Important Microrganisms
Converting Nitrogen to Nitrate
’Monera; Bactaria; Rhizobiaceae
’A family of gram-negative bacteria which are saprophytes, symbionts, or
plant pathogens.
’ Bradyrhizobium
’ A genus of gram-negative, aerobic, rod-shaped bacteria usually containing granules of polybeta-hydroxybutyrate. They characteristically invade the root hairs of leguminous plants and
act as intracellular symbionts.
Nitrogen fixation is a remarkable prokaryotic skill in which inert atmospheric nitrogen
gas is converted into ammonia. Through another bacterial process called nitrification,
the ammonia is converted into nitrites and nitrates, thereby making the vital element
nitrogen readily available to the roots of higher plants. Since this process commonly
occurs in the root nodules of legumes, farmers often rotate their crops with
leguminous species (such as alfalfa and clover). The economic importance of
legumes and root nodules is astonishing. For example, the average annual crop of
clover seed in Ohio (250,000 bushels) will plant approximately 3 million acres in
clover. This acreage would yield about 4.5 million tons of hay (worth about $90
million). Because of nitrogen fixation in the root nodules of clover, about 273 million
pounds of nitrogen is added to the soil (worth about $50 million annually).
http://waynesword.palomar.edu/trmar99.htm
http://www.termsciences.fr/
http://quorumsensing.ifas.ufl.edu/HCS200/LegRhiz.html
Important Microrganisms
Converting Nitrogen to Nitrate
http://quorumsensing.ifas.ufl.edu/HCS200/LegRhiz.html
’Monera; Bactaria; Rhizobiaceae
’ For example : Bradyrhizobium japonicum.
’ Forms symbiosis with soybeans
notice that the bacterial cells have flagella,
thread-like organs that allow bacteria to
swim and move in soils toward the host
plants.
Roots of legumes produce
flavonoids, - chemicals that
attract rhizobia. Different
legumes produce different
flavonoids to attract
different rhizobia.
Inside the root, rhizobia invade expanded cells of cortex,
and then bacteria differentiate into Nitrogen-fixing
"bacteroids".
Important Microrganisms
Converting Nitrogen to Ammonia
’Monera; Cyanobacteria
’A phylum of oxygenic photosynthetic bacteria comprised of unicellular
to multicellular bacteria possessing CHLOROPHYLL “a” and carrying
out oxygenic PHOTOSYNTHESIS. Cyanobacteria are the only known
organisms capable of fixing both CARBON DIOXIDE (in the presence
of light) and NITROGEN. Cell morphology can include nitrogen-fixing
heterocysts and/or resting cells called akinetes. Formerly called bluegreen algae, cyanobacteria were traditionally treated as ALGAE.
Nitrogen fixation is also accomplished by a number of
species of microscopic cyanobacteria, some of which live
symbiotically in nonleguminous plants, including the leaves
of water fern (Azolla) and the roots of cycads. The actual
sites of nitrogen fixation in the cyanobacteria are special
cells called heterocysts.
http://waynesword.palomar.edu/trmar99.htm
http://www.termsciences.fr/
Important Microrganisms
Converting Nitrogen to Nitrate
’Monera; Actinomycetes
’Class of BACTERIA with diverse morphological properties. Strains of Actinobacteria show
greater than 80% 16S rDNA/rRNA sequence similarity among each other and also the
presence of certain signature nucleotides. (Stackebrandt E. et al, Int. J. Syst.
Bacteriol.(1997) 47:479-491) http://www.termsciences.fr/
The roots of alder trees (Alnus), wax myrtle (Myrica) and California lilac
(Ceanothus) contain nitrogen-fixing actinomycetes rather than eubacteria.
Nodules of the actinomycete Frankia on alder roots greatly resemble the
Rhizobium nodules of legumes. Actinomycetes include a large group of
filamentous, fungus-like soil bacteria. They form long, threadlike, branched
filaments that resemble gray spiderwebs throughout compost piles. In fact, the
characteristic earthy smell of compost and recently overturned rotten logs in a
forest is caused by thriving populations of actinomycetes. Electron
microscopy and other studies have shown unequivocally that these organisms
are bacteria and not fungi. Some authors refer to actinomycetes as
actinobacteria and place them in their own phylum.
http://waynesword.palomar.edu/trmar99.htm
High Magnification of actinomycete
sporesPhoto credit: Paul R. August,
Biological Process Technological
Institute, University of Minnesota
Important Microrganisms
Converting Ammonia or Nitrite to Nitrate
’Monera; Bactaria; Nitrobacteraceae
’The nitrifying bacteria,
’a family of gram-negative, chemolithotrophic bacteria;
autotrophs which derive energy from nitrification of
ammonia or nitrite, and obtain carbon for growth by
fixation of carbon dioxide.
’ Nitrobacter
Nitrifying bacteria isolated from landfill leakage Prof.
UW Aleksandra Sk³odowska , department of
Environmental Pollution Analysis, Faculty of Biology
Warsaw University
’ A genus of gram-negative, rod-shaped bacteria that oxidizes nitrites to
nitrates. Its organisms occur in aerobic environments where organic
matter is being mineralized, including soil, fresh water, and sea water
’ Nitrosomonas
’ A genus of gram-negative, ellipsoidal or rod-shaped bacteria whose
major source of energy and reducing power is from the oxidation of
ammonia to nitrite. Its species occur in soils, oceans, lakes, rivers, and
sewage disposal systems.
’ Nitrosomonas europea: type species of the genus NITROSOMONAS,
a gram-negative chemolithotroph that oxidizes ammonia to nitrite. It is
found in soil, sewage, freshwater, and on building walls, and especially
in polluted areas where air contains high levels of nitrogen compounds.
Nitrifying bacteria cross
sectionPhoto credit: Mary Ann
Bruns, Center for Microbial
Ecology, Michigan State University
http://www.termsciences.fr/
Important Microrganisms
Converting Ammonia , Nitrite or Nitrate
back to Nitrogen
’Monera; Bactaria; Denitrifying bacteria
’A group of bacteria that reduce nitrates or nitrites to nitrogen-containing
gases. Potential examples include
’ Thiobacillus denitrificans,
’ Micrococcus denitrificans,
’ Serratia
’ Acrobacter and
’ Pseudomonas.
’These bacteria have also been implicated in depletion of soil fertility, and
thereby agricultural productivity.
Brettar, I., R. Christen, and M. G. Hofle. 2002.
Shewanella denitrificans sp nov., a vigorously denitrifying
bacterium isolated from the oxic-anoxic interface of the
Gotland Deep in the central Baltic Sea. International Journal
of Systematic and Evolutionary Microbiology 52: 22112217.
http://www.termsciences.fr/