Effects of Mercury II on Cupriavidus metallidurans Strain MSR33 during Mercury Bioremediation under Aerobic and Anaerobic Conditions

Abstract

Mercury is a toxic element that harms organisms and disturbs biogeochemical cycles. Mercury bioremediation is based on the reduction of Hg (II) to Hg (0) by mercury-resistant bacteria. Cupriavidus metallidurans MSR33 possesses a broad-spectrum mercury resistance. This study aims to establish the effects of mercury on growth, oxygen uptake, and mercury removal parameters by C. metallidurans MSR33 in aqueous solution during aerobic and anaerobic mercury bioremediation. A new culture medium (GBC) was designed. The effects of mercury (II) (20 ppm) on growth parameters, oxygen uptake, and mercury removal were evaluated in GBC medium in a bioreactor (3 L) under aerobiosis. The anaerobic kinetics of mercury removal was evaluated by nitrogen replacement during mercury bioremediation in a bioreactor. Strain MSR33 reached a growth rate of µ = 0.43 h−1 in the bioreactor. Mercury inhibited oxygen uptake and bacterial growth; however, this inhibition was reversed after 5 h. Strain MSR33 was able to reduce Hg (II) under aerobic and anaerobic conditions, reaching, at 24 h, a metal removal of 97% and 71%, respectively. Therefore, oxygen was crucial for efficient mercury removal by this bacterium. Strain MSR33 was capable of tolerating the toxic effects of mercury (II) during aerobic bioremediation and recovered its metabolic activity.

Bioremediation by Cupriavidus metallidurans Strain MSR33 of Mercury-Polluted Agricultural Soil in a Rotary Drum Bioreactor and Its Effects on Nitrogen Cycle Microorganisms

“…Mercury is a toxic heavy metal that causes deleterious effects on organisms due to its high affinity to sulfhydryl and thioester groups on proteins [ 17 , 18 ]. Mercury causes growth arrest, oxidative stress, disruption of the integrity of cell membranes, interference with the electron transport system, enzymatic inhibition, and replacement of metallic centers of metalloproteins [ 19 , 20 , 21 , 22 ]. Heavy metal pollution causes major changes in soil microbial composition and their activities [ 3 , 13 , 23 ].…”

“…Bioremediation is an eco-friendly and low-cost treatment based on the capability of bacteria, fungi, archaea, and plants to remove or transform compounds or elements into less toxic forms [ 22 , 25 , 26 , 27 , 28 ]. Mercury bioremediation by mercury-resistant bacteria is based on the reduction of Hg (II) to gaseous Hg (0) by proteins encoded by the mer genes [ 16 , 19 , 29 , 30 , 31 , 32 , 33 ].…”

“…Mercury bioremediation by mercury-resistant bacteria is based on the reduction of Hg (II) to gaseous Hg (0) by proteins encoded by the mer genes [ 16 , 19 , 29 , 30 , 31 , 32 , 33 ]. Cupriavidus metallidurans is a facultative anaerobic bacterium capable of removing heavy metals (Hg, Cd, Cu) and degrading toxic organic pollutants such as toluene under aerobic and anaerobic conditions [ 19 , 22 , 34 , 35 , 36 , 37 ]. C. metallidurans strain MSR33 is a transconjugant derivative of C. metallidurans CH34, which contains the environmental plasmid pTP6 [ 19 ].…”

“…C. metallidurans strain MSR33 is a transconjugant derivative of C. metallidurans CH34, which contains the environmental plasmid pTP6 [ 19 ]. Strain MSR33 possesses an increased mercury resistance (2.4-fold), reducing Hg (II) and organomercurial compounds into Hg (0) under aerobic and anaerobic conditions [ 19 , 22 ]. A method for the bioremediation of environments polluted with mercury, copper, and cadmium using C. metallidurans strain MSR33 has been patented [ 38 ].…”

“…A method for the bioremediation of environments polluted with mercury, copper, and cadmium using C. metallidurans strain MSR33 has been patented [ 38 ]. Several processes for mercury bioremediation from aqueous solutions have been described [ 19 , 22 , 29 , 39 , 40 ]. However, the bioremediation of mercury-polluted soil has been scarcely studied.…”