Microorganisms….
Microorganisms are ubiquitous on the earth. They are found in
water, soil, air and interior and exterior surfaces of other organisms. Marine
and freshwater microorganisms from the basis of food chain in oceans and
freshwaters. Some of them do photosynthesis and are primary producers in
aquatic environments. Soil microorganisms help recycling of chemical elements
between soil, water, air and living organisms. Microorganisms suspended in air
as bio-aerosols, have the opportunity to travel long distances with the wind
current and precipitate. Pathogenic bio-aerosols, causes opportunities for
disease spreading. Only a minority of microorganisms that associate with other
organisms such as plants, animals and human are pathogenic. Majority of them
are advantageous or harmless. However, all viruses are harmful to organisms
they attached to. Some microorganisms are capable of inhabiting extreme
environmental conditions that are unfavorable or even lethal for other
organisms. Such microorganisms are known as extremophiles. Extremophiles have
been found inside the earth’s crust, deep sea at high pressures, extreme acidic
or extreme basic conditions, hydrothermal vents, frozen sea water and anaerobic
conditions. Extremophiles are classified according to the conditions in which
they grow.
Types of extremophiles
|
Type |
Condition |
|
Thermophiles |
High temperatures |
|
Psychrophiles |
Low temperatures |
|
Acidophiles |
Acid pH |
|
Alkaliphiles |
Basic pH |
|
Halophiles |
Require NaCl |
|
Barophiles |
High pressure |
Some of
these extreme environments consist of more than one extreme condition.
EX: 1. Many hot springs are acidic or alkaline
in nature at the same time.
2. Deep seas are cold and remain in high pressure.
Microorganisms
live in such environments are adapted to live with more than one extreme
condition.
Why microorganisms have high growing
rate?
Rates of
growth and reproduction of microorganisms are high. Microorganisms possess a
high surface area/volume ratio due to their smaller size. This means that they
have large surface area available for exchange of materials from external
environment. As a result, flowing rate of materials in to the inside of cells
and the exit of waste materials to the outside of the cells increases and
results in high metabolic rate. Therefore, average generation time or the time
required to double the population of microorganisms is relatively less.
Morphological, nutritional and
physiological diversity of microorganisms.
Microorganisms
possess diverse morphological forms. Bacteria possess diversity in their
shapes, basically three distinct shapes,
1. 1. Rod shape/Bacillus
2. 2. Spherical shape/Coccus
3. 3. Spiral shape/Spirillum.
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The coccus
bacteria may arrange in different forms,
1.
Coccus/Mono-coccus
2.
Diplococcus
3.
Streptococcus
4.
Staphylococcus
5.
Tetrads
6.
Sarcinae
Bacillus
bacteria may arrange in to either Diplobacillus
or Streptobacillus. Spiral bacteria
may arrange in to either Vibrio or Spirillum or Spirochete.
Cyanobacteria exhibit a great variety of shapes and arrangements, unicellular to long multi cellular filaments. Multi cellular Cyanobacteria may appear as either filamentous or non-filamentous. Filamentous appear as chains and the non-filamentous appear as clusters or colonies forming spherical, cubical, square or irregular shape. Two morphological varieties are found in viruses based on their symmetry of protein coats, Icosahedral and Helical.
In fungi, some of them are unicellular and others multicellular, consists of a mass of fine tubular branching threads known as hyphae, collectively form mycelium. Hyphae may be septate or aseptate.
Prions are
smaller proteinaceous particles. Unicellular protists possess wide range of
morphological diversity. Mollecutes are pleomorphic (Variable Shapes).
Microorganisms
show a diversity of nutritional types. Based on the sources of carbon and
energy, nutritional types of microbes are classified. There are four major
nutritional types can found among microorganisms.
1. Chemoautotrophs
2. Chemo-heterotrophs
3. Photoautotrophs
4. Photo-heterotrophs
Based on the
oxygen utilization, microorganisms can be classified in to four physiological
groups.
1. Obligate aerobes
2. Obligate anaerobes
3. Facultative anaerobes
4. Microaerophiles
Some microbes
capable of fixing atmospheric molecular nitrogen, show physiological diversity,
free living nitrogen fixing microbes and symbiotic nitrogen fixing microbes.
From this we
want to tell you about a basic introduction of microorganisms. There are lot
more to discuss about this topic and we hope to give you more in detailed information
about microorganisms in our next posts.
(Reference: Grade
13 Biology recourse book – Sri Lanka)
