4. CULTURABLE BACTERIA IN SOIL
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Bacteria have perhaps the greatest influence in the soil
environment of all organisms. Species are either autotrophic or
heterotrophic. They perform many functions in the ecosystem,
most importantly in enzymatic transformations. They are able to
oxidize or reduce many chemical elements in the soil. Bacteria in
soil are mostly decomposers that consume simple carbon
compounds, such as root exudates and fresh plant litter. By this
process, bacteria convert energy in soil organic matter into forms
useful to the rest of the organisms in the soil food web. A number
of decomposers can break down pesticides and pollutants in soil.
Despite the abundance of bacterial species in soil, more than 99%
of these species cannot be cultured by traditional techniques.
Common bacterial genera isolated from soil include Bacillus,
Arthrobacter, Pseudomonas, Agrobacterium, Alcaligenes,
Clostridium, Flavobacterium, Corynebacterium, Micrococcus,
Xanthomonas, and Mycobacterium.
5. ACTINOMYCETES
Actinomycetes are Gram-positive
mycelial bacteria.
Morphology: Filamentous lengths
of cocci
Respiration: Mostly aerobic, can
be anaerobic
Commonly found: In soil
6. Characteristics of Actinomycetes
o Actinomycetes are unicellular, Gram-positive bacteria that belong
to the Order Actinomycetales.
o Actinomycetes are found in many habitats, such as freshwater,
sea- water, cold- and warm-blooded animals, and composts. The
soil, however, is their most important habitat. Viable counts of
several millions per gram are common, and over 20 genera have
been isolated from soil.
o They have been shown to share a number of characteristics with
fungi (e.g. mycelial growth).
o They are also nutritionally versatile and capable of producing
different kinds of spores, this characteristics of theirs help them
to survive in nature comepetiting with many other organisms
present.
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7. o As members of the Phylum Actinobacteria, Actinomycetes are
Gram-positive bacteria characterized by a high G+C content in
their DNA.
o They form branched filamentous hyphae having resemblance
with fungal hyphae. But their hyphal diameter is approximately
1µm, whereas in fungi it is 5 to 10 µm.
o The Actinomycetes superficially resemble fungi for having
subterranean and aerial hyphae and chains of spores. But their
hyphal diameter, cytology and chemical composition of cell
walls are quite decidedly bacterial in pattern.
o These organisms reproduce by asexual spores which are termed
conidia when they are naked or sporangiospores when
enclosed in a sporangium. Although these spores are not heat-
resistant, they are resistant to desiccation.
o Actinomycetes are known to grow ideally between a pH range
of 6.0 - 8.0 and are mostly seen to dominate dry, high pH soils.
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8. o In soil they are saprophytic and chemoorganotrophic, and they have
the important function of degrading plant or animal resides.
o Some species of the group are known to produce diseases (eg:
Actinomyces is caused by Actinomyces israelii) many other species
are known to play an important role in breaking down organic
compounds present in soil, also producing biologically active
compounds that have been used as antibiotics and insecticides, etc.
o Marine Actinomycetes have been shown to possess novel secondary
metabolites that add a new dimension to microbial natural products
that have been discovered within soil Actinomycetes.
o Actinomycetes are known to grow ideally between a pH range of 6.0
- 8.0 and are mostly seen to dominate dry, high pH soils.
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9. o Many of the Actinomycetes have the ability to synthesize
metabolites which hinder the growth of bacteria; these are called
antibiotics.
o Produces streptomycin, chloromphenicol (Chloromycetin is the
trade name of this substance), aureomycin and terramycin.
o They excrete extracellular enzymes which are decomposers of
dead organic material. These enzymes lyse bacteria and thereby
keep the bacterial population in check and thus help to maintain
the microbial equilibrium of the soil thereby playing a vital part
in organic matter turnover and carbon cycle, replenishing the
supply of nutrients in the soil.
o Produce Geosmin, the compound which gives soil and water a
characteristic earthy odour.
o Capable of biological nitrogen fixation with species of the non-
legume-associated Frankia.
FUNCTIONS
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10. NITRIFICATION
o Nitrification is a microbial process by which reduced
nitrogen compounds (primarily ammonia) are
sequentially oxidized to nitrite and nitrate by different
organisms. Nitrification is an important step in the nitrogen
cycle in soil.
o Nitrification is a two-step process in which NH3/ NH4+ is
converted to NO3-. First, the soil bacteria Nitrosomonas
and Nitrococcus convert NH3 to NO2-, and then another
soil bacterium, Nitrobacter, oxidizes NO2- to NO3-.
o Conventional nitrification occurs in soils, sediments, and
aquatic environments. It is very important in agriculture,
where it determines the availability of fertilizer nitrogen,
and in wastewater treatment systems, where it participates
in the removal of excess nitrogen.
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11. o Nitrifying bacteria: They are chemolithotrophic
organisms that include species of the genera
e.g. Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina,
Nitrospira and Nitrococcus.
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12. FUNGI
The fungi comprise a diverse group of
organisms that are heterotrophic and
typically saprozoic. In addition to the
well-known macroscopic fungi (such
as mushrooms and molds), many
unicellular yeasts and spores of
macroscopic fungi are microscopic.
They usually grow as long threads or
strands called hyphae, which push
their way between soil particles, roots,
and rocks. Aspergillus flavus, Penicillium
notatum, Cladosporium fulvum are
examples of microscopic fungi.
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13. Characteristics
Constitute high proportion of biomass
Mostly as indigenous and sometimes allochthonous
They display two distinct morphological stages: the vegetative
and reproductive. The vegetative stage consists of a tangle of
slender thread-like structures called hyphae (singular, hypha ),
whereas the reproductive stage can be more conspicuous. The
mass of hyphae is a mycelium.
Fungi play a crucial role in the balance of ecosystems. They
colonize most habitats on earth, preferring dark, moist
conditions. They can thrive in seemingly-hostile environments.
As decomposers, pathogens, and mutualistic symbionts with
plants and animals, fungi play a major role in ecosystem
processes including nutrient cycling, bioconversions, and
energy flows
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14. YEAST
Yeasts are eukaryotic, single-celled
microorganisms classified as
members of the fungus kingdom. It
accounts for about 1% of all the
fungi on earth. For the most part,
they are unicellular, but a number
of them form hyphal threads. They
can grow through a process called
budding in which a small yeast cell
grows on the outside of a mature
one, until it is fully grown and
ready to separate. Candida
albicans, Rhodotorula rubra,
TorulopsisSaccharomyces
cerevisiae are all examples of yeast.
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15. Characteristics
Yeasts are chemo-organotrophs as they can use
inorganic chemicals as a source of energy
Yeasts contribute to essential ecological processes such
as the mineralization of organic material and dissipation
of carbon and energy through the soil ecosystem.
Most indiginous soil yeasts are Fungi imperfecti
(deuteromycota).
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17. “
Aero-microbiology and Aero-
microflora
o Study of microorganisms and their spores which are invisible to
naked eyes suspended in air. Study of aerospoilation, aerial
transmission and biological matters.
o It includes the study of diseases transmitted through respiratory
routes.
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18. HISTORY
▪ During 1930s the term aero-microbiology was used to
denote the air borne spores.
▪ Further in 1951 the term was elaborated to include
dispersion of insect population, fungal spores, bacteria
and viruses.
▪ In 1964, the term included the research work of air borne
materials of biological significance.
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19. Bioaerosol
▪ Bio-aerosols: Microbes are called as bio-aerosol.
They are subcategory of particles released from terrestrial and
marine ecosystems into the atmosphere. They consist of both
living and non-living components, such as fungi, pollen,
bacteria and viruses. Common sources include soil, water, and
sewage.
▪ Found normally in atmosphere within 300- 10000 feet above
from the land. There are significantly less atmospheric
microorganisms than there are in soil or in ocean.
▪ Microbes can travel for extensive distances with the help of
wind or other carrier and precipitate increasing the rate of
infectious diseases caused by these microbes. For example,
Novel Coronavirus started from China travelled throughout the
world affecting even the most remote countries.
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20. ▪ Important gases affecting the microorganisms are
hydrogen sulphide, sulphur dioxide, carbon monoxide,
chlorine, hydrogen fluoride, ozone, etc.
▪ The microbial forms are bacteria, fungi, actinomycetes,
algae, spores of pteridophytes, pollen grains, micro-
insects and viruses.
▪ The study of aero-microbiology is important as it
involved the study of formation of aerosols.
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22. Indoor Micro-flora
▪ Indoor air contains more disease causing microbes
having higher rate of infections than the air outside.
▪ Common genera of fungi in indoor air are Penicillium,
Aspergillus.
▪ The common genera of bacteria found in indoor air are
Staphylococci, Bacillus and Clostridium.
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23. Outdoor Microflora
▪ Dominant microflora of the air outside is fungi.
▪ The two very common genera of fungi are Clodosporiul
and sporobolomyces.
▪ Aspergillus, Alternaria, Phytophthora and Erysipheare
other fungal aerosols.
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24. ATMOSPHERE
The atmosphere is the layer of gases around the Earth. It is
held in place by Earth's gravity. There are total 5 layers of
atmosphere, named stratosphere, troposphere, mesosphere,
thermosphere, and exosphere. The atmosphere protects life
on Earth by absorbing (taking) ultraviolet rays from the sun.
It is very essential for sustainability of life on earth.The
atmosphere contains the air that we breathe; protects us
from the harmful radiation of the Sun; helps to keep the
planet's heat on the surface, and plays a very important role
in the water cycle.
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25. Characteristics
Earth’s atmosphere is made up of five layers namely,
troposphere, stratosphere, mesosphere, thermosphere
and exosphere. Only earth’s atmosphere can sustain life.
Earth’s atmosphere It contains roughly 78% nitrogen
and 21% oxygen 0.97% argon and carbon dioxide
0.04% trace amounts of other gases, and water vapor.
There are traces of dust particles, crystals and microbes
in atmosphere.
Physical and chemical parameters do not favour the
growth of microbes in air. Microbes are very much
concentrated in the boundary layer of atmosphere, upto
the height of 01km from earth’s surface.
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27. Layers of the atmosphere
(defined by temperature
maxima and minima and
pressure gradient)
Trophosphere: contains 80
percent of all air
Stratosphere: absorbs U.V. rays
Mesosphere: protects Earth from
meteorites
Thermosphere: most meteorites
burn here.
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28. CLOUDS
o A cloud is a mass of water drops or ice crystals
suspended in the atmosphere. Clouds form when water
condenses in the sky. The condensation lets us see the
water vapor.
o They are temporary habitats for microbes to live in. The
carbon dioxide concentration and light intensities are
suitable to aid the growth of photoautotrophic
microorganisms.
o Condensation nuclei may supply some nutrients.
o Water droplets and acidic pH (3-7)favors the growth of
microbes such as extremophiles.
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29. Aerosols
An aerosol is a suspension of fine solid particles or liquid
droplets in air or another gas. Aerosols can be natural or
anthropogenic. Examples of anthropogenic aerosols are
particulate air pollutants and smoke while there might be some
which are natural and not visible to naked eye like dust, pollen
grains ,etc.
Aerosols of smaller sixe can enter the respiratory system
causing many health related problems.
The Unites States Environmental Protection Agency (USEPA)
has divided air borne particles in two size categories:
o PM10, referring to particles having diameters less than or equal
to 10 m (10,000nm)
o PM2.5, for particles which are less than or equal to 2.5 m
(2500nm) in diameter. 29
30. Influence of particle size on velocity of
deposition of particles in air, calculated
using Stoke’s Law
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Particle Diameter
(mm)
Particle Type Rate of Fall (cm s-1)
1 Sand 7880
0.1 Silt 79
0.001 Clay 7.9 x 10-5
0.002 Clostridial spore 0.016
