Influence of marine Shewanella putrefaciens and mediated calcium deposition on Q235 carbon steel corrosion.

The microbiologically influenced corrosion inhibition (MICI) of Q235 carbon steel by Shewanella putrefaciens and mediated calcium deposition were investigated by regulating microbial mineralization. In a calcium-rich medium, S. putrefaciens rapidly created a protective calcium carbonate layer on the steel surface, which blocked Cl- diffusion. Without calcium, the biofilm and rust layer mitigated pitting corrosion but did not prevent Cl- penetration. Potentiodynamic polarization results indicated that the current densities (icorr values) of the corrosion produced in the S. putrefaciens-inoculated media with and without calcium were 0.4 µA/cm2 and 0.6 µA/cm2, respectively. Similarly, compared with those under sterile conditions, the corrosion inhibition rates were 92.2% and 87.4% higher, respectively. Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) confirmed that the MICI was caused by the combination of microbial aerobic respiration and the deposited layers. Even under nonbiological conditions, S. putrefaciens-induced calcium carbonate deposition inhibited corrosion.

Synergistic D-Amino Acids Based Antimicrobial Cocktails Formulated via High-Throughput Screening and Machine Learning.

Antimicrobial resistance (AMR) from pathogenic bacterial biofilms has become a global health issue while developing novel antimicrobials is inefficient and costly. Combining existing multiple drugs with enhanced efficacy and/or reduced toxicity may be a promising approach to treat AMR. D-amino acids mixtures coupled with antibiotics can provide new therapies for drug-resistance infection with reduced toxicity by lower drug dosage requirements. However, iterative trial-and-error experiments are not tenable to prioritize credible drug formulations, owing to the extremely large number of possible combinations. Herein, a new avenue is provide to accelerate the exploration of desirable antimicrobial formulations via high-throughput screening and machine learning optimization. Such an intelligent method can navigate the large search space and rapidly identify the D-amino acid mixtures with the highest anti-biofilm efficiency and also the synergisms between D-amino acid mixtures and antibiotics. The optimized drug cocktails exhibit high antimicrobial efficacy while remaining non-toxic, which is demonstrated not only from in vitro assessments but also the first in vivo study using a lung infection mouse model.

Extracellular Electron Transfer in Microbiologically Influenced Corrosion of 201 Stainless Steel by Shewanella algae.

The microbiologically influenced corrosion of 201 stainless steel by Shewanella algae was investigated via modulating the concentration of fumarate (electron acceptor) in the medium and constructing mutant strains induced by ΔOmcA. The ICP-MS and electrochemical tests showed that the presence of S. algae enhanced the degradation of the passive film; the lack of an electron acceptor further aggravated the effect and mainly affected the early stage of MIC. The electrochemical tests and atomic force microscopy characterization revealed that the ability of ΔOmcA to transfer electrons to the passive film was significantly reduced in the absence of the c-type cytochrome OmcA related to EET progress, leading to the lower corrosion rate of the steel.

Microbiologically influenced corrosion of FeCoNiCrMn high-entropy alloys by Pseudomonas aeruginosa biofilm.

Pseudomonas aeruginosa is widely found in industrial water and seawater. Microbiologically influenced corrosion (MIC) caused by P. aeruginosa is a serious threat and damage to the safe service of steel materials. In this study, the MIC behavior of FeCoNiCrMn high-entropy alloy (HEA) by P. aeruginosa biofilm was investigated in the simulated marine medium. The maximum pitting depth of the HEA coupons in the P. aeruginosa-inoculated medium was ~4.77 µm, which was 1.5 times that in the sterile medium. EIS and potentiodynamic polarization results indicated that P. aeruginosa biofilm reduced the corrosion resistance of the passive film of HEA coupons and promoted its anodic dissolution process. XPS and AES results further demonstrated that P. aeruginosa interfered with the distribution of elements in the passive film and significantly promoted the dissolution of Fe.

Matrine@chitosan-D-proline nanocapsules as antifouling agents with antibacterial properties and biofilm dispersibility in the marine environment.

Antifoulants are the most vital substances in antifouling coatings to prevent marine organisms from colonizing the undersea substrate surfaces. In addition to antibacterial performance, inhibition of biofilm formation is an important criterion for antifouling coatings. In this study, we synthesized pH-responsive matrine@chitosan-D-proline (Mat@CS-Pro) nanocapsules of about 280 nm with antibacterial properties and biofilm dispersibility. The prepared Mat@CS-Pro nanocapsules exhibited high-level antibacterial properties, reaching about 93, 88, and 96% for E. coli, S. aureus, and P. aeruginosa, respectively. Such nanocapsules can cause irreversible damage to bacteria and cause them to lose their intact cell structures. Moreover, Mat@CS-Pro nanocapsules also possessed outstanding dispersal biofilm performances, in which the biofilm thickness of E. coli, S. aureus, and P. aeruginosa was decreased by 33, 74, and 42%, respectively, after 3 days of incubation. Besides, the Mat@CS-Pro nanocapsules had remarkable pH-responsive properties. As the environmental pH became acidic, the nanocapsules swelled to about 475 nm and the released concentration could reach 28.5 ppm after immersion for 10 h but maintained a low releasing rate in pH 8 conditions.

The effect of riboflavin on the microbiologically influenced corrosion of pure iron by Shewanella oneidensis MR-1.

The microbiologically influenced corrosion of pure iron was investigated in the presence of Shewanella oneidensis MR-1 with various levels of exogenous riboflavin (RF) serving as electron shuttles for extracellular electron transfer (EET). With more RF available, a larger and denser phosphate layer was formed on the surface of pure iron by the bacteria. The results of electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic polarization tests showed that the product layer provided good corrosion protection to the pure iron. Using electrochemical noise, we observed that the addition of RF accelerated the corrosion at the initial stage of immersion, thereby accelerating the deposition of products to form a protective layer subsequently.

Microbiologically influenced corrosion inhibition mechanisms in corrosion protection: A review.

Microbial activities can change the properties of biofilm/metal interfaces to accelerate or decelerate the corrosion of metals in a given environment. Microbiologically influenced corrosion inhibition (MICI) is the inhibition of corrosion that is directly or indirectly induced by microbial action. Compared with conventional methods for protection from corrosion, MICI is environmentally friendly and an emerging approach for the prevention and treatment of (bio)corrosion. However, due to the diversity of microorganisms and the fact that their metabolic processes are greatly complicated by environmental factors, MICI is still facing challenges for practical application. This review provides a comprehensive overview of the mechanisms of MICI under different conditions and their advantages and disadvantages for potential applications in corrosion protection.

Responses of soil microbiome to steel corrosion.

The process of microbiologically influenced corrosion (MIC) in soils has received widespread attention. Herein, long-term outdoor soil burial experiments were conducted to elucidate the community composition and functional interaction of soil microorganisms associated with metal corrosion. The results indicated that iron-oxidizing (e.g., Gallionella), nitrifying (e.g., Nitrospira), and denitrifying (e.g., Hydrogenophaga) microorganisms were significantly enriched in response to metal corrosion and were positively correlated with the metal mass loss. Corrosion process may promote the preferential growth of the abundant microbes. The functional annotation revealed that the metabolic processes of nitrogen cycling and electron transfer pathways were strengthened, and also that the corrosion of metals in soil was closely associated with the biogeochemical cycling of iron and nitrogen elements and extracellular electron transfer. Niche disturbance of microbial communities induced by the buried metals facilitated the synergetic effect of the major MIC participants. The co-occurrence network analysis suggested possible niche correlations among corrosion related bioindicators.

Investigation of microbiologically influenced corrosion of 304 stainless steel by aerobic thermoacidophilic archaeon Metallosphaera cuprina.

In this study, the influence of thermoacidophilic archaeon Metallosphaera cuprina on the corrosion of 304 stainless steel was investigated. 304 stainless steel in M. cuprina-inoculated culture medium exhibited more marked pitting corrosion behavior than that seen in sterile culture medium. After 14 days, the average pit depth under M. cuprina biofilms was nearly twice as great as that in sterile culture medium. Electrochemical measurements also showed that 304 stainless steel had lower charge transfer resistance and smaller pitting potential after 14 days of exposure in inoculated culture medium. The ferrous ion oxidation ability of M. cuprina biofilms can cause a change in the composition of passive films and accelerate the anodic dissolution of the steel substrate, to promote the pitting corrosion process at 304 stainless steel.

Microbial ingress and in vitro degradation enhanced by glucose on bioabsorbable Mg-Li-Ca alloy.

Biodegradable magnesium alloys are challenging to be implanted in patients with hyperglycemia and diabetes. A hypothesis is suggested that glucose accelerates microbial ingress and in vitro degradation of Mg-Li-Ca implants. Corrosion resistance and mechanical properties was demonstrated using electrochemical, hydrogen evolution and tensile tests. The bacteria from Hank's solution were isolated via 16S rRNA gene analysis. The results revealed that Mg-1Li-1Ca alloy exhibited different responses to Hank's solution with and without glucose. The solution acidity was ascribed to Microbacterium hominis and Enterobacter xiangfangensis, indicating that glucose promoted microbial activity and degradation and deterioration in mechanical property of Mg-1Li-1Ca alloy.

Microbiologically influenced corrosion of 304 stainless steel by nitrate reducing Bacillus cereus in simulated Beijing soil solution.

In this work, microbiologically influenced corrosion (MIC) of 304 stainless steel (SS) caused by Bacillus cereus was investigated by electrochemical measurements and surface analyses in simulated Beijing soil solution under aerobic condition. The nitrate-reducing bacterium (NRB), B. cereus, was isolated from Beijing soil and identified using 16S rDNA. Confocal laser scanning microscopy (CLSM) images showed that the largest pit depths on 304 SS with and without B. cereus after 14 days of incubation were 7.17 and 4.59 µm, respectively, indicating that pitting corrosion was accelerated by B. cereus. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS) results revealed that B. cereus and its metabolic products were detrimental to the integrity of the passive film on 304 SS. The electrochemical results showed that B. cereus significantly reduced the corrosion resistance of 304 SS and accelerated the anodic dissolution reaction, thereby speeding up the corrosion process.

Effect of Dissolved Oxygen Concentration on the Microbiologically Influenced Corrosion of Q235 Carbon Steel by Halophilic Archaeon Natronorubrum tibetense.

The influence of dissolved oxygen concentration (DOC) on the microbiologically influenced corrosion (MIC) of Q235 carbon steel in the culture medium of halophilic archaeon Natronorubrum tibetense was investigated. The increase of DOC from 0.0 to 3.0 ppm was found to strengthen the oxygen concentration cell by promoting cathodic reaction. Meanwhile, the increased DOC also promoted archaeal cell growth, which could consume more metallic iron as energy source and aggravated the localized corrosion. When the DOC further increased to 5.0 ppm, the uniform corrosion was dominant as the biofilms became uniformly presented on the steel surface. Combined with the stronger inhibition effect of oxygen diffusion by the increased biofilm coverage, the MIC of carbon steel in the 5.0 ppm medium was weaker than that in the 3.0 ppm medium. From weight loss and electrochemical tests, the results all demonstrated that the carbon steel in the 3.0 ppm medium had the largest corrosion rate.

Recent Advances in Scanning Electrochemical Microscopy for Biological Applications.

Scanning electrochemical microscopy (SECM) is a chemical microscopy technique with high spatial resolution for imaging sample topography and mapping specific chemical species in liquid environments. With the development of smaller, more sensitive ultramicroelectrodes (UMEs) and more precise computer-controlled measurements, SECM has been widely used to study biological systems over the past three decades. Recent methodological breakthroughs have popularized SECM as a tool for investigating molecular-level chemical reactions. The most common applications include monitoring and analyzing the biological processes associated with enzymatic activity and DNA, and the physiological activity of living cells and other microorganisms. The present article first introduces the basic principles of SECM, followed by an updated review of the applications of SECM in biological studies on enzymes, DNA, proteins, and living cells. Particularly, the potential of SECM for investigating bacterial and biofilm activities is discussed.

Mussel-inspired superhydrophobic surfaces with enhanced corrosion resistance and dual-action antibacterial properties.

In this study, a multilayer antibacterial film was assembled onto 316L stainless steel via mussel-inspired depositions of polydopamine (PDA) and silver (Ag) nanoparticles followed by post-modification with 1H, 1H, 2H, 2H-perfluorodecanethiol. The resulting surface exhibited excellent superhydrophobicity with hierarchical micro/nanostructures that were constructed by both PDA and Ag nanoparticles. The crystal structure and chemical composition of these surfaces were investigated using X-ray photoelectron spectroscopy (XPS) analysis. Potentiodynamic polarization measurements revealed that the corrosion resistance of the as-prepared surfaces were sequentially increased after each step of the fabrication process. Compared with the surface covered with only Ag nanoparticles, the superhydrophobic surfaces exhibited substantially enhanced antibacterial activity against the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, resulting from the synergistic antibacterial actions of the superhydrophobic surface and Ag nanoparticles. The superhydrophobic surface exhibited lower cytotoxicity, compared to the surface covered with Ag nanoparticles.

Depside derivatives with anti-hepatic fibrosis and anti-diabetic activities from Impatiens balsamina L. flowers.

Eighteen compounds (1-18), seven new (3-9) and eleven previously reported (1, 2, and 10-18), were isolated from the flowers of Impatiens balsamina (Linn). The structures of the isolated compounds were elucidated using different spectroscopic methods, including NMR (1D and 2D), UV, IR, and HR-ESI-MS. Analysis of the bioassay results showed the compounds had notable anti-hepatic fibrosis activity against murine Hepatic Stellate Cells (t-HSC/Cl-6) and anti-diabetics activity against α-glucosidase. Specifically, new compounds 7, 8, 9 showed significant inhibitory activity on t-HSC/Cl-6 cells with IC50 values of 42.12, 109.2, and 34.04 µg/mL respectively, while the IC50 values of positive control Silymarin and Fufang Biejia Ruangan Pian were 202.34 and 231.56 µg/mL, respectively. In addition, compounds 2, 4, 7, 8, 10, 11, 17, and 18 exhibited excellent α-glucosidase inhibitory activity. Among these compounds, 7 exhibited the highest activity with an IC50 value of 0.72 µg/mL, while the IC50 value of the positive control acarbose was 3.36 µg/mL. This is the first study evaluating the anti-hepatic fibrosis and anti-diabetic activities of compounds isolated from the flowers of I. balsamina.

Antihepatic Fibrosis Effect of Active Components Isolated from Green Asparagus (Asparagus officinalis L.) Involves the Inactivation of Hepatic Stellate Cells.

Green asparagus (Asparagus officinalis L.) is a vegetable with numerous nutritional properties. In the current study, a total of 23 compounds were isolated from green asparagus, and 9 of these compounds were obtained from this genus for the first time. Preliminary data showed that the ethyl acetate (EtOAc)-extracted fraction of green asparagus exerted a stronger inhibitory effect on the growth of t-HSC/Cl-6 cells, giving an IC50 value of 45.52 µg/mL. The biological activities of the different compounds isolated from the EtOAc-extracted fraction with respect to antihepatic fibrosis were investigated further. Four compounds, C3, C4, C10, and C12, exhibited profound inhibitory effect on the activation of t-HSC/Cl-6 cells induced by TNF-α. The activation t-HSC/Cl-6 cells, which led to the production of fibrotic matrix (TGF-ß1, activin C) and accumulation of TNF-α, was dramatically decreased by these compounds. The mechanisms by which these compounds inhibited the activation of hepatic stellate cells appeared to be associated with the inactivation of TGF-ß1/Smad signaling and c-Jun N-terminal kinases, as well as the ERK phosphorylation cascade.