AQUATIC MICROBIOLOGY

It describe about the fresh and marine water microbial communities.

1. AQUATIC MICROBIOLGY
Aquatic microbiology deals with study of microbes of aquatic system such as fresh or salt
water systems. It includes microscopic plants, animals, bacteria, viruses and fungi and their
behavior, relation with other organisms in aquatic environment.
Aquatic Ecology is the scientific study of how organisms interact with each other and with their
environment. This includes relationships between individuals of the same species, between
different species, and between organisms and their physical and chemical environments. Aquatic
ecology includes the study of these relationships in all aquatic environments, including oceans,
estuaries, lakes, ponds, wetlands, rivers, and streams.
An ecosystem is a community of living organisms and their physical and chemical environment,
linked by flows of energy and nutrients.
The physical characteristics of aquatic habitats affect the types of organisms found there. Living
organisms in a particular environment are directly affected by environmental characteristics such
as nutrient concentrations, temperature, water flow, and shelter. Only the organisms that are able
to survive in the conditions of a particular habitat and use the resources available there will
thrive.
Interactions between living organisms also affect the type of organisms found in an aquatic
ecosystem, as competition for resources (e.g., food, habitat) and predation affects species
abundance and diversity. In turn, the living organisms in an environment can influence some
aspects of their environment (e.g., beaver dams can change water flows).
FRESH WATER ECOSYSTEM MARINE WATER ECOSYSTEM

2. MARINE WATER ENVIRONMENT
The marine environment supplies many kinds of habitats that support life. Marine life partially
depends on the saltwater that is in the sea (“marine” comes from the Latin “mare,” meaning sea
or ocean).
A habitat is an ecological or environmental area inhabited by one or more living species. Marine
habitats can be divided into coastal and open ocean habitats.
 Coastal habitats are found in the area that extends from as far as the tide comes in on the
shoreline, out to the edge of the continental shelf. Most marine life is found in coastal
habitats, even though the shelf area occupies only seven percent of the total ocean area.

 Open ocean habitats are found in the deep ocean beyond the edge of the continental
shelf.
Alternatively, marine habitats can be divided into pelagic and demersal habitats.
 Pelagic habitats are found near the surface or in the open water column, away from the
bottom of the ocean. An organism living in a pelagic habitat is said to be a pelagic
organism, as in pelagic fish.

 Demersal habitats are near or on the bottom of the ocean. Similarly, an organism living
in a demersal habitat is said to be a demersal organism, as in demersal fish.


Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp,
mangroves and sea grasses, are ecosystem engineers, which reshape the marine environment to
the point where they create habitats for other organisms.
Marine habitats include coastal zones, intertidal zones, sandy shores, rocky shores, mudflats,
swamps and salt marshes, estuaries, kelp forests, sea grasses, and coral reefs. In addition, in
the open ocean there are surface waters, deep sea and sea floor.
 Intertidal zones (those areas close to shore) are constantly being exposed and covered by
the ocean’s tides. A huge array of life lives within this zone.
 Sandy shores also called beaches are coastal shorelines where sand accumulates. Waves
and currents shift the sand, continually building and eroding the shoreline. Long shore
currents also commonly create offshore bars, which give beaches some stability by
reducing erosion.
 The rocky shores seem to give them a permanence compared to the shifting nature of
sandy shores. In contrast to sandy shores, plants and animals can anchor themselves to
the rocks.

3.  Mudflats are coastal wetlands that form when mud is deposited by tides or rivers. They
are found in sheltered areas such as bays, bayous, lagoons, and estuaries.
 Mangrove swamps and salt marshes form important coastal habitats in topical and
temperate areas respectively. An estuary is a partly enclosed coastal body of water with
one or more rivers or streams flowing into it, and with a free connection to the open sea.
 Kelp forests are underwater areas with a high density of kelp. They are recognized as
one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored
kelp are called kelp beds. Kelp forests occur worldwide throughout temperate and polar
coastal oceans.
 Seagrasses are flowering plants from one of four plant families which grow in marine
environments. They are called sea grasses because the leaves are long and narrow and are
very often green, and because the plants often grow in large meadows, which look like
grassland.
 Reefs comprise some of the densest and most diverse habitats in the world. The best-
known types of reefs are tropical coral reefs, which exist in most tropical waters;
however, reefs can also exist in cold water. Reefs are built up by corals and other
calcium-depositing animals, usually on top of a rocky outcrop on the ocean floor. Reefs
can also grow on other surfaces; this has made it possible to create artificial reefs. Coral
reefs also support a huge community of life, including the corals themselves, their
symbiotic zooxanthellae, tropical fish, and many other organisms.
Planktonic Communities
 Plankton (singular plankter) are any organisms that live in the water column and are
incapable of swimming against a current.
 They provide a crucial source of food to many large aquatic organisms, such as fish and
whales.
 These organisms include drifting animals, plants, archaea, algae, or bacteria that inhabit
the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton is defined by
their ecological niche rather than Phylogenetic or taxonomic classification.
Although many planktic (planktonic) species are microscopic in size, plankton consists
organisms covering a wide range of sizes, including large organisms such as jellyfish.
Plankton is primarily divided into broad functional (or trophic level) groups:
 Phytoplankton
 Zooplankton
 Bacterioplankton

4. 1. Phytoplankton:
(From Greek phyton, or plant), autotrophic, prokaryotic, or eukaryotic algae live near the
water surface where there is sufficient light to support photosynthesis. Among the more
important groups are the diatoms, cyanobacteria, dinoflagellates, and coccolithophores.
2. Zooplankton:
(From Greek zoon, or animal), it is small protozoan’s or metazoans (e.g. crustaceans and
other animals) that feed on other plankton and telonemia. Some of the eggs and larvae of
larger animals, such as fish, crustaceans, and annelids, are included here.
3. Bacterioplankton:
Bacteria and archaea, which play an important role in remineralising organic material
down the water column (note that the prokaryotic phytoplanktons are also
Bacterioplankton).
Freshly hatched fish larvae are also plankton for a few days as long as they cannot swim against
currents. Zooplankton are the initial prey item for almost all fish larvae as they switch from their
yolk sacs to external feeding. Fish rely on the density and distribution of zooplankton to match
that of new larvae, which can otherwise starve.
Natural factors (e.g., current variations) and man-made factors (e.g. river dams) can strongly
affect zooplankton, which can in turn strongly affect larval survival and therefore breeding
success.
Planktonic Food Webs
Plankton communities are divided into broad categories of producer, consumer, and recycler
groups. Primarily by grazing on phytoplankton, zooplankton provides carbon to the planktic food
web, either respiring it to provide metabolic energy, or upon death as biomass or detritus.
Typically more dense than seawater, organic material tends to sink. In open-ocean ecosystems
away from the coasts this transports carbon from surface waters to the deep. This process is
known as the biological pump, and is one reason that oceans constitute the largest carbon sink
on Earth.
The growth of phytoplankton populations is dependent on light levels and nutrient availability.
Freshly-hatched fish larvae are also plankton for a few days as long as they cannot swim against
currents. Zooplankton are the initial prey item for almost all fish larvae as they switch from their
yolk sacs to external feeding. Fish rely on the density and distribution of zooplankton to match
that of new larvae, which can otherwise starve.

5. Natural factors (e.g., current variations) and man-made factors (e.g. river dams) can strongly
affect zooplankton, which can in turn strongly affect larval survival, and therefore breeding
success.
Ocean Floor
Ocean floor extremophiles chemosynthetic microbes provide energy and carbon to the other
organisms in these environments.
Microbial life plays a primary role in regulating biogeochemical systems in virtually all of our
planet‘s environments, including some of the most extreme, from frozen environments and acidic
lakes, to hydrothermal vents at the bottom of deepest oceans, and some of the most familiar, such
as the human small intestine.
Microbes, especially bacteria, often engage in symbiotic relationships (either positive or
negative) with other organisms, and these relationships affect the ecosystem. One example of
these fundamental symbioses is chloroplasts, which allow eukaryotes to conduct photosynthesis.
Chloroplasts are considered to be endosymbiotic cyanobacteria, a group of bacteria that are
thought to be the origins of aerobic photosynthesis.
They are the backbone of all ecosystems, but even more so in the zones where light cannot
approach and therefore photosynthesis cannot be the basic means to collect energy. In such
zones, chemosynthetic microbes provide energy and carbon to the other organisms. Other
microbes are decomposers, with the ability to recycle nutrients from other organisms’ waste
products. These microbes play a vital role in biogeochemical cycles. The nitrogen cycle, the
phosphorus cycle and the carbon cycle all depend on microorganisms in one way or another. For
example, nitrogen which makes up 78% of the planet’s atmosphere is “indigestible” for most
organisms, and the flow of nitrogen into the biosphere depends on a microbial process called
fixation.
Large deep sea communities of marine life have been discovered around black and white
smokers – hydrothermal vents emitting typical chemicals toxic to humans and most of the
vertebrates. This marine life receives its energy from both the extreme temperature difference
(typically a drop of 150 degrees) and from chemosynthesis by bacteria. In depths, water pressure
is extreme. There is no sunlight, but some life still exists.
Cold-Seep Ecosystems
A cold seep is an area of the ocean floor where hydrogen sulfide, methane, and other
hydrocarbon-rich fluid seepage occurs.
A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide,
methane, and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool.

6. Cold seeps develop unique topography over time, where reactions between methane and
seawater create carbonate rock formations and reefs. These reactions may also be dependent on
bacterial activity.
Organisms living in cold seeps are known as extremophiles.
The first type of organism to take advantage of this deep-sea energy source is bacteria.
Aggregating into bacterial mats at cold seeps, these bacteria metabolize methane and hydrogen
sulfide (another gas that emerges from seeps) for energy. This process of obtaining energy from
chemicals is known as chemosynthesis.
This microbial activity produces calcium carbonate (CaCO3), which is deposited on the seafloor
and forms a layer of rock.
The Deep Sea and Barophilism
A piezophile (also called a barophile) is an organism which thrives at high pressures, such as
deep sea bacteria or archaea.
The three main sources of energy and nutrients for deep sea communities are marine snow,
whale falls, and chemosynthesis at hydrothermal vents and cold seeps.
A zone of the deep sea includes;
 The mesopelagic zone – 200 Meter
 The bathyal zone – 1000 Meter
 The abyssal zone – 4000 Meter
 The hadal zone – 6000 Meter
They are generally found on ocean floors, where pressure often exceeds 380 atm (38 MPa).
Some have been found at the bottom of the Pacific Ocean where the maximum pressure is
roughly 117 MPa. The high pressures experienced by these organisms can cause the normally
fluid cell membrane to become waxy and relatively impermeable to nutrients. These organisms
have adapted in novel ways to become tolerant of these pressures in order to colonize deep sea
habitats. One example, xenophyophores, has been found in the deepest ocean trench, 6.6 miles
(10,541 meters) below the surface.
Barotolerant bacteria are able to survive at high pressures, but can exist in less extreme
environments as well. Obligate barophiles cannot survive outside of such environments. For
example, the Halomonas species Halomonas salaria requires a pressure of 1000 atm (100 MPa)
and a temperature of three degrees Celsius. Most piezophiles grow in darkness and are usually
very UV-sensitive; they lack many mechanisms of DNA repair.

7. Sea Coral and Sea Anemone Zooxanthellae
Zooxanthellae refer to a variety of species that form symbiotic relationships with other marine
organisms, particularly coral.
Symbiodinium are colloquially called “zooxanthellae” (or “zoox”), and animals symbiotic with
algae in this genus are said to be “zooxanthellate”. The term was loosely used to refer to any
golden-brown endosymbionts, including diatoms and other dinoflagellates. These unicellular
algae commonly reside in the endoderm of tropical cnidarians such as corals, sea anemones, and
jellyfish, where they translocate products of photosynthesis to the host and in turn receive
inorganic nutrients (e.g. CO2, NH4+). They are also harbored by various species of sponges,
flatworms, mollusks (e.g. giant clams), foraminifera (soritids), and some ciliates. Generally,
these dinoflagellates enter the host cell through phagocytosis, persist as intracellular symbionts,
reproduce, and disperse to the environment (note that in most mollusks, Symbiodinium are inter-
rather than intra-cellular). Cnidarians that are associated with Symbiodinium occur mostly in
warm oligotrophic (nutrient-poor) marine environments where they are often the dominant
constituents of benthic communities. These dinoflagellates are therefore among the most
abundant eukaryotic microbes found in coral reef ecosystems.
Symbiodinium are known primarily for their role as mutualistic endosymbionts. In hosts, they
usually occur in high densities, ranging from hundreds of thousands to millions per square
centimeter. Each Symbiodinium cell is coccoid in hospite (living in a host cell) and surrounded
by a membrane that originates from the host cell plasma lemma during phagocytosis. This
membrane probably undergoes some modification to its protein content, which functions to limit

8. or prevent phago-lysosome fusion. The vacuole structure containing the symbiont is therefore
termed the symbiosome, and only a single symbiont cell is found within each symbiosome. It is
unclear how this membrane expands to accommodate a dividing symbiont cell. Under normal
conditions, symbiont and host cells exchange organic and inorganic molecules that enable the
growth and proliferation of both partners.







Sponge Communities
Sponge reefs serve an important ecological function as habitat, breeding and nursery areas for
fish and invertebrates.
Sponge reefs serve an important ecological function as habitat, breeding, and nursery areas for fish and
invertebrates. The reefs are currently threatened by the fishery, offshore oil, and gas industries. Attempts
are being made to protect these unique ecosystems through fishery closures, and potentially the
establishment of Marine Protected Areas (MAPs) around the sponge reefs.
Sponge Reefs
Each living sponge on the surface of the reef can be over 1.5 m tall. The reefs are composed of
mounds called “bioherms” that are up to 21 m high, and sheets called “biostromes” that are 2-
10 m thick, and may be many km wide. The growth of sponge reefs is thus analogous to that of
coral reefs.
Dead sponges become covered in sediment, but do not lose their supportive siliceous skeleton.
The sponge sediments have high levels of silica and organic carbon. The reefs grow parallel to
the glacial troughs, and the morphology of reefs is due to deep currents.
Microbial Community In Marine Ecosystem
These microbes can be divided up between three main groups, which are three domains of living
things on this planet:

9.  Bacteria
 Archaea, which look similar to bacteria, but are an entirely separate domain.
 Eukaryotes, a group that includes animals, plants, fungi, protists, and algae.
The microbes listed below are grouped by these three domains. Within each domain, they are
grouped according to their roles in nitrogen cycling. These microbes are important for nitrogen
cycling in that they “assimilate” nitrogen and convert it into living tissue or “particulate
nitrogen.”
Several terms are used to describe microbes that perform certain roles in nitrogen cycling, but
which may or may not be related to one another. The bacteria and archaea that can convert
nitrogen gas into more biologically useful forms such as ammonium are known as “nitrogen
fixers” or “diazotrophs.” Microbes that convert ammonium to nitrate is called “nitrifying
organisms.”
MARINE BACTERIA
Marine bacteria are single-celled organisms that can be shaped like little spheres, rods, or (less
commonly) spirals. They are often very small, with cell diameters of just a few microns (about
1/100th the width of a human hair). They perform all kinds of chemical processes in the open
ocean, including most of the steps in nitrogen cycling.
Cyanobacteria are a large group of photosynthetic bacteria, some of which can “fix” nitrogen,
converting nitrogen gas into more biologically useful compounds. Cyanobacteria live in all kinds
of environments, but are especially important in open-ocean ecosystems. They were formerly
known as “blue-green algae” but are now recognized as a type of bacteria, not a type of algae
(algae are eukaryotes).
MARINE BACTERIA THAT “FIX” NITROGEN
Trichodesmium
Trichodesimium is a genus of colonial cyanobacteria that is one
of the most important and well -studied nitrogen-
fixing organisms found in open-ocean areas such as Station
ALOHA. It is one of the few organisms involved in the oceanic
nitrogen cycle that is visible to the naked eye. Trichodesmium is
a colonial organism that forms hair-like strands, which
sometimes aggregate into tiny “puffballs” up to a millimeter or
two across. When winds are light, Trichodesmium colonies may
clump together and float right on the sea surface, where they are known as “sea sawdust.”
Trichodesmium uses an enzyme called “nitrogenase” to transform nitrogen gas into more
biologically useful compounds (a process called “nitrogen fixation.”) However, nitrogenase is
inactivated in the presence of oxygen (which is produced by many photosynthetic organisms as a
byproduct of photosynthesis). Because of this, most nitrogen-fixing microbes separate the

10. processes of nitrogen fixation and photosynthesis either spatially (using different types of cells
for each process), or temporally, by performing photosynthesis in the daytime and fixing
nitrogen at night.
Trichodesmium, however, uses neither of these strategies. It is able to fix nitrogen during the
daytime, but does not have specialized cells to perform the job. Researchers are very interested
in figuring out how Trichodesmium is able to fix nitrogen in the daytime.
Heterocystus cyanobacteria
Heterocystus cyanobacteria are multi-celled organisms that form microscopic filaments and
perform nitrogen fixation in the open ocean. The most common genus of heterocystus
cyanobacteria in open-ocean areas is Richelia, which is almost always found living inside of
diatoms, a type of microscopic marine algae.
As part of this “symbiotic” living arrangement, the heterocystus cyanobacteria provide the
diatoms with “fixed” nitrogen and other nutrients. It is not entirely clear what the bacteria get out
of the arrangement.
Like all nitrogen fixing organisms, heterocystus cyanobacteria use an enzyme called
“nitrogenase” to transform nitrogen gas into more useable forms of nitrogen. However,
nitrogenase is inhibited in the oxygen-rich environment that exists inside most cells. As multi-
cellular organisms, heterocystus cyanobacteria have evolved specialized cells called
“heterocysts,” which provide an environment more conducive to nitrogen fixation.
Crocosphaera
Crocosphaera is a genus of singled-celled cyanobacteria that lives through photosynthesis and
can “fix” nitrogen. It grows in many tropical ocean areas where the water is about 24° Celsius
(75° Fahrenheit). At about two to four microns across, Crocosphaera is much smaller
than Trichodesmium. Like all nitrogen-fixing organisms, Crocosphaera uses an enzyme called
“nitrogenase” to transform nitrogen gas into more biologically useful compounds. However,
nitrogenase doesn’t work well in the presence of oxygen (a byproduct of photosynthesis). As a
solution to this problem, Crocosphaera performs photosynthesis during the day and nitrogen
fixation at night.
Alphaproteobacteria and gammaproteobacteria
Proteobacteria are an extremely diverse group of bacteria. Some alphaproteobacteria and
gammaproteobacteria, two subgroups within the proteobaceria, carry the nifH gene, and may be
able to fix nitrogen. The proteobacteria also include some key players in the process of
“nitrification,” as described below.
MARINE BACTERIA INVOLV ED IN NITRIFICATION
Ammonium oxidizing bacteria (AOB)

11. The ammonium oxidizing bacteria (AOB) are bacteria that are all involved in a specific
biochemical process (nitrification), but which may or may not be related to one another. They are
involved in the first step of nitrification—the conversion of ammonium to nitrite (also known as
“ammonium oxidation”).
Most of the known ammonium oxidizing bacteria is betaproteobact eria and
gammaproteobacteria. These bacteria are believed to be involved in this process because they
carry a gene that codes for the ammonia monooxygenase enzyme (amoA).
Nitrite oxidizing bacteria
Several different genera of marine bacteria are involved in in the second step in the nitrification
process—converting nitrite to nitrate (also known as “nitrite oxidation”). These
include Nitrobacter, Nitrospira, and Nitrospina. Of these, Nitrospira is believed to be the most
important in the open ocean.
MARINE BACTERIA THAT ARE PRIMARY PRODUCERS BUT DO NOT FIX
NITROGEN
Prochlorococcus
This scanning electron microscope image, taken by Claire
Ting, shows several Prochlorococcus cells, including one in the
process of dividing.
Prochlorococcus is a genus of cyanobacteria that is very
common in open-ocean areas around the world. Although
extremely tiny, with cells only 0.5 to 0.8 microns
across, Prochlorococcus (along with another
genus, Synechococcus) are so widespread and abundant that
may produce a third of the oxygen in the Earth’s
atmosphere. Prochlorococcus are “obligate photoautotrophs,”
obtaining all of their energy through photosynthesis. However, they require nitrogen as a
nutrient, and can use either nitrate or ammonium as a source of nitrogen. Thus, they are a key
part of the “assimilation” process in oceanic nitrogen cycles.
Synechococcus
Synechococcus is another common type of marine cyanobacteria. It is arguably the second most
common group of photosynthetic marine bacteria, after Prochlorococcus. It has a similar shape
as Prochlorococcus, but is typically a little bit larger, at 0.8 to 1.5 microns across.
Like Prochlorococcus, Synechococcus are “obligate phototrophs,” which means that they can
only obtain energy through photosynthesis, and require nitrate as a key nutrient. They can use
nitrate or ammonium as sources of nitrogen, and are a key part of the “assimilation” process in
oceanic nitrogen cycles.

12. MARINE ARCHAEA
Archaea are single celled organisms that look similar to bacteria, but which are in an entirely
separate biological domain. Historically, archaea were thought of as living mostly in extremely
hot, acidic, or low oxygen environments. However, in the last decade, using DNA and RNA
analysis, molecular biologists have found them to be very common in both freshwater and
saltwater environments.
Ammonium oxidizing archaea (AOA)
Like ammonium oxidizing bacteria, ammonium oxidizing archaea are important in the
nitrification process in open-ocean areas. They perform the first step of nitrification—the
conversion of ammonium to nitrite, which is also known as “ammonium oxidation.” In the
process of performing ammonium oxidation process, AOA may produce nitrous oxide, a
greenhouse gas that is sometimes released from open-ocean waters into the atmosphere.
All of the known ammonium oxidizing archaea are in the group Thaumarchaea (formerly known
as Crenarchaeota). These archaea are common in soils, in estuaries, and in the deeper parts of
the open ocean, where there is little light and oxygen concentrations are relatively low.
Like ammonium oxidizing bacteria (AOB), AOA are able to make an enzyme called ammonia
monooxygenase. Researchers often use DNA analysis to determine if a sample of seawater
contains the gene (amoA) that allows AOA and AOB to produce ammonia monooxygenase.
Once they identify organisms with this gene, the researchers can use genetic probes to tell if the
organisms are bacteria or archaea.
FRESHWATER ENVIRONMENT
Fresh water is naturally occurring water on the Earth’s surface in ice sheets, ice caps, glaciers,
bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and
underground streams. Fresh water is generally characterized by having low concentrations of
dissolved salts and other total dissolved solids. The term specifically excludes seawater and
brackish water but it does include mineral rich waters such as chalybeate springs. The term
“sweet water” has been used to describe fresh water in contrast to salt water.
Scientifically, freshwater habitats are divided into 2 categories;
 Lentic systems, which are the Stillwater’s including ponds, lakes, swamps and mires
 Lotic systems, which are running water and groundwater which flows in rocks and
aquifers.

13. Fresh water creates a hypotonic environment for aquatic organisms. This is problematic for some
organisms with pervious skins or with gill membranes, whose cell membranes may burst if
excess water is not excreted. Some protists accomplish these using contractile vacuoles, while
freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a
limited ability to regulate their osmotic balance and therefore can only live within a narrow range
of salinity, diadromous fish have the ability to migrate between fresh water and saline water
bodies. During these migrations they undergo changes to adapt to the surroundings of the
changed salinities; these processes are hormonally controlled. The eel (Anguilla anguilla) uses
the hormone prolactin, while in salmon (Salmo salar) the hormone cortisol plays a key role
during this process.
Many sea birds have special glands at the base of the bill through which excess salt is excreted.
Similarly the marine iguanas on the Galápagos Islands excrete excess salt through a nasal gland
and they sneeze out a very salty excretion.
Fresh water habitat is home to a plethora of microbes such as Proteobacteria, Actinobacteria,
Cyanobacteria, and Bacteroidetes. These microbes help sequester inorganic compounds,
mineralize nitrogen, and decompose organic matter, as well as other important processes.
Microbial community in fresh water
The microbial community in freshwater lakes is as diverse as any other ecosystem found on
earth. These microbes have found a way to take advantage of the different resources provided
from lake habitats oppose to terrestrial soil habitats microbes are usually thought to live. The
main players are Proteobacteria, Cyanobacteria, Actinobacteria, and Bacteroidetes. All of these
different microbes contribute to important processes carried out in freshwater lakes.
Proteobacteria
This is the most abundant and commonly found group of microbes in freshwater lakes. Taxa
include Rickettsia prowazekii, Coxiella burnetti, and Wolinella succinogenes. Proteobacteria is
broken up into alpha-, beta-, delta-, and gammaproteobacteria, each with their own distinct
characteristics.
Alpha/Gammaproteobacteria
Alphaproteobacteria and Gammaproteobacteria are mostly commonly found in marine habitats,
but still can be found in freshwater water columns. They tend to be phototrophic and contribute
to increasing the amount of dissolved oxygen in a lake. Taxa
include Acetobacter and Acinetobacter for Alphaproteobacteria and Gammaproteobacteria
respectively.
Betaproteobacteria
Betaproteobacteria are most common of the proteobacteria in lakes. They consist of
Chemolithotrophes and phototrophs, which in some places makes up 60% of the
bacterioplankton. They also play an important role in nitrogen fixation and oxidation of
ammonium Taxa include Alcaligenes and Nitrosomonas

14. Deltaproteobacteria
Deltaproteobacteria tend to live in anaerobic conditions such as the bottom of lakes or in
sediment and they commonly reduce sulfur as a source of energy. Taxa
include Desulfovibrio and Geobacter.
Cyanobacteria
Cyanobacteria are bacteria that carry out photosynthesis. They tend to be the dominant bacterial
phototrophs in open parts of a lake and are important in the carbon cycle, but also the nitrogen
cycle because some are capable of nitrogen fixation.
Actinobacteria
This microbe can be found in a wide range of aquatic conditions. They are decomposers of
organic matter and tend to favor conditions with low concentrations of organic carbon because
they can be outcompeted when carbon concentration rise.
Bacteroidetes
This microbe is a commonly particle associated in bacterial communities. They are found at the
bottom of lakes where they can degrade larger molecules.

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 https://courses.lumenlearning.com/boundless-microbiology/chapter/aquatic-
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