Isolation, characterisation, and identification of sulphate-reducing bacteria from oil field environments
The sulphidogenic activity of sulphate-reducing bacteria (SRB) is of great economic importance to many industrial sectors, since it is strongly implicated in a range of problems, including the souring of oil reservoirs and the anaerobic corrosion of mild steel. Despite increasing reports of SRB activity throughout oil fields, little attention has yet been given to further characterisation and identification of those SRB species involved. In an attempt to understand the role of these organisms in the oil field environments this work is to isolate, characterise, and identify SRB present in a range of samples from different oil fields. Using selective enrichment cultivation methods, a number of nutritional types of mesophilic and thermophilic SRB cultures have been obtained from a range of oil field samples. This suggests that SRB are widespread throughout oil fields and may be important contributors in the biogenic production of H2S in such environments. The successful isolation of 7 SRB pure cultures (6 mesophiles and 1 thermophile) was achieved. Using both classical methods and nucleic acid analyses, 3 types of SRB strains have been identified: 5 mesophiles (strains FM3, EF2, FM2, GF2, and MM6) are members of Desulfomicrobium; mesophilic strain EM2 is a Desulfovibrio; thermophile NM2 is an archaebacterium, phylogenetically closely related to Archaeoglobus fulgidus. Such strains may be the causative micro-organisms in the generation of H2S in oil fields. 16S rDNA comparative analysis was applied to directly identify SRB present in 4 thermophilic enrichment cultures from 3 different oil field samples (sandstone core, drilling mud, and production water). The results show that thermophilic SRB, Desulfotomaculum-related species, were commonly distributed in all oil field samples. Micro-organisms related to Gram-positive, thermophilic, non-sulphate-reducing, anaerobic bacteria were also found in cultures from sandstone core and production water. These organisms may play an important ecological role alongside SRB in oil field environments.