Bacterial diversity and influence of SRB presence on metal behaviour within the oil & gas industry

Biocorrosion concerns especially the Oil and Gas (O&G) industry, where it leads to extensive and costly damages for the equipment and consequent production losses. Sulfate Reducing Bacteria (SRB) are an important group of microorganisms involved in the biocorrosion process. In this work we aim to analyze microbial diversity and the electrochemical behaviour of metals from offshore installations, using a model SRB organism. Four bio-coupons were placed in anaerobic bottles with VMN Sulfate medium (VMN-S) flushed with argon and incubated at 37°C and 30°C for a period of 48h to 2 weeks. The samples presented a limited growth and were used as inoculums for a second incubation in VMN Nitrate medium (VMN-N), under the same conditions. Cells were harvested and used for DNA extraction followed by PCR and DGGE analysis. After this, the bio-coupons were prepared to be used as working electrodes in the presence of Desulfovibrio desulfuricans 27774. The Open Circuit Potential (OCP) was measured over 6 days using VMN-S as electrolyte. Four ecotypes were observed in the DGGE gel and are being prepared for DNA sequencing. The OCP showed a variation around 200mV when both conditions were compared. The increase of potential is concomitant to the appearance of a stationary phase and could be related to biofilm establishment or normal metabolism (as sulfides production). Further analyses are in progress to confirm the role of bacterial attachment in the metal behaviour. Our study gives new proofs of the growth phase influence within the biocorrosion evolution in carbon steel used by the O&G industry.