Identification of key factors in Accelerated Low Water Corrosion through experimental simulation of tidal conditions: influence of stimulated indigenous microbiota.

Biotic and abiotic factors favoring Accelerated Low Water Corrosion (ALWC) on harbor steel structures remain unclear warranting their study under controlled experimental tidal conditions. Initial stimulation of marine microbial consortia by a pulse of organic matter resulted in localized corrosion and the highest corrosion rates (up to 12-times higher than non-stimulated conditions) in the low water zone, persisting after nine months exposure to natural seawater. Correlations between corrosion severity and the abundance and composition of metabolically active sulfate-reducing bacteria (SRB) indicated the importance and persistence of specific bacterial populations in accelerated corrosion. One phylotype related to the electrogenic SRB Desulfopila corrodens appeared as the major causative agent of the accelerated corrosion. The similarity of bacterial populations related to sulfur and iron cycles, mineral and tuberculation with those identified in ALWC support the relevance of experimental simulation of tidal conditions in the management of steel corrosion exposed to harbor environments.

Intraluminal pressure modulates eicosanoid enzyme expression in vascular endothelium of intact human conduit vessels at physiological levels of shear stress.

OBJECTIVE: Biosynthesis of eicosanoid metabolites in blood vessels regulates vascular tone and platelet function. We investigated whether intraluminal pressure modulates gene and protein expression of key eicosanoid enzymes in intact human conduit vessels and/or release of their vasoactive metabolites. METHODS: Paired segments of human umbilical veins were perfused under laminar flow for 1.5, 3 and 6 h at high versus low intraluminal pressure (40/20 mmHg) with identical shear stress (10 dyn/cm(2)). Endothelial cell mRNAs encoding cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), prostaglandin synthase (PGS), and thromboxane synthase (TXS) were measured by quantitative real-time RT-PCR. Secretion of PGI2 and TXA2 to the perfusion medium was measured by enzyme immunoassay of their metabolites 6-keto-prostaglandin F(1alpha) and TXB2. RESULTS: Intraluminal pressures were 39.9 +/- 0.02 and 20.0 +/- 0.03 mmHg (P < 0.0001) in high and low pressure circuits, and shear stress levels were 10.6 +/- 0.60 and 9.7 +/- 0.36 dyn/cm(2) (NS, not significant). COX-1 mRNA was significantly up-regulated after 1.5 h of high pressure stimulation and continued up to 3 h, but fell thereafter significantly below baseline after 6 h. COX-2 mRNA was initially significantly down-regulated, followed by a significant up-regulation after 6 h. Gene expressions of PGS and TXS were significantly induced after 6 h of high pressure perfusion. High pressure depressed the production of PGI(2) (P < 0.05) but did not alter TXA(2) formation. CONCLUSIONS: Intraluminal pressure has differential effects on gene and protein expression of key eicosanoid enzymes and biosynthesis of prostanoid metabolites in intact human conduit vessels. The new, computerized biomechanical perfusion system may be a useful tool to elucidate specific effects of various biomechanical forces on intact mammalian conduit vessels.