A MANGANESE OXIDIZING Pseudomonas IS APPLICABLE FOR MERCURY BIOREMEDIATION

LOMBARDO R; LESCANO J; OTTADO J; CHECA SK; GOTTIG N

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General

Nowadays, heavy metal pollution has become one of the most serious environmental problems. The treatment of these metals is of special concern due to their recalcitrance and persistence in the environment. Various physical-chemical methods for heavy metal removal from wastewater have been extensively studied but they are inefficient, expensive and produce additional waste with greater potential for contamination. In a previous work, a Pseudomonas sagittaria strain named MOB-181 (MOB: Manganese-oxidizing bacteria) was isolated from two groundwater treatment plants currently in operation in Argentina. This environmental isolate formed biofilms and efficiently directed Mn removal from groundwater. Since MOB-181 has the potential to be used for metal bioremediation, its genome was sequenced to search for genes implicated in metal resistant. Here, we found genes possibly involved in Mercury (Hg) resistance, grouped in three different clusters throughout the MOB- 181 genome. Therefore, it was interesting to evaluate the Hg resistance of this bacterium and its potential to remove this toxic metal from contaminated water. In addition, two reference bacterial strains P. aeruginosa PAO1 and P. putida KT2440, which do not contain Hg resistance genes, were included as controls. First, MOB-181 growth on solid Lept-Mn medium, especially used for Mn(II) oxidation, in the presence of different Hg(II) concentrations was evaluated. The results showed that this bacterium resisted up to 50 μM Hg(II), and is significantly more tolerant than P. aeruginosa PAO1 and P. putida KT2440 (0,5 μM and 15 μM, respectively). Second, the tolerance to Hg(II) was evaluated in biofilms of MOB-181 formed on liquid Lept-Mn medium, after a 6 days statical incubation at 28ºC, showing that MOB-181 biofilms are also resistant to Hg(II) .Finally, to determine if Mn oxides formed by MOB-181 have an impact on Hg(II) removal, MOB-181 biofilms were grown in the Lept medium in the presence or absence of Mn(II), in the last condition the biofilms are covered with Mn oxides. Then, these biofilms were incubated statically at 28ºC with Lept or groundwater supplemented with 1 μM or 5 μM Hg(II). Daily samples of the supernatants were taken during 4 days, and the remanent toxic metal was determined using a bacterial biosensor. This biosensor is a genetically modified bacterium that couples the detection of soluble Hg2+ to the production of green fluorescent protein (GFP) that can be easily detected and quantified using a fluorescence reader. The results obtained showed that MOB-181 biofilm can remove Hg(II) in all the conditions tested with minimal differences between them. This work indicates that MOB-181 has a high biotechnological potential to be applied to Hg(II) bioremediation processes.