Bioencapsulation of microbial inoculants for better soil–plant fertilization. A review

Abstract

Plant fertilization is a major issue in the context of increasing population and food risk, higher cost of fertilizers, and low target efficiency of traditional mineral fertilization practices. Alternatively, application of microbial inoculants to the soil can enhance the uptake of nutrients by plants and increase the efficiency of mineral fertilizers and manures. Encapsulation methods involve covering and protecting the microorganisms. Encapsulation of bacterial cells has been challenged and used mainly in the agricultural industry using processes, such as spray drying, interfacial polymerization, or cross-linking. Here, we review techniques for microbial inoculants and their benefits for sustainable agriculture. Techniques include fluidized bed, extrusion, molecular inclusion, coacervation, liposomes, ionic or inverse gelation, and oil-entrapped emulsion. Major topics discussed are formulation of microbial inoculants, conventional inoculants, bioencapsulation materials, bioencapsulation techniques, and future trends. We found that (1) conventional inoculant does not provide adequate protection for microorganisms. (2) Bioencapsulation improves the protection and controlled release of bacteria. (3) Sodium alginate is one of the most used products for the bioencapsulation of microorganisms. (4) The bioencapsulation of microbial inoculants is performed with the incorporation of an active ingredient into a matrix followed by a mechanical operation, and finally stabilization by a chemical or physical-chemical process. (5) Spray-drying process works on a continuous basis, low operating cost, and high quality of capsules in good yield, although the high temperature used in the process is not very appropriate for encapsulating non-spore-forming bacteria. 6) Fluid-bed process is a promising encapsulation technique for large-scale production in agricultural industry. (7) Ionic gelation is currently the most adequate method found to encapsulate bacteria. (8) Some advantages and drawbacks are found for each technique; therefore, the selection of suitable bioencapsulation method will depend on bacteria strain, cost, processing conditions, and handling.

Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013)

“…However, a good inoculant should have as many as possible of these desired features at reasonable quality. Synthesizing "super-inoculants" or finding a polymer used in more expensive industries, such as pharmaceuticals, nanotechnology, or cosmetics to accommodate all the desired features is theoretically possible and was proposed (John et al 2011;Schoebitz et al 2013), so far in small quantities and with no commercial products. As far as we know, no effort to synthesize a carrier with predefined superior characteristics for agricultural and environmental purposes has been reported, presumably because of the high cost.…”

“…Although these were done without specific reference to agricultural/environmental inoculants, they may provide insight for future developments (John et al 2011;Schoebitz et al 2013). Three examples with potential for inoculant production are provided here.…”

Determining soil enzyme activities for the assessment of fungi and citric acid-assisted phytoextraction under cadmium and lead contamination

“…Microbial metabolite, such as low-molecular-weight acid, can also change the chemical availability of heavy metals in soil to assist the phytoextraction (Braud et al 2009). Furthermore, application of beneficial microbial inoculants to soil promotes the uptake of nutrients by plants and then enhances phytoextraction effectiveness by promoting plant growth (Schoebitz et al 2013). Nevertheless, the potential biotoxicity of chelate agents and microorganisms to soil and plant health limited the applications in soil (Leštan et al 2008).…”

Promoting fruit seedling growth by encapsulated microorganisms

“…Encapsulation is important for maintaining the stability of microorganisms and for increasing the resistance of bacteria in the substrate. Among the many types of encapsulating materials, calcium and sodium alginate, as well as whey proteins and gums have been the most widely used (SCHOEBITZ et al, 2013;VEMMER;PATEL, 2013). Clay is also a good encapsulating agent with properties different from alginate, but maintaining the desired properties of an encapsulating agent.…”