Screening of bacterial strains for heavy metal stress tolerance, antimicrobial potential, and optimum growth at a wide range of pH and temperatures

Abstract

The growing global population calls for sustainable and eco-friendly methods to enhance food production. One such solution is the use of plant growth-promoting rhizobacteria (PGPR), which can improve both plant and soil nutrient status, thereby boosting crop yields. In this study, PGPR were isolated from the Lower Dir region and assessed for their antibacterial activity against two phytopathogens, Ralstonia solanacearum and Xanthomonas citri, as well as their tolerance to heavy metals. The growth of these PGPR was evaluated across a wide range of pH levels and temperatures. Of the 59 isolates, 15 demonstrated antibacterial activity against Ralstonia solanacearum, and 13 showed resistance to Xanthomonas citri. The isolate DJ 15 exhibited the largest inhibition zones against both pathogens, measuring 33.33 mm for Ralstonia solanacearum and 18.16 mm for Xanthomonas citri. In terms of heavy metal tolerance, the highest growth rate (OD) was observed in the presence of lead (2.05), followed by nickel (1.61) and cadmium (1.38). Growth rates were also monitored at varying pH levels, with the highest recorded at pH 6 after three hours (0.22), and at pH 7 after 24 hours (1.38). Temperature variation also affected growth, with the highest growth rates at 50 degrees C (0.33) and 30 degrees C (1.39) after three and 24 hours, respectively. These findings highlight the potential of PGPR as effective biocontrol agents capable of tolerating heavy metals and combating plant pathogens, making them valuable for sustainable agricultural practices.