Microbiota of spent nuclear fuel pool water with emphasis on their biofilm forming ability on stainless steel (SS-304L)

Spent nuclear fuel (SNF) pool is an essential unit of a nuclear power plant infrastructure, where radioactive fuel rods arekept for cooling and shielding, before reprocessing. This study explored the presence of bacteria in SNF pool water withemphasis on their capability to form biofilms on pool wall cladding material stainless steel (SS-304L). Bacteria wereisolated from SNF pool water and were characterized using 16S rRNA gene sequencing. The six bacterial isolates (Bacillussubtilis, Staphylococcus sps., S. arlettae, S. epidermidis, S. auricularis and Chryseobacterium gleum) can grow and formbiofilms at very low nutrient condition as well as in chronic radioactivity. The bacterial isolates formed biofilm on SS-304Land glass. However, the biofilm parameters assessed by CLSM microscopy showed that the strains preferred SS-304Lsurface for biofilm formation. On SS-304L, the maximum biomass (0.45 lm3/lm2) was formed by S. arlettae whencompared to maximum biomass (0.054 lm3/lm2) by Staphylococcus sp., on glass. Maximum biofilm thickness on SS304L was observed by Staphylococcus sp. (8.81 lm) when compared to that of S. epidermidis (4.16 lm) on the glasssurface. The biofilm formation on SS-304L surface suggests the possible risk of microbial-induced corrosion of SNF poolcladding material. This study highlights the need for mandatory monitoring of microbial biofilm formation in an extremeenvironment such as SNF pool.

Streptomyces lunalinharesii 235 prevents the formation of a sulfate-reducing bacterial biofilm

ABSTRACT Streptomyces lunalinharesii strain 235 produces an antimicrobial substance that is active against sulfate reducing bacteria, the major bacterial group responsible for biofilm formation and biocorrosion in petroleum reservoirs. The use of this antimicrobial substance for sulfate reducing bacteria control is therefore a promising alternative to chemical biocides. In this study the antimicrobial substance did not interfere with the biofilm stability, but the sulfate reducing bacteria biofilm formation was six-fold smaller in carbon steel coupons treated with the antimicrobial substance when compared to the untreated control. A reduction in the most probable number counts of planktonic cells of sulfate reducing bacteria was observed after treatments with the sub-minimal inhibitory concentration, minimal inhibitory concentration, and supra-minimal inhibitory concentration of the antimicrobial substance. Additionally, when the treated coupons were analyzed by scanning electron microscopy, the biofilm formation was found to be substantially reduced when the supra-minimal inhibitory concentration of the antimicrobial substance was used. The coupons used for the biofilm formation had a small weight loss after antimicrobial substance treatment, but corrosion damage was not observed by scanning electron microscopy. The absence of the dsrA gene fragment in the scraped cell suspension after treatment with the supra-minimal inhibitory concentration of the antimicrobial substance suggests that Desulfovibrio alaskensis was not able to adhere to the coupons. This is the first report on an antimicrobial substance produced by Streptomyces active against sulfate reducing bacteria biofilm formation. The application of antimicrobial substance as a potential biocide for sulfate reducing bacteria growth control could be of great interest to the petroleum industry.

Occurrence of sulphate reducing bacteria (SRB) associated with biocorrosion on metallic surfaces in a hydroelectric power station in Ibirama (SC) - Brazil

The aim of this study was evaluate, two methods for the detection and identification of sulphate reducing bacteria (SRB): ML medium and PCR with specific primers for SRB groups. SRB were detected through the selective medium only on carbon steel, which showed corrosion. Employing specific PCR primer, SBR were detected from all the metallic components assayed, even those that did not present visible corrosion spots, such stainless steel and copper alloys. Despite the presence or absence of corrosion at the later stages effectively by using the selective medium,, the initial stages of the corrosion could only be detected by the amplification of total DNA with SRB specific primers. The early detection of SRB could be employed for preventing the damages on metal surfaces before the installation of corrosion processes. Strategies for reducing the time spent on SRB isolation and identification could be auxiliary tools for controlling the corrosion of materials.

Effect of biofilm formation, and biocorrosion on denture base fractures

PURPOSE: The aim of this study was to investigate the destructive effects of biofilm formation and/or biocorrosive activity of 6 different oral microorganisms. MATERIALS AND METHODS: Three different heat polymerized acrylic resins (Ivocap Plus, Lucitone 550, QC 20) were used to prepare three different types of samples. Type "A" samples with "V" type notch was used to measure the fracture strength, "B" type to evaluate the surfaces with scanning electron microscopy and "C" type for quantitative biofilm assay. Development and calculation of biofilm covered surfaces on denture base materials were accomplished by SEM and quantitative biofilm assay. According to normality assumptions ANOVA or Kruskal-Wallis was selected for statistical analysis (alpha=0.05). RESULTS: Significant differences were obtained among the adhesion potential of 6 different microorganisms and there were significant differences among their adhesion onto 3 different denture base materials. Compared to the control groups after contamination with the microorganisms, the three point bending test values of denture base materials decreased significantly (P.05). CONCLUSION: All the tested microorganisms had destructive effect over the structure and composition of the denture base materials.

Bacterial contamination of automotive fuels in a tropical region: the case of Costa Rica

Microbial contamination of fuel has been the cause of several problems in transportation and storage of these products. Due to the lack of previous studies related to these problems in Costa Rica, bacterial quality was evaluated biannually in automotive fuels stored in the four oil distribution facilities of the Costa Rican Petroleum Refinery (RECOPE). In 12 oil storage tanks, for a total of 96 samples, mesophilic, heterotrophic aerobic/facultative counts (ASTM D6974-04) and identification of bacteria presented in regular gas, premium gas and diesel from the bottom and superior part of the tanks were done; in the samples containing an aqueous phase, sulfate reducing bacteria (SRB) were also quantified by the most probable number technique (MPN), according to the ASTM D4412-84 standard. The higher contamination was shown at the bottom of the tanks (populations up to 10(4) UFC/l), especially if there was accumulated water, in which case populations reached 10(8) UFC/l. The most contaminated fuel was diesel (counts up to 10(4) UFC/l), whereas the less contaminated was premium gas. The less contaminated fuels were from the facilities of La Garita and Barranca, whereas the most contaminated were from Ochomogo. Nevertheless, the quantified populations did not cause significant alteration in quality physicochemical parameters in the samples analyzed. A total of 149 bacterial strains were isolated, 136 (91.3%) Gram positive and 13 (8.7%) Gram negative. The most frequent genera were Staphylococcus (24.0%), Micrococcus (21.9%), Bacillus (18.8%) and Kocuria (11.5%) among Gram positive bacteria and Pseudomonas (7.3%) among Gram negative bacteria. The majority of these genera have been found as fuel contaminants or even as degraders of this kind of products; nevertheless, some species for which their appearance or growth in hydrocarbons have not been described were found with low frequencies. SRB were present in counts up to 10(5) MPN/l in 42.9% of water containing samples (including all from diesel tanks), indicating biocorrosion processes risk in fuel transport and storage systems. From the findings in this study it is recommended to give a frequent maintenance to fuel containers, based on continuous drainage and removal of accumulated water, antimicrobial agent addition and microbial quality monitoring in country’s fuels. Rev. Biol. Trop. 57 (3): 489-504. Epub 2009 September 30.

Se evaluó semestralmente durante dos años la calidad bacteriana de los combustibles almacenados en los cuatro planteles de la Refinadora Costarricense de Petróleo (Costa Rica). Para un total de 96 muestras se realizaron recuentos (norma ASTM D6974-04) e identificación de las bacterias presentes en gasolina regular, gasolina súper y diesel en los niveles superior e inferior de los tanques contenedores; en las muestras con fase acuosa se cuantificaron las bacterias reductoras de sulfato (SRB, norma ASTM D4412-84). La mayor contaminación se observó en el fondo de los tanques, sobretodo si se presentó una capa de agua almacenada. El diesel fue el combustible más contaminado, sin embargo, no se observó alteración importante en los parámetros fisicoquímicos de las muestras evaluadas. Se aislaron 149 cepas, 136 (91.3%) Gram positivas y 13 (8.7%) Gram negativas; los géneros más frecuentes fueron Staphylococcus (24.0%), Micrococcus (21.9%), Bacillus (18.8%), Kocuria (11.5%) y Pseudomonas (7.3%). Con bajas frecuencias se encontraron algunas especies para las que no se ha descrito su aparición o crecimiento en hidrocarburos. Las SRB se presentaron con recuentos de hasta 105 MPN/l en un 42.9% de las muestras con agua residual, principalmente en diesel, lo cual es indicativo de alerta por biocorrosión. A partir de los resultados se recomienda dar un mantenimiento frecuente a los contenedores, la adición de compuestos antimicrobianos y el monitoreo de la calidad microbiana de los combustibles del país.

Evaluación del molibdato y nitrato sobre bacterias sulfato-reductoras asociadas a procesos de corrosión en sistemas industriales / Evaluation of molybdate and nitrate on sulphate-reducing bacteria related to corrosion processes in industrial systems

Se estudió la cinética de crecimiento de bacterias sulfato-reductoras (BSR) y la biotransformación de sulfato a sulfuro de hidrógeno bajo condiciones de laboratorio, para establecer el efecto inhibitorio de sales de molibdato y nitrato de sodio. Los microorganismos estudiados fueron aislados del agua de producción contenida en un sistema de transporte de gas natural, donde se encontraban relacionados con procesos de corrosión influenciada microbiológicamente. Con 5 mM de molibdato se obtuvo una reducción de células libres a niveles no detectables y de seis órdenes de magnitud en las biopelículas, con una disminución del sulfuro de alrededor del 100%. Con 75 mM de nitrato se observó una reducción de cuatro y dos órdenes de magnitud en las células libres y en las adheridas en forma de biopelículas, respectivamente, con una disminución del sulfuro de alrededor del 80%. La reducción de la tasa de corrosión observada sustenta la posibilidad de emplear estas sales como biocidas no convencionales no contaminantes del medio ambiente, para el control y mitigación efectiva de los procesos de biocorrosión interna de tanques de almacenamiento y de líneas de transporte en sistemas industriales de gas natural y petróleo.

The sulfate-reducing bacteria growth kinetics and the biotransformation of sulfate into hydrogen sulfide were studied under laboratory conditions, using batch and continuous assays to determine the effect of molybdate and nitrate as metabolic inhibitors. The microorganisms were isolated from water coming from a natural gas dehydration plant, where they were associated with Microbiologically Influenced Corrosion (MIC) processes, and later cultured in planktonic and sessile states. The addition of 5 mM molybdate showed a growth reduction to levels of non - detectable floating cells and a six order of magnitude reduction in biofilms, concomitant with a sulfide decrease of around 100% in all cultures inhibited by this compound. The addition of 75 mM nitrate showed a four order of magnitude reduction in free bacterial cells and a two order of magnitude reduction in adhered bacterial cells, respectively, as well as a sulfide decrease of around 80%. The decreased corrosion rate detected suggests that these inorganic salts could be nonconventional biocides for an effective and environmentally non contaminant way of controlling and mitigating internal biocorrosion processes in storage tanks and pipelines in natural gas and petroleum industrial systems.