Purple non-sulfur photosynthetic bacteria monitor environmental stresses

Abstract

a b s t r a c tHeavy metal ion pollution and oxygen deficiency are major environmental risks for microorganisms in aqueous habitat. The potential of purple non-sulfur photosynthetic bacteria for biomonitoring and bioremediation was assessed by investigating the photosynthetic capacity in heavy metal contaminated environments. Cultures of bacterial strains Rhodobacter sphaeroides, Rhodospirillum rubrum and Rubrivivax gelatinosus were treated with heavy metal ions in micromolar (Hg 2+ ), submillimolar (Cr 6+ ) and millimolar (Pb 2+ ) concentration ranges. Functional assays (flash-induced absorption changes and bacteriochlorophyll fluorescence induction) and electron micrographs were taken to specify the harmful effects of pollution and to correlate to morphological changes of the membrane. The bacterial strains and functional tests showed differentiated responses to environmental stresses, revealing that diverse mechanisms of tolerance and/or resistance are involved. The microorganisms were vulnerable to the prompt effect of Pb 2+ , showed weak tolerance to Hg 2+ and proved to be tolerant to Cr 6+ . The reaction center controlled electron transfer in Rvx. gelatinosus demonstrated the highest degree of resistance against heavy metal exposure.

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

“…The kinetics of absorption changes of the whole cells induced by Xe flash were detected by a home-constructed spectrophotometer (Maróti and Wraight 1988). The electrochromic band shift of the carotenoid pigments in the photosynthetic membrane was monitored at 530 nm with reference to 510 nm (Kis et al 2014(Kis et al , 2015. Induction of BChl fluorescence.…”

“…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 − ).…”

Fluorescence induction of photosynthetic bacteria

“…In order to track the electron transfer steps and for the evaluation of the physiological status of the purple anoxygenic phototrophs, induction and relaxation of BChl fluorescence have largely prevailed (Koblizek et al 2005, Maróti 2008Asztalos et al 2010Asztalos et al , 2015Kis et al 2014Kis et al , 2015. While the RCs are photooxidized and effectively become closed during the fluorescence induction phase, they open again during the fluorescence relaxation phase.…”

Characterization of mercury(II)-induced inhibition of photochemistry in the reaction center of photosynthetic bacteria

“…These studies highlight mercury(II) as a global priority contaminant whose importance as a chemical of major concern to the phototrophs (bacteria and algae) and plants has been underscored by a number of recent publications. They describe the influence of Hg stress on agroecosystem (Zhao et al 2014), the cellular and molecular targets of Hg toxicity in phototrophs (Asztalos et al 2012;Deng et al 2013;Kis et al 2015Kis et al , 2017, and how phototrophs affect Hg cycling (i.e., alteration of Hg redox state, Hg scavenging, potential for methylation) (Gregoire and Poulain 2014). The mercury(II) ion is one of the most toxic agents to photosynthetic bacteria (Giotta et al 2006) and primarily attacks the RC protein (Asztalos et al 2010(Asztalos et al , 2012.…”