Detoxification of Hexavalent Chromium Using Biofilm Forming Paenochrobactrum pullorum Isolated from Tannery Wastewater Effluents

Abstract

Bioremediation for wastewater using microbes that can detoxify the harmful effects of Cr-VI is concerned. Ninety-two isolates were collected from tannery effluents and screened based on their abilities to remediate hexavalent chromium using LB agar media supplemented by K2Cr2O7 as a source for Cr-VI. Out of the total isolates, 44 isolates can grow at 200 ppm of CR-VI, while 7, 6, 21, 11, and 3 isolates showed growth at concentrations of 400, 600, 800, 1000, and 1200 ppm of Cr-VI, respectively. Furthermore, determination of Cr-VI reduction efficiency for isolates was performed using 1,5-diphenylcarbazide (DPC) method, and the highest reduction efficiency (70.6%) was achieved by isolate 16R. This isolate was identified genetically based on the 16S rRNA gene with a higher similarity of 99.83% to Paenochrobactrum pullorum, and the genetic tree relationship was constructed. The optimization process was conducted to obtain the optimal reduction conditions, including contact time, pH, temperature, inoculum size, and Cr-VI concentration, using the One Factor at a Time (OFAT) method. The highest chromium reduction efficiency increased to 92.5% after optimization for the most potent isolate at pH 9, temperature 30-35°C, and inoculum size 3-4 ml after 5 days of incubation; biofilm formation was also represented. This study is the first to prove the chromium-reducing characteristic of this strain, along with its ability to form a biofilm, which strongly enhances the use of this strain in reduction and biological treatment processes in wastewater treatment contaminated with Cr-VI.