The reaction center is the sensitive target of the mercury(II) ion in intact cells of photosynthetic bacteria

Abstract

The sensitivity of intact cells of purple photosynthetic bacterium Rhodobacter sphaeroides wild type to low level (~100 µM) of mercury (Hg 2+ ) contamination was evaluated by absorption and fluorescence spectroscopies of the bacteriochlorophyll-protein complexes. All assays related to the function of the reaction center (RC) protein (induction of the bacteriochlorophyll fluorescence, delayed fluorescence and light-induced oxidation and reduction of the bacteriochlorophyll dimer and energization of the photosynthetic membrane) showed prompt and later effects of the mercury ions. The damage expressed by decrease of the magnitude and changes of rates of the electron transfer kinetics followed complex (spatial and temporal) pattern according to the different Hg 2+ sensitivities of the electron transport (donor/acceptor) sites including the reduced bound and free cytochrome c2 and the primary reduced quinone. In contrast to the RC, the light harvesting system and the bc1 complex demonstrated much higher resistance against the mercury pollution. The 850 and 875 nm components of the peripheral and core complexes were particularly insensitive to the mercury(II) ions. The concentration of the photoactive RCs and the connectivity of the photosynthetic units decreased upon mercury treatment. The degree of inhibition of the photosynthetic apparatus was always higher when the cells were kept in the light than in the dark indicating the importance of metabolism in active transport of the mercury ions from outside to the intracytoplasmic membrane. Any of the tests applied in this study can be used for detection of changes in photosynthetic bacteria at the early stages of the action of toxicants.

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

“…Mercury affects both light and dark reactions of bacterial photosynthesis and strongly inhibits the photosynthetic electron transport chain in which the reaction center (RC) protein is the most sensitive target (Asztalos et al 2012;Kis et al 2015). On the acceptor side, the Hg-induced inhibition is attributed to the damage of the interquinone electron transfer from QA to QB and/or to the increase of the fraction of closed RCs (QA − ).…”

Ecological strategy for soil contaminated with mercury

“…Mercury and its compounds are considered to be potentially hazardous to all biological organisms (Asztalos et al 2012;Boening 2000;Chen and Yang 2012). Mercury cannot be destroyed biologically but only transformed into volatile metallic mercury, HgO (Hobman and Brown 1997) or biomethylated by a number of bacterial species to gaseous methyl mercury (De et al 2008) or dimethyl mercury (Rodriguez et al 2005).…”

Dynamic change of wheat eco-physiology and implications for establishing high-efficient stable agro-ecosystems under Hg stress

“…In higher plants, photosynthesis is reduced indirectly by heavy metal accumulation in leaves which influences the stomata performance (Yu et al, 2014a,b). In addition, Hg 2+ ions affected both light and dark reactions of photosynthesis and strongly inhibited the photosynthetic electron transport chain, photosystem (PS) II being the most sensitive target (Asztalos et al, 2012). In this research, the absorption and accumulation of heavy metal ion Hg 2+ led to the drop in Pn of wheat seedlings to some extent at different times.…”