Cadmium-Tolerant Plant Growth-Promoting Bacteria Curtobacterium oceanosedimentum Improves Growth Attributes and Strengthens Antioxidant System in Chili ( Capsicum frutescens )

The remediation of potentially toxic element-polluted soils can be accomplished through the use of microbial and plant-assisted bioremediation. A total of 32 bacteria were isolated from soil samples contaminated with potentially toxic elements. The isolated bacterial strain DG-20 showed high tolerance to cadmium (up to 18 mM) and also showed bioaccumulative Cd removal properties, as demonstrated by atomic absorption spectroscopy studies. By sequencing the 16S rRNA gene, this strain was identified as Curtobacterium oceanosedimentum . Under stress and normal conditions, isolate DG-20 also produced a wide range of plant growth promoting traits, including ammonia production (51–73 µg/mL) and IAA production (116–183 µg/mL), alongside siderophore production and phosphate solubilization. Additionally, pot experiments were conducted to determine whether the strain could promote Chili growth when Cd salts are present. Over the control, bacterial colonization increased root and shoot lengths significantly up to 58% and 60%, respectively. Following inoculation with the Cd-tolerant strain, the plants also increased in both fresh and dry weight. In both the control and inoculated plants, Cd was accumulated more in roots than in shoots, indicating that Chili was phytostabilizing Cd levels. Besides improving the plant attributes, Cd-tolerant bacteria were also found to increase the amount of total chlorophyll, proline, total phenol, and ascorbic acid in the soil when added to the soil. These results suggest that the inoculant provides protection to plants from negative effects. The results of the present study predict that the combined properties of the tested strain in terms of Cd tolerance and plant growth promotion can be exploited for the purpose of the bioremediation of Cd, and for the improvement of Chili cultivation in soils contaminated with Cd.