Regarding bacteria and fungi in the soil, they play off one another.
Most species of terrestrial plants have very "leaky" roots, and in some instances secrete up to 40% of the total photosynthate during the plants lifetime, in the form of various carbohydrates.
When a seed is germinating and growing in soil it begins excreting carbohydrates into the soil, usually simpler sacharides. As this occurs, the bacterial population in the rhizosphere rapidly increases. The bacteria in turn "mine" other inorganic nutrients in the soil so that they can grow and reproduce using the carbon sugar source.
As plant growth continues, many plants will start synthesizing and excreting lipids and fatty acids like mono-acyl gylercerols. When the plant begins excreting these through the roots, the bacteria population begins to die off. Bacteria do not have the proper metabolic pathways to digest fatty molecules.
When this occurs the fungal population begins to grow rapidly, since they can metabolize lipids. Simultaneously, the inorganic nutrients "mined" by the dead bacteria are now in a biologically active form.
As the mycorrhizal fungi continue to grow they exchange nutrients and moisture for food. A lot of the research suggests these fungi are really good at scavenging phosphorus, and are inhibited by high concentrations of it.
So basically fungi and bacteria are all present in healthy situations, and it is not as simple as they kill each other, they just fill a different niche.
If you want a good fungal population use a reputable mycorrhizal inoculant like mycoapply, don't add any extra phosphorus to your soil, don't till, and keep a good mulch layer on the soil