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The science of microbiology is vast and diverse. Scholars and biologists who

have devoted their careers to the various subtopics of the science are constantly

making new discoveries that may very well change the world forever. Most people

dont realize just how much the microscopic world that they have never seen truly

affects their everyday lives. Over the years, science has taught us that some bacteria

can make us sick, so we should take precautionary measures to avoid these. We aretold to sanitize our hands regularly as a means to kill such dangerous bacteria, and to

be sure to thoroughly cleanse and cook our food to be sure that it is safe for

consumption. Antibiotics have been developed as a means to kill off these dangerous

bacteria should something actually make an individual sick. However, even though

there are some very dangerous illnesses out there that can be caused by bacteria,

over 90 % of the microbes out there are non-pathogenic. On the contrary, they can

be and are beneficial for most living organisms. One might go so far as to say that

microbes are integral for all living creatures because they assist in the building of

immunities against infection and they also help with growth in agriculture and in

defense of many predatory species. For mankind, microbes in agriculture are of the

utmost importance, as they quite literally fill the soil that plants grown in. As time

progresses, the methods for vegetative farming are being modified in order to keep

up with demand and to maximize profits. Different farmers use different fertilizers

and entirely different methods for maintaining their soil. Through personal research, I

have been able to attain some information about how fertilizers affect the levels of

microbes in different types of soil.

All organic matter is made up of long chains of many molecules and always contains

some carbon. Bacteria need to break the bonds holding the chains of these organic

molecules into smaller simple sugars and amino acids. The bacteria break these

bonds and digest these by secreting enzymes in a disorderly fashion. The ingestionof this organic matter is quite a task in itself due to bacterias diminutive size.

(Calvaruso p.3023) Most of these microbes need to produce adenosine triphosphate

or ATP. Simply put, this is created via active transport through the cells membrane

powered by charged electrons on each side of the membrane. Only aerobic bacteria

produce ATP and ATP is the most ubiquitous form of energy in the prokaryotic world.

Anaerobic bacteria not only have a foul odor most times, but many times are

pathogenic or can produce alcohol and are not beneficial for the soil in any way.

Even worse, these bacteria kill the beneficial, aerobic bacteria.

Microbes are the real farmers when it comes down to the basic elements. A farmer

can say he makes his own compost, but who does the real composting? The meansof using bacteria to farm with is much more beneficial and practical than trying to

fight nature by using synthetic fertilizers.

Bacteria play a major role in the recycling of a few major elements in nature

which are carbon, sulfur and nitrogen in the soil. The soil carbon cycle is just the

same as the carbon cycle on a global level and is a part of it. CO2 is a by-product of

aerobic bacterial metabolism. Then the bacterium dies and its gas is cycled into CO2

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during decay. Through photosynthesis, the plant then converts the CO2 into organic

compounds which are consumed by bacteria and recycled back into CO2. (Janzen

400-409) Sulfur is recycled in a similar way except anaerobic bacteria oxidize sulfur.

Both nitrogen and sulfur are key elements for any type of farming. Instead of adding

a synthetic version of these elements, the bacteria produce them themselves.

The nitrogen cycle is one of the most specialized and important in the

maintenance of terrestrial life. Nitrogen is the most abundant and inert for any

practical purpose and is useless for plants in this state. Nitrogen must be combined

with oxygen or hydrogen (nitrogen fixation) to become useful for vegetation thus

becoming ammonium, nitrate or nitrite. There are only a few genuses of bacteria that

can accomplish nitrogen fixation which are Azotobacter, Azosperillum, Clostridium,

and Rhizobium. Nitrifying bacteria generally do not like acidic soil, therefore, their

numbers decrease when the pH drops below 7. (Grayston 1691-93) A soil that has a

basic pH is not ideal for annual plants like tomatoes. However, if the colony is large

enough, they can create a biofilm and keep the pH above 7 in the colonies local.

These biofilms are most common in the rhizosphere where pH is most crucialcomponent for proper nutrient uptake. This can be beneficial by keeping the pH

relatively stable with no extra human effort. Not only do biofilms help with the pH,

they help protect these bacteria from antibiotics and other predators.

Natural soil is chalked full of bacteria. A culture of bacteria the size of a period

on this page can contain anywhere from 250,000 to 500,000 prokaryotic cells. One

teaspoon of healthy soil can potentially contain up to one billion bacteria, and an acre

can contain a metric ton. (USDA) With that said, one might say that the microbes are

far more in control of how well a plant grows than the farmer is. If the person in

charge does not have a firm grasp on how bacteria affect pH levels and Nitrogen,

Phosphorous and Potassium availability levels in their soil, they could very well lose

their crop for lack of knowledge.

Each bacterium plays its own essential role in the soil food web as you can see

with the carbon and nitrogen cycles. Most important, is the bacteriums ability to

retain nutrients will help the plants have a constant food supply. Bacteria are Earths

primary decomposers with fungi coming in at a close second. Bacteria can

decompose all plant and animal material and waste and ingest mainly nitrogen and

carbon compounds along with other nutrients. These broken down nutrients are then

retained and immobilized within the bacterias membranes and the cells are attached

to the soil particles, thus preventing mobilization and leaching of the nutrients fromthe rhizosphere during a heavy rain for example. (USDA)

The highest concentration and most active area for binary fission of bacteria is

in the rhizosphere. In this area, the soil is directly affected by the secretions and

exudates of sugars and proteins by the plants roots. In addition to the secretions, the

bacteria obtain sustenance from the cells shed off from the growing root-tip. Life in

this area for microbes is like a walk in the park when it comes to finding food

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therefore, bacteria dont have to travel far from the root zone. When the nutrients

are released from the bacteria due to death, or more likely consumption, the wastes

will be deposited in the rhizosphere for easy absorption by the roots. (Appuhn 1044-

46)

Soil fungi are also very beneficial to a plants overall health. They help controlnutrient uptake, decompose and recycle, just like bacteria. Their physical

appearance, however, can be much different. Unlike most bacteria, fungi have long

strands called hyphae that grow between soil particles, holding them together and

forming a stable place for the roots as well as help with water retention. Mycorrhizal

fungi are the most beneficial of all. They colonize the roots and help with the uptake

of phosphorous specifically. Phosphorous promotes explosive growth in the flowering

or budding stages of plants. Fungi enjoy a basic soil on the pH scale. So, an organic

gardener can water the plants with water that has a slightly higher pH during the

flowering stage to encourage a prolific presence of fungi, therefore providing more

phosphorous for root uptake. (Harris 1522)

Farmers that grow annual plants such as tomatoes prefer acidic soils therefore,

support a bacterial dominant soil through all stages of growth. Through my research,

I can assume organic soils will host many more microbes than soil which is

bombarded with synthetic fertilizers at an interval. I obtained samples from three

different soil beds. These samples were taken from the surface and subsurface to get

a broad view of the entire soil system. I took 5 gram samples from the three and

placed them in 10ml of sterile water in a sterile test tube. These were then let to sit

for a period of one hour. The tubes were then shaken and then a loop was used to

make a culture on a tryptic soy agar plate. The plates were then placed in a dark

area at room temperature for 48 hours before my observations were made.

The first soil sample was from a tomato patch in a green house. The soil mix

consisted of cow, rabbit and chicken manures. Every year, before the seedlings were

planted, the soil was tilled to aerate the soil. In addition, a synthetic chemical

fertilizer was applied weekly. This culture showed no colonies after the 48 hour

period. The plate was even allowed to sit for an additional 48 hours with no signs of

growth. The use of the chemical fertilizers and tilling of the soil causes a large

amount of stress and is not conducive for a strong bacterial of fungal population.

The second soil sample was also from a tomato patch that is located outside.

The farmer tilled the field before planting and also added cow, rabbit and chicken

manure. However, he fertilized this field with only custom organic teas with his

manures. The results were drastically different than the first sample. The bacterial

content of the soil was diverse and abundant. The colonies were white, yellow and

brown, and they were all opaque.

The final culture was of a three year no-till organic field. Every season the field

had cow, rabbit and chicken manure placed as a top dressing. The fertilizer was also

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of a custom manure tea. This culture was exploding with colonies. Large fuzzy

colonies of fungi were also visible. The uninterrupted, all natural process of farming

also proved to be very beneficial as his yields are increasing yearly as well as

maintenance decreasing.

As time and science progress, many people have come to think that they canoutwit Mother Nature. The data that I collected and the research that I conducted

have bolstered my feelings that one must not tamper with the organic, natural

methods for farming that have stood the test of time. Organic fields yield heartier,

healthier crops than the fields that have been fed with unnatural fertilizers placed

there by the farmer. I feel that if one were to conduct further research on this

subject, they would only find data that would collaborate with the information I

collected. In the meantime, I will do my best to eat more organics and learn more

about the conditions in which my produce has been grown.

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Work Cited

http://soils.usda.gov/sqi/concepts/soil_biology/biology.html. 6/1/07

Appuhn, Astrid;Joergensen, Rainer Georg. Microbial colonisation of roots as a function

of plant specie.

Soil Biology and Biochemistry. 38:5, pp. 1040-1051. 6/1/07

Calvaruso, C ; Uroz, S. Effect of the Mycorrhizosphere on the Genotypic and

Metabolic Diversity of the

Bacterial Communities Involved in Mineral Weathering in a Forest Soil.Journal ofApplied and

Environmental Microbiology. 73: 9, pp. 3019-3027. 6/1/07.

Grayston, Susan J; Ross, DesJ. Changes in soil carbon and nitrogen properties and

microbial communities

in relation to growth of Pinus radiata and Nothofagus fusca trees after 6 years at

ambient and

elevated atmospheric CO sub(2). Global Change Biology . 12:9, pp. 1690-1706.

6/1/07.

Harris, Jodie N; New, Peter B. Laboratory tests can predict beneficial effects of

phosphate-solubilising

bacteria on plant. Soil Biology and Biochemistry . 38:7, pp. 1521-1526. 6/1/07.

Janzen, H. H. (2004). Carbon cycling in earth systems a soil science perspective. In

Agriculture,

ecosystems and environment, 104, 399 417. 6/1/07

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