Microencapsulation by spray drying of nitrogen-fixing bacteria associated with lupin nodules

Abstract

Plant growth promoting bacteria and nitrogen-fixing bacteria (NFB) used for crop inoculation have important biotechnological potential as a sustainable fertilization tool. However, the main limitation of this technology is the low inoculum survival rate under field conditions. Microencapsulation of bacterial cells in polymer matrices provides a controlled release and greater protection against environmental conditions. In this context, the aim of this study was to isolate and characterize putative NFB associated with lupin nodules and to evaluate their microencapsulation by spray drying. For this purpose, 21 putative NFB were isolated from lupin nodules and characterized (16S rRNA genes). Microencapsulation of bacterial cells by spray drying was studied using a mixture of sodium alginate:maltodextrin at different ratios (0:15, 1:14, 2:13) and concentrations (15 and 30% solids) as the wall material. The microcapsules were observed under scanning electron microscopy to verify their suitable morphology. Results showed the association between lupin nodules of diverse known NFB and nodule-forming bacteria belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Bacteroidetes. In microencapsulation assays, the 1:14 ratio of sodium alginate:maltodextrin (15% solids) showed the highest cell survival rate (79%), with a microcapsule yield of 27% and spherical microcapsules of 5-50 µm in diameter. In conclusion, diverse putative NFB genera and nodule-forming bacteria are associated with the nodules of lupine plants grown in soils in southern Chile, and their microencapsulation by spray drying using sodium alginate:maltodextrin represents a scalable process to generate a biofertilizer as an alternative to traditional nitrogen fertilization.

Encapsulation Techniques for Plant Growth-Promoting Rhizobacteria

“…The results obtained by Schoebitz et al (2012) confirm this statement as these authors demonstrated that a large proportion of cells are destroyed during capsule dehydration. In fact, cell mortality during the drying of encapsulated cells has been recognized as a critical point of the encapsulation process by various authors (Bashan et al 2002;Campos et al 2014). The survival yield after drying did not exceed 1 % of the initial cell count for various Azospirillum and Pseudomonas species.…”

“…Other studies have confirmed these observations, also reporting that the lowest air temperature was associated with the highest survival rate for the microorganisms during the drying process (Gardiner et al 2000;Golowczyc et al 2010). In fact, Campos et al (2014) reached a bacterial survival of 91 % for Enterobacter sp. immobilized using sodium alginate and maltodextrin as wall materials (2:13 w/w), feed flow rate of 73 m 3 h À1 , inlet temperature of 100 C, and outlet temperature of 65 C. In contrast, Schoebitz et al (2013b) found lower cell survival after the encapsulation of microorganisms such as Serratia sp., using only maltodextrin as wall material, inlet temperature of 145 C, and outlet temperature of 90 C. In this sense, the type of strain, temperature of the drying process, and formulations of the polymer mixture used as vehicles are important parameters for the encapsulation of beneficial microorganism in order to obtain a successful microbial inoculant.…”

“…Spray drying, which is a dehydration process, is one of the immobilization techniques used for the production of microbial inoculants that can be incorporated into agricultural and nonagricultural systems. The use of spray drying as a standard production technique is challenging due to its detrimental impact on the cellular integrity of microorganisms during drying (if not correctly optimized) and resultant reduction in the survival of immobilized bacteria (Campos et al 2014). It has been demonstrated that heat-induced cellular damage is primarily associated with changes in the physical state of the membranes (BehboudiJobbehdar et al 2013).…”

“…Numerous studies have focused on developing different encapsulation techniques to improve the survival of microbial inoculants (Herrmann and Lesueur 2013;Schoebitz et al 2013a;Bashan et al 2014;Campos et al 2014). Encapsulation of microorganisms is one of the newest and most efficient techniques.…”

Bakteri̇yofaj Enkapsülasyonu Ve Potansi̇yel Uygulamalari

“…Ürünlerin içerisindeki suyun uzaklaflt›r›lmas›, depolama ve tafl›ma maliyetlerinin azalt›lmas› ve ürünlerin spesifik özelliklerinin korunmas› amac›yla g›da sanayinde yayg›n olarak kullan›lan bu yöntem, süttozu üretimi ile birlikte gelifltirilmifltir. Sprey kurutma yöntemi en yayg›n ve en ucuz teknik olmas›na ra¤men bu yöntemde kapsülleme amac›yla tercih edilecek olan materyal seçimi oldukça önemlidir (27)(28)(29). Uygulamada atomizer içerisinde hem çekirdek ad› verilen kaplanacak materyal hem de kaplama materyali bir arada bulunmaktad›r.…”