Review--Interactions between diatoms and stainless steel: focus on biofouling and biocorrosion

There is a considerable body of information regarding bacterially enhanced corrosion, however, this review focuses on diatoms (unicellular algae) whose contribution to biocorrosion is less well studied. The reasons why diatoms have been neglected in studies of biocorrosion in natural waters are discussed and the question whether diatoms should be considered as inert with respect of electrochemical processes is considered. A particular focus is given to the case of stainless steels (SS), which are widely used in variety of applications in natural waters. Basic information on the cell biology of diatoms is included in the review, particularly with respect to their ability to 'sense' and adhere to surfaces. Investigations at the nanoscale are reviewed as these studies provide information about the behavior of cells at interfaces. Recent advances include the use of atomic force microscopy (AFM), although only a few studies have been applied to diatoms. Regarding the electrochemical behavior of SS, the mechanisms by which diatoms influence the potential ennoblement process is discussed. Such studies reveal the association of diatoms, in addition to bacteria, with biocorrosion processes.     

Both sulfate-reducing bacteria and Enterobacteriaceae take part in marine biocorrosion of carbon steel

AIMS: In order to evaluate the part played in biocorrosion by microbial groups other than sulfate-reducing bacteria (SRB), we characterized the phylogenetic diversity of a corrosive marine biofilm attached to a harbour pile structure as well as to carbon steel surfaces (coupons) immersed in seawater for increasing time periods (1 and 8 months). We thus experimentally checked corroding abilities of defined species mixtures. METHODS AND RESULTS: Microbial community analysis was performed using both traditional cultivation techniques and polymerase chain reaction cloning-sequencing of 16S rRNA genes. Community structure of biofilms developing with time on immersed coupons tended to reach after 8 months, a steady state similar to the one observed on a harbour pile structure. Phylogenetic affiliations of isolates and cloned 16S rRNA genes (rrs) indicated that native biofilms (developing after 1-month immersion) were mainly colonized by gamma-proteobacteria. Among these, Vibrio species were detected in majority with molecular methods while cultivation techniques revealed dominance of Enterobacteriaceae such as Citrobacter, Klebsiella and Proteus species. Conversely, in mature biofilms (8-month immersion and pile structure), SRB, and to a lesser extent, spirochaetes were dominant. CONCLUSIONS: Corroding activity detection assays confirmed that Enterobacteriaceae (members of the gamma-proteobacteria) were involved in biocorrosion of metallic material in marine conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: In marine biofilms, metal corrosion may be initiated by Enterobacteriaceae.     

Prevention and control of biocorrosion

Microbial colonization of metals and alloys of industrial usage takes place through the formation of biofilms made of bacteria, extracellular polymeric substances (EPS) and mainly water. These biological deposits can drastically modify the corrosion behavior of structural metals and alloys enhancing localized alterations in the type and concentrations of ions, pH, and oxygen levels. However, biofilms also facilitate the formation of diffusional barriers to the exchange of chemical species from and towards the metal/solution interface. Problems due to biocorrosion and biofouling of industrial systems range from heavy microbiological contamination with consequent energy and efficiency losses to structural failures owing to corrosion.The use of appropriate monitoring strategies complemented with field and laboratory microbiological techniques is necessary to reach a proper understanding of the effects derived from microbiological activity and the role of biofilms in the corrosion reaction to later implement effective control and preventive countermeasures. It must be emphasized that this assessment should be made for each industrial system, considering its previous history, present operational conditions, physicochemical composition of the intake water and the number and identity of microbial contaminants.Cleaning procedures, most relevant biocides and other methods for prevention and control of biocorrosion like coatings, and cathodic protection are successively described. Updated information about monitoring strategies is also included in the final part of the paper.     

Initial stages of 2,4,6-trinitrotoluene transformation by microorganisms

Screening of a wide range of microorganisms (32 strains) isolated from various anthropogenic and natural environments and of a number of collection strains showed that the early stages of 2,4,6-trinitrotoluene (TNT) transformation by the majority of the strains studied resulted in the formation of hydroxylaminodinitrotoluenes (HADNTs). The levels of HADNTs were in a number of cases comparable to the initial TNT level. The alternative reductive attack at TNT through the reduction of the aromatic ring was not characteristic of most of the prokaryotes studied. The susceptibility to the toxic effect of TNT was different for gram-positive and gram-negative bacteria.     

Initial stages of DNA Base Excision Repair in Nucleosomes

Molecular Biology - In mammalian cells, base excision repair (BER) is the main pathway responsible for the correction of a variety of chemically modified DNA bases. DNA packaging in chromatin...     

Initial stages of trisporic acid synthesis in Blakeslea trispora

Biotransformation of beta-carotene with enzyme preparations isolated from the mycelium of Blakeslea trispora resulted in the formation of its hydroxylated metabolite and apocarotenals, products of oxidative degradation of this compound. By spectral, chromatographic, and chemical properties, the beta-carotene derivative was identified as 4-hydroxy-beta-carotene (isocryptoxanthine). One of the products of oxidative degradation of beta-carotene, beta-apo-13-carotenone, underwent modification in the presence of enzyme preparations from Blakeslea trispora with the formation of trisporic acid precursors. It should be emphasized that beta-apo-13-carotenone transformation proceeded more rapidly than beta-carotene oxidation by carbon in the 4-position. Our findings suggest that under conditions of oxidative stress, oxidative degradation of beta-carotene into beta-apo-13-carotenone leads to the formation of considerable amounts of trisporic acids.     

Determination of minimal concentrations of biocorrosion inhibitors by a bioluminescence method in relation to bacteria, participating in biocorrosion

By using a bioluminescence ATP assay, we have determined the minimal concentrations of some biocorrosion inhibitors (Katon, Khazar, VFIKS-82, Nitro-1, Kaspii-2, and Kaspii-4) suppressing most common microbial corrosion agents: Desulfovibrio desulfuricans, Desulfovibrio vulgaris, Pseudomonas putida, Pseudomonas fluorescens, and Acidithiobacillus ferrooxidans. The cell titers determined by the bioluminescence method, including not only dividing cells but also their dormant living counterparts, are two- to sixfold greater than the values determined microbiologically. It is shown that the bioluminescence method can be applied to determination of cell titers in samples of oil-field waters in the presence of iron ions (up to 260 mM) and iron sulfide (to 186 mg/l) and in the absence or presence of biocidal corrosion inhibitors.     

Initial stages of lichen hydration observed by proton magnetic relaxation

The hydration of selected lichens ( Cladonia mitis , Cladonia bellidiflora , Cetraria islandica , Parmelia saxatilis , and Xanthoria parietina ) was investigated using gravimetry and proton magnetic free induction decays (FIDs).
The hydration from gaseous phase and dehydration to gaseous phase showed first-order kinetics. The amount of water which was non-removable in the air-dry state (relative humidity p / p ₀=9%) did not depend significantly on the lichen species and was found to be 5·6±1·0% of the d. wt.
The proton FID Gaussian component from the solid matrix of thallus structure, and two (or, depending on lichen species, one averaged) liquid signals coming from water tightly bound on the surface of thallus solid matrix and from loosely bound or free water, were recorded. The bound-water component was distinguished by its motional properties and by its proximity to endogenous paramagnetic centres present in solid matrix (presumably PS II reaction centres of the photobiont). Mild dehydration (from gaseous phase) could completely remove the loosely bound water fraction, leaving the system below the water percolation threshold and below the water clustering point, emphasizing the passivity of lichen response to desiccation shock. In the species in which the one average liquid component was recorded, bound water behaved similarly.
The hydration at which free water pool vanishes (Δ M / m ₀) and the relative (scaled to water) proton densities of solid matrix of lichen (β) were evaluated for all lichens investigated.     

Initial stages of mammary tumor virus infection are superantigen independent

Exogenous mouse mammary tumor virus (MMTV) is transmitted via the milk from infected mothers to newborn pups. Efficient MMTV transmission is dependent on proliferation of T cells with particular TCR beta-chains, which occurs upon recognition of virally encoded superantigen (SAg) bound to MHC class II molecules. It is assumed that infection of these dividing cells favors MMTV amplification. SAg is important for MMTV infection, as mice that lack SAg-cognate T cells due to expression of endogenous Mtv loci or mice that express inappropriate MHC haplotypes unable to present viral SAg efficiently were shown to be resistant to MMTV infection. However, this resistance was not absolute, as these mice developed late onset MMTV-induced mammary tumors. In this study, we show that the success of initial MMTV infection in neonates is independent of SAg function but depends on the developmentally regulated proliferation of target cells. However, SAg was absolutely required for virus spread following completion of this proliferative stage.     

Initial stages in the onset of senescence in tobacco leaves

A marked loss of leucine ¹⁴C incorporation occurred in chloroplasts isolated from Nicotiana rustica L. leaves exposed to 24 hours of darkness. This loss is not due to an initial decline in RNA-synthesis potential of the chloroplasts, as was inferred from the extent of UTP incorporation by the isolated chloroplasts. Upon reillumination of the leaves, leucine incorporation by the isolated chloroplasts reverted to its original level within 3 to 4 hours, hence it is doubtful whether the period of 24 hours after detachment should be regarded as the initial phase of leaf senescence.     

Control of biocorrosion using laboratory and field assessments

Biofouling and biocorrosion can be significant problems in oilfield water injection systems, despite extensive use of chemical biocides. This work set out to establish relevant testing and monitoring procedures to optimise microbiological control in these systems.A combination of laboratory based sessile biocide screening trials and onsite monitoring of biofilm bacteria was developed to ensure that an effective biocontrol programme was set up. It is important to use a mixed population of bacteria freshly isolated from biofilms in the system to ensure that any biocide tolerance of the system bacteria is reflected in the laboratory tests. In general, the results are borne out by the site audits of the control regime against sessile bacteria in the system.In an industrial system, biocide resistant populations develop from time to time. In practice it was found that even a small change to the biocide formulation could improve biocontrol, with concomitant reduction in corrosion rates and maintenance costs.