Membrane shell permeability of Rs-198 microcapsules and their ability for growth promoting bioactivity compound releasing

Abstract

Microencapsulation of bacteria is an alternative technology to enhance viability during processing and application. Different from drug microcapsules, controlled release of the dynamic target bacteria and its metabolites from capsules to the rhizosphere is becoming an important issue for the success of microencapsulated PGPR. This work describes in detail the diffusion permeability coefficient (DPC) of rhizobacteria-loaded microcapsules and their relationship to growth metabolite release and bacterial survival rate. Results showed that the DPC value increased with the decrease of the molecular weight of the model probes, and also the increase of sodium alginate and bentonite concentrations. Importantly, the DPC value was negatively correlated with the survival rate of Rs-198. For storage features, the microencapsulation had no effect on the abilities of IAA production (65 μg mL⁻¹), ammonia nitrogen production (43 mg mL⁻¹), or phosphate dissolved (53 mg L⁻¹) after storing for 90 days. A pot experiment revealed that total nitrogen and phosphorus content of cotton plants in the microcapsules with Rs-198 treatment was increased by 43.48% and 46.51%; soil available phosphorus, ammonium nitrogen, alkali-hydrolysis nitrogen, and nitrate nitrogen contents also increased by 45.43%, 31.48%, 17.13% and 55.69%, respectively due to the synergistic effects of Pseudomonas putida Rs-198 and alginate–bentonite microcapsules. In conclusion, the DPC shows that microcapsules have appropriate permeability to control the bacterial growth metabolism and thus show a beneficial effect on cotton growth. This paper reports the release profile of the bacterial growth metabolism from live rhizobacteria-loaded microcapsules, and will provide valuable guidance on living microcapsule application.