Effects of heavy metal cations on chromate reduction by enterobacter cloacae strain hol.

Abstract

Wastewaters containing hexavalent chromium (chromate: Cr042 ) are generated in many industrial processes, including chromium plating, metal cleaning and processing, wood preservation, and alloy preparation (6). Since Cr042 is harzardous to fauna and flora in natural ecosystems, these wastewaters must be treated before being discharged into the environment (7,8,10,11).In our previous studies (2, 4, 5, 9), we demonstrated the potential of a chromate-reducing bacterium, Enterobacter cloacae (strain HO 1), to remove Cr042 from wastewaters. To develop the biological treatment process, however, it must be considered that chromate-bearing wastewaters from industrial processes generally contain heavy metal cations, such as Cu2', Cd2~, Zn2, and Ni2+ (6). Since the heavy metal cations are known to be toxic for most organisms, they may greatly influence the performance of the biological process for treating Cr042 . However, there are presently no data published as to the effects of heavy metal cations on the bacterial reduction of Cr042 . In this communication, we demonstrate how heavy metal cations affect Cr042 reduction by E, cloacae strain HOI.Growth and reduction experiments were conducted anaerobically in KSC medium, as previously described (6,13). The pH of the KSC medium was 7.2. The heavy metal cations tested were Ag`' , Cd2 , Cot +, Cu`D , Hg2 +, Mn2D , Nit +, and Zn2' . The metal salts used were of the chloride type, except for ZnSO4, and the metal solution was added to the culture at various final concentrations just before the start of incubation. The concentration of viable cells was determined by plating 100,u1 of appropriately diluted culture onto nutrient agar and incubating the plates at 37°C for 16--20 h.

Effect of heavy metals on chromate reduction by Bacillus subtilis.

“…However, similar results indicating the strong inhibition caused by heavy metal cations on the reduction of chromate were reported by Hardoyo et al (1991) for anaerobically grown E. cloacae. B. subtilis cells appear to be significantly more resistant to the presence of these metal cations, as derived from the lower values of percent inhibition of chromate reduction found in our studies in comparison with those reported by Hardoyo et al (1991).…”

“…In fact, to our knowledge, there is only one report published as to the effects of heavy metals on the anaerobic reduction of chromate by Gram-negative Enterobacter cloacae (Hardoyo et al, 1991). Here, we report for the first time, the effect of the most common heavy metal cations found in chromate-bearing wastewaters on chromate reduction by the aerobic Gram-positive bacterium Bacillus subtilis.…”

Aerobic and Anaerobic Reduction of Cr(VI) by Shewanella oneidensis Effects of Cationic Metals, Sorbing Agents and Mixed Microbial Cultures

“…GARBISU et al [45] showed that Cr(VI) reduction in cell suspensions of Bacillus subtilis was inhibited by Cd 2+ , Cu 2+ , Zn 2+ and Ni 2+ . Similar results were obtained in studies using anaerobically grown cells of Enterobacter cloacae [46]. In conclusion, S. oneidensis-mediated Cr(VI) reduction has been demonstrated under a variety of environmentally relevant conditions.…”

Hexavalent molybdenum reduction to Mo-blue by Acinetobacter calcoaceticus

“…The high optimum temperature suggests that the bacterium should be useful in a tropical climate like Malaysia where normal soil temperatures could reach as high as 35 °C (Sinnakkannu et al 2004). In other similar works on the biological reduction of Cr(VI), the requirement of near-neutral pH and a moderate temperature range is shared by many chromate-reducing bacteria (Horitsu et al 1978;Gvozdyak et al 1986;Hardoyo et al 1991;Rege et al 1997;Koósz et al 2008).…”