Isolation and characterization of a heavy metal resistant Comamonas sp. from industrial effluents

In this study, eight bacterial isolates showing a suitable resistance to heavy metals were obtained from electroplating effluents. The isolates were grown on nutrient agar including 1 mM of each heavy metal of cobalt (Co), chromium (Cr), mercury (Hg), zinc (Zn) and copper (Cu). The minimum inhibitory concentrations (MICs) of the isolates were determined using different concentrations of heavy metals (1-5 mM) by broth dilution method. One of the isolates showed higher MICs of 5, 5, 4, 3 and 3 mM when grown on Co, Cr, Hg, Zn and Cu, respectively and selected for further study. The bacterial identity was determined by various biochemical and physiological experiments. The optimum temperature and pH for the growth of the strain were 30°C and 7, respectively. The isolate was resistant to ampicillin, cephalotin, amikacin and gentamicin. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate belongs to the genus Comamonas with 99% similarity to Comamonas testosteroni; it was then designated as Comamonas sp. HM_AF12. Atomic absorption spectrometer analysis showed that 80% of chromium was removed from 5 mg/L of chromium solution after 1 h. The results suggest that Comamonas sp. HM_AF12 obtained from effluent owing to its high resistance to toxic heavy metals has great potential to be employed for bioremediation of chromium contaminated effluents.