATP….)
Sources of P:
Inorganic – preferable source (H2PO4HPO42- PO43Organic – the use usually connected
with the activity of enzyme
phosphatase (mineralization)
 SULPHUR (present in amino acids methionine and cysteine; biotin, thiamin)
Sources of S:
Inorganic – (usually preferable) SO42Organic – cysteine (a few)
 OTHER ELEMENTS
Usually they are used as inorganic ions:
Ca2+, Mg2+, K+, Na+………..
6.2. Nutrient uptake
 Passive (simple) diffusion
Nutrients moving from a region of higher
concentration to one of lower (influence of
concentration gradient) – ions, glycerol,
O2, CO2 – no energy consumption
 Osmosis
Some solvent molecules and water move
across membrane
Isotonic – Hypotonic - Hypertonic
 Facilitated diffusion
For nutrient movements (glucose) special
carriers proteins are used (transporters permeases situated in plasma membrane),
increase with concentration gradient, no
energy consumption; limited in
prokaryotic cells, typical esp. for
eukaryotic cells
 Active transport
Transport both to higher concentration or
against concentration gradient, with the
use of metabolic energy input (ATP), it
needs also carrier proteins (inhibition of
energy production inhibits active
transport)
 Group translocation
Molecules during the transport across the
membrane are modified, the best known
example:
phosphoenolpyruvate + sugar
+ sugarphosphate
pyruvate
Composition of microbial cell
Water
Ø 80% (73-90%)
Dry matter
Ø 20% (10-27%)
Elements in dry matter:
C 40-63%
50
N
8
2-15%
96 %
H 7-8%
8
O 20-44%
30
99,5
P 3-5%
3
3,5%
S
1
K,Mg,Ca,Na…
Fe,Cu,Mn, Co, F, J..
99,9%
0,4%
0,1
Substances in microbial cell (dry matter):
N-substances:
Viruses
81 – 100%
Bacteria
50 – 94%
Yeasts
31 – 63%
Molds
14 – 44%
Main N-substances:
Proteins (amino acids) building and
metabolic functions
DNA – genetic code
RNA – protein synthesis
Other substances:
Lipids
Saccharides
Minerals

Escherichia coli
Proteins
60%
DNA
3%
RNA
16%
Saccharides
3%
Lipids
15%
Total
97%
Others
Total
3%
100%