Nutritional classification of microorganisms for MPM subject

1. Nutritional classification of
Microorganisms
By
Mr. K. VIJAY,
Assistant Professor,
Sacred Heart College,
Tirupattur District.

2. The main determinants of a microbe’s nutritional type
are its sources of carbon and energy. In a previous
section, microbes were defined as autotrophs, whose
primary carbon source is inorganic carbon (CO2), and
heterotrophs, which are dependent on organic carbon
compounds.
In terms of energy source, microbes that
photosynthesize are generally classified as
phototrophs, and those that oxidize chemical
compounds are chemotrophs.
The terms for carbon and energy source are often
merged into a single word for convenience. The
categories described here are meant to describe only
the major nutritional groups and do not include unusual
exceptions.

4. Autotrophs and Their Energy Sources
Autotrophs derive energy from one of two possible
nonliving sources: sunlight (photoautotrophs) and
chemical reactions involving simple inorganic chemicals
(chemoautotrophs).
Photoautotrophs are photosynthetic; that is, they capture
the energy of light rays and transform it into chemical
energy that can be used in cell metabolism.
Because photosynthetic organisms (algae,plants, some
bacteria) produce organic molecules that can be used by
themselves and heterotrophs, they form the basis for
most food webs. Their role is to act as primary
producers of organic matter

5. A significant type of bacteria called chemoautotrophs
have an unusual nutritional adaptation that requires
neither sunlight nor organic nutrients.
Some microbiologists prefer to call them
lithoautotrophs (rock feeders) in reference to their total
reliance on inorganic minerals. These bacteria derive
energy in diverse and rather amazing ways.
In very simple terms, they remove electrons from
inorganic substrates such as hydrogen gas, hydrogen
sulfide, sulfur, or iron and combine them with carbon
dioxide.

6. This reaction provides simple organic molecules and a
modest amount of energy to drive the synthetic
processes of the cell.
Chemoautotrophic bacteria play an important part in
recycling inorganic nutrients.
For an example of chemoautotrophy and its importance
to deep-sea communities.
An interesting group of chemoautotrophs are
methanogens, which produce methane (CH4) from
hydrogen gas and carbon dioxide.
4H2 + CO2 → CH4 + 2H2O

7. Methane, sometimes called “swamp gas,” is formed in
anaerobic, hydrogen-containing microenvironments of
soil, swamps, mud, and even in the intestines of some
animals.
Many methanogens are archaea that live in extreme
habitats such as ocean vents and hot springs, where
temperatures reach up to 125°C.
Methane can be harvested and used as an inexpensive
energy source in certain industries.

8. Biogas generators are devices primed with a mixed
population of microbes (including methanogens) and
fueled with various waste materials that can supply
enough methane to drive a steam generator.
Methane also plays a role as one of the greenhouse
gases that is currently an environmental concern.

9. Autotrophic bacteria - Phytosynthetic bacteria
Few purple sulphur (e.g., Chromatium) bacteria possess
pigments, such as, purple pigment, the bacteriopurpurin, and
green pigment, the bacterial chloroyhyll etc.
Bacterioviridin occurs hi green sulphur bacteria, e.g.,
Chlorobium. Such bacteria synthesize their carbohydrate food
in presence of sunlight by photosynthesis and are known as
chlorophyll bacteria.

10. Autotrophic bacteria - Chemosynthetic bacteria
These bacteria get their energy for food synthesis from
the oxidation of certain inorganic chemicals. Light
energy is not used.
The energy obtained from the chemical reactions is
exothermic. The Chemosynthetic bacteria are of the
following types:
(a)Sulphomonas (Sulphur bacteria): These bacteria
get their energy by oxidation of hydrogen sulphide into
H2SO4, e.g., Thiobacillus, Beggiatoa.

11. (b) Hydromonas (Hydrogen bacteria): These convert
hydrogen into water, e.g., Bacillus pantotrophus.
(c) Ferromonas (Iron bacteria): These bacteria get
their energy by oxidation of ferrous compounds into
ferric forms,. e.g., Leptothrix.
(d) Methanomonas (Methane bacteria): These
bacteria get their energy by oxidation of methane into
water and carbon dioxide.
(e) Nitrosomonas (Nitrifying bacteria): These bacteria
get their energy by oxidation of ammonia and nitrogen
compounds like nitrites, nitrates. Nitrosomonas oxidises
NH3 to nitrites.
Nitrobacter converts nitrites to nitrates.

12. Heterotrophs and Their Energy Sources
The majority of heterotrophic microorganisms are
chemoheterotrophs that derive both carbon and energy
from organic compounds. Processing these organic
molecules by respiration or fermentation releases
energy in the form of ATP.
An example of chemoheterotrophy is aerobic respiration,
the principal energy yielding reaction in animals, most
protozoa and fungi, and aerobic bacteria. It can be
simply represented by the equation:
Glucose [(CH2O)n] + O2 → CO2 + H2O +Energy (ATP)

13. Chemoheterotrophic microorganisms belong to one of
two main categories that differ in how they obtain their
organic nutrients: Saprobes are free-living
microorganisms that feed primarily on organic detritus
from dead organisms, and parasites ordinarily derive
nutrients from the cells or tissues of a host.

14. Saprobic Microorganisms –
Saprobes occupy a niche as decomposers of plant litter,
animal matter, and dead microbes.
If not for the work of decomposers, the earth would
gradually fill up with organic material, and the nutrients it
contains would not be recycled.
Most saprobes, notably bacteria and fungi, have a rigid
cell wall and cannot engulf large particles of food. To
compensate, they release enzymes to the extracellular
environment and digest the food particles into smaller
molecules that can pass freely into the cell.

15. Obligate saprobes exist strictly on organic matter in soil
and water and are unable to adapt to the body of a live
host.
This group includes many free-living protozoa, fungi, and
bacteria.
Apparently, there are fewer of these strict species than
was once thought, and many supposedly nonpathogenic
saprobes can infect a susceptible host.
When a saprobe infects a host, it is considered a
facultative parasite. Such an infection usually occurs
when the host is compromised, and the microbe is
considered an opportunistic pathogen.

16. For example, although its natural habitat is soil and
water, Pseudomonas aeruginosa frequently causes
infections in hospitalized patients.
The yeast Cryptococcus neoformans causes a severe
lung and brain infection in AIDS patients, yet its natural
habitat is the soil.

17. Parasitic Microorganisms
Parasites live in or on the body of a host, which they
usually harm to some degree. Parasites inclined to
cause damage to tissues (disease) or even death are
called pathogens.
Parasites range from viruses to helminth worms, and
they can live on the body (ectoparasites), in the organs
and tissues (endoparasites), or even within cells
(intracellular parasites, the most extreme type).

18. Although there are several degrees of parasitism, the
more successful parasites generally have no fatal effects
and eventually evolve to a less harmful relationship with
their host.
Obligate parasites (for example, the leprosy bacillus and
the syphilis spirochete) are unable to grow outside of a
living host.
Parasites that are less strict can be cultured artificially if
provided with the correct nutrients and environmental
conditions.

19. Bacteria such as Streptococcus pyogenes (the cause of
strep throat) and Staphylococcus aureus can grow on
artificial media as saprobes.
Obligate intracellular parasitism is an extreme but
relatively common mode of life.
Microorganisms that spend all or part of their life cycle
inside a host cell include the viruses, a few bacteria
(rickettsias, chlamydias), and certain protozoa
(apicomplexa).
Contrary to what one might think, the inside of a cell is
not completely without hazards, and microbes must
overcome some difficult challenges.

20. Obligate intracellular parasitism is an extreme but
relatively common mode of life.
Microorganisms that spend all or part of their life cycle
inside a host cell include the viruses, a few bacteria
(rickettsias, chlamydias), and certain protozoa
(apicomplexa).
Contrary to what one might think, the inside of a cell is
not completely without hazards, and microbes must
overcome some difficult challenges to infect other cells.

21. Intracellular parasites obtain different substances from
the host cell, depending on the group.
Viruses are the most extreme, parasitizing the host’s
genetic and metabolic machinery.
Rickettsias are primarily energy parasites, and the
malaria protozoan is a hemoglobin parasite.