Microbial induced corrosion of metallic antiquities and works of art: a critical review

Metallic antiquities and works of art are no exception to the phenomenon of microbial corrosion. Thus, all those which are buried, sunk or poorly conserved are susceptible to microbial corrosion. Although the last few decades have seen a marked development in the study of microbial corrosion of metals in industrial use, the same cannot be said for metallic antiquities and works of art. This work reviews the practical cases published, historical materials affected, and the micro-organisms involved and their mechanisms of action. Despite the great social importance of recovering these metallic cultural properties, and conserving them in a good state, there is a lack of documentation and of research groups dedicated to their study. The bringing together of researchers in works of art, microbiology and corrosion in metallic materials is shown to be necessary.     

White Blood Cell Counts as Risk Markers of Developing Metabolic Syndrome and Its Components in the Predimed Study

Background

The Metabolic Syndrome (MetS) is a cluster of metabolic abnormalities that includes hyperglucemia, hypertension, dyslipidemia and central obesity, conferring an increased risk of cardiovascular disease. The white blood cell (WBC) count has been proposed as a marker for predicting cardiovascular risk. However, few prospective studies have evaluated the relationship between WBC subtypes and risk of MetS.

Methods

Participants were recruited from seven PREDIMED study centers. Both a baseline cross-sectional (n = 4,377) and a prospective assessment (n = 1,637) were performed. Participants with MetS at baseline were excluded from the longitudinal analysis. The median follow-up was 3.9 years. Anthropometric measurements, blood pressure, fasting glucose, lipid profile and WBC counts were assessed at baseline and yearly during the follow-up. Participants were categorized by baseline WBC and its subtype count quartiles. Adjusted logistic regression models were fitted to assess the risk of MetS and its components.

Results

Of the 4,377 participants, 62.6% had MetS at baseline. Compared to the participants in the lowest baseline sex-adjusted quartile of WBC counts, those in the upper quartile showed an increased risk of having MetS (OR, 2.47; 95%CI, 2.03–2.99; P-trend<0.001). This association was also observed for all WBC subtypes, except for basophils. Compared to participants in the lowest quartile, those in the top quartile of leukocyte, neutrophil and lymphocyte count had an increased risk of MetS incidence. Leukocyte and neutrophil count were found to be strongly associated with the MetS components hypertriglyceridemia and low HDL-cholesterol. Likewise, lymphocyte counts were found to be associated with the incidence of the MetS components low HDL-cholesterol and high fasting glucose. An increase in the total WBC during the follow-up was also associated with an increased risk of MetS.

Conclusions

Total WBC counts, and some subtypes, were positively associated with MetS as well as hypertriglyceridemia, low HDL-cholesterol and high fasting glucose, all components of MetS.

Trial registration

Controlled-Trials.comISRCTN35739639.     

Effect of sulfur starvation on the morphology and ultrastructure of the cyanobacterium Gloeothece sp. PCC 6909

Gloeothece sp. PCC 6909 is a unicellular, nitrogen-fixing cyanobacterium that accumulates sulfate in its sheath. An ultrastructural study of sulfate-deficient and normal Gloeothece sp. PCC 6909 cells was carried out. The physiological alterations, caused by sulfur starvation, were related to important morphological alterations in the cell: a structureless sheath, accumulation of cyanophycin, polyhydroxybutyrate and glycogen granules, and disintegration of thylakoidal membranes. Most of these changes were reversed by the addition of sulfate to the culture medium. The important role of sulfate in the sheath structure was demonstrated.     

Roles of bacterial attachment and spontaneous partitioning in the biodegradation of naphthalene initially present in nonaqueous-phase liquids.

The mineralization by an Arthrobacter sp. of naphthalene initially dissolved in di(2-ethylhexyl)phthalate exhibited a slow phase followed by a rapid phase. Triton X-100, which inhibited cell attachment, prevented the onset of the second phase. Triton X-100 increased the extent of mineralization of naphthalene initially present in 2,2,4,4,6,8,8-heptamethylnonane. Cells attached to the interface mineralized the aromatic hydrocarbon at a rate four times higher than the rate of partitioning in the absence of microorganisms, but this microbial activity was markedly reduced by Triton X-100. We suggest that utilization of naphthalene originally present in nonaqueous-phase liquids may involve a partitioning-limited initial stage carried out by bacteria freely suspended in the aqueous phase and a subsequent, more rapid stage effected by bacteria present directly at the nonaqueous-liquid-water interface.     

Comparison of mineralization of solid-sorbed phenanthrene by polycyclic aromatic hydrocarbon (PAH)-degrading Mycobacterium spp. and Sphingomonas spp.

The mineralization of ¹⁴C-phenanthrene, sorbed to porous synthetic amberlite sorbents, i.e., IRC50, XAD7-HP, and XAD2, by three phenanthrene-degrading Mycobacterium soil isolates, i.e., strains VM552, VM531, and VM451 and three phenanthrene-degrading Sphingomonas soil isolates, i.e., strains LH162, EPA505 and LH227, was compared. In P-buffer and in the presence of IRC50, for all strains the maximum rate of mineralization of ¹⁴C-phenanthrene was significantly higher (1.1–1.9 ng ml⁻¹ h⁻¹) than the initial abiotic desorption rate (0.2 ng ml⁻¹ h⁻¹), indicating that both Mycobacterium and Sphingomonas utilize sorbed phenanthrene with a higher rate than can be explained by abiotic desorption. Because all Mycobacterium and Sphingomonas strains belonged to different species, it can be suggested that this feature is intrinsic to those genera rather than a specific feature of a particular strain. The final mineralization extent in P-buffer in the presence of IRC50 was about a factor of two higher for the Mycobacterium strains compared to the Sphingomonas strains. Moreover, a significantly higher normalized phenanthrene mineralization ratio in the presence of IRC50 to the control (without IRC50) was found for the Mycobacterium strains compared to the normalized ratio found for the Sphingomonas strains. Addition of minimal nutrients had a more beneficial effect on phenanthrene mineralization by Sphingomonas compared to Mycobacterium, resulting into similar mineralization extents and rates for both types of strains in the presence of IRC50. Our results show that Mycobacterium is better adapted to utilization of sorbed phenanthrene compared to Sphingomonas, especially in nutrient-poor conditions.     

Distribution of the Mycobacterium community and polycyclic aromatic hydrocarbons (PAHs) among different size fractions of a long-term PAH-contaminated soil

Summary Mycobacterium is often isolated from polycyclic aromatic hydrocarbon (PAH)-contaminated soil as degraders of PAHs. In model systems, Mycobacterium shows attachment to the PAH substrate source, which is considered to be a particular adaptation to low bioavailability as it results into increased substrate flux to the degraders. To examine whether PAH-degrading Mycobacterium in real PAH-contaminated soils, in analogy with model systems, are preferentially associated with PAH-enriched soil particles, the distribution of PAHs, of the PAH-mineralizing capacity and of Mycobacterium over different fractions of a soil with an aged PAH contamination was investigated. The clay fraction contained the majority of the PAHs and showed immediate pyrene- and phenanthrene-mineralizing activity upon addition of (14)C-labelled pyrene or phenanthrene. In contrast, the sand and silt fractions showed a lag time of 15-26 h for phenanthrene and 3-6 days for pyrene mineralization. The maximum pyrene and phenanthrene mineralization rates of the clay fraction expressed per gram fraction were three to six times higher than those of the sand and silt fractions. Most-probable-number (MPN)-polymerase chain reaction demonstrated that Mycobacterium represented about 10% of the eubacteria in the clay fraction, while this was only about 0.1% in the sand and silt fractions, indicating accumulation of Mycobacterium in the PAH-enriched clay fraction. The Mycobacterium community composition in the clay fraction represented all dominant Mycobacterium populations of the bulk soil and included especially species related to Mycobacterium pyrenivorans, which was also recovered as one of the dominant species in the eubacterial communities of the bulk soil and the clay fraction. Moreover, Mycobacterium could be identified among the major culturable PAH-degrading populations in both the bulk soil and the clay fraction. The results demonstrate that PAH-degrading mycobacteria are mainly associated with the PAH-enriched clay fraction of the examined PAH-contaminated soil and hence, that also in the environmental setting of a PAH-contaminated soil, Mycobacterium might experience advantages connected to substrate source attachment.     

Simultaneous biodegradation of creosote-polycyclic aromatic hydrocarbons by a pyrene-degrading <Emphasis Type="Italic">Mycobacterium</Emphasis>

When incubated with a creosote-polycyclic aromatic hydrocarbons (PAHs) mixture, the pyrene-degrading strain Mycobacterium sp. AP1 acted on three- and four-ring components, causing the simultaneous depletion of 25% of the total PAHs in 30 days. The kinetics of disappearance of individual PAHs was consistent with differences in aqueous solubility. During the incubation, a number of acid metabolites indicative of distinctive reactions carried out by high-molecular-weight PAH-degrading mycobacteria accumulated in the medium. Most of these metabolites were dicarboxylic aromatic acids formed as a result of the utilization of growth substrates (phenanthrene, pyrene, or fluoranthene) by multibranched pathways including meta- and ortho-ring-cleavage reactions: phthalic acid, naphthalene-1,8-dicarboxylic acid, phenanthrene-4,5-dicarboxylic acid, diphenic acid, Z-9-carboxymethylenefluorene-1-carboxylic acid, and 6,6′-dihydroxy-2,2′-biphenyl dicarboxylic acid. Others were dead-end products resulting from cometabolic oxidations on nongrowth substrates (fluorene meta-cleavage product). These results contribute to the general knowledge of the biochemical processes that determine the fate of the individual components of PAH mixtures in polluted soils. The identification of the partially oxidized compounds will facilitate to develop analytical methods to determine their potential formation and accumulation in contaminated sites. An erratum to this article can be found at     

Bioavailability of solid and non-aqueous phase liquid (NAPL)-dissolved phenanthrene to the biosurfactant-producing bacterium Pseudomonas aeruginosa 19SJ

The biodegradation of phenanthrene by the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ was investigated in experiments with the compound present either as crystals or dissolved in non-aqueous phase liquids (NAPLs). Growth on solid phenanthrene exhibited an initial phase not limited by dissolution rate and a subsequent, carbon-limited phase caused by exhaustion of the carbon source. Rhamnolipid biosurfactants were produced from solid phenanthrene and appeared in solution and particulate material (cells and phenanthrene crystals). During the carbon-limited phase, the concentration of rhamnolipids detected in culture exceeded the critical micelle concentration (CMC) determined with purified rhamnolipids. The biosurfactants caused a significant increase in dissolution rate and pseudosolubility of phenanthrene, but only at concentrations above the CMC. Externally added rhamnolipids at a concentration higher than the CMC increased the biodegradation rate of solid phenanthrene. Mineralization curves of low concentrations of phenanthrene initially dissolved in two NAPLs [2,2,4,4,6,8,8-heptamethylnonane and di(2-ethylhexyl)phthalate] were S-shaped, although no growth was observed in the population of suspended bacteria. Biosurfactants were not detected in solution under these conditions. The observed mineralization was attributed not only to suspended bacteria, but also to bacterial populations growing at the NAPL–water interface, mineralizing the compound at higher rates than predicted by abiotic partitioning. We suggest that rhamnolipid production and attachment increased the bioavailability of phenanthrene, so promoting biodegradation activity.