Biodegradation of picric acid (2,4,6-trinitrophenol, TNP) by free and immobilized marine Enterococcus thailandicus isolated from the red sea, Saudi Arabia

Nitroaromatic effluents are common wastes generated from different industrial activities. These wastes can cause various environmental problems due to their toxicity on living organisms and difficulties to decompose either chemically or biologically. However, picric acid (2,4,6-trinitrophenol, TNP) could be used as a sole carbon, nitrogen, and energy source by a few bacterial cells. In this study, a bacterial strain isolated from the Red Sea, Jeddah, Saudi Arabia, has been shown to utilize picric acid as a sole carbon and nitrogen source at a relatively high concentration. The growth medium altered from yellow into the orange-red color (hydride-Meisenheimer complex) after 48 h of incubation as detected using High-Performance Liquid Chromatography (HPLC). The stoichiometric release of 0.285 mol of nitrite showed strong evidence that the picric acid was completely mineralized. Molecular identification using 16S rRNA analysis indicated that the isolated strain is Enterococcus thailandicus RF1 (Genbank Accession No. MN960654). This strain is capable of utilizing TNP aerobically at pH 7.0 and 30 °C with nitrite release. Furthermore, Enterococcus thailandicus RF1 cells were immobilized by adsorption on polyurethane foam and TNP degradation was enhanced and increased to 1.12-folds of free cells. The immobilized cells were found to be used efficiently for bioremediation of TNP from wastewaters.