?Biofilm on steel or planktonic cells? What drives either growth form?.

ROBLEDO, ALEJANDRO; ESCALADA, LISANDRO; BUSALMEN, JUAN P.; SILVIA SIMISON; DIEGO A. MASSAZZA

VIRTUAL

Congreso; LVII Reunión Anual de SAIB y el XVI Congreso Anual de la Asociación Civil de Microbiología General; 2021

sAMIGE

Microbiologically influenced corrosion (MIC), also known as biocorrosion, is estimated to account for 20% of overall corrosion damages. Sulfate reducing bacteria (SRB) are the most important anaerobes organisms associated to MIC because sulfate exists in many environments. In oilfield water flood systems, SRB cause the largest number of recorded instances of corrosion problems. Biofilms formed by SRB can modify the metal/solution interface to induce, accelerate, and/or inhibit the anodic or cathodic process that controls corrosion. These biofilms are formed by a matrix composed by polysaccharides, proteins, and nucleic acids with high water content where metabolites and microorganisms are suspended. Bacteria able to form biofilm exhibit a free-living planktonic state and a sessile biofilm state by adhering to the substrate. The transition among these states is a highly regulated process, which might be initiated due to intercellular and intracellular signals (pH and nutrition level). In this work, we evaluated the influence of organic matter in the formation of SRB biofilms and its impact on the steel MIC. Coupons of C1010 carbon steel were evaluated in anaerobic vial with SRB at different lactate concentrations (0, 5, 25 or 100%). Samples were extracted after three incubation times (7,14 and 21 days). Planktonic cells and sessile cells were measured by ODƛ600 and weight loss was registered in order to calculate the average corrosion rate. Our results demonstrated that the presence of dissolved organic matter in the culture medium decreases the ratio biofilm / planktonic bacteria, in a dose dependent way. On the other hand, the corrosion rate increased notably in the presence of organic matter, although the damage on the metallic surface did not show significant differences between the evaluated conditions. In conclusion, the presence of organic matter favored a free-living planktonic state over the sessile biofilms state with respect to starvation conditions. In the presence of a dissolved energy source such as lactic acid, bacteria should easily have access to this resource and the planktonic life form might be benefited. On the other hand, when organic matter decreases, bacterial might prefer to switch into sessile biofilm form. In this state, biofilms use other strategies to obtain energy sources, such as electrons uptake from the metallic iron, which implies direct contact with the metal surface through cytochromes of the outer membrane. Moreover, the higher corrosion rate increased with the higher concentrations of organic matter, probably due to the greater number of total bacteria in the culture. This implies that not only sessile bacteria influence the corrosive process. Planktonic bacteria might produce organic acids and other metabolites that indirectly attack metals and accelerate corrosion via chemical reactions.