Plant Growth-Promoting Rhizobium Nepotum Phenol Utilization: Characterization and Kinetics

Abstract

Phenol is a severe pollutant that harms the environment and, potentially, human health. This study aimed to investigate the biodegradability of phenol by the plant growth-promoting bacterium R. nepotum. That included studying the growth kinetics and the effects of growth conditions such as incubation temperature, pH, and the use of different substrate concentrations. As the primary substrate, six different starting concentrations of phenol were utilized. The ability of these cells to biodegrade phenol was greatly influenced by the culture conditions. After 36 and 96 hours of incubation at pH 7 and a temperature of 28 C, this organism grew the fastest and had the highest phenol biodegradation. The biodegradation rate is much higher at 700 mg/L, the highest of the six concentrations tried. In less than 96 hours of incubation, more than 90% of the phenol (700 mg/L) had been eliminated. The Haldane model has been the most accurate for determining the relationship between the initial concentration of phenol and growth rate. In contrast, the refined Gompertz model provided the most accurate depiction of phenol biodegradation over time. As predicted by the Haldane equation, the highest specific growth rate, half-saturation coefficient, and Haldane's growth kinetics inhibition coefficient are 0.7161 h1, 15.8 parts per million (ppm), and 292 parts per million (ppm), respectively. The equation of Haldane successfully fitted the experimental data by reducing the SSR (sum of squared errors) to 3.8x10 3. According to the results of the analysis by GC-MS for the bacterial culture sample, the hydroxylase enzyme was the first to convert the phenol molecule into catechol. The catechol was subsequently broken down into 2-hydroxymucconic semialdehyde by the 2,3-dioxygenase enzyme, which occurred through the meta-pathway. It is the first study showing that R. nepotum, a plant growth promoter, has high efficiency of phenol. In phenol-stressed conditions, this could help with rhizoremediation and crop yield preservation.