Biofouling and biocorrosion by microbiota from a marine oil pipeline: A metagenomic and proteomic approach

Biofouling and biocorrosion in oil pipelines are serious problems capable of causing expensive, irreparable losses. For a better understanding of biocorrosion processes, several lines of evidence are required, not least experimental considerations that emulate natural conditions inside pipelines. Herein, an omics approach is used to unveil the microbial involvement in the deterioration and electrochemical process on X52 steel with Shewanella (SW), the oil pipeline microbiota (AK), and a mixed culture (AK5), the latter two obtained from a sludge of pig pipeline cleaning in the Gulf of Mexico. Shotgun metagenomics showed diverse communities at species level in pipeline sludge: bacteria up to 112, 34 archaea, 9 fungi, and 23 viruses. In AK the most abundant taxa were Petrotogaceae with Petrotoga (31.16%) and Methanomicrobiaceae (48.51%). In AK5 were Methylobacterium (49%) and Methanomicrobiaceae (19.49%). Concerning fungi and viruses, respectively: Clavariaceae (43.26%), Picciniaceae (35.59), Onygenaceae (3.77%), Siphoviridae (46.8%), Myoviridae (33.50%), Podoviridae (7.36%) in AK5. Proteomics revealed 32,284 proteins in AK, 13,664 in AK5, and 7 in SW. Expressed proteins were oxidoreductases, lyases, nitrogenases, metalloproteases, and hydrolases associated with the biocorrosion process, for instance, electron transport, sulfur oxidation, nitrate reduction, biofilm formation, and oxygen reduction. In addition to the functional annotation of metagenomes in KEGG pathways, through the Multigenomic Entropy Based Score (MEBS) the metabolic functions were evaluated explaining the relation to energy transfer processes of the biogeochemical cycles. The sludge was analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), and Mössbauer spectroscopy suggesting the microbiota involvement in the biofouling and biocorrosion processes. Regarding the electrochemical assessments, scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) coupled to SEM, AK, AK5, and SW biofilms on X52 steel behaved differently. Three electrochemical mechanisms of biocorrosion are proposed.