Assessment of the corrosion resistance of self-ordered anodic aluminum oxide (AAO) obtained in tartaric-sulfuric acid (TSA)

The corrosion performance of self-ordered porous anodic aluminum oxide (AAO) has been studied and correlated to its structure. High purity aluminum alloy (> 99.999%) has been anodized using three different conditions: (a) in tartaric-sulfuric electrolyte employing common disordered conditions (TSA), (b) in sulfuric acid applying self-ordering conditions (SA), and (c) in tartaric-sulfuric electrolyte applying self-ordering conditions (TSA-SA). Some samples were post-treated in boiling water with the aim of sealing their pores. The morphology and order of the AAOs were determined by means of scanning electron microscopy and Fast Fourier Transform (FFT), while their corrosion behavior was assessed in 0.59M NaCl employing potentiodynamic polarization tests (LP) and electrochemical impedance spectroscopy (EIS). The evolution of impedance of samples SA and TSA was monitored during 1000 h of immersion in 0.59M NaCl. The three types of samples present similar pore diameter (Dpo) and certain degree of order, although TSA shows the lowest. However, TSA shows smaller interpore distance (Dint), thinner cell wall thickness (tw) and higher pore density (ρpo) and porosity (P) than SA and TSA-SA, which feature very similar values for these structural parameters. The LP curves do not allow to discriminate between samples. SA and TSA-SA have higher impedance than TSA among samples not sealed, probably because a thicker barrier layer forms in samples with self-ordering regime. When sealed, TSA samples show higher impedance than SA and TSA-SA in the medium frequency range because porous membranes with lower order are more easily sealed. All types of AAO, both unsealed and sealed, undergo self-sealing process during the immersion experiments. According to EIS interpretation, TSA porous oxide is self-sealed in a more efficient manner than SA and TSA-SA. These findings imply that self-ordering conditions can enhance the corrosion resistance of AAO

Genomic resources for a commercial flatfish, the Senegalese sole (Solea senegalensis): EST sequencing, oligo microarray design, and development of the Soleamold bioinformatic platform

Background: The Senegalese sole, Solea senegalensis, is a highly prized flatfish of growing commercial interest for aquaculture in Southern Europe. However, despite the industrial production of Senegalese sole being hampered primarily by lack of information on the physiological mechanisms involved in reproduction, growth and immunity, very limited genomic information is available on this species. Results: Sequencing of a S. senegalensis multi-tissue normalized cDNA library, from adult tissues (brain, stomach, intestine, liver, ovary, and testis), larval stages (pre-metamorphosis, metamorphosis), juvenile stages (post-metamorphosis, abnormal fish), and undifferentiated gonads, generated 10,185 expressed sequence tags (ESTs). Clones were sequenced from the 3'-end to identify isoform specific sequences. Assembly of the entire EST collection into contigs gave 5,208 unique sequences of which 1,769 (34%) had matches in GenBank, thus showing a low level of redundancy. The sequence of the 5,208 unigenes was used to design and validate an oligonucleotide microarray representing 5,087 unique Senegalese sole transcripts. Finally, a novel interactive bioinformatic platform, Soleamold, was developed for the Senegalese sole EST collection as well as microarray and ISH data. Conclusion: New genomic resources have been developed for S. senegalensis, an economically important fish in aquaculture, which include a collection of expressed genes, an oligonucleotide microarray, and a publicly available bioinformatic platform that can be used to study gene expression in this species. These resources will help elucidate transcriptional regulation in wild and captive Senegalese sole for optimization of its production under intensive culture conditions

Acidic Digestion in a Teleost: Postprandial and Circadian Pattern of Gastric pH, Pepsin Activity, and Pepsinogen and Proton Pump mRNAs Expression

Two different modes for regulation of stomach acid secretion have been described in vertebrates. Some species exhibit a continuous acid secretion maintaining a low gastric pH during fasting. Others, as some teleosts, maintain a neutral gastric pH during fasting while the hydrochloric acid is released only after the ingestion of a meal. Those different patterns seem to be closely related to specific feeding habits. However, our recent observations suggest that this acidification pattern could be modified by changes in daily feeding frequency and time schedule. The aim of this study was to advance in understanding the regulation mechanisms of stomach digestion and pattern of acid secretion in teleost fish. We have examined the postprandial pattern of gastric pH, pepsin activity, and mRNA expression for pepsinogen and proton pump in white seabream juveniles maintained under a light/dark 12/12 hours cycle and receiving only one morning meal. The pepsin activity was analyzed according to the standard protocol buffering at pH 2 and using the actual pH measured in the stomach. The results show how the enzyme precursor is permanently available while the hydrochloric acid, which activates the zymogen fraction, is secreted just after the ingestion of food. Results also reveal that analytical protocol at pH 2 notably overestimates true pepsin activity in fish stomach. The expression of the mRNA encoding pepsinogen and proton pump exhibited almost parallel patterns, with notable increases during the darkness period and sharp decreases just before the morning meal. These results indicate that white seabream uses the resting hours for recovering the mRNA stock that will be quickly used during the feeding process. Our data clearly shows that both daily illumination pattern and feeding time are involved at different level in the regulation of the secretion of digestive juices

Changes in gastric pH as a function of the wet weight in fed larvae, juveniles and adults of <i>Diplodus sargus</i>.

<p>Lines indicate the regression of pH in relation to wet weight (W) in fed animals.</p

Pepsin activity (mean ± SD) during the 24 h cycle in juveniles of <i>Diplodus sargus</i>.

<p>Red line indicates the analyses done at pH 2. Black line indicates the analyses done at the actual luminal pH. Same letter indicates no significant difference (<i>P</i>>0.05). Green area: feeding period. Grey area: dark period.</p

Gene expression of pepsinogen and H⁺/K⁺-ATPase mRNA during the 24 h cycle in juveniles of <i>Diplodus sargus</i>.

<p>Same letter indicates no significant difference (<i>P</i>>0.05); a and b: proton pump; a′ and b′: pepsinogen. Green area: feeding period. Grey area: dark period.</p

Oligonucleotides designed for real time RT-PCR.

<p>Oligonucleotides designed for real time RT-PCR.</p

Evolutionary relationships of 40 taxa for pepsinogen precursors.

<p>The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test is shown next to the branches. GenBank or NCBI Reference Sequence accession number appears to the right of each taxon.</p

Evolutionary relationships of 28 taxa for proton/potassium and sodium/potassium pumps.

<p>The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test is shown next to the branches. GenBank or NCBI Reference Sequence accession number appears to the right of each taxon.</p

Relative stomach fullness during the 24 h cycle in juveniles of <i>Diplodus sargu</i>s.

<p>Green area: feeding period. Grey area: dark period.</p