Serratia rubidaea SR19: A cadmium -tolerant bacteria enhancing phosphate solubilization, IAA production, and promoting cucumber seed germination

Abstract

Cadmium (Cd) contamination in soil poses significant environmental and health risks due to its toxicity. A sustainable way to detoxify heavy metals from soil is to use rhizobacteria that promote the growth of plants (PGPR). In this study, we measured the production of IAA and the solubility of inorganic phosphate to evaluate the plant growth-promoting traits of four isolates that show cadmium tolerance. None of the four isolates grew at 300 ppm cadmium chloride, indicating that this concentration represents the Minimum Inhibitory Concentration (MIC) for all isolates. Based on 16S rRNA molecular identification, four isolates are classified as Serratia rubidaea. The B3 isolate was selected for whole genome sequencing and deposited in the Japanese database as SR19 to clarify the genetic basis of features that promote plant growth and cadmium tolerance. Annotation revealed the presence of genes linked to heavy metal resistance, stress defense response, siderophore biosynthesis, nitrogen metabolism, sulfur metabolism, and phosphate solubilization. Additionally, we found that under both normal and cadmium stress conditions, S. rubidaea SR19 promoted the germination of cucumber seeds and the growth of seedlings in vitro. Our study suggests that using the isolated strain S. rubidaea SR19 may help mitigate the harmful effects of cadmium and other heavy metals in contaminated agricultural soil.