Encapsulation efficiency and survival of plant growth-promoting microorganisms in an alginate-based matrix – A systematic review and protocol for a practical approach

In recent years, there has been increasing interest in the immobilization of plant growth-regulating microorganisms in various carriers, showing different degrees of effectiveness. Among the carriers, polymeric materials, including alginate-based, have attracted considerable attention. This review aims to provide an overview of research related to matrix selection for the effective encapsulation of microorganisms. To regulate the network properties, particular focus was given to biopolymeric structures, including alginate and various fillers. Searches were conducted on October 30, 2021 in the Scopus and Web of Science databases. A total of 421 publications were collected; 43 items (from 2011 to 2021) were included for further study. Basing on the full-text analysis, the formulation of the most favorable matrix for high microbial survival and controlled release in the soil environment was identified. The most commonly used encapsulation matrix parameters were concentration of sodium alginate 1–3%, crosslinking agent CaCl 2 1–2%, the effect of additives is highly dependable on the type of microorganism and the desired properties of the beads. Additives such as starch, bentonite , gelatin are generally utilized for structure changes, increase of survival, biodegradation rate, as well as porosity. The positive effect of bacterial encapsulation was evaluated based on the impact on the plant's growth parameters such as shoot and roots length (growth be up to 100%), colonization rate (approximately 80%). This literature review presents the state-of-the-art on immobilization parameters, selection of alginate matrix components, encapsulation efficiency, methods for the physicochemical analysis of hydrogel capsules, and techniques for testing the efficacy of applied formulations on plants. A protocol for matrix selection and tests necessary to verify inoculant efficacy was proposed, which may become part of future biotechnology trends. • The matrix composition has a keynote impact on microorganisms survival rate. • Encapsulation efficiency can be dependent on the type of crosslinking agent. • Storage at low temperatures (4 °C) ensures a higher microorganisms survival rate. • Key strategies for matrix component selection were identified.