The PIT Crowd

Secondary oil recovery from marine reservoirs usually involves marine water injection. The pipes used in this process can be subjected to biofilm formation which may cause corrosion. Usually biocides are used to protect the pipes however they are usually short term solutions and pipes become corroded resulting in economic losses. This study examines the total bacterial diversity in corrosive biofilms found in marine water pipelines from the Gulf of Mexico.

Coupons of steel were fixed to pipelines used in marine water injection and left for three months. The coupons were then removed and they attempted to isolate some of the bacteria present in the biofilms using various anaerobic and aerobic media. As well as culturing they also used molecular techniques. They extracted DNA from the biofilms and constructed a 16S rRNA gene library by cloning PCR-amplified 16S rRNA genes followed by restriction fragment length polymorphism (RFLP) to differentiate between operative taxonomic units (OTU). They also used PCR-DGGE to compare the bacterial diversity on different coupons.  The different isolates cultured and clones were sequenced and phylogenetic trees were constructed.

All coupons showed hard pitting corrosion after the three months. The abundances of bacteria at the class level for the ribosomal library were 0.67%, 96.66% and 2.67% and in the cultured samples 7.14%, 28.57% and 64.29% for Alphaproteobacteria, Gammaproteobacteria and Bacilli respectively. The three main genera found were Idiomarina, Halomonas and Bacillus. There were no sulphate-reducing bacteria detected throughout the experiment which is not surprising as the pipes were under aerobic conditions. The DGGE analysis showed twelve bands of which only two were common between different coupons. Overall there was very limited diversity in the biofilms however there were problems with inhibitors especially rust which will affect results.

The study suggests that most of the species in these corrosive biofilms belong to the Gammaproteobacteria and Bacilli which differs to the results of many other corrosion papers. Other than the genera Idiomarina and Halomonas which have been linked with EPS and organic acid production, respectively, not much is known of how many of the other bacteria indentified act in biofilms. It also shows the importance of using different methods for measuring bacterial diversity as separate methods can give very different results. Knowing the different bacterial communities associated with corrosive biofilms will help in developing new methods for controlling them. As there were a lot of differences between samples it would be good to examine the communities in other pipelines however it is very hard and costly to sample as the water injection must be stopped. However as previously mentioned the results were undoubtedly affected by PCR inhibitors.

López, M.A., Zavala-Díaz de la Serna, F.J., Jan-Roblero, J., Romero, J.M. and Hernández-Rodríguez, C. (2006) Phylogenetic analysis of a biofilm bacterial population in a water pipeline in the Gulf of Mexico. FEMS Microbiology. 58, 145-54.