Biological and physical stabilization by formulating and often drying microorganisms is necessary to produce manageable, easily applied and storage-stable bio products.
Even so, drying and storage will inevitably expose the microorganisms to environmental stress. Tolerance to drying can be improved by optimizing the physiological state of the cells prior to their desiccation.
Two principal approaches can help to achieve this. The first one is to optimize the growth conditions with respect to medium composition and abiotic cultivation parameters so that maximum stress tolerance in stationary growth phase is obtained.
The second approach is that of pre-conditioning or stressing the cells after cultivation through exposure to non-lethal environmental stressors. In other words, microorganisms can sometimes be trained to better cope with adverse conditions. A little stress can result in increased fitness and better chances of surviving stress levels that otherwise would be lethal for a non-preconditioned cell.
Mikroorganisms being grown in a bio-reactor under carefully controlled conditions. Photo: Cajsa Lithell.
Biological adaptations alone are not sufficient to ensure high survival in dry biological products. Addition of compounds that provide outside protection from harmful effects of freezing or drying is also necessary. These additives are often substances that the microorganisms can produce themselves and use for protection inside, such as disaccharides, amino acids and various amino acid derivatives.
Production of these compounds by microorganisms is often a response to stress or pre-conditioning and by including these compounds in the formulation survival can often be improved. However, each new microorganism will very likely require individual formulation optimization with regards to preconditioning regimes and formulations additives.
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