The reaction center is the sensitive target of the mercury(II) ion in intact cells of photosynthetic bacteria
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The sensitivity of intact cells of purple photosynthetic bacterium Rhodobacter sphaeroides wild type to low level (<100 μM) of mercury (Hg2+) 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 Hg2+ sensitivities of the electron transport (donor/acceptor) sites including the reduced bound and free cytochrome c 2 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.
KeywordsBacterial photosynthesis Intact cells Reaction center Antenna Mercury contamination Bacteriochlorophyll spectroscopy
- cyt c22+
Reduced cytochrome c 2
Primary acceptor (ubiquinone)
We are indebted to Ms Diana Nyúli for absorption measurements in the early phase of this project and to the support of NKTH-OTKA (K-67850), TÁMOP 4.2.2/B, COST Action on “Molecular machineries for ion translocation across biomembranes” (CM0902) and MTA-CNR Bilateral agreement on “Bacterial photosynthesis: artificial photosystems and bioremediation”.
- Antal TK, Graevskaia EE, Matorin DN, Volgusheva AA, Osipov VA, Krendeleeva TE, Rubin AB (2009) Study of the effect of methylmercury and copper ions on primary photosynthesis processes in the green algae Chlamydomonas moevusii using the parameters of kinetic curves of the variable of chlorophyll fluorescence. Biofizika 54(4):681–687PubMedGoogle Scholar
- Borsetti F, Martelli PL, Casadio R, Zannoni D (2009) Metals and metalloids in photosynthetic bacteria: interactions, resistance and putative homeostasis revealed by genome analysis. In: Hunter CN, Daldal F, Thurnauer MC, Beatty JT (eds) The purple phototrophic bacteria, Springer, Dordrecht, pp 655–689Google Scholar
- Lavergne J, Trissl H-W (1995) Theory of Fluorescence Induction in Photosystem II: Derivation of Analytical Expressions in a Model Including Exciton-Radical-Pair Equilibrium and Restricted Energy Transfer Between Photosynthetic Units. Biophys J 68:2474–2492Google Scholar
- Lavergne J, Vermeglio A, Joliot P (2008) Functional coupling between reaction centers and cytochrome bc1 complexes. In: Hunter CN, Daldal F, Thurnauer M, Beatty JT (eds) The purple photosynthetic bacteria. Springer, Dordrecht, pp 509–536Google Scholar
- Maróti P, Asztalos E (2012) Calculation of connectivity of photosynthetic units in intact cells of Rhodobacter sphaeroides. In: Congming L (ed) Photosynthesis: research for food, fuel and future—15th international conference on photosynthesis, Symposium 02-01. Zhejiang University Press, Springer-Verlag GmbH, pp 27–31Google Scholar
- Mishra S, Dubey RS (2005) Heavy metal toxicity induced alterations in photosynthetic metabolism in plants, Chapter 44. In: Pessarakli M (ed) Handbook of photosynthesis, 2nd edn. CRC Press, Boca RatonGoogle Scholar
- Murthy SDS, Mohanty N, Mohanty P (1995) Prolonged incubation of mercury alters energy transfer and chlorophyll (Chl) a protein complexes in Synechococcus 6301: changes in Chl a absorption and emission characteristics and loss of the F695 emission band. Biometals 8:237–242PubMedCrossRefGoogle Scholar