-MAIZE ROOT EXUDATES STIMULATE BACTERIAL RELEASE FROM INDUSTRIAL GRADE STARCH/CHITOSAN BEADS

FERNANDEZ, MACARENA; PAGNUSSAT LA; CREUS CECILIA

Congreso; SAMIGE 2022; 2022

Immobilization of Plant growth-promoting rhizobacteria (PGPR) in biodegradable polymeric matricesconstitutes a promising technology for plant growth promoting to overcome the challengingconditions of the rhizosphere. One of the crucial aspects for plants to acquire the beneficial effects ofPGPRs is the gradual release from the polymeric matrix allowingsubsequent colonization of the rootsystem. Radical exudates are perceived as the first line of communication between plants and PGPRin the rhizosphere. Since the presence of attractants and repellents in the environment influences themotility of bacteria, the aim of this work was to study how radical exudates affect the release ofencapsulated PGPRs. Fluorescent derivatives of Azospirillum argentinensis Az39 and Pseudomonasfluorescens ZME4 were single or jointly immobilized in industrial grade starch/chitosan macrobeads.Az39 was transformed with pME7134mob plasmid expressing the fluorescent red protein (dsRED),and ZME4 was transformed with the plasmid Pmp5655 expressing fluorescent green protein (gfp).Root exudates were obtained from pre-germinated maize seeds soaked in water at a ratio of 1:1.5(g/mL). The collected fluid was lyophilized and resuspended in a volume that was a third of their initialvolume, right before the experiments. Bacterial release kinetics were assayed by placing PGPR-loadedbeads in water or exudates. Colony forming units CFU in the suspension and the remaining bacteriainside the beads were measured at three time intervals using drop plate method. The impact of wholemaize roots on the release of immobilized PGPR and their subsequent colonization was also examined24 hours after inoculation, using the same methods. Our findings show that PGPR progressivelyrelease and multiply once beads are hydrated. This was especially notable for ZME4 because after 24h CFU were two orders higher than the initial inoculum. In the first five hours after inoculation, theexudates stimulated the bacterial release of both strains. Az39 had a longer- lasting and persistentrelease from the beads that lasted for more than 48 hours. ZME4 and Az39 were able to colonize maize root within the first 24 hours after inoculation, with titers of 108 CFU.g-1 and 104 CFU.g-1,respectively. Our study provides evidence that maize root exudates play a crucial role in the bacterialrelease from biodegradable polymers, attraction and PGPR colonization in the roots. PGPRencapsulation technology that allow regulated release of PGPR with high bacterial titers near to theseed environment could guarantee successful inoculation.