Effect of pH on Mercury Uptake by an Aquatic Bacterium:  Implications for Hg Cycling

Abstract

We studied the effect of increasing hydrogen ion (H+) concentration on the uptake of mercury (Hg(II)) by an aquatic bacterium. Even small changes in pH (7.3-6.3) resulted in large increases in Hg(II) uptake, in defined media. The increased rate of bioaccumulation was directly proportional to the concentration of H+ and could not be explained by assuming that the source of Hg to the bacteria was diffusion of neutrally charged species such as HgCl2. Thus, pH appeared to affect a facilitated mechanism by which Hg(II) is taken up by the cells. Lowering the pH of Hg solutions mixed together with natural dissolved organic carbon, or with whole lake water, also increased bacterial uptake of Hg(II). These findings have several potential implications for mercury cycling, including effects on elemental mercury production, mercury sedimentation, and microbial methylation of Hg(II), and could be part of the explanation for the observed positive correlation between lake acidity and methyl mercury levels in fish.

Characterization of a marine-isolated mercury-resistant Pseudomonas putida strain SP1 and its potential application in marine mercury reduction

“…injected with 100 μL of P. putida SP1 suspension of 5.0×10 8 CFU mL −1 , 1.0×10 9 CFU mL −1 , 5.0× 10 9 CFU mL −1 , 1.0× 10 10 CFU mL −1 , and 5.0× 10 10 CFU mL −1 . Mortality was monitored over a period of 14 days after the challenge induce the expression of merA, accumulated in the cell with the decrease of pH (Kelly et al 2003;Ahn et al 2010). Considering all of these results, it was suggested that, besides the expression of merA and the concentration of Hg 2+ accumulated in bacteria, the transformation of Hg 2+ by P. putida SP1 may also require other specific detoxification reactions to contribute to its ability to volatilize Hg 2+ , such as the production of DNDPH by bacteria.…”

“…Mortazavi et al (2005) studied the effect of pH on the efficiency of removal of HgCl 2 by a P. putida strain. Other studies have indicated that pH is an important factor that significantly affects the concentration of bioavailable mercury, higher concentrations of mercury accumulating in the bacteria with the decreasing of pH (Golding et al 2002;Kelly et al 2003;Golding et al 2008;Ahn et al 2010). However, until now, the effect of pH on the expression of merA at the transcriptional level, an important process during mercury transformation, has not been examined.…”

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

“…Here, we observed pH-dependent bioaccumulation of mercury with the largest value at the neutral pH range and decreased substantially upon acidification and alkalization of the solution. Kelly et al (2003) reported an opposite pHtendency by an aquatic bacterium in a narrow (6.3<pH<7.3) range. Le Faucheur et al (2011) have examined the influence of pH on Hg(II) uptake (mainly in the form of the lipophilic complex HgCl2) by the green, unicellular alga, Chlamydomonas reinhardtii and observed that the uptake of the dichloro complex increased by a factor of 1.6 to 2 when the pH was lowered from 6.5 to 5.5.…”

“…The pH-dependence of mercury accumulation is a diverse field of research with many particular observations and results that are difficult to treat comprehensively (Kelly et al 2003;Le Faucheur et al 2011;Italiano et al 2009). Here, we observed pH-dependent bioaccumulation of mercury with the largest value at the neutral pH range and decreased substantially upon acidification and alkalization of the solution.…”

pH Dependence of CH3Hg+-binding Sites in Humic Acid: An X-ray Absorption Study

“…중성 pH에서는 유기물이 존재하면 미생물의 수은 흡수 가 급격히 감소하며 이는 아마도 거대분자인 유기물의 반 응기(특히 티올기)에 수은이 결합하면서 미생물 세포를 통 과하지 못하기 때문일 것이다 (Kelly et al, 2003). 그런데, pH가 중성에서 조금만 낮아져도 미생물의 수은흡수가 크 게 증가하며 유기물이 존재하여도 흡수감소 정도가 현격 히 줄어든다 (Kelly et al, 2003).…”