Impact of Vetiveria zizanioides rhizosphere bacterial isolates on PGPR traits and cadmium resistance

Abstract

In our study we have proved that most vetiver rhizosphere bacterial isolates are potent biomolecule synthesizers. We isolated culturable bacterium associated with vetiver rhizosphere using three carbon sources and phenotypic characterizations were performed. The medium and cultural conditions of the isolates were optimized under shake flask conditions. Further, the isolates were assessed for their ability to synthesize biomolecules and plant growth promoting rhizobacterial (PGPR) traits. Siderophore production was determined in all the tested isolates; Phosphate solubilization was performed and seven isolates were shown to solubilize phosphate. Indole 3-acetic acid (IAA) was produced by all isolates when grown on MS medium supplemented with tryptophan and the amount of IAA produced were quantified with standards. Metal tolerance concentration (MTC) was performed and it was observed that most isolates were able to survive till 300mg L^-1 on cadmium amended minimal medium. The isolate (VITJCSKK14) was able to show resistance till 500mg L^-1. Solubilization of zinc metal (0.1%) was analysed using LGI medium; halos were observed and quantified by checking the growth, pH and optical density. The soluble Zn present in the culture broth was determined using an atomic absorption spectrophotometer (AAS-Model Varian C) at different periods of growth and the maximum solubilization was recorded after 120 h with a 0.1% Zn metal amendment was 634mgl^-1. Further the intracellular proteins were separated to observe the whole cell protein and stress tolerant proteins from VITJCSKK14. The intracellular proteins were extracted from the cultures grown in Tris minimal media supplemented with cadmium and quantification was performed using Bradford’s method. The proteins were separated on SDS-PAGE and the stress protein bands were observed. It was found that high molecular weight protein was appeared in the test sample. The molecular taxonomy of the active isolate VITJCSKK14 was carried out by 16S rRNA analysis and phylogenetic tree was constructed using CLUSTALV software. Based on the phenotypic and phylogenetic analysis, the isolate VITJCSKK14 was identified as Acinetobacter Sp. This study also gives a hypothesis that Vetiveria zizanioides rhizosphere bacterium may aid in plant growth promotion and their survivability in adverse conditions.