Field testing of an enzymatic quorum quencher coating additive to reduce biocorrosion of steel.

Microbial colonization can be detrimental to the integrity of metal surfaces and lead to microbiologically influenced corrosion. Biocorrosion is a serious problem for aquatic and marine industries in the world and severely affects the maritime transportation industry by destroying port infrastructure and increasing fuel usage and the time and cost required for maintenance of transport vessels. Here, we evaluate the potential of a stable quorum quenching lactonase enzyme to reduce biocorrosion in the field. Over the course of 21 months, steel samples coated with lactonase-containing acrylic paint were submerged at two different sites and depths in the Duluth-Superior Harbor (Lake Superior, MN, USA) and benchmarked against controls, including the biological biocide surfactin. In this experiment, the lactonase treatment outperformed the surfactin biocide treatment and significantly reduced the number of corrosion tubercles (37%; P < 0.01) and the corroded surface area (39%; P < 0.01) as compared to the acrylic-coated control coupons. In an attempt to evaluate the effects of signal disruption of surface microbial communities and the reasons for lower corrosion levels, 16S rRNA sequencing was performed and community populations were analyzed. Interestingly, surface communities were similar between all treatments, and only minor changes could be observed. Among these changes, several groups, including sulfate-reducing bacteria (SRB), appeared to correlate with corrosion levels, and more specifically, SRB abundance levels were lower on lactonase-treated steel coupons. We surmise that these minute community changes may have large impacts on corrosion rates. Overall, these results highlight the potential use of stable quorum quenching lactonases as an eco-friendly antifouling coating additive. IMPORTANCE Biocorrosion severely affects the maritime transportation industry by destroying port infrastructure and increasing fuel usage and the time and cost required to maintain transport vessels. Current solutions are partly satisfactory, and the antifouling coating still largely depends on biocide-containing products that are harmful to the environment. The importance of microbial signaling in biofouling and biocorrosion is not elucidated. We here take advantage of a highly stable lactonase that can interfere with N-acyl homoserine lactone-based quorum sensing and remain active in a coating base. The observed results show that an enzyme-containing coating can reduce biocorrosion over 21 months in the field. It also reveals subtle changes in the abundance of surface microbes, including sulfate-reducing bacteria. This work may contribute to pave the way for strategies pertaining to surface microbiome changes to reduce biocorrosion.

Correlation between Macrophage Polarization and PD-L1-Related Tumor Microenvironmental Alteration and Metastasis in Pancreatic Ductal Adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a poor prognosis; nearly 80% patients have regional or distant metastasis when diagnosed. Tumor microenvironment (TME) alteration and epithelial-to-mesenchymal transition (EMT) have been reported to play a key role in cancer metastasis. However, the correlation between TME and EMT was poorly studied in PDAC. This study aims to explore the correlation between EMT markers and TME alteration, mainly including macrophage polarization and PD-L1 expression change, in primary and metastatic PDAC tissues by immunohistochemistry. The results indicated that macrophage polarization was found in metastases with the number of M1 macrophages (CD86+) decreased and M2 (CD163+) increased, though PD-L1 expression did not have a significant alteration. Compared to primary tumors, E-cadherin was significantly lower, while snail was higher, while no difference was found with N-cadherin and ZEB1. Correlation analysis indicated that snail, but not ZEB1, E-cadherin, or N-cadherin, was highly correlated with macrophage polarization. To conclude, the number of CD86+ M1 macrophages was increased while CD163+ M2 macrophages decreased in metastases, with no significant alteration of PD-L1 expression compared to primary tumors. EMT markers-Snail and E-cadherin-but not ZEB1 or N-cadherin, were found to be higher/lower in metastases, which mean that EMT played an important role in PDAC metastasis. Further analysis indicated that snail was highly correlated with M1 to M2 macrophage polarization, which prompted that EMT may be one reason for macrophage polarization induced TME alteration in PDAC metastasis.

Correction: Evaluation of biological and enzymatic quorum quencher coating additives to reduce biocorrosion of steel.

[This corrects the article DOI: 10.1371/journal.pone.0217059.].

Balancing carbon, nitrogen and phosphorus concentration in seawater as a strategy to prevent accelerated membrane biofouling.

Membrane biofouling remains a significant challenge in seawater reverse osmosis desalination for drinking water production. This study investigated nutrient imbalance as the cause of biofouling in lab-scale experiments and carried out a year-long field-testing at a seawater desalination pilot plant. Lab experiments showed that growth medium with excess of organic carbon (C) but with low nitrogen (N) and phosphorus (P) accelerated the formation of bacterial biofilm. Balancing C to N and P ratios by adding N and P to growth medium increased the proliferation of free-living cells but reduced attached form of bacteria as biofilm. The cell excretion of excess C in the form of extracellular polysaccharides (EPS) was considered as a strategy for nutrient storage for future use. Cell enzyme activity assays indicated some of the bacteria had enhanced enzyme activities to degrade polysaccharides in the absence of organic C in growth medium, possibly using EPS in the biofilm. A year-long field study indicated that accelerated biofouling of seawater reverse osmosis (SWRO) membranes was associated with the elevated content of total organic carbon (TOC) in the intake seawater. Adding N and P to the intake seawater to balance the increase of TOC resulted in reduction of membrane biofouling. Microbial community analysis of the biofouling layer using 16S rRNA gene sequencing indicated biofouling communities varied with seasonal changes. Dosing of N and P did not induce dramatic changes in the fouling microbial community growing on the membrane surface. The outcome of this work implies that membrane biofouling associated with the elevated concentration of TOC in intake seawater is caused by imbalance of C:N:P in the source seawater which occurs often during algal blooms. Addition of N and P to rebalance the nutrients can prevent accelerated SWRO membrane biofouling.

Evaluation of biological and enzymatic quorum quencher coating additives to reduce biocorrosion of steel.

Microbial colonization can be detrimental to the integrity of metal surfaces and lead to microbiologically influenced corrosion (MIC). Biocorrosion is a serious problem for aquatic and marine industries in the world. In Minnesota (USA), where this study was conducted, biocorrosion severely affects the maritime transportation industry. The anticorrosion activity of a variety of compounds, including chemical (magnesium peroxide) and biological (surfactin, capsaicin, and gramicidin) molecules were investigated as coating additives. We also evaluated a previously engineered, extremely stable, non-biocidal enzyme known to interfere in bacterial signaling, SsoPox (a quorum quenching lactonase). Experimental steel coupons were submerged in water from the Duluth Superior Harbor (DSH) for 8 weeks in the laboratory. Biocorrosion was evaluated by counting the number and the coverage of corrosion tubercles on coupons and also by ESEM imaging of the coupon surface. Three experimental coating additives significantly reduced the formation of corrosion tubercles: surfactin, magnesium peroxide and the quorum quenching lactonase by 31%, 36% and 50%, respectively. DNA sequence analysis of the V4 region of the bacterial 16S rRNA gene revealed that these decreases in corrosion were associated with significant changes in the composition of bacterial communities on the steel surfaces. These results demonstrate the potential of highly stable quorum quenching lactonases to provide a reliable, cost-effective method to treat steel structures and prevent biocorrosion.