Metabolites Of Composite Microbial Inoculants
During the processes of colonization and proliferation in the soil, composite microbial inoculants produce a variety of metabolites; these substances form the crucial basis for their functions, such as promoting growth, conferring disease resistance, and improving soil quality.
The metabolites produced by composite microbial inoculants enhance crop uptake of nutrients like nitrogen, phosphorus, and potassium, while also stimulating root growth through the secretion of hormones, amino acids, and polysaccharides. These metabolites improve soil aggregate structure and increase water and nutrient retention capacities; they also facilitate nitrogen fixation and the solubilization of phosphorus and potassium, converting immobilized soil nutrients into plant-available forms.
Antibiotic-like substances (such as subtilin and polymyxin) and various active enzymes secreted by beneficial bacteria can effectively inhibit or kill pathogenic bacteria. By competing for nutrients and space, exerting antibiotic effects, and producing lytic substances, they suppress harmful microorganisms, thereby reducing the incidence of soil-borne diseases.
These metabolites regulate nutrient uptake and photosynthetic efficiency, leading to increased crop yields. They can reduce nitrate and heavy metal levels in plants while boosting the content of Vitamin C, soluble sugars, essential amino acids (lysine and methionine), B-group vitamins, and unsaturated fatty acids in fruits, thereby improving the taste, appearance, and storage stability of agricultural produce.
In the field of post-harvest preservation, metabolites from specific microbial strains can effectively inhibit spore germination of pathogens (such as Colletotrichum species), delay fruit ripening and softening, and maintain levels of total soluble solids and titratable acidity. Furthermore, they enhance the activity of disease-resistance enzymes-such as β-1,3-glucanase, peroxidase, and phenylalanine ammonia-lyase-thereby boosting the post-harvest disease resistance of fruits and vegetables.
Metabolites produced by different microbial strains serve distinct functions; for instance, metabolites from Nocardia species are highly effective against soil-borne diseases; Bacillus subtilis produces various antimicrobial substances, including subtilin; Bacillus mucilaginosus secretes growth-promoting substances such as hormones, amino acids, and polysaccharides; and phosphate-solubilizing Bacillus megaterium is capable of degrading organic phosphorus.
