Corrosion Mechanism And Protection Of Pseudoalteromonas And Its Mutant Strains For Marine Steel

In marine environments,various aggregates of bacterial cells tend to colonize on metal surfaces to form biofilms,resulting in microbiologically influenced corrosion,which severely affects the reliability,integrity,and security of marine engineering facilities.According to 2017 statistics,domestic corrosion loss is about 310 billion USD/year,of which 20% is related to MIC.Therefore,microbiological corrosion of marine engineering equipment and marine steel should be paid attention and be solved.Herein,a wild type Pseudoalteromonas lipolytica(P.lipolytica)strain and their variants of P.lipolytica strain were selected to investigate the key factor effecting the marine steel and stainless-steel corrosion behavior in seawater.Moreover,a novel and “green”approach for the protection of steel by a marine bacterium P.lipolytic was investigated.This approach protects steel from corrosion in seawater via the formation of a biofilm followed by the formation of an organic-inorganic hybrid film and superhydrophobic film.A new microbial corrosion research method is constructed by highly combining biology and materials science.In the field of corrosion,multifunctional mutant strains of the same bacteria are innovatively used as the research model bacteria to minimize the research errors caused by different microbial species and genera.Herein,wild type strain was taken as the control group,and the key factors affecting microbial corrosion were accurately found through the differential genes controlling bacterial phenotypes,exploring the mechanism of microbial corrosion and develop green protective methods.In this study,it was found for the first time that Marine melanin producing bacteria significantly accelerated the corrosion of low alloy steel and stainless steel,and the melanin secreted by mutant strains was identified as the key factor of corrosion.The expression of ?hmg A gene regulating the pyomelanin production in P.lipolytica,and the pyomelanin secretion increased the pitting formation and the corrosion rate of steels.The production of pyomelamin was influenced positively by some factors including temperature,light and tyrosine substrate.When the biofilm formed on the steel surface,the bacterial pyomelamin secreted by P.lipolytica could have adhered to surface of the steel and acted as an electron acceptor or mediator.Three P.lipolytica strains,namely WT,?bcs,and ?17125 variants,exhibited different effects on steel corrosion.The ?bcs strain,which lacked cellulose polysaccharide,accelerated corrosion,whereas the ?17125 strain,which lacked capsular polysaccharide,inhibited corrosion,which was because cellulose facilitated the biofilm continuity and activity.Moreover,the addition of BC extracted from the ?17125 strain to a medium containing corrosive bacteria(?bcs)resulted in a system with corrosion-inhibition ability,verifying the anticorrosion effect of exogenous cellulose.These results reveal that the endogenous cellulose was beneficial to the formation of uniform biofilms,while the exogenous BC provided a stable anticorrosion activity on the steel surface through biomineralization.The biomineralized film formation of P.lipolytica WT strain provides protective effects against steel corrosion with the help of the exogenous BC.The hybrid film is composed of multiple layers of calcite and bacterial extracellular polymeric substances.However,the stability and applied range of biomineralized film anticorrosion need to be strengthened.Therefore,a superhydrophobic film was then formed on the biomineralized film using soaking and spraying methods.The micro-nano pattern of biomineralized film is beneficial to the formation of superhydrophobic activity.Meanwhile,the organic matter fills the gaps and holes in the biomineralized film,thereby enhancing the corrosion protection of the films.Thus,this study provides a novel,environmentally friendly superhydrophobic coating based on the biomineralized film.