Nano-carriers effects on the viability and efficiency of Pseudomonas strains as phosphate solubilizing bacteria

In order to develop nanotechnology application in the agricultural systems achieving more sustainability in the environment, we have used different nano-carriers for phosphate solubilizing bacteria. The viability and efficacy of two bacterial species; Pseudomonas putida (PP20) and Pseudomonas kilonensis (PK11) in solubilizing phosphate sources (i.e., tricalcium phosphate and hydroxyapatite) with different nano-carriers including nanoclay, natural char micro-particles (NCMPs), nanoclay + alginate, NCMPs + alginate, and natural char nano-particles (NCNPs)+alginate were investigated. Clay, talc powder, and natural char (NC) were included for comparison. The synthesized NCNPs and NCMPs were characterized using FTIR, SEM and Boehm titration analyses. The results confirmed that the chemical oxidation of pristine char made many oxygenated functional groups on the surface of tiny and spherical NCNPs (14.8 nm) which caused their effective incorporation in the matrix of alginate beads. Results of phosphate solubilizing study showed that P. kilonensis was the superior species for viability and stability of its performance on solubilizing phosphorus. The six months evaluation showed that NCNPs + alginate and nanoclay + alginate carriers at both temperatures (4 °C and 28 °C), were the proficient carriers for preserving both bacteria. The results of solubilizing phosphorus sources revealed that both bacteria solubilized tricalcium phosphate more than hydroxyapatite and PK11 showed more privilege in this regard. In addition, the solubilizing index determined after storage for 6 months at 4 °C was higher for all the carriers. Analysis of variance for phosphatase activity revealed that embedding both bacteria in nanoclay + alginate carrier guaranteed the highest phosphatase activity, even though differences between this carrier and NCNPs + alginate and NCMPs + alginate were not significant for the PK11.