Protein Crystallization in a Microfluidic Contactor with Nafion®117 Membranes.

Protein crystallization still remains mostly an empirical science, as the production of crystals with the required quality for X-ray analysis is dependent on the intensive screening of the best protein crystallization and crystal's derivatization conditions. Herein, this demanding step was addressed by the development of a high-throughput and low-budget microfluidic platform consisting of an ion exchange membrane (117 Nafion® membrane) sandwiched between a channel layer (stripping phase compartment) and a wells layer (feed phase compartment) forming 75 independent micro-contactors. This microfluidic device allows for a simultaneous and independent screening of multiple protein crystallization and crystal derivatization conditions, using Hen Egg White Lysozyme (HEWL) as the model protein and Hg2+ as the derivatizing agent. This microdevice offers well-regulated crystallization and subsequent crystal derivatization processes based on the controlled transport of water and ions provided by the 117 Nafion® membrane. Diffusion coefficients of water and the derivatizing agent (Hg2+) were evaluated, showing the positive influence of the protein drop volume on the number of crystals and crystal size. This microfluidic system allowed for crystals with good structural stability and high X-ray diffraction quality and, thus, it is regarded as an efficient tool that may contribute to the enhancement of the proteins' crystals structural resolution.

New insights about the monomer and homodimer structures of the human AOX1.

Human aldehyde oxidase (hAOX1) is a molybdenum dependent enzyme that plays an important role in the metabolism of various compounds either endogenous or xenobiotics. Due to its promiscuity, hAOX1 plays a major role in the pharmacokinetics of many drugs and therefore has gathered a lot of attention from the scientific community and, particularly, from the pharmaceutical industry. In this work, homology modelling, molecular docking and molecular dynamics simulations were used to study the structure of the monomer and dimer of human AOX. The results with the monomer of hAOX1 allowed to shed some light on the role played by thioridazine and two malonate ions that are co-crystalized in the recent X-ray structure of hAOX1. The results show that these molecules endorse several conformational rearrangements in the binding pocket of the enzyme and these changes have an impact in the active site topology as well as in the stability of the substrate (phthalazine). The results show that the presence of both molecules open two gates located at the entrance of the binding pocket, from which results the flooding of the active site. They also endorse several modifications in the shape of the binding pocket (namely the position of Lys893) that, together with the presence of the solvent molecules, favour the release of the substrate to the solvent. Further insights were also obtained with the assembled homodimer of hAOX1. The allosteric inhibitor (THI) binds closely to the region where the dimerization of both monomers occur. These findings suggest that THI can interfere with protein dimerization.

Micro-computed tomography and histomorphometric analysis of human alveolar bone repair induced by laser phototherapy: a pilot study.

Immediate dental implant placement in the molar region is critical, because of the high amount of bone loss and the discrepancy between alveolar crest thickness and the implant platform. Laser phototherapy (LPT) improves bone repair. The aim of this study was to evaluate the human alveolar bone repair 40 days after molar extraction in patients submitted to LPT. Twenty patients were selected for this randomized controlled clinical trial; 10 underwent LPT (laser group) with a GaAlAs diode laser (808 nm, 100 mW, 0.04 cm(2), 75 J/cm(2), 30s per point, 3 J per point, at five points). The control group patients (n=10) were not irradiated. Forty days later, the tissue formed inside the sockets was analyzed by micro-computed tomography and histomorphometry. Data from the two groups were compared with Student's t-test and Pearson's correlation test. The relative bone volume was significantly higher in the laser group (P<0.0001). The control group showed negative correlations (P<0.01) between number and thickness, and between number and separation of trabeculae, and a positive correlation between thickness and separation of trabeculae. The laser group showed a significant negative correlation between the number and thickness of trabeculae (P<0.01). The results suggest that LPT is able to accelerate alveolar bone repair after molar extraction, leading to a more homogeneous trabecular configuration represented by thin and close trabeculae.

New insights concerning the occurrence of fungi in water sources and their potential pathogenicity.

Fungi are known to occur ubiquitously in the environment. In the past years, the occurrence of filamentous fungi in the aquatic environment has been a subject of growing interest. This study describes the occurrence of various fungal genera in different drinking water sources being Penicillium and Trichoderma the most representative ones (30% and 17%, respectively). Also, 24 fungal species that have not been previously described in the aquatic environment are reported in this study, being once again the major species from the Penicillium genera. This study therefore contributes to the knowledge on the richness of fungi diversity in water. 68% of the described species were found to be able to grow at 30 °C but only Aspergillus fumigatus, Aspergillus viridinutans and Cunninghamella bertholletiae were able to grow at the higher temperature tested (42 °C). 66% of the species that were able to grow at 30 °C have spore sizes below 5 µm which enables them to cause breathing infections. These were therefore identified as potential pathogenic species.

New insights into the chemistry of fac-[Ru(CO)3]²âº fragments in biologically relevant conditions: the CO releasing activity of [Ru(CO)3Cl2(1,3-thiazole)], and the X-ray crystal structure of its adduct with lysozyme.

Complexes of the general formula fac-[Ru(CO)(3)L(3)](2+), namely CORM-2 and CORM-3, have been successfully used as experimental CO releasing molecules (CO-RMs) but their mechanism of action and delivery of CO remain unclear. The well characterized complex [Ru(CO)(3)Cl(2)(1,3-thiazole)] (1) is now studied as a potential model CO-RM of the same family of complexes using LC-MS, FTIR, and UV-vis spectroscopy, together with X-ray crystallography. The chemistry of [Ru(CO)(3)Cl(2)(1,3-thiazole)] is very similar to that of CORM-3: it only releases residual amounts of CO to the headspace of a solution in PBS7.4 and produces marginal increase of COHb after long incubation in whole blood. 1 also reacts with lysozyme to form Ru adducts. The crystallographic model of the lysozyme-Ru adducts shows only mono-carbonyl Ru species. [Ru(H(2)O)(4)(CO)] is found covalently bound to a histidine (His15) and to two aspartates (Asp18 and Asp119) at the protein surface. The CO release silence of both 1 and CORM-3 and their rapid formation of protein-Ru(CO)(x)(H(2)O)(y) (x=1,2) adducts, support our hypothesis that fac-[Ru(CO)(3)L(3)] CO-RMs deliver CO in vivo through the decay of their adducts with plasma proteins.

Perosomus elumbis in a puppy.

A 2-day-old poodle puppy was seen to have hypoplastic and arthrogrypotic hindlimbs and no tail. Palpation revealed an absence of lumbar and sacral vertebrae. At necropsy examination, the colon had a blind ending at the umbilical area, there were no urinary system organs, the spinal cord ended at the thoracic level and no genital system organs were found except for a structure similar to a rudimentary penis. The pelvis was abnormal with no articulation with the spine. This congenital anomaly was consistent with perosomus elumbis, a rare condition of unknown aetiology with few reported cases.

PP061. The role of heat shock protein 60 and 70 in early- and late-onset preeclampsia differentiation.

INTRODUCTION: Preeclampsia is a human pregnancy-specific syndrome characterized by the onset of hypertension and proteinuria. These manifestations may occur before the 34th week of gestation or from this period on, being denominated early-onset or late-onset preeclampsia respectively. The etiology of both disorders seems to differ qualitatively; therefore, different strategies of prevention and treatment must be studied. OBJECTIVES: The aim of the present study is to determine whether the plasma levels of heat-shock proteins Hsp60 and Hsp70 as well as specific antibodies anti-Hsp60 and anti-Hsp70 may differentiate early-onset from late-onset preeclampsia. METHODS: We evaluated 175 pregnant women with PE (55 early-onset PE and 120 late-onset PE). Plasma was obtained from peripheral blood and Hsp60, Hsp70 as well as anti-Hsp60 and anti-Hsp70 antibody levels were determined by enzyme immunoassay. Uric acid levels were also determined in the plasma of patients. For statistical analyses, the Mann-Whitney U-test and the Spearman rank order correlation were applied with significance level set at 5%. RESULTS: Hsp70 levels obtained from early-onset PE group were significantly higher than the late-onset PE women and showed positive correlation with uric acid (r=0.4547; p=0.0028). The Hsp60 production was similar in both groups. Our results also indicate that there was no significant difference of anti-Hsp60 and anti-Hsp70 antibody levels between women with early- and late-onset PE. However,these antibody levels were high,indicating a strong relationship with the production of HSP60 and Hsp70 protein. CONCLUSION: Association between levels of Hsp70 and uric acid in plasma of patients with early-onset PE seems to reflect the oxidative stress in this group of patients. This study provides evidence that Hsp70 determination may be utilized to assess the differentiation between early- and late-onset PE. FINANCIAL SUPPORT: FAPESP 2010/09241-2.

PP063. TLR-4 expression and pro-inflammatory cytokine production by peripheral blood monocytes from preeclamptic women.

INTRODUCTION: Toll-like receptor (TLR)-4 and TLR-2 are involved in inflammatory response of monocytes. These cells are activated in pregnant women with preeclampsia (PE), and over-produce inflammatory cytokines. TLR4 may recognize endogenous ligands, the so-called danger signals released by damaged cells, leading to production of pro-inflammatory cytokines. OBJECTIVES: This study investigated TLR2 and TLR4 expression and cytokine production by monocytes from women with PE before and after stimulation with TLR ligands. METHODS: Monocytes (5×10(5)cell/mL) were obtained from 32 preeclamptic (PE) and 20 normotensive (NT) pregnant women in the last trimester of pregnancy. TLR2 and TLR4 expression on monocyte surface was determined by flow cytometry in non-stimulated cells, and after 18h of culture with lipopysaccharide (LPS) and peptidoglycan (PG). TNF-α, IL-10 and IL-12p70 production by these cells stimulated or not with LPS or PG was evaluated by enzyme immunoassay. Results were analyzed by non-parametric tests with significance level set at 5%. RESULTS: In the absence of stimulation, the basal TLR4 expression by monocytes detected by the median fluorescence intensity (MFI) was significantly higher in the PE group than in the NT group while no significant differences were observed between groups in relation to endogenous TLR2 expression. An increase in TLR4 MFIs was detected after monocytes from NT pregnant women were stimulated with LPS while TLR2 expression was increased after PG-stimulation. No alterations in TLR expression was detected after LPS or PG-stimulation in monocytes from patients with PE. Evaluation of endogenous cytokine levels in supernatant culture of monocytes showed higher concentrations of TNF-α and IL-12p70 in preeclamptic women in comparison with the NT group, whereas IL-10 values were significantly higher in NT pregnant women than in the PE group. In contrast, when monocytes were stimulated with the TLRs ligands LPS and PG, the release of TNF-α was significantly reduced, while IL-12p70 levels were significantly higher in women with PE compared to NT group. IL-10 production was similar in both groups studied. CONCLUSION: The basal up-regulation of TLR4 expression associated with endogenous high TNF-α and IL-12p70 production by monocytes from preeclamptic women confirms the activated profile of these cells by the disease process. These findings provide new insights into possible roles for TLRs in the pathogenesis of systemic inflammation detected in PE. FINANCIAL SUPPORT: FAPESP 2009/11924-3 and 2010/20207-0.

PP064. M1 Monocyte subpopulation is associated with pro-inflammatory cytokineproduction in pregnant women with preeclampsia.

INTRODUCTION: Monocytes from peripheral blood of pregnant women with preeclampsia are endogenously activated and secrete high levels of free radicals and inflammatory cytokines. OBJECTIVES: This study aimed at evaluating whether the inflammatory state of monocytes observed in preeclampsia is associated with the polarization of monocyte to M1 profile in peripheral blood, correlating the expression of surface receptors CD64, TLR2, TLR4, and CD163 and CD206 with cytokine production. METHODS: We studied 90 pregnant women, 30 normotensive and 60 with preeclampsia, matched for gestational age. Peripheral blood monocytes obtained from normotensive pregnant or preeclamptic pregnant women were cultured for 18h, and the expression of surface receptors on M1 inflammatory monocyte subpopulation (TLR2, TLR4 and CD64) and M2 suppressor monocyte subpopulation (CD163 and CD206) were evaluated by flow cytometry, using specific monoclonal antibodies, labeled with fluorochromes. The values were expressed as ??the mean fluorescence intensity. Moreover, the production of proinflammatory cytokines associated with M1 profile (TNF-α, IL-12p70 and IL-23) and the anti-inflammatory cytokine associated with M2 profile (IL-10) were evaluated in the monocyte supernatant of culture by enzyme immunoassay. Results were analyzed using nonparametric tests with significance level set at 5%. RESULTS: The expression of CD4 and TLR4 on monocyte surface, from women with preeclampsia was significantly higher, while the expression of CD163 and CD206 was significantly decreased compared with normotensive pregnant women, suggesting the predominance of monocyte M1 profile. Endogenous production of TNF-α, IL-12p70 and IL-23 by monocytes was increased, while synthesis of IL-10 was lower in women with preeclampsia compared with normotensive pregnant women. Positive correlations between TLR4 and CD64 (r=0.5849), TLR4 and TNF-α (r=0.5126) or TLR4 and IL-23 (r=0.8095), as well as between CD64 and TNF-α (r = 0.7133) or CD64 and IL-23 (r = 0.6051) were observed in the preeclamptic group. The results confirm the activated state of monocytes from women with preeclampsia by increased production of proinflammatory cytokines and the expression of receptors characteristic of the M1 subpopulation. CONCLUSION: This study provides evidence that monocytes from women with preeclampsia are classically activated and the systemic inflammatory environment may differentiate and polarize these cells to the M1 profile. FINANCIAL SUPPORT: CNPq, FAPESP 2009/11924-3 and 2010/20207-0.

Understanding the role of device level interoperability in promoting health - lessons learned from the SmartPersonalHealth Project.

OBJECTIVES: To summarize lessons learned from the European Commission (EC) co-funded project SmartPersonalHealth, a project to promote a greater understanding of the value of interoperability among Personal Health Systems (PHS) and between them and other eHealth systems, in the landscape of continuity of care and across multi-cultural environments in Europe. METHODS: Key concepts in PHS interoperability, challenges, barriers and benefits were discussed with stakeholders (policy makers, regulators, procurers, healthcare providers, health professionals, patient representatives, industry, researchers) in three consultation workshops and a final conference. The results were synthesized in final report to the European Commission. RESULTS: The survey and analysis presented, which are designed to set the scene on the key requirements of device level interoperability within a context of using sensors, signals and imaging informatics in healthcare, set out key interoperability standards for PHS as provided for in the Continua Health Alliance Guidelines and explores further the need for wider organisational and regulatory aspects of interoperability. CONCLUSION: Achieving interoperability of eHealth systems is a complex process involving various actors and challenges far beyond technical and standardisation issues. For harnessing the key benefits of PHS, any interoperability scenario needs to account for value-based business cases for all stakeholders involved. It must foresee to enable seamless and consistent data and information flows by integrating and mixing devices used by patients/consumers at home, for remote monitoring, for home hospitalisation and/or within the hospital.

Towards improved therapeutic CORMs: understanding the reactivity of CORM-3 with proteins.

The biological role of carbon monoxide (CO) has completely changed in the last decade. Beyond its widely feared toxicity, CO has revealed a very important biological activity as a signaling molecule with marked protective actions namely against inflammation, apoptosis and endothelial oxidative damage. Its direct use as a therapeutic gas showed significant and consistent positive results but also intrinsic severe limitations. The possibility of replacing the gas by pro-drugs acting as CO-Releasing Molecules (CO-RMs) has clearly been demonstrated with several experimental compounds. Transition metal carbonyls complexes have proven to be the most versatile experimental CO-RMs so far. Presently, the challenge is to equip them with drug-like properties to turn them into useful pharmaceuticals. This requires studying their interactions with biological molecules namely those that control their pharmacokinetic and ADME profiles like the plasma proteins. In this account we analyze these questions and review the existing interactions between Metal Carbonyls and proteins. The recently explored case of CORM-3 is revisited to exemplify the methodologies involved and the importance of the results for the understanding of the mode of action of such pro-drugs.

Volatile compounds in samples of cork and also produced by selected fungi.

The production of volatile compounds by microbial communities of cork samples taken during the cork manufacturing process was investigated. The majority of volatiles were found in samples collected at two stages: resting after the first boiling and nontreated cork disks. Volatile profiles produced by microbiota in both stages are similar. The releasable volatile compounds and 2,4,6-trichloroanisole (TCA) produced in cork-based culture medium by five isolated fungal species in pure and mixed cultures were also analyzed by gas chromatography coupled with mass spectrometry (GC-MS).The results showed that 1-octen-3-ol and esters of fatty acids (medium chain length C8-C20) were the main volatile compounds produced by either pure fungal species or their mixture. Apparently, Penicillium glabrum is the main contributor to the overall volatile composition observed in the mixed culture. The production of releasable TCA on cork cannot be attributed to any of the assayed fungal isolates.

Skeletogenesis of the pectoral girdle and forelimbs in embryos of Caiman yacare (Daudin, 1802) (Crocodylia, Alligatoridae)

Embryos of Caiman yacare were collected and subjected to the bone clearing and staining protocol in orderto analyze the ontogenetic patterns of ossification of the pectoral girdle and forelimb skeleton. The osseousstructure of the girdle and forelimbs of C. yacare begins to ossify starting at 30 days of incubation, withthe presence of dye retention in the scapula, coracoids, humerus, radius and ulna bones. During embryonicdevelopment, the autopodio of C. yacare has four bones in the carpus, the radial, ulnar, pisiform and carpaldistal 4+5 bone. Their ossification begins at 39 days of incubation with the radial, followed by the ulnar, and at54 days, the pisiform and the distal carpal 4 + 5. Each mesopodio has 5 metacarpi and are present 15 phalanges,two in digits I and V, three in digits II and IV, and four in digit III (phalangeal formula 2:3:4:3:2). Ossificationof the metacarpi starts at 27 days of incubation, following the sequence MCII=MCIII=MCIV>MCI>MCV.The first phalanges begin the process of ossification on day 36, continuing up to the last day of incubation.The sequence of ossification of the proximal phalanges is PPI=PPII=PPIII>PPIV=PPV, that of the medialphalanges is MPII>MPpIII>MPdIII>MPIV, and that of the distal phalanges is DPI>DPII>DPIII>DPV>DPIV.The ontogenetic pattern of the bones of the forepaw of C. yacare generally differs from that of other reptiles,although there are some similarities.

Crystal structure of the zinc-, cobalt-, and iron-containing adenylate kinase from Desulfovibrio gigas: a novel metal-containing adenylate kinase from Gram-negative bacteria.

Adenylate kinases (AK) from Gram-negative bacteria are generally devoid of metal ions in their LID domain. However, three metal ions, zinc, cobalt, and iron, have been found in AK from Gram-negative bacteria. Crystal structures of substrate-free AK from Desulfovibrio gigas with three different metal ions (Zn(2+), Zn-AK; Co(2+), Co-AK; and Fe(2+), Fe-AK) bound in its LID domain have been determined by X-ray crystallography to resolutions 1.8, 2.0, and 3.0 Å, respectively. The zinc and iron forms of the enzyme were crystallized in space group I222, whereas the cobalt-form crystals were C2. The presence of the metals was confirmed by calculation of anomalous difference maps and by X-ray fluorescence scans. The work presented here is the first report of a structure of a metal-containing AK from a Gram-negative bacterium. The native enzyme was crystallized, and only zinc was detected in the LID domain. Co-AK and Fe-AK were obtained by overexpressing the protein in Escherichia coli. Zn-AK and Fe-AK crystallized as monomers in the asymmetric unit, whereas Co-AK crystallized as a dimer. Nevertheless, all three crystal structures are very similar to each other, with the same LID domain topology, the only change being the presence of the different metal atoms. In the absence of any substrate, the LID domain of all holoforms of AK was present in a fully open conformational state. Normal mode analysis was performed to predict fluctuations of the LID domain along the catalytic pathway.

Assessment of the presence and dynamics of fungi in drinking water sources using cultural and molecular methods.

A comparison of different isolation techniques and culture media for detection of filamentous fungi and yeasts in the aquatic environment revealed that the use of membrane filtration with the media dichloran rose bengal chloramphenicol (DRBC) optimized fungi detection in terms of abundance and variety in three untreated water sources with very different characteristics (surface water, spring water, and groundwater). The diversity of the fungi population captured by direct DNA extraction of fungi collected by membrane filtration was compared with the isolates obtained after selective growth using different culture media through amplification of the internal transcribed spacer gene and denaturing gradient gel electrophoresis (DGGE). The Czapek-Dox agar, Sabouraud dextrose agar, and DRBC media showed closer similarities to those obtained by the uncultured biomass for the different water sources. Based on these data and the best enumeration results, DRBC is recommended for the assessment of fungi in water sources using culture-based methods. DGGE was also used to monitor temporal variations in the fungal population structure and showed that each water matrix possessed a distinct population profile as well as that changes in the fungal community can be expected in the different matrices throughout the year.

Real-time monitoring of molecular dynamics of ethylene glycol dimethacrylate glass former.

The isothermal cold-crystallization of the glass-former low-molecular-weight compound, ethylene glycol dimethacrylate (EGDMA), was monitored by real-time dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC). The alpha-relaxation associated with the dynamic glass transition as detected by DRS was followed at different crystallization temperatures, T(cr), nearly above the glass transition temperature, 176 K (1.06 < or = T(cr)/T(g) < or = 1.12). It was found that the alpha-process depletes upon cold-crystallization with no significant changes in either shape or location. At advanced crystallization states, a new relaxation, alpha'-process, evolves that was assigned to the mobility of molecules lying adjacent to crystalline surfaces. From the time evolution of the normalized permittivity, it was possible to get kinetic information that was complemented with the calorimetric data. From DSC measurements that were also carried out under melt-crystallization, an enlarged temperature range was covered (up to T(cr)/T(g) = 1.24), allowing us to draw a diagram of time-temperature crystallization for this system. Dielectric relaxation spectroscopy proved to be a sensitive tool to probe the mobility in the remaining amorphous regions even at high crystallinities.

Cobalt-, zinc- and iron-bound forms of adenylate kinase (AK) from the sulfate-reducing bacterium Desulfovibrio gigas: purification, crystallization and preliminary X-ray diffraction analysis.

Adenylate kinase (AK; ATP:AMP phosphotransferase; EC 2.7.4.3) is involved in the reversible transfer of the terminal phosphate group from ATP to AMP. AKs contribute to the maintenance of a constant level of cellular adenine nucleotides, which is necessary for the energetic metabolism of the cell. Three metal ions, cobalt, zinc and iron(II), have been reported to be present in AKs from some Gram-negative bacteria. Native zinc-containing AK from Desulfovibrio gigas was purified to homogeneity and crystallized. The crystals diffracted to beyond 1.8 A resolution. Furthermore, cobalt- and iron-containing crystal forms of recombinant AK were also obtained and diffracted to 2.0 and 3.0 A resolution, respectively. Zn(2+)-AK and Fe(2+)-AK crystallized in space group I222 with similar unit-cell parameters, whereas Co(2+)-AK crystallized in space group C2; a monomer was present in the asymmetric unit for both the Zn(2+)-AK and Fe(2+)-AK forms and a dimer was present for the Co(2+)-AK form. The structures of the three metal-bound forms of AK will provide new insights into the role and selectivity of the metal in these enzymes.

Weissella halotolerans W22 combines arginine deiminase and ornithine decarboxylation pathways and converts arginine to putrescine.

AIMS: To demonstrate that the meat food strain Weissella halotolerans combines an ornithine decarboxylation pathway and an arginine deiminase (ADI) pathway and is able to produce putrescine, a biogenic amine. Evidence is shown that these two pathways produce a proton motive force (PMF). METHODS AND RESULTS: Internal pH in W. halotolerans was measured with the sensitive probe 2',7'-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein. Membrane potential was measured with the fluorescent probe 3,3'-dipropylthiocarbocyanine iodine. Arginine and ornithine transport studies were made under several conditions, using cells loaded or not loaded with the biogenic amine putrescine. ADI pathway caused an increase in DeltapH dependent on the activity of F(0)F(1)ATPase. Ornithine decarboxylation pathway generates both a DeltapH and a DeltaPsi. Both these pathways lead to the generation of a PMF. CONCLUSIONS: Weissella halotolerans W22 combines an ADI pathway and an ornithine decarboxylation pathway, conducing to the production of the biogenic amine putrescine and of a PMF. Transport studies suggest the existence of a unique antiporter arginine/putrescine in this lactic acid bacteria strain. SIGNIFICANCE AND IMPACT OF THE STUDY: The coexistence of two different types of amino acid catabolic pathways, leading to the formation of a PMF, is shown for a Weissella strain for the first time. Moreover, a unique antiport arginine/putrescine is hypothesized to be present in this food strain.

Occurrence of filamentous fungi and yeasts in three different drinking water sources.

In order to determine the occurrence of fungi in different drinking water sources and capture variability in terms of matrix composition and seasonal effects, surface water, spring water, and groundwater samples were collected in numerous sampling events. The occurrence and significance of fungi detected in the different water sources are reported and discussed in terms of colony-forming units per millilitre and by the identification of the most frequently detected isolates, at the species level, based on morphology and other phenotypic characters. All the samples were also analyzed in terms of total coliforms and Escherichia coli that are widely monitored bacteria considered as microbiology indicators of water quality. All the groundwater samples showed significantly lower levels of total coliforms, E. coli, and fungi compared to the surface and spring water samples. No significant correlations were found between the levels of fungi detected in all the matrices and the physico-chemical parameters and bacteria regularly monitored by drinking water utilities. Fifty-two fungi isolates were identified in this study, most of which have never been described to occur in water sources. The results obtained show that fungi occur widely in drinking water sources and that further studies should be conducted to address their biodegradation potential as well as if the drinking water treatment processes currently used are effective in removing these organisms and the potential secondary metabolites produced.

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase.

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton-electron transfer stage, where the Mo(V) species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo-dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo(VI) ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl-dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur-based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo(V) species. Mo(VI) intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo(VI) species allow water molecule dissociation, and, the concomitant enzymatic turnover.