Isolation and Characterization of Citrobacter farmeri SCO1: A Novel m -Cresol-Degrading Strain

Abstract

A bacterium capable of biodegrading m-cresol was isolated from aerobic sludge of a coking wastewater treatment plant. Morphological and biochemical analyses, as well as 16S rRNA gene sequence comparisons, demonstrated that the selected strain, SCO1, belongs to the species Citrobacter farmeri. Growth of the bacterium is coupled with the biodegradation of m-cresol. Optimal biodegradation conditions were pH 7 and a temperature of 35°C. Under these conditions, C. farmeri SCO1 degraded approximately 700 mg · L⁻¹ m-cresol completely with 200 mg · L⁻¹ biomass in 114 h. Lag periods varied from 0.5 h to 70 h when C. farmeri SCO1 biodegraded m-cresol at concentration ranges between 19 and 697 mg · L⁻¹. The average biodegradation rate (ABR) increased with an increasing initial concentration of m-cresol from 20 to 300 mg · L⁻¹, to a maximum ABR of 9.80 mg · L⁻¹ · h⁻¹. The kinetics followed a zero-order model when lag phase is excluded. Results indicated that C. farmeri SCO1 was an efficient strain and its maximum m-cresol concentration tolerance was higher than for previously described bacteria. A Haldane model was used to interpret the free cell specific growth rate on m-cresol biodegradation. Kinetic parameters were estimated up to an initial concentration of 696 mg · L⁻¹ yielding model constants for maximum specific growth rate (μ_max = 0.429 h⁻¹), half saturation (K_s = 37.65 mg · L⁻¹), and substrate inhibition constant (K_i = 165.68 mg · L⁻¹) for cell growth on m-cresol. Results demonstrated that the Haldane model was acceptable for describing the dynamic behavior of m-cresol biodegradation by C. farmeri strain SCO1.