Benefits of Nitrogen
Fixing Bacteria in Agriculture
Michael Reed
Artificial nitrogen fertilizers provide
food for billions of people but also cause major environmental
problems. Here Michael Reed discusses nitrogen-fixing bacteria
and his experiments with them. This is a field ripe for
study by students and amateur scientists. Editor.
Nitrogen-fixing bacteria are some of the
more useful organisms on Earth because they can contribute
to the growth of organisms through their conversion of N2
into compounds that plants can use. These compounds are
useful for the production of proteins and hormones that
plants can use in their metabolism. Therefore, these kinds
of bacteria are essential for the nitrogen cycle on Earth.
Cyanobacteria and purple bacteria are two
of the major groups of nitrogen-fixing bacteria that are
essential to the survival of plants and other organisms
on Earth. These bacteria, Divisions Cyanobacteria and Proteobacteria,
are common in many habitats on Earth, but they live different
lives. Cyanobacteria inhabits aerobic environments, which
contain oxygen, while many purple bacteria genera live in
anaerobic settings, with no or little oxygen levels. However,
both of these groups have an ability to fix nitrogen gas
(N2) into ammonium ions and other compounds.
Cyanobacteria (Division Cyanobacterea)
are found in most moist areas, including lichen. These organisms
have the ability to form nitrogen compounds from N2,
and release them into their surroundings. They can fix their
compounds in two locations, the heterocysts and membranes.
Anabaena and Nostoc are some of the cyanobacteria
genera that can fix nitrogen gas in compounds in the heterocysts,
specific cells that do not photosynthesize, but contain
nitrogenase in the system. Oscillatoria and Arthospira
are other genera that do not have heterocysts, but
can fix N2 in their photosynthesis.
Besides nitrogen compounds, cyanobacteria
have the ability to release O2 into the atmosphere
through their photosynthesis. Like plant and algae chloroplasts,
cyanobacteria has thykaloid membranes, the third sets of
membranes that are the site of photosynthesis in the cell
or organelle. The cyanobacteria membrane contains proteins
that can assist in the conversion of H2O, CO2,
and light into energy, glucose, and O2 .
Some genera of purple bacteria (Division
Proteobacteria) have the ability to produce nitrogen compounds;
however, they are anaerobic. Unlike cyanobacteria, these
bacteria do not produce O2 as a byproduct during
their photosynthesis, but other compounds such as SO from
H2S and N2O (Margalis and Schurartez
1998). Nevertheless, they are essential to the nitrogen
cycle by producing compounds for plants, especially legumes,
which are essential for their metabolism (Burris 1974).
Many kinds of nitrogen-fixer bacteria can
help to produce hormone compounds that are essential for
plant growth. Many purple bacteria genera, such as Rhizobium
, help to produce glibberlin acid (GA) and auxins in
the nodules. These compounds assist in the growth of the
plant by increasing the length of the cell walls. It has
been known that certain cyanobacteria produce these compounds
for plants in their environments.
Benefits of Nitrogen-Fixers
for Agriculture
Farmers and scientists have recognized
the properties of nitrogen-fixers for years. Farmers in
parts of Africa and Asia had learned that certain plants
and bacteria form a relationship that is essential for the
fertilization of rice fields. Azolla , a water
fern, thrives in the water environment of the fields, and
Anabaena , a cyanobacteria species, inhabits the
plant. When Azolla dies, the rice plants used the
decaying material for their growth. The cyanobacteria used
the nitrogen gas that is emitted from the surroundings and
produce compounds for the growth of the rice plants.
The relationship between purple bacteria
and legumes, such as beans, peas, and clovers, is useful
in the benefit of farmers. They recognized that the dead
plants help to refertilize the soil for the new set of crops.
The plants help to form a partnership with Rhizobium
and other nitrogen-fixing purple bacteria genera for
the exchange of nutrients. The bacteria help to produce
nitrogen compounds and hormones, while the colonies receive
carbon products from the plant.
Many microbiologists have been studying
the functions and cultivation of several nitrogen-fixing
bacteria species. In India , microbiologists have been cultivating
several cyanobacteria species in indoor environments for
the transport of the colonies to the rice fields. Singh
(2003) had stated that cyanobacteria can fix enough nitrogen
compounds than the Haber-Boseh process, which required high
temperature, energy, money, and HO2 gas for nitrogen
production.
The study of cyanobacteria in India had
help to determine how these organisms can be cultivated
and transported to the rice fields. Studies in cyanobacteria
transport had determined that carrier materials could be
added to the colonies, which are formed into specific flakes
to be transported to the rice fields. The cyanobacteria
can fix enough nitrogen in high temperature and population
density. In addition, the fear of contamination is reduced
(Mishra and Pabbi, 2004).
My Experience with Nitrogen-Fixers: Cyanobacteria &
Purple Bacteria Legume Plants
Since the summer of 2004, I have been experimenting
on the use of cyanobacteria on plant growth on several species:
pumpkin (Cucurbita pepo); summer squash (C
. pepo var. melopepo); and navy
bean (Phaseolus vulgaris var.). I used some colonies
of cyanobacteria from the glass wall of my terrarium, some
old potting soil, and plant seeds.
In a previous experiment, in 2004, I used
some C . pepo seeds. First, I took some
colonies of the cyanobacteria from the terrarium and add
a drop to a plastic cup of potting soil. I left the other
cup without treatment. Second, I planted the seeds in the
cups, and watered them. Third, I placed the plastic bags
over the cups, and put them on the window panel, inside
of the house. Fourth, I moved them to the outside of the
back porch, the cups were unwrapped and recorded the growth
of the seedlings. Finally, I transported the seedlings to
the garden of my landlord, Mr. Brewer, and observed their
growth.
During 2005-2006, I observed the growth
of the plants in his garden. I saw that the bell pepper
(Capsicum annuum) plants produced more fruit than
the previous year and the collard was bigger. This can be
due to fertilizer that Mr. Brewer added to the plants. However,
in 2006, I repeated the experiment of 2004, but I used two
plant species, summer squash (C . pepo var.
melopepo) and navy bean (Phaseolus vulgaris
var) as test plants. The procedure was different from
the earlier experiment by the use of two species and the
addition of cyanobacteria from a microcosm. The results
are summarized in Tables 1-3.
Handling cyanobacteria for the previous
experiments involved the use of simple equipment such as
isopropyl rubbing alcohol and an eyedropper. I used the
alcohol to clean the eyedropper in order to prevent contamination,
and used it to remove a colony from the terrarium. During
this procedure, I wore rubber gloves to protect myself from
touching the cyanobacteria with my hands because most species
can be harmful to humans when ingested. Through the use
of the Tasco Light Microscope, I identified the genera Anabaena,
Oscillatoria, and Arthospira as the main
kinds that I used in the experiments.
| Table 1: Hypocotyl and Cotyledon Measurements of Cucurbita pepo Seedlings (mm) |
|
|
| Experimental |
Control |
|
|
| 15 |
|
0 |
|
| 19 |
|
0 |
|
| 33 |
|
0 |
|
| 0 |
|
31 |
|
| 0 |
|
41 |
|
|
| Geomean |
|
| 35.65109 |
|
21.10828 |
|
| Standard
Dev |
|
| 20.03247 |
|
13.93915 |
|
| Z-test |
|
| 0.991156 |
|
0.89187 |
|
| Confidence |
|
| 17.55891 |
|
12.21798 |
|
|
|
| Table
2: Mean Measurements of Cotyledon Distance of P. vulgaris and
C.pepo var. melopepo (mm) |
|
|
| Experimental |
|
Control |
|
Ordinary |
|
|
| C. pepo |
P. vulgaris |
|
C. pepo |
P. vulgaris |
|
C. pepo |
P. vulgaris |
|
|
|
| 38 |
7 |
|
0 |
0 |
|
0 |
0 |
|
| 36 |
15 |
|
0 |
0 |
|
19 |
0 |
|
| 37 |
20 |
|
0 |
0 |
|
20 |
0 |
|
| 56 |
20 |
|
0 |
0 |
|
42 |
0 |
|
| 63 |
20 |
|
0 |
0 |
|
45 |
0 |
|
| 70 |
20 |
|
0 |
0 |
|
58 |
0 |
|
| 71 |
19 |
|
0 |
0 |
|
66 |
0 |
|
|
| Geomean |
|
| 50.91923 |
16.40084 |
|
0 |
0 |
|
37.42854 |
0 |
|
| Confidence
Level |
|
| 10.51876 |
1.361498 |
|
0 |
0 |
|
14.96637 |
0 |
|
| Standard
Dev. |
|
| 14.19925 |
1.837883 |
|
0 |
0 |
|
20.20307 |
0 |
|
| Z-Test |
|
| 0.349115 |
0.101361 |
|
0 |
0 |
|
0.588814 |
0 |
|
|
|
| Table
3: Height of P.
vulagris and C. pepo var. melopepo Seedlings (mm) |
|
|
| Experimental |
|
Control |
|
Ordinary |
|
|
| C. pepo |
P. vulgaris |
|
C. pepo |
P. vulgaris |
|
C. pepo |
P. vulgaris |
|
|
|
| 0 |
12 |
|
0 |
0 |
|
0 |
0 |
|
| 12 |
31 |
|
0 |
0 |
|
11 |
6 |
|
| 20 |
35 |
|
0 |
0 |
|
20 |
7 |
|
| 20 |
31 |
|
0 |
0 |
|
30 |
22 |
|
| 16 |
31 |
|
0 |
0 |
|
34 |
20 |
|
| 16 |
38 |
|
0 |
0 |
|
36 |
24 |
|
| 20 |
39 |
|
0 |
0 |
|
0 |
0 |
|
|
| Geomean |
|
| 17.05108 |
29.30105 |
|
0 |
0 |
|
24.06939 |
13.470467 |
|
| Confidence
Level |
|
| 5.332169 |
6.694551 |
|
0 |
0 |
|
11.40213 |
7.7307656 |
|
| Standard
Dev. |
|
| 7.197883 |
9.036961 |
|
0 |
0 |
|
15.39171 |
10.435744 |
|
| Z-Test |
|
| 0.790003 |
0.309453 |
|
0 |
0 |
|
0.821348 |
0.7101748 |
|
|
|
|
|
|
|
|
|
|
Sources
Burris, R. H. "Biological Nitrogen
Fixation, 1924-1974". Plant Physiology. 54:
443-449 (1974).
Margalis L. and Schurartez K.V. Five
Kingdoms: An Illustrated Guide to the Phyla of Life on Earth.
New York : W. H. Freeman and Company. 78-81 (1998).
Mishra, U. and Pabbi S. "Cyanobacteria.
A Potential Biofertilizer for Rice". Resonance.
6-10 (2004).
Singh Y. Biofertilizer
Potential of Nitrogen-Fixing Cyanobacteria. Science
Tech Entrepreneur E-Zine. July 2003.
Wolfe D.W. Tales from the Underground:
A Natural History of Subterranean Life. Cambridge:
Perseus Publishing (2001).
