Gel entrapment and micro-encapsulation: methods, applications and engineering principles

The ecological competence (the ability of microbial cells/inocula to compete and survive in nature) of laboratory/bioreactor prepared inocula is paramount to commercial exploitation of biotechnological processes initiated by the addition of microbial cultures to natural habitats. Such processes include waste-treatment, bioremediation, dairy and food, agricultural and environmental systems and are characterized by a general inability to regulate the process environment stringently. Such inocula systems will require, as a first step, an efficient formulation and delivery system, based on microenvironmental control, directed at minimizing the lag period and maximizing competitive advantage to the introduced microorganisms.

Controlled Release of Immobilized Cells as a Strategy to Regulate Ecological Competence of Inocula

A non-toxic phase separation method was developed for microencapsulation of inoculum used in biological control. Aqueous sodium alginate or gelatin and agar was mixed with inocula of various biopesticides and emulsified in a mixture of corn oil, n-hexadecane, and lecithin. Gelatin and agar globules gelled in the emulsion; alginate globules gelled after settling into a lower phase of aqueous CaCl2. A layer of gelatinous material thus surrounded the inoculum as 'capsules'. Mixing with n-hexadecane reduced the specific gravity and surface tension of the oil, allowing aqueous extraction of the capsules. Successful extraction of alginate capsules depended upon lecithin (>0.17%), n-hexadecane (>30%), and CaCl2 (>0.01 M) concentrations. Alginate-encapsulated macroconidia of Fusarium avenaceum caused 23±3% leaf area damage to seedlings of marsh reed grass, versus 4±3% for unformulated controls. In green foxtail seedlings, gelatin and agar-encapsulated conidia of Bipolaris sorokiniana caused 21.3 vs. 7.9 ...

https://www.cfs.nrcan.gc.ca/pubwarehouse/pdfs/21348.pdf

Microencapsulation: A Strategy for Formulation of Inoculum

New materials and technology for cell immobilization

The widespread development and application of gel immobilised cell technology has significantly increased the interest in the physiology of immobilised cells. A number of reports have appeared suggesting that the immobilisation has a profound effect on the metabolic behaviour of immobilised cells compared to free cells. On the other hand, results of other reports suggest that the observed changes are caused by a change in local concentrations due to mass transfer limitations.

Physiology of Immobilised Microbial Cells

Yeast protoplasts may regenerate the cell wall and revert to cells if immobilized in a 2%–5% Ca-alginate gel and cultured in an osmotically stabilized medium. The method of protoplast immobilization and subsequent isolation from the gel is described in detail. The reversion yield is dependent of the actual gel concentration, gel shape (beads vs. sheets) and of a medium molarity, and it may be up to 90%. The morphology of the cell wall regeneration and morphology of reversion to the cell forms correspond to protoplast development in gelatin or agar gels.

Petr Ouředníček

Papers

Yeast protoplasts immobilized in alginate: Cell wall regeneration and reversion to cells