Biodegradation of phenol by Ewingella americana: Effect of carbon starvation and some growth conditions

Ewingella americana was grown in batch cultures using a phenol-containing M9 minimal medium. Phenol was found to be the sole source for carbon and energy. Phenol was found to inhibit the growth rate with a maximum concentration of 1100 ppm, beyond which no growth occurred. The Haldane model was used to predict the specific growth rate-concentration data. The maximum growth rates on phenol (300 ppm) for starved and non-starved cells reached only 0.32 and 0.29 h−1, respectively. When the phenol-containing M9 minimal medium was supplemented with different C and N sources, different degradation rates (ppm/h) were obtained. Only fructose as the carbon source showed catabolic repression of the degradation activity; however, yeast extract, casein and glutamine caused the same effect, as did the fructose. The data showed that different initial (inocula) densities did not affect the induction time for phenol degradation. However, carbon-starvation minimized the acclimation period, accelerated the complete degradation achievement of phenol and affected the growth of cells differently based on the data obtained for growth phases. In the log phase, a higher growth rate was shown for starved cells with a shorter acclimation period, whereas in the stationary phase, a lower rate of growth was attained, compared with non-starved cells. Phenol degradation was optimally achieved at a 37 °C incubation temperature, a pH of 7.5 and an agitation rate of 200 rpm.