Download aquatic microbiology-2012

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Aquatic Microorganisms
The biosphere of our planet contains a large number of ecosystems in which microorganisms play an
important part. Water is the dominant environment of these ecosystems, since ocean covers about 71 % of
the globe's surface. Although water forms the basis for all aquatic environments, the difference in the
characteristics of natural water distinguishes several different aquatic environments. Thus, microbial
ecology of natural waters remains an important and diversified field.
Ingeneral, aquatic microorganisms experience highly fluctuating, highly varying environmental
factors.These factors vary not only among different aquatic environments, even within the same aquatic
environment. This contributes to the well pronounced microbial biodiversity in aquatic environments.
Inspite of the continuing researches in aquatic microbiology, much have to be deciphered about the
aquatic microorganisms. The difficulties in the study of aquatic microorganisms and their environment are
slowly being rectified with the introduction of modern techniques.
There are two major types of water.
1. Ground water - It originates from deep wells and subterranean springs. This is virtually free of bacteria
due to filtering action of soil, deep sand and rock. However, it may become contaminated when it flows
along the channels.
2. Surface water - It is
found in streams,
lakes, and shallow
wells. The air through
which the rain passes
may contaminate the
water. Other sources
are the various types of
establishments and
agricultural farms etc.
by the sides the water
flows.
Possible sources of
microbial
contamination of a
body of water are soil
and agricultural run
off, farm animals, rain
water, industrial waste,
discharges from
sewage treatment
plants and storm water
run off from urban
areas.
In water microbiology the water is contaminated when it contains a chemical or biological poison or an
infectious agent.
These conditions also apply to water which is polluted except that the agent or poison is often obvious and
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the water carries an unpleasant taste or appearance. Potability refers to the drinkability of water. When
potable, it is fit for drinking. When unpotable it is unfit due to some contaminant or pollutant.
Atmospheric Waters
Rain, snow and hail which fan on land tend to carry down particles of dust, soot, and other materials
suspended in the air. These often bear bacteria and other microorganisms -on their surface. The number of
organisms depends upon local conditions. After heavy rain or snow the atmosphere is washed free of
organisms.
Surface Waters - As soon as ram or snow reaches the earth and flows over the soil, some of the soil
organisms are gathered up by the water. Bodies, of water such as streams, rivers, and oceans represent
surface water.
Microbial populations depend upon their numbers in the soil and, also, upon the kinds and quantities of
food material dissolved out of the soil by water. Climatic, geographical and biological conditions bring
about great variations in microbial populations of surface waters.
Rivers and streams show their highest count during the rainy period Dust blowing into rivers and streams
also contributes many microorganisms. Animals also make considerable contribution to the microbial
flora of the surface waters. They bathe and often drop their excreta in the water.
Stored Waters - Inland waters held in ponds, lakes or reservoirs represent stored waters. Storage
generally reduces the numbers of organisms in water. A certain degree (If purity and stability is
established.
Study of Aquatic Microorganisms -The study of aquatic microorganisms is quite difficult because of the
nature of their habitat and their unique characteristic features. The study is particularly difficult when the
samples are from sea. Pelczar et.al. (1986) have analysed some of the problems associated with the study
of
aquatic
microflora
which
are
as
follows:
Isolation of many aquatic microorganisms is very difficult since they will not readily grow on the usual
laboratory media such as nutrient agar or nutrient broth. Thus, a number of microbes still have to be
discovered from estuaries and oceans.
A large proportion of aquatic bacteria have a natural tendency to grow attached on solid surfaces, like
particulate
matter
or
on
large
organisms.
The time period between the sample collection and its transport to the laboratory usually leads to loss of
viability of many microorganisms. This necessitates the use of laboratory-equipped ships for on-location
culturing
of
specimens,
which
is
very
costly.
The study requires
special
sampling
devices especially for
collecting
samples
from
the
deeper
regions of the estuary
or
ocean.
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Another important problem is the lack of routine techniques for the isolation of aquatic viruses.
Microbial Communities in Aquatic Environments- Various habitats can be recognized within an
aquatic environment and their actual size may vary from one another. Each habitat is characterized by one
or more microbial communities and thus the microorganisms within an aquatic environment can be
grouped as distinct communities.
Microbial Communities - In neutral and slightly alkaline waters of ponds and lakes, planktons are
represented by the group diatoms which includes Fragilaria and Melosira varians. Acidic, oligotrophic
lakes
have
flagellated
planktons
like
Euglena
and
Chlamydomonas.
Eutrophic lakes include planktons of the groups Chlorococcales such as Scenedesmus, Chlorella etc.,
Coccoid cyanophyta such as Microcystis and Coelosphaerium and filamentons cyanophyta such as
Anabaena and Oscillatoria etc.
Ground Water Microbiology - About 29% of the earth's surface is represented by continental surface.
Beneath all these continental surface is the, groundwater habitat. Thus, groundwater ecosystems include
vast
area
on
a
global
scale.
The typical composition of the continental areas of the earth includes, in vertical sequence, the following:
the A and B soil horizons; the C soil horizon from which the above two horizons might have been derived;
an unsaturated or vadose zone which is bound between the C soil horizon and the water table; a capillary
fringe zone just above the water table and a saturated zone which may extend through several geological
strata.
Major Groundwater Microbial Groups - Only limited informations are available on the major groups of
microorganisms and their spatial distribution within the groundwater ecosystem. Comparatively,
groundwater ecosystem contains less number of microorganisms than any other aquatic habitats or the
terrestrial surface as well. This can be related to the infiltration of water through various geological strata.
Bacteria- The major group of microorganisms found in groundwater ecosystem is bacteria. The
abundance and distribution of bacteria in a given subsurface zone is actually determined by the nature of
geological stratum, mineral type, particle size distribution, texture, hydraulic conductivity etc. The nutrient
levels decline, when moving down from A and B soil horizons to C horizon accompanied by a
proportional
decline
in
bacterial
abundance.
However, the number of bacteria does not continue to diminish with depth. Indeed there is again an
increase in the bacterial numbers at the capillary fringe zone and at the water table. This is due to the
horizontal saturated flow as well as the vertical seasonal fluctuations of the water table which lead to a
dynamic mixing of oxygen and nutrients in these regions.
The high relative abundance of bacteria in the saturated zone can be attributed to the hydrological,
Filamentous Spore Forming Microorganisms - Both actinomycetes and fungi are spore-forming
filamentous microorganisms. Inspite of their spore-forming ability they are found in very low numbers in
groundwater ecosystems. However their contributions to the aerobic heterotrophic metabolism is quite
high within the larger subsurface microbial community.
Metabolic diversity of Microorganisms- Groundwater ecosystem is inhabitated by metabolically diverse
groups of microorganisms each mediating its own characteristic metabolic activity.
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Some important microbial activity in the groundwater ecosystem includes carbon dioxide production,
denitrification, methanogenesis, methane oxidation and biodegradation of polycyclic aromatic
hydrocarbons.
Freshwater
Ecosystem
The study of freshwater habitats is called limnology. Fresh water environments include the flowing waters
(lotic environment) and standing bodies of water (lentic environment). The dominant feature of lotic
environments, is the continuous movement of water and currents, which cuts the channel, moulds the
character of the stream and influences the chemical and organic composition of the water.
Water running off the land follows courses of least resistance and develops these as distinct channels by
erosion. Young or rejuvenated streams, with a high velocity, erode more than they deposit.
Water in slow-moving rivers reflects the characteristic of the terrain; nutrient level and sediment load vary
according to region. The slow-moving stream often develops floodplains, meanders, and associated
features
and
terminates
in
a
lake
or
estuary.
The lentic and lotic ecosystems are fundamentally different from one another because of differences in
energy input and flow, and mineral input and circulation.
Microorganisms of The Aquatic (Freshwater) Habitat
1. Bacteria Most aquatic bacteria are gram negative because of the following reasons.
Gram negative envelope is suited for the nutrient diluted environment (oligotrophic).
Important hydrolytic enzymes are retained in the periplasmic space rather than being excreted and lost to
the aquatic environment as in gram positive bacteria.
Gram negative bacterial cell wall contains lipopolysaccharide (LPS) that protects the cell against toxic
molecules like fatty acids and antibiotics. Specially found are Pseudomonas sp., Flavobacterium,
Achromobacter and Alcaligenes, Vibrio sp., Acinetobacter, Staphylococcus sp. Bacteria in surface region
are pigmented.
2. Molds Deuteromycetes members, Phycomycetes and Myxomycetes members are found in the marine
environments.
3. Protozoa Species of Foraminifera and Rodidaxia and many ciliate species are common.
Aquatic Microbiology-Lakes
Eutrophic Lakes - Eutrophic lakes are those which have a high nutrient content. They are shallower than
the oligotrophic lakes. Because of the high nutrient content, extensive aerobic decomposition of organic
matter occurs in eutrophic lakes. And this makes them to have a low dissolved oxygen concentration.
However, they are characterized by very high primary productivity.
Thermal Stratification - Biological processes within the lake water are influenced by the physical state
of water which in turn is governed by the temperature. For example, at 4°C water has its maximum
density.
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In lakes, the increase in depth with a corresponding change in the temperature leads to a more or less
stable seasonal stratification called thermal stratification.
Hypolimnion- In this region the temperature will be more or less the same throughout its depth. This
region is subjected to wide variation as the temperature fluctuates with that of the atmosphere. Below the
epilimnion is a colder deep region known as hypolimnion which has a more or less constant temperature.
Metalimnion Thermolimnion - In between these two regions is a transition zone characterized by an
abrupt change in the temperature. This region is called as metalimnion or thermocline. The lithosphere
underlying the lake is referred to as sediment which is enriched with organic nutrients.
Redox discontinuity Layer Chemocline- Oxygen consuming catabolic process from the sediment render
the hypolimnion anaerobic. But the epilimnion is always in contact with atmospheric air and regularly
mixed
up
by
the
air
current.
This facilitates the aeration of the region and makes epilimnion aerobic. Thus, thermal stratification also
leads
to
a
gradient
of
redox
potential
and
chemical
parameters.
Since the redox potential and chemical parameters are quite different in the regions both above and below
the thermocline, it is also called as redox discontinuity layer or chemocline.
Seasonal Changes of Lakes - In spring, the lake water in the epilimnion is heated by sun, creating a less
dense layer. The water in the hypolimnion is cooler and remains at the bottom. The same stratification
continues
throughout
the
summer.
In autumn, the epilimnion cools off by radiating the heat. When the temperature in both the epilimnion
and the hypolinmion is equal, the two layers mix with each other. This mixing is assisted by autumn
winds.
Holomictic Lakes - Lakes which have a complete circulation cycle like this are referred to as holomictic
lakes.
Meromictic Lakes- If the mixing of water is incomplete that type of lakes are referred to as meromictic
lakes.
Amictic Lakes- If the mixing of water is completely absent that type of lakes are referred to as amictic
lakes
. Biological Process in Holomictic Lakes -Various biological activities taking place in a holomictic lake
allows
a
complete
cycling
of
nutrients
and
oxygen.
In the epilimnion light penetration allows photosynthesis to take place. Carbon dioxide, produced in the
bottom region, is made available in the form of dissolved carbon dioxide.
Oxygenic Photosynthesis - Phytoplanktons are the most common microflora in the epilimnion which
include diatoms, flagellates, green algae and cyanobacteria. Thus epilimnion is characterized by the
primary production through oxygenic photosynthesis.
Anoxygenic Photosynthesis - When hydrogen sulphide is present and sufficient illumination is available
purple as well as green sulphur bacteria like Chlorobium and Chromatium start primary production
through
anoxygenic
Photosynthesis.
These bacterial species are provided with either gas vacuoles or flagella so that they can be maintained
just below the metalimnion to trap any available light. Gas vacuole containing bacteria occurring in this
region include Amoebobacter, Lamprocystis, Thiopedia, Thiodictyon and Ancalochloris.
Zonation - Penetration of light through water varies with the depth in lakes and ponds. Based on this
various zones can be recognized within the lake. The depth upto which effective penetra60n of light
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occurs
is
referred
to
as
light
compensation
level.
The open area found above the light compensation level in a lake is called limnetic zone. Photosynthetic
activity is maximum in this zone. Organisms include photosynthetic bacteria, flagellates and diatoms.
Microbial Communities - In neutral and slightly alkaline waters of ponds and lakes, planktons are
represented by the group diatoms which includes Fragilaria and Melosira varians. Acidic, oligotrophic
lakes
have
flagellated
planktons
like
Euglena
and
Chlamydomonas.
Eutrophic lakes include planktons of the groups Chlorococcales such as Scenedesmus, Chlorella etc.,
Coccoid cyanophyta such as Microcystis and Coelosphaerium and filamentons cyanophyta such as
Anabaena and Oscillatoria etc.
Biofilm - Any wetted surface submerged in a river tend to be coated with microorganisms within an hour.
These include algae, bacteria and protozoa and the presence of algae is limited by the availability of light.
These attached forms are generally regarded as biofilm.
Mucilage - The biotic elements of the epilithic biofilm are fixed to the rock surfaces by a continuous
matrix of extracellular polysaccharides, also called mucilage, produced by the microbes involved.
Functions of Mucilage-1. A site for entrapping both soluble and particulate matter.
2. A retaining as well as protective mechanism for the extracellular enzymes produced by the
microorganisms
involved.
3.
A
retaining
mechanism
for
the
products
of
extracellular
enzymatic
hydrolyses.
4. A framework for different groups of autotrophic and heterotrophic microorganisms forming a complex
under suitable conditions.
Nutrient Spiralling - The path of nutrients in a river is spiral rather than a cycle and this phenomenon in
known as nutrient spiralling. The suspended nutrients in a river is usually absorbed by attached microbial
communities
which
act
upon
them.
After the death of these attached forms the absorbed nutrients are left free in the flowing water. After a
flow for a small distance downstream these nutrients are again absorbed by some other attached forms.
As a result of this interruption, the nutrients carried along with the running water do not move with the
speed of current. Thus, the nutrients involve a downstream movement before a cycle.
Spiral Length - Spiral length has been defined as the distance traveled by a substance in a stream before
assimilation
by
attached
organisms
of
the
streambed.
Thus, if a nutrient is at limiting concentrations in a stream it may be possible that the nutrient will be
rapidly
recycled
and
hence
it
will
have
short
spiral
length.
On the other hand, if the nutrient is found abundant, it will be recycled less rapidly and hence will have a
long spiral length.
Ground Water Microbiology - About 29% of the earth's surface is represented by continental surface.
Beneath all these continental surface is the, groundwater habitat. Thus, groundwater ecosystems include
vast
area
on
a
global
scale.
The typical composition of the continental areas of the earth includes, in vertical sequence, the following:
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the A and B soil horizons; the C soil horizon from which the above two horizons might have been
derived; an unsaturated or vadose zone which is bound between the C soil horizon and the water table; a
capillary fringe zone just above the water table and a saturated zone which may extend through several
geological strata.
It should be noted that the transition between soil and groundwater habitats is not delineated by soil
horizons, thus making the terms 'groundwater' habitat and 'terrestrial subsurface' synonyms.
Aquifers- In its simplest hydrogeological sense ground water has been referred to water that is easily
extractable from saturated, highly permeable geological strata known as aquifers. In addition to these
aquifers, groundwater also includes capillary water and water vapors from the unsaturated zones.
For microorganisms which live within these microhabitats all available forms of water may certainly be
important. Moreover, unsaturated zones may be transiently saturated during recharge events and they may
influence
the
microbiology
of
the
saturated
zone.
Thus, in a broader sense, groundwater refers to all subsurface water found beneath the soil A and B
horizons that is available to sustain and influence microbial life in the terrestrial subsurface (Madsen &
Ghiorse, 1993).
Major Groundwater Microbial Groups - Only limited informations are available on the major groups of
microorganisms and their spatial distribution within the groundwater ecosystem. Comparatively,
groundwater ecosystem contains less number of microorganisms than any other aquatic habitats or the
terrestrial surface as well. This can be related to the infiltration of water through various geological strata.
Bacteria- The major group of microorganisms found in groundwater ecosystem is bacteria. The
abundance and distribution of bacteria in a given subsurface zone is actually determined by the nature of
geological stratum, mineral type, particle size distribution, texture, hydraulic conductivity etc. The nutrient
levels decline, when moving down from A and B soil horizons to C horizon accompanied by a
proportional
decline
in
bacterial
abundance.
However, the number of bacteria does not continue to diminish with depth. Indeed there is again an
increase in the bacterial numbers at the capillary fringe zone and at the water table. This is due to the
horizontal saturated flow as well as the vertical seasonal fluctuations of the water table which lead to a
dynamic mixing of oxygen and nutrients in these regions.
The high relative abundance of bacteria in the saturated zone can be attributed to the hydrological,
physical and geochemical properties of each stratum rather than the depth. Also, there occurs a wide
variation in the morphology and physiology of bacteria found in each geological stratum.
The occurrence of endospore-forming bacteria in significant numbers is a notable point in the groundwater
ecosystem. Because endospores are appreciated for their long term survival.
Filamentous Spore Forming Microorganisms - Both actinomycetes and fungi are spore-forming
filamentous microorganisms. Inspite of their spore-forming ability they are found in very low numbers in
groundwater ecosystems. However their contributions to the aerobic heterotrophic metabolism is quite
high within the larger subsurface microbial community.
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Estuary - Estuary, which is the coastal adjunct of the marine ecosystem, can itself be studied as an
ecosystem since its physical, chemical and biological characteristics are much different from the marine
environment. An estuary is a semiepclosed coastal body of water which has a free connection with the
open
sea
(pelczar
et
al,
1986)
Unlike those of ocean waters, the characteristics of an estuary such as salinity, temperature, turbidity, and
nutrient load are not generally constant. These characteristics fluctuate over a wide range in relation to
space and time.
Bacterial Production - Estuary, which is the coastal adjunct of the marine ecosystem, can itself be
studied as an ecosystem since its physical, chemical and biological characteristics are much different from
the marine environment. An estuary is a semiepclosed coastal body of water which has a free connection
with
the
open
sea
(pelczar
et
al,
1986).
Unlike those of ocean waters, the
characteristics of an estuary such as
salinity, temperature, turbidity, and
nutrient load are not generally constant.
These characteristics fluctuate over a
wide range in relation to space and time.
For example, an ideal estuary has a
salinity gradient from less than 5% at the
upper end to more than 25% at the mouth.
Estuaries are complex and are
characterized by intensive exchange of
water, energy and materials across the
margin between marine and freshwater
environments.
Structure of Lentic Habitat
Lentic ecosystems include all standing
water (freshwater) habitats such as lakes,
ponds, marshes, swamps, bogs, etc. Lakes
are inland depressions containing
standing water. They may vary in size
from small ponds of less than a hectare to
large lakes covering thousands of square
kilometres. They may range in depth
from a few centimetres to over 1666
metres.
Ponds however are considered as small
bodies of standing water so shallow that
rooted plants can grow over most of the bottom. Most ponds and lakes have outlet streams and both are
more or less temporary features on the landscape.
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The aquatic habitats of lake and pond remain vertically stratified in relation to light intensity, wavelength
absorption, hydrostatic pressure, temperature etc. In a lake there are well recognised horizontal strata
which include:
i. Shallow water near the shore forms the littoral zone. It contains upper warm and oxygen-rich circulating
water layer which is called epilimnion. The littoral zone includes rooted vegetation.
ii. Sublittoral zone extends from rooted vegetation to the non-circulating cold water with poor oxygen
zone, i.e. hypolimnion.
iii. Limnetic zone is the open water zone away from the shore. It is the zone upto the depth of effective
light penetration where rate of photosynthesis is equal to the rate of respiration.
iv. Profundal zone is the deep water area beneath
limnetic zone and beyond the depth of effective
light penetration.
v. Abyssal zone is found only in deep lakes, since it
begins at about 2,000 meters from the surface.
Ponds have little vertical stratification. In ponds, the littoral zone is larger than the limnetic zone and
Profundal zone. In a small pond the limnetic and Profundal zone are not found.
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Biota of Lentic Habitat
Different organisms of the lentic environment can be ecologically classified based on whether they are
dependent on the substratum or free from it. Organisms depending on the substratum are called pedonic
forms and those that are free from it are the limnetic forms. Further, the aquatic organisms may also be
classified into the following groups depending upon their sizes and habits.
Neuston These are unattached organisms that live at the air-water interface. They may consist of
microbial forms, plants and animals. Animals and microbial forms that spend their lives on top of the airwater interface, such as water striders are termed epineuston while others including insects such as beetles
which spend most of their time on the underside of the air-water interface and obtain much of their food
from within water, are termed hyponeuston
Plankton These are forms which are found in all aquatic ecosystems except fast moving rivers. They are
small plants and microbial forms whose powers of self-locomotion are so limited that they cannot
overcome currents. Thus their distribution is controlled largely by the currents in their ecosystems. The
phytoplanktons and zooplanktons can move a bit, either to control their vertical distribution or to seize
prey. Certain zooplanktons are exceedingly active and move relatively great distances considering their
small size, but they are so small that their range is still controlled largely by currents and such plank tons
are also called nektoplankton.
Nekton Nektonic animals are swimmers and are found in all aquatic systems except for fast moving
rivers. In order to overcome currents, these animals are relatively large and powerful.
Benthos The benthos include the organisms living at the bottom of the water mass. They occur virtually in
all aquatic ecosystems. The benthos organisms living above the sediment-water interface are termed
benthic epifauna and those living in the sediment itself are termed infauna.
The water surface of a lake or pond contains certain free floating hydrophytes such as Azolla, Lemma,
Wolffa, etc. The microbial community lives associated with the surface film. The habitat is unusual in
many ways since it is subjected to rapid temperature fluctuations, increasing to high light intensity and is
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very well aerated. Organic matter especially particulate and inorganic nutrients such as phosphates,
accumulate on the surface of the film. The habitat is favourable for photoautotrophs. There are increased
numbers of bacteria especially Pseudomonas and Caulobacter
Neuston is a stressed habitat and microbial growth rate is low. Bacteria in neuston have hydrophobic
surfaces and produce extracellular polysaccharides both of which are concerned with adsorption on the
surface film.
Bubbles arising through the neuston layer and bursting play a major role in water-to-air transfer of
bacteria and viruses. Characteristic autochthonous neuston microbiota include algae, fungi and protozoa.
Cyanobacterial species include Aphanizomenon, Anabaena, Microcytis. Filamentous fungus include
Cladosporium. Yeasts are also found. Among protozoan species include Diffugia, Arcella, Acinata, etc.
Aquatic life is most prolific in the littoral zone. The littoral zone of a lake
remains rich in pedonic flora especially up to the depth to which effective light penetration is possible
facilitating the growth of rooted vegetation. Microorganisms exhibit different absorption spectra
determining which
wavelength of light can be utilised for photosynthesis. Green and purple
sulphur bacteria grow at the sediment-water interface below the layers of
short wavelength absorbing algal and cyanobacterial growth by utilising wavelength of light not absorbed
by the overlying phytoplankton because the purple and green sulphur bacteria obtain electrons from
hydrogen sulphide at lower energy loss than water splitting photoautotrophs and thus require lower light
intensities for carrying out photosynthesis. Conditions in the euphotic zone (area of light penetration) are
favourable for the growth of photoautotrophs.
The bottom of the lake (benthos) represents the interface between hydrosphere and lithosphere.
Sedimented organisms in the profundal zone are largely secondary producers and are dependent on the
transport of organic compounds from the overlying zone. Particulate nutrients sedimented by gravitational
forces concentrate on the surface of the sediment. Growth occurs on the sand grains (sediment) if they are
relatively undisturbed by currents and wave action.
Flora consists of bacteria and small diatoms (Fragilaria, Opephora). There are also some motile organisms
like diatoms (Nitzhia), cyanobacteria and bacteria. In a fresh water lake, mud found at the sediment, the
acidity, water type and the nutrient status controls the microorganisms found there. All muds have diatoms
as the major group of microflora. Bacteria are more on the surface and anaerobes are found for some depth
in the mud. Oxygen can diffuse only very slowly in the waterfilled pore spaces of sediments.
Concentration of inorganic nutrients (nitrogen and phosphorus) are important in determining the ability of
the habitat to support microbial growth and metabolism. Salt concentration of water and pH also influence
the characteristic autochthonous microbes of some lakes with high salt concentration (28%) to develop
halophilic (organisms which can grow at high salt concentrations) population (archaea and some algae,
e.g. Dunaliella).
Structure of the Lotic Habitat
Running or moving water or lotic ecosystems include rivers, streams and related environment. They are
remarkably variable, ranging in size from large rivers to the trickling small springs.
The lotic habitat is primarily determined by the velocity of the current which can create either slow-
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moving or fast-moving streams; each has very distinct characteristics. The base of the food chain is
dependent on detritus from upstream or from the edges. In slow-moving streams, plant and animal
communities largely resemble those found in lentic (lake and pond) habitats.
The significant phytoplankton populations that usually exist contribute to a higher rate of primary
productivity than that found in fast-moving streams. The level of productivity is dependent upon water
temperature and the amount of nutrient input received from the surrounding environment, and therefore
subject to seasonal variation. The diversity of consumer organisms varies according to the physical
conditions and vegetation. Planktonic populations are relatively high, although not as dense as those found
in lakes. In fast-moving streams, there is very little primary production in the open-water habitat, due to
the velocity and turbulence of the current. Populations of consumer organisms (mainly particulate feeders)
are low. Riffle areas provide valuable habitat for juvenile trout and salmon. Pools are important resting
areas for several fish species, including Atlantic salmon. The quality of these areas can be adversely
affected when shade trees are removed from the banks.
Successional Sequence
The normally understood process of ecological succession does not apply to open water. In slow-moving
streams, the development of habitat depends upon the depositional and erosional characteristics of the
river. The fast flowing, young streams will always be present as the river erodes the landscape. Over time,
the young stream will mature into a slow-moving stream, but it can be rejuvenated when a geological
obstacle (e.g. a waterfall) is encountered. In mature streams, there is a progressive downstream movement
of meanders, leaving shallow or deep pools, backwaters, braided channels and oxbow ponds. There is an
associated change in the character of the open water
Biota of the Lotic Habitat
Vegetation in the lotic open-water habitat consists mainly of phytoplankton found in slow-moving
streams. There are no plankton species unique to rivers; those found there originate mostly from
backwaters or lakes. Several species of desmids and diatoms present in slow-moving rivers, although not
as abundant as in lakes.
Some zooplankton species and rotifers can be found in slow-moving streams. Their abundance depends on
the amount of the predation from invertebrates and small fish. Fish species such as redbelly dace and
white sucker, and introduced species such as brown trout are commonly found in slow-moving streams.
Fast-moving streams provide excellent habitat for many kinds of fish, including brook trout, Atlantic
salmon parr, common shiner, white suckers and yellow perch.
Several factors affect the microbial flora of stored waters. These are as follows
Sedimentation:
Microorganisms have a specific gravity slightly greater than that of' water, and therefore slowly settle
down. However, the most important factor is their attachment to suspended particles. Microorganisms are
removed from the upper layers of the water as the suspended particles settle down.
Activities of other organisms:
Predatory Protozoa engulf living or dead bacteria for food, provided the water contains sufficient
dissolved oxygen.
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Light ray: Direct sunlight is toxic to both vegetative cells and spores of microorganisms. The toxicity
of ultraviolet rays is inversely proportional to the turbidity of water. In tropical countries direct sun light is
a very effective sterilizing agent.
Temperature. Temperature has variable effects. It may kill some organisms and may stimulate the
growth of others. During colder months the multiplication rate of microorganisms is considerably reduced.
Food supply. If there is considerable vegatation or suspended food particles in the body of water, it is
likely to increase the number of organisms. On the other hand, certain toxic substances may bring about
marked reduction in the number of, organisms.
Microflora of Different Water
Unpolluted
Actinomycetes
Yeasts
Bacillus spores
Clostridium spores
Cellulose digesters
Autotrophic bacteria
Euglena
Paramecium
Polluted
Coliform bacteria
Escherichia coli
Desulfovibrio sp.
Clostridium sp.
Fecal streptococcci
Pritozoan cysts
Blue-green algae
Enteric viruses
Marine
Halophilic organisms
Psychrophilic organisms
Diatoms
Dinoflagellates
Mold spores
Pseudomonas sp.
Forminiferans
Luminous microbes
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Microbial Communities in Aquatic Environments- Various habitats can be recognized within
an aquatic environment and their actual size may vary from one another. Each habitat is
characterized by one or more microbial communities and thus the microorganisms within an
aquatic environment can be grouped as distinct communities.
Neuston - The microorganisms which are found at the surface of an aquatic environment,
exactly at the air-water interface, are referred to as neuston.
Pleuston - specific term pleuston may be used to denote the organisms occupying the air-water
interface in a marine biota. These neuston and pleuston can be regarded as specialized
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communities as their air-water interface habitat is subjected to widely fluctuating
environmental conditions.
Plankton - Plankton refers to the free floating microorganisms, which are maintained in the
water column. An important criterion for the plankton is that they should exist, at least for a
part of their life, free in the open water. It should not include stray organisms washed in from
the surrounding land or from other aquatic environments.
Phytoplankton - Plankton can also be classified on the basis of the constituent organisms and
their feeding habits. Phytoplankton includes photosynthetic forms like algae.
Usually phytoplankton occupies the top layers of water bodies where light is available to carry
out photosynthesis. Phytoplanktons are the major primary producers in an aquatic environment
and they convert the radiant energy into chemical energy.
Zooplankton - Zooplanktons are found in regions just below that of phytoplanktons.
Zooplanktons are motile forms with cilia or flagella and show vertical migration.
Vertical Migration - Zooplanktons are motile forms with cilia or flagella and show vertical
migration. During day time and feed on their prey.
Diurnal Migration - Zooplanktons are motile forms with cilia or flagella and show vertical
migration. During day time and feed on their prey. Thus they exhibit a diurnal migration.
Sometimes, bacteria in the water column may be considered as a separate planktonic group
which are called bacterioplankton.
Bacterioplankton - The second group namely zooplankton consists mainly of protozoans which
feed on phytoplanktons, bacteria and detritus. Zooplanktons are found in regions just below
that of phytoplanktons they try to escape from light and sink to the bottom regions. During
night they come to the surface Zooplanktons are motile forms with cilia or flagella and show
vertical
migration.
During day time and feed on their prey. Thus they exhibit a diurnal migration. Sometimes,
bacteria in the water column may be considered as a separate planktonic group which are called
bacterioplankton.
Seston Epipelon- Seston produced by nekton, i.e. large swimming animals, may also act as a
habitat along with other organic debris. Microorganisms inhabiting these detritus matters and
other fine sediment surface are referred to as epipelon.
Epibiotic Communities Epibacteria Periphytes - Inanimate as well as animate surfaces also
provide habitats for microorganisms. These attached microorganisms are referred to as epibiotic
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communities. Sometimes the attached bacteria are also referred to as epibacteria or
periphytes. In contrast to the epibiotic community, endobiotic community inhabits the tissues of
larger aquatic forms. Microorganisms belonging to this community may exhibit a mutualistic or
parasitic relationship with the host organisms.
Epizooic Community Epiphyton- The term epizooic community is also used to denote the
microorganisms associated with aquatic animals. Similarly, epiphyton refers to microorganisms
found on various aquatic plants and algae.
Epilithon Epixylon Episammon- Epilithon is another community which includes the attached
microorganisms found on the rocks and stones of the aquatic environment. Epixylon refers to
the microorganisms found on the fallen woods in water bodies. Sand grains also support
microbial growth and the associated microorganisms are referred to as episammon.
Benthic Community Benthos-Organisms inhabiting the bottom sediment of aquatic
environments constitute the benthic community or benthos.
Peleagic Community-Apart from these, a separate waterborne community has also been
recognized which occurs at precise depths. It is referred to as pelagic community. Starting from
the surface of water and descending to the bottom four different pelagic habitats occur. They are
epipelagic, mesopelagic, bathypelagic and abyssopelagic.
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