The very first antibiotics to be discovered (penicillin being
the first) were produced by microbes in nature, including common molds. Roughly a decade later several more natural antibiotics were discovered by Selman Waksman, a biochemist who was studying soil microorganisms and decomposition. He coined the term 'antibiotic' and those he discovered included streptomycin, neomycin and actinomycin.
We should all have some idea what 'chemical' means; all things physical in the world have mass and volume. Everything is composed of matter, and consequently chemicals. Some very familiar things consist of primarily a single simple chemical such as water in and of itself, the nitrous oxide you inhale from whippets, baking soda, etc.
Most things, like the atmosphere or living organisms, are actually made up of several chemicals. In the case of living things there are hundreds if not thousands of a variety of 'chemicals' that interact on various levels and together form organelles, which are components of the cells that form the tissues which make up organs.
There are chemicals that we know to be ubiquitous in our environments. These are produced naturally on earth, either by the reactive nature of the Earth itself or as a consequence of certain fundamental or specialized (specific only to certain species) processes carried out by the living organisms that exist on it.
Synthetic chemicals are those which are not known to occur naturally anywhere upon the earth and are instead synthesized by man. They are not necessarily horrendous, just as natural chemicals are not necessarily innocuous. However, there is a lessened ability to determine exactly what sort of impact a synthetic chemical is going to have on organisms in our environment. A specific concern with many synthetic substances (especially pesticides) is that the forces of nature wont allow for them to degrade at an acceptable rate and if such a chemical interacts in any manner with an organisms biology the impact will be devastating.
Elaborating on my previous post, soil organisms contribute a
lot to the soil, and to plants. To say that the microbes are 'breaking down organic matter into chemical fertilizer anyways' is oversimplified misinformation if there ever was such a thing. Of course, no microbes break any organic matter down into synthetic nutrients, salts or EDTA.
Within soil, outdoors or in living soil grows there are various organisms, all of which are depending on each other and building off of one another, all of which are metabolizing, assimilating and building components of varying complexities. In soil we have various species of bacteria, fungi, protozoa, nematodes, arthropods and other detritivores working both with and against each other; engaging in symbiotic relationships with the plant directly and/or other organisms in the soil or competing with one another in order to sustain the food web, and make life possible and easier for one another.
The competition itself is a remarkable thing. When you have a variety of good organisms and detritivores thriving in your soil, there is much less chance that any bad parasitic pests would be capable of doing harm. Some of your good stuff is just competing for the same food source, while others are more directly engaged in eradicating parasites either by consuming them or producing compounds which are lethal to them).
Aside from specific chemicals that they produce (which I'll elaborate on momentarily), these organisms are directly affecting the soil composition. They are sequentially contributing to the content of organic matter and humic substances (humus) present in the soil as well as influencing such things as particle size, porosity and water retention. Earthworms are the greatest detritivores, enriching soil with available nutrients, increasing microbial populations, and enhancing soil structure.
Actinobacteria are decomposing bacteria, important to humus formation and nutrient recycling. It includes the genus Streptomyces, species of which produce some of the antibiotics I mentioned previously, including streptomycin, actinomycin and neomycin.
Some strains of bacteria such as Pseudomonas fluorescens, and streptomyces griseoviridis produce fungicides. Bacillus subtilis attacks parasitic fungi and various species of bacillus thuringiensis are toxic to specific insects such as israelensis which is effective against mosquito and fungus gnat larvae.
There are bacteria such as those within the Azotobacter genus that fix nitrogen from the atmosphere and convert it into usable forms. These and other bacteria also produce compounds which are growth stimulants, or phytohormones including auxins and cytokines (Bacillus). Azotobacter also assists in bioremediation of heavy metals, and biodegradation of certain pollutants.
I don't even want to get started on all that mycorrhizae does in assimilating nutrients and regulating uptake. But, they also happen to produce B-Vitamins which are supposed to stimulate growth and disease resistance.
Of course there are multiple perspectives here, depending on whether you grow indoors or out. If you grow outdoors and use chemical nutrients you are also hindering soil biota, diminishing the capacity of the soil food web to provide nutrients and sustain life. Some of those highly soluble chemicals will wash out of the soil and into the water supply.
I view 'organic' gardening as embracing the progression of the natural cycles of life/death/rebirth. A key aspect is nutrient recycling; taking dead organic matter or byproducts which would otherwise be quite useless, letting all of that life happen within it and allowing it to produce food for my plants, plus a whole lot more.
Awesome soil biology primer
Soil ecology
Actinobacteria overview
Streptomyces info
Bacillus subtilis info
Azotobacter info
Plant hormones
