Mechanism Research Of D-Amino Acid To Alleviate Bacterial Adhesion,Corrosion And Enhance Corrosion Inhibitor Performance

Microbiological Influenced Corrosion(MIC)refers to the corrosion process of metallic materials caused by the life activities of microorganisms themselves or their metabolites.It is assessed that in the industrial sector of developed countries,the economic loss caused by metal corrosion has accounted for 2%to 3%of the gross domestic product(GDP).the economic loss caused by corrosion in China in 2014 has reached 2 trillion-yuan,accounting for about 3.34%of the GDP.Therefore,MIC has become an increasing problem of concern.At present,the addition of corrosion inhibitors is the main method to alleviate the corrosion of cooling water pipes in industry.The phosphorus corrosion inhibitors have been most widely used because of their excellent corrosion inhibition properties,especially in high hardness and high pH water can still be applied.For example,1hydroxyethylene-1,1-diphosphonic acid(HEDP)can prevent corrosion by forming a protective film on the surface of the pipe through adsorption because it has two phosphonate groups with high adsorption capacity(C-PO3H2)and a stable C-P bond.However,the phosphate corrosion inhibitors used are difficult to be degraded by wastewater plants,resulting in the release of large amounts of phosphorus elements into the environment,causing eutrophication and algal blooms in water bodies.Therefore,there is an urgent need to develop new green corrosion inhibitors to achieve MIC control.D-amino acids,a signaling molecule substance,can regulate the generation of biofilm,thus reducing the contact between microorganisms and metal interfaces,and thus it has the conditions to be a corrosion inhibitor.In this study,we take D-amino acids as the research object,analyze their adhesion inhibition effect on typical microorganisms in the process of pipeline corrosion,investigate their corrosion inhibition performance under different salinities,and reveal their mechanism of action to achieve corrosion inhibitor reduction in cooperation with traditional corrosion inhibitors.The main research contents and conclusions are as follows:(1)The effect of D-tyrosine on the adhesion properties of Escherichia coli(E.coli)was investigated.It was found that under the effect of D-tyrosine,the number of E.coli adhering to membrane,steel and glass surfaces was significantly reduced and all showed the lowest inhibition rate at the initial stage of bacterial growth.By analyzing the adhesion force on the bacterial surface,it was found that in the presence of Dtyrosine,the force curve interval gradually shifted to the right with increasing incubation time.Meanwhile,D-tyrosine changed the physicochemical properties of hydrophobicity and aggregation on the surface of E.coli,but did not change the bacterial surface charge.This is since D-tyrosine can achieve the alteration of bacterial adhesion ability by inhibiting the secretion of extracellular proteins.Transcriptome analysis showed that D-tyrosine regulates the production and transport of tryptophan in E.coli metabolism,thus achieving control over the signaling molecule indole,which in turn reduces biofilm formation;secondly,it inhibits the synthesis of curli protein and adhesion-like protein,decreases the content of proteins in EPS,leading to a decrease in bacterial outer surface adhesion properties,and also alters the hydrophobicity of the bacterial surface;in addition,D-tyrosine also interfered with the polymerization of peptidoglycan,reduced the rigidity of the cell wall,and weakened the tightness of interbacterial connections during the aggregation process,resulting in poor autonomous aggregation.(2)The mechanism of action of D-amino acids in slowing down the corrosion of sulfate-reducing bacteria(SRB)at different salinities was analyzed.It was found that dextro-phenylalanine(D-Phe)in low salinity environment did not play a role in corrosion inhibition,and it would accelerate the corrosion rate to some extent.With the increase of salinity,the corrosion inhibition ability of D-Phe was gradually strengthened,and D-Phe showed the optimal corrosion inhibition effect at high salinity,maintaining the minimum corrosion rate.The analysis of biofilm and iron sheet morphology showed that D-Phe did not change the structure of biofilm at low salinity and EPS secretion increased under salt stress;the fine pitting pits increased at sea salt salinity and the surface cracks of steel sheet increased,the addition of D-Phe did not change the surface roughness,but the depth of pitting pits decreased;the inhibition of biofilm by D-Phe was more significant at high salinity,and the EPS content increased.The metabolic results showed that the addition of D-Phe did not affect the bacterial growth at all salinities;the addition of D-Phe did not affect the sulfur metabolic process at low and high salinities in the sulfate metabolism test,but the sulfate reduction process was significantly inhibited at high salinities,and the inhibition effect was more significant after the addition of D-Phe.The transcriptomic analysis revealed that D-Phe mainly altered the amino acid metabolism and synthesis process,regulating tryptophan and indole synthesis,thus inhibiting biofilm formation;while D-Phe also altered the sulfur metabolism process in the high salinity group,in which the sulfate to sulfite reduction process was significantly inhibited;meanwhile,peptidoglycan and tricarboxylic acid related genes were also regulated,inhibiting the SRB biofilm generation.(3)The enhancement effect of D-Phe on corrosion inhibitors was investigated using the compounding of D-Phe and corrosion inhibitor HEDP.It was found that Damino acids could significantly enhance the corrosion inhibition performance of HEDP,prolong the time of corrosion inhibitor film formation and strengthen the corrosion inhibition ability;D-Phe mainly alleviated the corrosion of Fe(0)by inhibiting the cathodic reaction.Characterization analysis of biofilm revealed that D-Phe achieved synergistic effects by reducing biofilm biomass and extracellular protein secretion.Further investigation of the mechanism of D-Phe and HEDP corrosion inhibition revealed that the complex group mainly regulated the following metabolic pathways to achieve synergistic corrosion inhibition:peptidoglycan hydrolysis and synthesis,synthesis of electron transporters(cytochrome,transporter ABC),secretion of QS signaling molecules(sigma 54,histidine kinase)and iron oxygen reducing protein.