A structural model for the assembly of the reaction centre and the B808-866 complex in the membranes of <i>Chloroflexus aurantiacus</i> based on the calculation of the triplet minus singlet spectrum of the primary donor

A well resolved triplet minus singlet spectrum of the primary donor P870 of the green bacterium Chloroflexus au- rantiacus, detected by optically detected magnetic resonance (ODMR), in intact membranes, was reported in our previous work [Photosynth. Res. 71 (2002) 45]. The spectrum is now interpreted and reconstructed by calculating the electronic interactions between the primary donor and the BChl a molecules belonging to the 866 absorption com- ponent of the B808-866 light-harvesting complex. The good agreement between the calculation and the experimental data strongly supports a topological model for the B808-866 complex which consists in a circular aggregate structure of a number of polypeptide units binding BChl a molecules assembled as in the LH2 peripheral antenna complex of purple bacteria, giving rise to two spectral forms. The aggregate surrounds the reaction centre (RC) resembling in this respect the LH1 core antenna complex of purple bacteria.</p

Fluorescence and Absorption Detected Magnetic Resonance of Chlorosomes from Green Bacteria <i>Chlorobium tepidum</i> and <i>Chloroflexus aurantiacus</i>. A Comparative Study

A comparative study on the isolated chlorosomes from Chloroflexus aurantiacus, a green filamentous photosynthetic bacterium and Chlorobium tepidum, a green sulfur photosynthetic bacterium, was done by ODMR (optically detected magnetic resonance). Correlation between the results obtained by fluorescence and absorption detection is shown to be a source of information about the functional interactions among pigments. Analogies and differences are pointed out between the light-harvesting systems of the two species. Triplet states are easily detected in both bacteria at 1.8 K under steady-state illumination and are assigned to BChl c, BChl a, and carotenoid molecules. Carotenoids are found to be able to quench BChl a triplet states, but no evidence of BChl c triplet states quenching by this triplet−triplet transfer mechanism is found in both systems. Then from the data it appears that some carotenoids are in close contact with BChl a molecules. The relevance of this finding to the localization of carotenoids in the chlorosomes is discussed. In Cb. tepidum three different pools of BChl c oligomers connected to BChl a were found by detection of their triplet state, while only one pool of BChl c was evidenced in Cf. aurantiacus. The latter appears to be unconnected, at least at 1.8 K, to BChl a. On the other hand, heterogeneity in the BChl a triplet population was detected in Cf. aurantiacus. Even though the two bacteria show common features in the way the light excitation induces triplet formation at low temperature, the detected triplet states show spectroscopic properties that strongly depend on the system. The results clearly indicate that differences in pigment organization exist both in the core and in the baseplate of the chlorosomes from the two different bacteria.</p

Optically detected magnetic resonance of intact membranes from <i>Chloroflexus aurantiacus</i>. Evidence for exciton interaction between the RC and the B808-866 complex

Optically detected magnetic resonance of chlorosome-containing membranes from the green filamentous bacterium Chloroflexus aurantiacus has been performed both by fluorescence and absorption detection. Triplet states localized in the chlorosomes and in the B808–866 complex have been characterized. After chemical reduction with ascorbate followed by illumination at 200 K, recombination triplet state localized in the primary donor becomes largely populated under illumination at low temperature while all the antenna triplet states, which are localized in carotenoids and BChl a molecules, are strongly quenched. We were able to obtain the T-S spectrum of the primary donor P870 surrounded by all the antenna complexes connected to the RC via energy transfer and then in its intact environment. We found clear spectroscopic evidence for exciton interaction between the RC and the B808–866 antenna complex. This evidence was provided by the comparison of the T−S spectrum of P870 in the membranes with that of isolated RC. The analogy of some features of the difference spectra with those previously found in the same kind of experiments for Rb. sphaeroides, allows to predict a similar coupling among the primary donor and the nearby antenna BChl a molecules, assembled as circular aggregate

Fluorescence and Absorption Detected Magnetic Resonance of Membranes from the Green Sulfur Bacterium Chlorobium limicola . Full Assignment of Detected Triplet States

Optically detected magnetic resonance of chlorosomes-containing membranes from the green sulfur bacterium Chlorobium limicola has been performed both by fluorescence and absorption detection. Triplet states localized in the chlorosomes and in the FMO complex have been characterized. After chemical reduction with dithionite followed by illumination at 200 K, a recombination triplet state localized in the primary donor P840 becomes populated under illumination at low temperature. A reaction center triplet state characterized by slightly different ZFS parameters, grows up irreversibly after prolonged illumination at low temperature in the presence of reductant. We were able to obtain the T−S spectra of the FMO complex and of the primary donor P840 in their native environment and to compare them to the spectra obtained in isolated complexes previously published, revealing differences in the spectra. Fluorescence detected magnetic resonance measurements demonstrate that the BChl c antenna pigments are connected via energy transfer to the BChl a molecules at the low temperature of the measurements (1.8 K) and that all the pigments carrying the triplet states are sensitive to the redox treatment. Dithionite reduction, in fact, induces an enhancement of the BChl c and, at a major extent, of the BChl a fluorescence yield accompanied by an increase of the yield of all the triplet states of the pigments. Evidence for the presence of BChl c excited states quenchers in the core chlorosome and for their selective effect at low temperature is provided, and the location of the quenchers close to BChl c molecules absorbing at longer wavelengths discussed.</p

Occurrence of Salmonell a enterica subsp. enterica in bivalve molluscs and associations with Escherichia coli in molluscs and faecal coliforms in seawater

he objectives of this study were to present data on the presence of Salmonella enterica subsp. enterica and on the enumeration of Escherichia coli and faecal coliforms respectively in different species of bivalve molluscs and seawater and to conduct a retrospective evaluation to assess the capacity of E. coli in molluscs and faecal coliforms and S. enterica subsp. enterica in sea and brackish water to predict the presence of S. enterica subsp. enterica in bivalve molluscs, and therefore, the risk of exposure for consumers. Data were collected from 4972 seawater samples and 5785 live bivalve molluscs samples (2877 Ruditapes philippinarum, 2177 Mytilus galloprovincialis, 256 Chamelae gallina and 475 C gigas and O. edulis) collected in the molluscs production area of Ferrara, Northern Italy, from 1997 to 2015. An overall S. enterica subsp. enterica occurrence of 2.2% was reported in water and molluscs, with percentages varying depending on the type of sample and on the classification areas. All the 237 Salmonella strains were identified as genus Salmonella and a total of 53 different serovars were observed. Significant associations between the fecal indicators and presence of S. enterica subsp. enterica were observed both applying EU and USA criteria, but, it should be noted that the EU approach seems to be more stringent achieving the goal of identifying the most critical batches (94 out of the 100) whereas, following the USA approach, a not negligible and higher number of batches compliant for faecal coliforms but contaminated by S. enterica subsp. enterica has to be mentioned. In any case, the faecal indicators E. coli in molluscs and faecal coliforms in seawaters reflect only in part the presence of S. enterica subsp. enterica in molluscs and the consequent potential risk for consumers. Microbiological evaluation of seawaters seems to have a minor impact into the prediction of S. enterica subsp. enterica presence in molluscs

Occurrence of Salmonella enterica subsp. enterica in bivalve molluscs and associations with Esherichia coli in molluscs and faecal coliforms in seawater

The objectives of this study were to present data on the presence of Salmonella enterica subsp. enterica and on the enumeration of Escherichia coli and faecal coliforms respectively in different species of bivalve molluscs and seawater and to conduct a retrospective evaluation to assess the capacity of E. coli in molluscs and faecal coliforms and S. enterica subsp. enterica in sea and brackish water to predict the presence of S. enterica subsp. enterica in bivalve molluscs, and therefore, the risk of exposure for consumers. Data were collected from 4972 seawater samples and 5785 live bivalve molluscs samples (2877 Ruditapes philippinarum, 2177 Mytilus galloprovincialis, 256 Chamelae gallina and 475 C. gigas and O. edulis) collected in the molluscs production area of Ferrara, Northern Italy, from 1997 to 2015. An overall S. enterica subsp. enterica occurrence of 2.2% was reported in water and molluscs, with percentages varying depending on the type of sample and on the classification areas. All the 237 Salmonella strains were identified as genus Salmonella and a total of 53 different serovars were observed. Significant associations between the fecal indicators and presence of S. enterica subsp. enterica were observed both applying EU and USA criteria, but, it should be noted that the EU approach seems to be more stringent achieving the goal of identifying the most critical batches (94 out of the 100) whereas, following the USA approach, a not negligible and higher number of batches compliant for faecal coliforms but contaminated by S. enterica subsp. enterica has to be mentioned. In any case, the faecal indicators E. coli in molluscs and faecal coliforms in seawaters reflect only in part the presence of S. enterica subsp. enterica in molluscs and the consequent potential risk for consumers. Microbiological evaluation of seawaters seems to have a minor impact into the prediction of S. enterica subsp. enterica presence in molluscs

Prospective Study on Incidence, Risk Factors and Outcome of Recurrent Clostridioides difficile Infections

Background: Limited and wide-ranging data are available on the recurrent Clostridioides difficile infection (rCDI) incidence rate. Methods: We performed a cohort study with the aim to assess the incidence of and risk factors for rCDI. Adult patients with a first CDI, hospitalized in 15 Italian hospitals, were prospectively included and followed-up for 30 d after the end of antimicrobial treatment for their first CDI. A case\u2013control study was performed to identify risk factors associated with 30-day onset rCDI. Results: Three hundred nine patients with a first CDI were included in the study; 32% of the CDI episodes (99/309) were severe/complicated; complete follow-up was available for 288 patients (19 died during the first CDI episode, and 2 were lost during follow-up). At the end of the study, the crude all-cause mortality rate was 10.7% (33 deaths/309 patients). Two hundred seventy-one patients completed the follow-up; rCDI occurred in 21% of patients (56/271) with an incidence rate of 72/10,000 patient-days. Logistic regression analysis identified exposure to cephalosporin as an independent risk factor associated with rCDI (RR: 1.7; 95% CI: 1.1\u20132.7, p = 0.03). Conclusion: Our study confirms the relevance of rCDI in terms of morbidity and mortality and provides a reliable estimation of its incidence