Characterization of lactic acid bacteria-based probiotics as potential heavy metal sorbents.

AIM: To isolate and characterize lactic acid bacteria (LAB) and determine whether they could potentially be used as heavy metal (cadmium and lead) absorbing probiotics. METHODS AND RESULTS: The study used 53 environmental (mud and sludge) samples to isolate cadmium- and lead-resistant LAB, by following spared plate technique. A total of 255 cadmium- and lead-resistant LAB were isolated from these samples. The survival of 26 of the LAB was found after passing through sequential probiotic characterizations. These 26 probiotic LAB exhibited remarkable variations in their metal-resistant and metal-removal abilities. Of 26, seven (Cd54-2, Cd61-7, Cd69-12, Cd70-13, Pb82-8, Pb96-19 and Cd109-16) and four (Pb71-1, Pb73-2, Pb85-9 and Pb96-19) strains displayed relatively elevated cadmium- and lead-removal efficiencies from water, respectively, compare with that of the remaining strains. Strains Cd70-13 and Pb71-1 showed the highest cadmium (25%) and lead (59%) removal capacity from MRS (De Man, Rogosa and Sharpe) culture medium, respectively, amongst the selected strains and showed a good adhesive ability on fish mucus. A phylogenetic analysis of their 16S rDNA sequences revealed that the strains Cd70-13 and Pb71-1 belong to Lactobacillus reuteri. CONCLUSION: Excellent probiotic, metal sorption and adhesive characteristics of newly identified Lact. reuteri strains Cd70-13 and Pb71-1 were isolated, which indicated their high potential abilities to survive in the intestinal milieu and to uptake the tested metals from the environment. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first study that has aimed to isolate, characterize and identify metal-resistant LAB strains that have potential to be a probiotic candidate for food and in vivo challenge studies in the intestinal milieu of fish for the uptake and control of heavy metal bioaccumulation.

Cytochrome b(6)f mutation specifically affects thermal dissipation of absorbed light energy in Arabidopsis.

Light-induced lumenal acidification controls the efficiency of light harvesting by inducing thermal dissipation of excess absorbed light energy in photosystem II. We isolated an Arabidopsis mutant, pgr1 (proton gradient regulation), entirely lacking thermal dissipation, which was observed as little non-photochemical quenching of chlorophyll fluorescence. Map-based cloning showed that pgr1 had a point mutation in petC encoding the Rieske subunit of the cytochrome b(6)f complex. Although the electron transport rate was not affected at low light intensity, it was significantly restricted at high light intensity in pgr1, indicating that the lumenal acidification was not sufficient to induce thermal dissipation. This view was supported by (i) slow de-epoxidation of violaXanthin, which is closely related to lumenal acidification, and (ii) reduced 9-aminoacridine fluorescence quenching. Although lumenal acidification was insufficient to induce thermal dissipation, growth rate was not affected under low light growth conditions in pgr1. These results suggest that thermal dissipation is precisely regulated by lumenal pH to maintain maximum photosynthetic activity. We showed that pgr1 was sensitive to changes in light conditions, demonstrating that maximum activity of the cytochrome b(6)f complex is indispensable for short-term acclimation.

Identification and characterization of Arabidopsis mutants with reduced quenching of chlorophyll fluorescence.

Regulation of nonradiative dissipation of absorbed light energy in PSII is an indispensable process to avoid photoinhibition in plants. To dissect molecular mechanisms of the regulation, we identified Arabidopsis mutants with reduced quenching of Chl fluorescence using a fluorescence imaging system. By analyses of Chl fluorescence induction pattern in the light and quantum yield of both photosystems, 37 mutants were classified into three groups. The first group was characterized by an extremely high level of minimum Chl fluorescence at the open PSII center possibly due to a defect in PSII. Mutants with significant reduction in the nonphotochemical quenching formation but not in quantum yield of both photosystems were classified into the second group. Mutants in the third group showed reduction in quantum yield of both photosystems possibly due to a defect in the electron transport activity. Mutants in the second and third groups were further characterized by light intensity dependence of Chl fluorescence parameters and steady state redox level of P700.