the Biogeochemical cycle, iron cycle and phosphorus cycle and the association of microbes

1. GEOCYCLE OF IRON AND PHOSPHORUS
MUMTHAS P K
2nd MSc MICROBIOLOGY

2.  Any biological element thus undergoes a continuous cycle, called
“biogeochemical cycle”, in which it passes alternately from a mineral,
non-living status to a status of living matter.
 Here the chemical substances moves through both Biotic(biosphere) and
Abiotic (lithosphere , atmosphere and hydrosphere) compartments of
earth.
 The oxidation state of organic elements such as carbon, nitrogen, or
sulfur forms can also be modified without being incorporated into living
organisms because these elements can be used as electron donors or
acceptors.

3.  This is valid for almost all natural elements susceptible to serve as
electron donors or acceptors (e.g., arsenic), or to be modified as a
consequence of a biological activity.
 The elemental composition of living matter is very different from the
composition of the three compartments of the biosphere .
 For mineral forms, transformation during the biogeochemical cycle can
be performed with or without change of valence.
 The phosphorus atom, for example, does not change valence unlike
carbon, oxygen, nitrogen, sulfur, iron or manganese etc.

4.  The use of an element will not always depend on its concentration in the
environment but its chemical status.
 The global cycle of an element can be expressed as the speed of movement
of an element from a compartment to another, each of which is
considered a “black box” or a reservoir where the elements are stored for a
period of time (residence time).
 The term reservoir can be applied to different compartments of the
biosphere (e.g., hydrosphere, lithosphere, atmosphere) or to the different
trophic levels of a food chain.

5.  The speed of transfer from one compartment to another, so-called
“flow”, provides quantitative information on the intensity of a
biogeochemical cycle.
 Particles are aggregates at sites of intense microbial activity often called
“hotspots”.
 CYCLING ELEMENTS
Macronutrients : required in relatively large amounts; Carbon,
Hydrogen, Oxygen, Nitrogen, Phosphorus, sulphur, potassium, calcium,
Iron, Magnesium etc.
Micronutrients : required in very small amounts but are still essential.
Boron , Copper, Molybdenum etc.

6. TYPES OF BIOGEOCHEMICAL CYCLE
Biogeochemical can be classified as ;
Gaseous cycle:
the term gaseous cycle refers to the transformation of gases between various
biogeochemical reservoirs : hydrosphere , atmosphere and biosphere.
Important cycles are :
 Nitrogen cycle
 Oxygen cycle
 Carbon cycle

7. Sedimentary cycle:
Sedimentary cycles include the leaching of minerals and salts from the
earth’s crust, which settle as sediment or rock before the cycle repeats.
Sedimentary cycle includes :
 Phosphorus cycle
 Sulphur cycle
 Iron cycle
 Calcium cycle
Sedimentary cycle vary from one elements to another, but each cycle
consists fundamentally of a solution phase and a sediment phase.

9.  Microorganisms will have a key role in the
functioning and transformation of
biogeochemical cycles and consequently, of
ecosystems.
 they are involved in almost all steps of the
cycles and they are the sole organisms
capable of performing some of these steps.
 In their absence, all essential elements for life
would remain trapped in organic molecules
of cadavers and wastes.
Role of Microorganisms in Biogeochemical Cycles

10.  Many microorganisms are involved in the biogeochemical cycles of metals
and metalloids, primarily by modifying their oxidation level and/or their
chemical forms.
 Among these elements, some are essential to life (iron, manganese, cobalt)
while others are toxic at low doses (mercury, cadmium, arsenic).
 Their biological transformations are typically related either to energetic
metabolisms (donor or electron acceptor) or to resistance and
detoxification mechanisms.
 Metals and metalloids are also subject to non-enzymatic redox reactions
and it is often difficult to distinguish between changes of biotic origin and
those generated by strictly physico-chemical processes.
Cycles of Metals and Metalloids

11.  The relative importance of these biotic versus abiotic transformations
depends on environmental conditions, such as the presence or absence of
oxygen.
 The standard potential of the couple Fe(III)/Fe(II) at +380 mV. The
oxidized forms of iron Fe(III) and manganese Mn(IV) are excellent
respiratory electron acceptors.
 Microorganisms involved in the dissimilatory reduction of these two
metal is for example Shewanella putrefaciens produces the energy
necessary to its growth by coupling the oxidation of formate into CO2 to
the reduction of iron.

12.  Formateˉ + 2 Fe (III)+ H2O →HCO3 + 2 Fe (II) + 2H+
 In part against the dissimilatory reduction, many bacterial species
derive their energy from the oxidation of iron .
 These organisms can be either aerobic (Thiobacillus spp) or denitrifying
anaerobic chemolithotrophs, or anoxygenic phototrophs (Rhodovulum
robiginosum and Rhodovulum iodosum).

13. Iron in the Environment
Iron is quantitatively the fourth constitutive element of the earth’s crust. It is abundant in
the continents and rare in the oceans where iron resources are often a limiting factor for
primary production and it is less common in oxygenated surface waters .
 Iron is present in the environment as oxides, carbonates, sulfides, and hydroxides.
 Iron is a key micronutrient in primary productivity and a limiting nutrient in the
Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as High-
Nutrient, Low-Chlorophyll (HNLC) regions of the ocean.
 It exists in different oxidation states, ranging from 0 to +VI1 (ferrate), but only two of
these states are involved in biological pathways.
 Fe2+(II) which is the reduced ferrous form, and Fe3+(III) which is the oxidized ferric
form.
1. THE IRON CYCLE

14.  The cycling of iron between its +2 and +3 oxidation states is referred to as the iron
cycle.
 This process can be entirely abiotic or facilitated by microorganisms, especially iron-
oxidizing bacteria.
 The abiotic processes include the rusting of iron-bearing metals, where Fe2+ is
abiotically oxidized to Fe3+ in the presence of oxygen, and the reduction of Fe3+ to
Fe2+ by iron-sulfide minerals.
 The biological cycling of Fe2+ is done by iron oxidizing and reducing microbes.
 Iron is an essential micronutrient for almost every life form.
 It is a key component of hemoglobin, important to nitrogen fixation as part of
the Nitrogenase enzyme family, and as part of the iron-sulfur core of ferredoxin it
facilitates electron transport in chloroplasts, eukaryotic mitochondria, and bacteria.

15.  Iron is an essential element in some enzymes: cytochromes, catalases,
peroxidases, nitrite reductases, and iron-sulfur metalloprotein
complexes.
 It is therefore an essential element in respiratory and photosynthetic
processes.
 The greater part of iron found in the environment is insoluble, the
solubility of ferric ion being very low at physiological pH.
 The solubility of Fe(II) form is substantially greater, but in anoxic
conditions. However, under these conditions, iron is usually precipitated
as black iron sulfide (FeS) or even as pyrite (FeS2), the last one forming a
crystalline structure, highly insoluble and very difficult to oxidize.
 Due to the high reactivity of Fe2+ with oxygen and low solubility of Fe3+,
iron is a limiting nutrient in most regions of the world.

16.  The oxidation of pyrite requires the sum of chemical and biological
reactions involving two electron acceptors: dioxygen and ferric ions.
 In the presence of sulfide (S2) and when anaerobic conditions prevail,
ferric iron (Fe3+) is chemically (i.e. by abiotic processes) reduced to iron
sulfide (FeS) and ferrous iron (Fe2+).
 During this reaction, a small portion of sulfide (S2ˉ) is oxidized to sulfur
which participates in the formation of pyrite by association with sulfide
iron.
 Sulfide iron can be chemically oxidized, in the presence of oxygen, to
ferric iron by releasing sulfur and thiosulfate (S2O3 2ˉ) .

17.  The ocean is a critical component of the Earth's climate system, and the iron
cycle plays a key role in ocean primary productivity and marine ecosystem
function.
 Iron limitation has been known to limit the efficiency of the biological
carbon pump. The largest supply of iron to the oceans is from rivers, where
it is suspended as sediment particles.
 Coastal waters receive inputs of iron from rivers and anoxic
sediments. Other major sources of iron to the ocean include glacial
particulates, atmospheric dust transport, hydrothermal vents and volcanic
ash.
 Iron supply is an important factor affecting growth of phytoplankton, and
the base of marine food web.
Oceanic Iron Sources

18.  In offshore regions, bacteria also compete with phytoplankton for
uptake of iron. Uptake of iron by phytoplankton leads to lowest iron
concentrations in surface seawater.
 Upwelling recycles iron and causes higher deep water iron
concentrations.
 On average there is 0.07±0.04 nmol Fe kg−1 at the surface (<200 m) and
0.76±0.25 nmol Fe kg−1 at depth (>500 m). Therefore, upwelling zones
contain more iron than other areas of the surface oceans.
 Soluble iron in ferrous form is bioavailable for utilization which
commonly comes from aeolian resources.
 Iron primarily present in particulate phases as ferric iron, and the
dissolved iron fraction is removed out of the water column by coagulation.
 For this reason, the dissolved iron pool turns over rapidly, in around 100
years.

19. Terrestrial ecosystems
 The iron cycle is an important component of the terrestrial ecosystems.
The ferrous form of iron, Fe2+, is dominant in the Earth's mantle, core, or
deep crust.
 The ferric form, Fe3+, is more stable in the presence of oxygen gas. Dust
is a key component in the Earth's iron cycle.
 Chemical and biological weathering break down iron-bearing minerals,
releasing the nutrient into the atmosphere.
 Volcanic eruptions are also a key contributor to the terrestrial iron cycle,
releasing iron-rich dust into the atmosphere in either a large burst or in
smaller spurts over time.
 The atmospheric transport of iron-rich dust can impact the ocean
concentrations.

20. IRON CYCLE

22.  The inventory of biological functions of iron shows that this element is essential to
life.
 In the cell, the iron must be in the Fe2+ state.
 Due to its low solubility, living organisms have developed systems to capture and
incorporate iron.
 Many microorganisms produce a wide variety of small organic molecules,
siderophores capable of fixing Fe3+ with a very high efficiency, ensuring its
transport within the cell, where it is reduced and incorporated into the organic
material.
 Some aquatic bacteria, described as magnetotactic microorganisms, such as
Aquaspirillum magnetotacticum, Magnetotacticum bavaricum, and Magnetospirillum
magnetotacticum, can transform iron extracellularly to crystal of magnetite (Fe3O4)
and construct “intracellular magnetic compasses” called magnetosomes which are
included in cytoplasmic vesicles .
Iron Assimilation by Microorganisms

23. Magnetotactic bacteria (Vibrio sp.) The magnetosomes
form chains inside the cell (1.5 0.4 μm)
Magnetotactic bacteria
 Some magnetotactic bacteria do not synthesize magnetite but greigite (Fe3S4).
 With this structure, these motile bacteria can move to areas rich in organic matter
(water-sediment interface), by following the Earth’s magnetic field.
 High concentrations of magnetotactic bacteria were detected in anoxic marine
sediments at 3,000 m depth .

24. MAGNATOTAXIS

25.  The oxidation of Fe(II) to Fe(III) iron by chemical or microbial processes
depends on pH and oxygen concentration.
 In oxic conditions, the oxidation pathways of iron will be a function of
pH.
 At neutral pH, ferrous iron is spontaneously oxidized (by abiotic
pathway) to ferric iron.
 at oxic–anoxic interfaces, it can also be oxidized by bacteria such as
Gallionella ferruginea, Leptothrix ochracea, or Sphaerotilus natans.
IRON OXIDATION

26.  The biological oxidation of iron is the most important at acidic pH (less
than 3) where the Fe2+ form is stable.
 This oxidation is carried out by autotrophic acidophilic micro-organisms
such as Acidithiobacillus ferrooxidans or Leptospirillum ferrooxidans,
which fix CO2 via the Calvin cycle and use iron as electron donor and
oxygen as terminal electrons acceptor.
 These bacteria are commonly encountered in polluted acidic
environments and their metabolism is used in the bioleaching process .
 They must oxidize a large amount of iron to grow. Indeed, the energy
released during the oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) is
low, because only one electron is transferred in this reaction:

27.  The oxidation of iron in such environments causes significant deposits of
iron oxides which may be visualized as rusty-colored deposits at the
surface of sediments.
 The oxidation processes of iron are at the origin of specific geological
formations, visible as brown oxidized iron strata in ancient sedimentary
rocks (i.e. BIFs for “Banded Iron Formation”).
 These accumulations of oxidized iron consist of hematite (Fe2O3) and
magnetite (Fe3O4).
 formation of these geological layers is due to the anaerobic oxidation of
iron either by chemosynthesis or by anoxygenic photosynthesis.

28.  The oxidation of Fe(II) does not happen only in oxic environments,
it also occurs in anoxic conditions at neutral pH.
 Indeed, in addition to aerobic acidophilic and neutrophilic
chemolithotrophs, anaerobic oxidation of iron is also performed by
bacteria which use nitrate as electrons acceptor.
 The description of this process in many natural ecosystems suggests
that it plays a significant role in the coupling of nitrogen and iron
cycles in anoxic sediments.
 Some anoxygenic photosynthetic microorganisms oxidize iron to fix
CO2 by using solar energy .
 Phylogenetically diverse,and they are represented by purple sulfur
(Thiodictyon sp. strain F4), purple non-sulfur (Rhodovulum iodosum
and R. robiginosum) and green sulfur (Chlorobium ferrooxidans)
bacteria.

29.  Iron reduction is carried out via both chemical and biological
processes.
 This type of respiration is common in anoxic sediments, soils, marshes,
bogs, and has also been highlighted in deep aquifers or fossil waters, oil
reservoirs, continental hot springs, and marine hydrothermal vents.
 Because the oxidized forms of iron (and manganese) are highly
insoluble, they behave differently compared with other potential
soluble electron acceptors (oxygen, nitrate, sulfate, or carbon dioxide),
which diffuse within the cell.
IRON REDUCTION

30.  To reduce these compounds, organisms will develop two strategies ;
 Either establishing a direct contact with the electron acceptor (e.g.
Geobacter metallireducens) or produce “shuttle carriers ” that transfer
electrons from the surface membrane to iron oxides (Shewanella spp,
Geothrix fermentans).
 The phylogenetic diversity of microorganisms capable of dissimilatory
reduction of iron is high, with representatives in both Bacteria and
Archaea domains.
 The most studied micro-organisms belong to the genera Shewanella,
Geobacter, and Geospirillum.

31.  Hyperthermophiles reduce iron, such as Thermotoga maritima and
Thermodesulfobacterium commune (in the domain Bacteria), and
Pyrobacterium islandicum and Ferroglobus placidus (in the domain
Archaea).
 Other electron acceptors can be used by microorganisms which carried
out the dissimilatory reduction of iron:
 Oxygen, other metals (manganese , uranium, cobalt, chromium, gold),
extracellular quinones (humic substances are the most abundant source
of extracellular quinones), some sulfur compounds (S˚ ), nitrate, fumarate
.

32.  Concerning the electron donors, the most frequently used are organic
acids.
 If hydrogen is an electron donor for several species of Geobacter and
Shewanella, the acetate, is the most important organic electron donor in
many environments, and it is most frequently used.
 The total oxidation of this molecule by Geobacter metallireducens is as
follows:

33.  This bacterium is also able to develop on a wide spectrum of
compounds, by coupling their oxidation to iron reduction:
benzaldehyde, benzoate, benzyl alcohol, butanol, butyrate, ethanol, p-
hydroxybenzaldehyde, p-hydroxybenzoate, p-hydrybenzyl alcohol, p-
cresol, isobutyrate, isovalerate, phenol, propanol, propionate, pyruvate,
toluene, valerate.

34.  Metabolism of sugars has also been demonstrated. It produces
enough energy to allow growth; oxidation may be total or incomplete
.

35. Interactions with other elemental cycles
 The iron cycle interacts significantly with the sulfur, nitrogen, and
phosphorus cycles.
 Soluble Fe(II) can act as the electron donor, reducing oxidized organic and
inorganic electron receptors, including O2 and NO3, and become oxidized
to Fe(III). The oxidized form of iron can then be the electron acceptor for
reduced sulfur, H2, and organic carbon compounds.
 This returns the iron to the oxidized Fe(II) state, completing the cycle.
 The transition of iron between Fe(II) and Fe(III) in aquatic systems interacts
with the freshwater phosphorus cycle.
 With oxygen in the water, Fe(II) gets oxidized to Fe(III), either abiotically or
by microbes via lithotrophic oxidation.

36.  Fe(III) can form iron hydroxides, which bind tightly to phosphorus,
removing it from the bioavailable phosphorus pool, limiting primary
productivity.
 In anoxic conditions, Fe(III) can reduced, used by microbes to be the final
electron acceptor from either organic carbon or hydrogen. This releases the
phosphorus back into the water for biological use.
 Iron plays a very important role in the nitrogen cycle, aside from its role as
part of the enzymes involved in nitrogen fixation.
 In anoxic conditions, Fe(II) can donate an electron that is accepted by
N03
− which is oxidized to several different forms of nitrogen compounds,
NO2
−, N20, N2, and NH4
+.

37.  The metabolic capacities of microbial iron-reducers have many
environmental applications.
 The Geobacteraceae can play an important role in the rehabilitation of
deep anoxic environments contaminated with aromatic hydrocarbons
(benzene, toluene, ethylbenzene, o-xylene, p-cresol, phenol).
 Their action in the cleanup of ground waters or sediments contaminated
by hydrocarbons was observed and provides opportunities for the
development of remediation techniques against contaminated sites.
 Human impact on the iron cycle in the ocean is due to dust concentrations
increasing at the beginning of the industrial era.

38.  Today, there is approximately double the amount of soluble iron in
oceans than pre-industrial times from anthropogenic pollutants and
soluble iron combustion sources.
 Other anthropogenic sources of iron are due to combustion. Highest
combustion rates of iron occurs in East Asia, which contributes to 20-
100% of ocean depositions around the globe.
 In the subtropics, tropics the increased inputs of iron may lead to
increased CO2 uptake, impacting the global carbon cycle.

39. 2. PHOSPHORUS CYCLE
 The phosphorus cycle is the slowest biogeochemical cycle that describes
the movements of phosphorus through the lithosphere, hydrosphere and
biosphere.
 Unlike many other biogeochemical cycles, the atmosphere dose not play
any significant role in the movement of P, because phosphorus and
phosphorus based compounds are usually solids at the typical ranges of
temperature and pressure found on earth.
 Low concentration of P in soils reduce plant growth and slows soil
microbial growth.
 Unlike other cycles, P cannot be found in the air as gas, it only occurs
under highly reducing conditions as the gas phosphine. So it is
specifically focused on the cycle in terrestrial and aquatic systems.

40.  Soil microorganisms act as both sink and source of available P in the
biogeochemical cycle.
 On the land, phosphorus gradually becomes less available to plants over
thousands of years, since it is slowly lost in runoff.
 Locally the transformations of P are chemical, biological and
microbiological ; the major long term transfer in the global cycle is
however driven by tectonic movements in geological time.
 Humans have caused major changes to the global P cycle through
shipping of P minerals, and use of P fertilizer, and also the shipping of
food from farms to cities, where it is lost as effluent.

41.  Phosphorus does enter the atmosphere in very small amounts when the
dust is dissolved in rainwater and seaspray but remains mostly on land
and in rock and soil minerals.
 Eighty percent of the mined phosphorus is used to make fertilizers.
Phosphates from fertilizers, sewage and detergents can cause pollution
in lakes and streams.
 Over-enrichment of phosphate in both fresh and inshore marine waters
can lead to massive algal blooms which, when they die and decay leads
to eutrophication of freshwaters only (Canadian Experimental Lakes
Area).
PHOSPHORUS IN THE ENVIRONMENT

42.  Phosphorus occurs most abundantly in nature as part of the orthophosphate ion
(PO4)3−, consisting of a P atom and 4 oxygen atoms.
 The phosphate salts are released from rocks through weathering usually dissolve in soil
water and will be absorbed by plants. The most common mineral being Apatite.
 Overall small losses occurs in terrestrial environment by leaching, erosion , through the
action of rain.
 Weathering of rocks and minerals release phosphorous in a soluble form, where it is
taken up by plants and it is transformed into organic compounds.
 The plants may then be consumed by herbivores and the phosphorus is either
incorporated in to their tissues or excreted.
 After death of animal or plant decays then phosphorus is returned to the soil where a
large part of the P is transformed in to insoluble compounds.
 Runoff may carry a small part of the P back to the ocean.
PROCESS OF PHOSPHORUS CYCLE

43. STEPS OF PHOSPHORUS CYCLE

45. SCHEMATIC REPRECENTATION
THE GLOBAL PHOSPHORUS CYCLE :
 By the process of weathering and erosion
phosphate enter rivers and streams that
transport them to ocean.
 Once in the ocean the phosphorus
accumulates on continental shelves in the
form of insoluble deposits.
 After millions of years, the crustal plates rise
from the sea floor and expose the phosphate
on land.
 After more times, weathering will release
them from rock and the cycle’s geochemical
phase begins again.

46.  The most abundant primary phosphorus-mineral in the crust is apatite,
which can be dissolved by natural acids generated by soil microbes and
fungi, or by other chemical weathering reactions and physical erosion.
 The dissolved phosphorus is bioavailable to terrestrial organisms and
plants and is returned to the soil after their decay.
 Phosphorus retention by soil minerals (e.g., adsorption onto iron and
aluminum oxyhydroxides in acidic soils and precipitation onto calcite in
neutral-to-calcareous soils) is usually viewed as the most important
processes in controlling terrestrial P-bioavailability in the mineral soil.
 This process can lead to the low level of dissolved phosphorus
concentrations in soil solution.
TERRESTRIAL ECOSYSTEM VEIW OF THE PHOSPHORUS CYCLE

47.  Various physiological strategies are used by
plants and microorganisms for obtaining
phosphorus from this low level of phosphorus
concentration.
 All organisms require phosphorus for
synthesizing phospholipids, NADPH, ATP, nucleic
acids and other compounds.
 Plants absorb phosphorus very quickly, and then
herbivores get phosphorus by eat plants.
 The carnivores get phosphorus as a waste.
 This decomposition will release phosphorus into
the soil.
 Plant absorb the phosphorus from the soil and
they recycle it within the ecosystem.

48. A SOIL BASED VEIW OF THE PHOSPHORUS CYCLE
 Initially, phosphate weathers from rocks. The small
losses in a terrestrial system caused by leaching
through the action of rain are balanced in the gains
from weathering rocks.
 In soil, phosphate is absorbed on clay surface and
organic matter particles, and becomes incorporated
(immobilized).
 Plants dissolve ionized forms of phosphate,
herbivores and carnivores excrete phosphorus by
eating plants, and carnivores by eating herbivores.
 Herbivores and carnivores excrete phosphorus as a
waste product in urine and feces.
 Phosphorus is released back to the soil when plants
or animal matter decomposes and the cycle repeats.

49. FORM OF EXISTANCE IN NATURE
 Unlike the other cycles, there is no volatile phosphorus containing to the
atmosphere in the way carbon dioxide, nitrogen gas and sulphur dioxide
are returned.
 Phosphorus tend to accumulate in the seas. It can be retrieved by mining
the above ground sediments of ancient seas, mostly as deposits of calcium
phosphate.
 Seabirds also get mine phosphorus from the sea by eating phosphorus
containing fish and depositing it as guano (bird droppings).
 Certain small island inhabited by such birds have long been mined for
these deposits as a source of phosphorus for fertilizers.

50. A series of diagenetic processes act to enrich sediment pore water phosphorus
concentrations, resulting in an appreciable benthic return flux of phosphorus to
overlying bottom waters.
These processes include
(i) microbial respiration of organic matter in sediments,
(ii) microbial reduction and dissolution of iron and manganese (oxyhydr)oxides with
subsequent
release of associated phosphorus, which connects the phosphorus cycle to the iron cycle,
(i) abiotic reduction of iron (oxyhydr)oxides by hydrogen sulfide and liberation of iron-
associated phosphorus.
(ii)Additionally, (i) phosphate associated with calcium carbonate and (ii) transformation of
iron oxide-bound phosphorus to vivianite play critical roles in phosphorus burial in
marine sediments.
These processes are similar to phosphorus cycling in lakes and rivers.

51. MICROBIOLOGICAL IMPORTANCE
 Phosphorus is a macronutrient necessary to all living cells. It is an
important component of adenosine triphosphate (ATP), nucleic acids
(DNA or RNA ) and phospholipids in cell membranes.
 It may be stored in intracellular volutin granules as polyphosphates in
both prokaryotes and eukaryotes.
 It is a limiting nutrient for algal growth in lakes. The average
concentration of total phosphorus (inorganic and organic) in
wastewater in the range 10-20 mg/L.

52.  The major transformations of phosphorus in aquatic environments
are describes below :
 Mineralization
 Assimilation
 Precipitation of phosphorus compounds
 Mineral solubilisation of insoluble forms of phosphorus.
Mineralization :
 Organic phosphorus compounds (eg; Phytin, inositol phosphates, nucleic
acids, phospholipids) are mineralized to orthophosphate by a wide
range of microorganisms that include bacteria ( B. subtilis , Arthrobacter
), Actinomycetes (Streptomyces) and fungi (Aspergillus , Penicillium ) .
 Phosphatases are the enzymes responsible for degradation of
phosphorus compounds.

53. Assimilation :
 Microorganisms assimilate phosphorus, which enters in the
composition of several macromolecules in the cell.
 Some microorganisms have the ability to store phosphorus as
polyphosphates in special granules.
Precipitation of Phosphorus Compounds
 The solubility of orthophosphate is controlled by the pH of the aquatic
environment and by the presence of Ca2+ , Mg2+ , Fe3+ and Al3+ .
 When precipitation occurs, there is formation of insoluble compounds
such as hydroxyapatite , vivianite or variscite .

54. MICROBIAL SOLUBILIZATION OF
INSOLUBLE FORM OF PHOSPHORUS
 Through their metabolic activity, microorganisms help in the solubilisation
of P compounds.
 The mechanisms of solubilisation are metabolic process involving :
1. Enzymes
2. Production of organic acid and inorganic acids by microorganisms (eg;
Succinic acid, oxalic acid, nitric acid and sulphuric acid )
3. Production of CO2, which lowers ph
4..Production of H2S which may react with iron phosphate and liberate
orthophosphate .
5. The production of chelators, which can complex Ca, Fe, or Al.

55. PHOSPHATIC MINERALS
 The availability of phosphorus in an ecosystem is restricted by the rate of
release of this element during weathering.
 The release of phosphorus from apatite dissolution is a key control on
ecosystem productivity.
 The primary mineral with significant phosphorus content, apatite
undergoes carbonation.
 Little of this released phosphorus is taken by biota (organic form ) whereas,
large proportion reacts with other soil minerals leading to precipitation in
unavailable forms.
 Available phosphorus is found in a biogeochemical cycle in the upper soil
profile, while phosphorus found in the lower depths is primarily involved
in geochemical reactions with secondary minerals.

56.  Plant growth depends on the rapid root uptake of phosphorus
released from dead organic matter in biochemical cycle. Phosphorus is
limited in supply for plant growth.
 Phosphate move quickly through plants and animals; however, the
processes that move them through the soil or ocean are very slow,
making the phosphorus cycle overall one of the slowest biogeochemical
cycles.
 Low-molecular weight organic acids are found in soils. They originate
from the activities of various microorganisms in soil or may be exuded
from the roots of living plant.
 Several those organic acid are capable of forming stable organo-metal
complex with various metal ions found in soil solution.
 The process may lead to release organic phosphorus associated with
aluminium, iron and calcium in soil minerals.

57.  The production and release of oxalic acid by mycorrhizal fungi
explain their importance in maintaining and supplying phosphorus to
plant.
 The availability of organic phosphorus to support microbial, plant and
animal growth depends on the rate of their degradation to generate free
phosphate.
 There are various enzymes such as phosphatases, nucleases and phytase
involved for the degradation.
 Some of the abiotic pathways in the environment studied are hydrolytic
reactions and photolytic reactions.
 Enzymatic hydrolysis is organic phosphorus is an essential step in the
biogeochemical phosphorus cycle, including the phosphorus nutrition of
plants and microorganisms and the transfer of organic phosphorus from
soil to water bodies.

58. HUMAN IMPACT OF PHOSPHORUS CYCLE
 Like nitrogen increased use of fertilizers increases phosphorus runoff into
our water bodies and contributes to eutrophication.
 Human have greatly influences the P cycle by mining P, converting it to
fertilizer and by shipping fertilizer and products around the globe.
 Transporting P in food from farms to cities has made a major change in the
global P cycle.
 Water are enriched in P from farms run off, and from effluent that is
inadequately treated before it is discharged to waters.
 Cultural or anthropogenic eutrophication is also associated with the
pollution.

59.  The process controlling soil P release to surface runoff and to subsurface
flow are a complex interaction between the type of P input. Soil type and
management and transport process depending on hydrological condition.
 In poorly drained soils or in areas where snowmelt can cause periodical
waterlogging , Fe reducing conditions can be attained in 7-10 days. This
cause a sharp increase in P concentration in solution and P can be leached.
 In addition, reduction of the soil causes a shift in phosphorus from resilient
to more labile forms. This could eventually increase the potential for P loss.

60.  This is of particular concern for the environmentally sound management of such
areas, where disposal of agricultural wastes has already become a problem.
 It is suggested that the water regime of soils that are to be used for organic waste
disposal is taken into account in the preparation of waste management regulations.

61. ECOLOGICAL FUNCTIONS
 P is an important nutrient for plants and animals, P is
also limiting nutrient for aquatic organisms.
 P does not enter the atmosphere, remaining mostly
on land, in rock and soil minerals.
 80% of the mined phosphorus is used to make
fertilizers. P from fertilizers, sewage can cause
pollution in lakes and streams.
 P normally occurs in nature as part of a phosphate
ion. The most abundant forms is orthophosphate.

62. IMPORTANT OF PHOSPHORUS
BIOLOGICAL FUNCTION
• The primary biological importance of phosphate is as a component of
nucleotides, which serves as energy storage within cells (ATP) or when
linked together form the nucleic acids DNA and RNA.
• The double helix of two strands of DNA is only possible because of phosphate
ester bridge that binds the helix.
• Besides making biomolecules, P is also found in bone and enamel of
mammalian teeth, whose strength is derived from calcium phosphate in the
form of Hydroxyl apatite.
• It is also found in the exoskeleton of insects and phospholipids.

63. OTHER USES
 Phosphorus catches fire rapidly, red phosphorus is
used in all matches.
 White phosphorus and zinc phosphate are mainly
used as a poison for rats.
 It is used in making incendiary (fire causing) bombs,
tracer bullets and for producing smoke screen.
 Many soluble phosphate are used to remove
unwanted metal from the water.

64.  Eutrophication is an enrichment of water by nutrient that lead to structural
changes to the aquatic ecosystem such as algae bloom, deoxygenation,
reduction of fish species.
 The primary source that contributes to the eutrophication is considered as
nitrogen and phosphorus. When these two elements exceed the capacity of
the water body, eutrophication occurs.
 Phosphorus that enters lakes will accumulate in the sediments and the
biosphere, it also can be recycled from the sediments and the water system.
 Drainage water from agricultural land also carries phosphorus and
nitrogen.
Phosphorus and Eutrophication

65.  Since a large amount of phosphorus is in the soil contents, so the overuse
of fertilizers and over-enrichment with nutrients will lead to increasing
the amount of phosphorus concentration in agricultural runoff.

66. REFERENCE
 MICROBIAL ECOLOGY BY LARRYL L. BARTON , DIANA E. NORTHUP
 ENVIRONMENTAL MICROBILOGY FOR ENGINEERS BY VOLONDYMYR IVANOV
 ENVIRONMENTAL MICROBIOLOGY FUNDENENTAL AND APPLICATIONS BY Jean-
Claude Bertrand · Pierre Caumette Philippe Lebaron · Robert Matheron Philippe
Normand · Télesphore Sime-Ngando / springer.
 PHOSPHORUS CYCLE BY Biological Dictionary editors.
 PHOSPHORUS BASICS BY Agronomy fact sheet series

67. THANK YOU