The Cast of Microbial Characters
1) Photosynthetic Bacteria (Rhodopseudomonas palustris)
The photosynthetic or phototropic bacteria are a group of independent, self supporting microbes. These bacteria synthesize useful substances from secretions of roots, organic matter and/or harmful gases (eg. hydrogen sulphide), by using sunlight and the heat of soil as sources of energy. Useful substances developed by these microbes include amino acids, nucleic acids, bioactive substances and sugars, all of which promote plant growth and development. The metabolites developed by these microorganisms are absorbed directly into plants and act as substrates for increasing beneficial populations. R. palustris in particular has been acknowledged by microbiologists to be one of the most metabolically versatile bacteria ever described with the ability to utilize four distinct trophic feeding elements.
2) Lactic acid bacteria ( Lactobacillus plantarum, Lactobacillus casei, Lactobacillus fermentum, Lactobacillus delbrueckii)
Lactic acid bacteria produce lactic acid from sugars and other carbohydrates, developed by photosynthetic bacteria and yeast. Therefore, some foods and drinks such as yogurt and pickles have been made with lactic acid bacteria for decades. However, lactic acid is a strong sterilizing compound, and suppresses harmful microorganisms and enhances decomposition of organic matter. Moreover, lactic acid bacteria promote the decomposition of material such as lignin and cellulose and ferments these materials, thereby removing undesirable effects of non-decomposed organic matter. Lactic acid bacteria have the ability to suppress disease-inducing microorganisms such as Fusarium, which occur in continuous cropping programs. Under normal circumstances, species such as Fusarium weaken crop plants, thereby exposing plants to diseases and increased pest populations such as root-feeding nematodes. The use of lactic acid bacteria reduces root-feeding nematode populations and controls propagation and spread of Fusarium, thereby inducing a better environment for crop growth.
3) Yeast (Saccharomyces cerevisiae)
Yeasts synthesis antimicrobial and other useful substances required for plant growth from amino acids and sugars secreted by photosynthetic bacteria, organic matter and plant roots. The bio-active substances such as hormones and enzymes produced by yeasts promote active cell and root division. These secretions are also useful substrates for microorganisms such as lactic acid bacteria and actinomycetes. When yeast lyse occurs they release the complete B vitamins into the soils aiding in recovery of plants from stresses.
4) Bacilli (Bacillus subtilis)
Bacillus work in the soil by forming bio-films composed of a multitude of microorganisms. These tend to be formed at the interface between the air and water and interacts with the plant's root system. These bio-films are beneficial because for many reasons. Bio-films are typically formed through the microbes use of quorum sensing. Beneficial microorganisms are able to inhibit pathogenic microorganisms to gain dominance in the bio-films. This ability aids in the control of pathogenic infections of plants. Many of the Bacillus microbes can degrade polymers such as protein, starch, and pectin, therefore, they are considered to be an important contributor to the carbon and nitrogen cycles. When the nutrient availability falls too low for Bacillus subtilis they will form endospores and hibernate until conditions return to more optimum levels. Bacillus subtilis has been found useful in foliar application to combat primary stages of powdery mildew infestation.