Investigation Of Microbiologically Influence Corrosion By Mixed Consortium Of Shewanella Oneidensis And Bacillus Licheiformis On 316L Staniless Steels

Stainless steel(SS)have been widely used in various environments due to their excellent mechanical properties and corrosion resistance.Naturally,microbiologically influenced corrosion(MIC)is always caused by multi-species biofilms.Considering the serious damage to the economy and infrastructures,incomprehensive and incipient study in the field of mixed consortium microbial corrosion.The present study investigated the MIC of 316L SS in the presence of the mixed consortium and individual strain of S.oneidensis and B.licheniformis.The roles of these two strains in the MIC process were evaluated,and the relationship established by electron shuttle between these two strains was investigated,devoting to provide a novel insight for understanding of extracellular electron transfer(EET)-MIC,fundamentally to prevent and availably control the corrosion of metal materials.Shewanella oneidensis MR-1can secrete redox-active electron transfer shuttles as an exoelectrogen,Bacillus licheniformis has been proved to cause aggressive corrosion as a nitrate reducing bacterium(NRB).Actually,there is no report regarding the MIC of a consortium of an electron shuttle secreted strain and a nitrate reducing strain.Based on the understanding of EET-MIC,it can be reasonably speculated that riboflavin secreted by S.oneidensis can enhance the electron transfer efficiency of corrosive B.licheniformis,accelerating electron harvest and leading to a much more severe MIC attack.The maximum pit depths caused by S.oneidensis,B.licheniformis were 3.3 ?m and 3.8 ?m,causing localized corrosion.The pH values in different media indicated acid attack caused by the metabolism of the microbes may be negligible.Thermodynamically,S.oneidensis and B.licheniformis can coupled iron oxidation with nitrate reduction,causing MIC attack.The addition of exogenous riboflavin into the B.licheniformis culture medium can accelerated corrosion rate of the MIC caused by B.licheniformis,and riboflavin did not affect the corrosion rate of 316L SS.It validated that B.licheniformis can utilized exogenous riboflavin improve the EET efficiency and accelerate MIC.Riboflavin used as an electron shuttle for many microorganisms in the EET.More than 20 ppm riboflavin was detected in the S.oneidensis culture and microbial consortium culture.From electrochemical test and pit depth,S.oneidensis and B.licheniformis mixed biofilms accelerated corrosion of 316L SS.The XPS results further confirmed why the consortium caused the most severe MIC in mixed biofilms.B.licheniformis was verified to utilize the riboflavin secreted by S.oneidensis for metallic corrosion,improving the electron transfer efficiency,which synergistically set up a syntrophy microbial consortium.Thus this work provides novel understanding in the MIC caused by the consortium biofilm from the perspective of EET,and EET is the key to regulate MIC process.