Formulations of polymeric biodegradable low-cost foam by melt extrusion to deliver plant growth-promoting bacteria in agricultural systems

Abstract

The extrusion technology of blends formed by compounds with different physicochemical properties often results in new materials that present properties distinctive from its original individual constituents. Here, we report the use of melt extrusion of blends made from low-cost materials to produce a biodegradable foam suitable for use as an inoculant carrier of plant growth-promoting bacteria (PGPB). Six formulations were prepared with variable proportions of the raw materials; the resulting physicochemical and structural properties are described, as well as formulation performance in the maintenance of bacterial viability during 120 days of storage. Differences in blend composition influenced foam density, porosity, expansion index, and water absorption. Additionally, differences in the capability of sustaining bacterial viability for long periods of time were more related to the foam composition than to the resulting physicochemical characteristics. Microscopic analyses showed that the inoculant bacteria had firmly attached to the extruded material by forming biofilms. Inoculation assays using maize plants demonstrated that the bacteria attached to the extruded foams could survive in the soil for up to 10 days before maize sowing, without diminishing its ability to promote plant growth. The results presented demonstrate the viability of the new matrix as a biotechnological material for bacterial delivery not only in agriculture but also in other biotechnological applications, according to the selected bacterial strains.

Maize Inoculation with Azospirillum brasilense Ab-V5 Cells Enriched with Exopolysaccharides and Polyhydroxybutyrate Results in High Productivity under Low N Fertilizer Input

“…Liquid inoculants simplify both the industrial production and the field application, although compared with solid formulations, such as peat- or polymer-based inoculants, bacteria in liquid inoculants appear to be more sensitive to stressful conditions and can exhibit decreased viability when used on seeds or soil (Herrmann and Lesueur, 2013 ). Effectiveness of PGPB inoculants has been improved by immobilization of inoculant cells in polymeric carriers, such as alginate and starch foam (Bashan et al, 2016 ; Marcelino et al, 2016 ). Thus, the actual demand is for improved liquid inoculant formulations, which are replacing peat-based inoculants and currently comprise ~80% of doses sold for soybean crops in Brazil (Hungria et al, 2015 ).…”

Efficacy of alginate- and clay-encapsulated microorganisms on the growth of Araçá-Boi seedlings (<I>Eugenia stipitata</I>)

“…Some studies have shown benefits in terms of the encapsulation of microbial inocula, increasing the survival time and establishment of microbes in the soil (Marcelino, Milani, Mali, Santos, & Oliveira, 2016). It is interesting that there were no significant differences in the total number of bacteria isolated from the soil that received the encapsulated microbial inoculum and the soil that received the nonencapsulated microbial inoculum (Figure 1).…”

“…Biological Sciences, v. 41, e43936, 2019 increased ammonium concentration in the soil that received alginate. Alginate is a polysaccharide and may serve as a carbon and energy source for heterotrophic soil bacteria, which need energy from plants (Marcelino et al, 2016). The alginate with or without inoculum did not increase the total number of bacteria in the soil (Table 2).…”

Shelf Life of Azospirillum brasilense in Alginate Beads Enriched With Trehalose and Humic Acid

“…In the literature, different concentrations of microorganisms in inoculant formulations (CFU mL -1 ) are reported: 10 9 (Reetha et al, 2014); 10 10 (Young et al, 2006); 10 6 (Marcelino, Milani, Mali, Santos, & Oliveira, 2016); 10 3 (O'Callaghan, 2016). Encapsulation demands high population density during inoculation in order to ensure the minimum population desired.…”