Laboratory

Microbiological studies of spent nuclear fuel pools at the Cofrentes Nuclear Power Plant (Valencia, Spain) were initiated to determine the microbial populations in the pools' water. Biofilm formation at the nuclear power plant facilities and the potential use of those microbial populations in the bioremediation of radioactive water were also studied. Biofilm formation was analyzed by immersing different austenitic stainless steel coupons (UNS S30400, UNS S30466, UNS S31600), as well as balls of stainless steel (UNS S44200) and titanium (99.9%) in a spent nuclear fuel pool (under static and dynamic conditions) for 34 months. Epifluorescence microscopy and scanning electron microscopy revealed that biofilm formed on the samples, in spite of the radioactive and oligotrophic conditions of the water. Based on standard culture methods and sequencing of 16S rDNA fragments, 57 bacteria belonging to alpha-, beta-, and gamma-Proteobacteria, Firmicutes and Actinobacteridae were identified in the biofilms. The radioactivity of the biofilm was measured using gamma-ray spectrometry, which revealed that biofilms were able to retain radionuclides, especially (60)Co. Using metallic materials to decontaminate radioactive water could become a new approach for bioremediation

There have been problems in the water-injection systems of the oil industry due to Microbiologically Induced Corrosion (MIC), associated with the presence of Sulphate-Reducing Bacteria (SRB), which produce H2S. Several investigators consider that this is the principal cause of bacterial corrosion in natural-water storage and distribution systems. Given the fact that other groups of bacteria are not considered in current microbiological treatments and controls, it would be useful to investigate the presence of other anaerobic microorganisms that produce this aggressive metabolite or its derivatives in water-injection systems. This article reports on SRB and Non-SRB strains isolated from injection systems and identified by DNA sequencing, among them, Desulfovibrio termitidis (SRB) and Escherichia coli (Non-SRB). Evaluation of the activity and corrosivity of the two types of bacteria indicated that there was a significant difference in activity in the selective media, mainly that sulphide generation by the sulphate dissimilation process is much greater than that of the group that generates it by fermentation, as well as corrosivity on the carbon steel API 5L grade X65, as determined by open circuit potential, polarization resistance and weight loss during 60 hours’ evaluation in selective media with no ferrous salts. Nevertheless, Scanning Electron Microscopy indicated biofilm development and localized attacks on the steel by both types of bacteria, which confirms the need for investigating and considering the role of these Non-SRB anaerobic groups so as to exercise better control over bacterial corrosion.

The aim of the present research was to isolate and identify bacteria from spent nuclear fuel pools of a Spanish nuclear power plant. Water samples were collected and inoculated onto different culture media to isolate the highest number of species. 16S rDNA fragments from colonies growing on solid media were amplified and analysed by denaturing gradient gel electrophoresis. Sequencing revealed the presence of 21 different bacteria belonging to several phylogenetic groups (a, b, and c-Proteobacteria, Actinomycetales, Flavobacterium, and the Bacillus/Staphylococcus group). The isolation of these microorganisms in this particular environment (oligotrophic and radioactive) is highly interesting because of the possibility of their being used for the bioremediation of radionuclide-contaminated
waters.

The objective of this study was to investigate the biofilm formation
on three different types of austenitic stainless steel (UNS S30400, S30466 and S31600) submerged in a spent nuclear fuel pool. The presence of microorganisms in coupons was characterised using standard culture microbiological methods, microscopic techniques (epifluorescence microscopy and scanning electron microscopy), and molecular biology techniques (denaturing gradient gel electrophoresis and sequencing fragments of 16S rDNA). The microscopy techniques showed signs of colonisationof stainless steels in spite of these extreme conditions. Based on sequencing of cultured microorganisms, different bacteria belonging to a, b, c-Proteobacteria, Bacilli, and Actinobacteria classes have been identified. The biofilm radioactivity was measured using gamma-ray spectrometry and, according to the data gathered, the radionuclides present in the water pool were entrapped in the biofilm increasing the amount of radiation at the surface of the different materials.

The microbiologically influenced corrosion (MIC) of water injection systems by sulphate-reducing prokaryotes (SRP) has caused many problems in the oil industry. These prokaryotes produce H2S, which reacts aggressively with steel and is thus widely considered to be the main cause of bacterial corrosion of
industrial oil equipment. However, current microbiological treatments and controls have not taken into account other groups of sulphidogenic prokaryotes, which also produce H2S or its derivatives and with the same adverse effects of MIC. In the present work, sulphidogenic prokaryotes were isolated from water injection systems and identified by DNA sequencing. The identified species included sulphate-reducing Desulfovibrio termitidis and non-sulphate-reducing Escherichia coli. Biocorrosion tests were carried out on API 5L grade X65 carbon steel. Electrochemical impedance spectroscopy, polarisation resistance, open circuit potential and weight loss were carried out. Steel corrosion resulting from the production of the metabolite H2S by SRP and non-SRP was observed, with sulphide generation by SRP much greater than that by non-SRP. These results confirm the need to investigate and consider the role of not only SRP but also non-SRP in order to improve the control over bacterial corrosion of oil-industryequipment

Summary. Microbiological studies of spent nuclear fuel pools at the Cofrentes Nuclear Power Plant (Valencia, Spain) were initiated to determine the microbial populations in the pools' water. Biofilm formation at the nuclear power plant facilities and the potential use of ...

La conservación de las cuevas con arte rupestre ha de plantearse desde el estudio y comprensión de todos los procesos naturales que han dado lugar a su formación y de las interferencias posteriores, tanto antrópicas como cambios climáticos, etc. En el presente trabajo se incluyen los factores de biodeterioro que suponen la alteración de los soportes con perjuicio para el arte parietal. Se esboza también las diferencias existentes entre las alteracionesde las cuevas y otros soportes pétreos y las técnicas de estudio y de control utilizadas para paliar dentro de lo posible los efectos negativos que los seres vivos producensobre el arte rupestre.

Microbial activity in spent nuclear fuel pools which contain ultrapure and radioactive water has been previously observed. The aim of the present research was to isolate and identify the microorganisms attached to the nuclear pool wall of a Spanish nuclear power plant. Amplification of 16S rDNA fragments from the culturable microorganisms by PCR using universal primers for the domain 'Bacteria', followed by Denaturing Gradient Gel Electrophoresis analysis revealed the presence of six different bacteria. The complete gene for 16S rDNA of each one was sequenced and identified as belonging to three different phylogenetic groups, viz. beta-Proteobacteria, Actinomycetales and the Bacillus/Staphylococcus group. A fungus was also found and identified as Aspergillus fumigatus by sequencing the D2 region of the large subunit rDNA gene. The isolation of these microorganisms in oligotrophic and radioactive conditions is of great interest due to the possibility of their use in bioremediation processes of radionuclide-contaminated environments.