Detection of SRP Activity by Quantification of mRNA for the Dissimulatory (bi) Sulfite Reductase Gene (dsrA) by Reverse Transcriptase Quantitative PCR

Molecular biological methods have been used for some years to identify and quantify active microorganisms present in a commercial oil reservoir where biogenic sulphide production is routinely controlled by nitrate injection. In order to gain a more complete understanding of the effects of nitrate injection on the activity of SRP, the mRNA for dsrA present in produced water samples was quantified by RT-qPCR; mRNA for dsrA should only be produced by SRP actively reducing sulphate. The aims of this study were: to help further our understanding on the mode of action of nitrate on SRP activity e.g. competitive inhibition by NUB, nitrite toxicity, change in REDOX potential or a metabolism switch from sulphate to nitrate reduction and; to provide a rapid monitoring tool for SRP activity.

Since messenger RNA is known to be unstable and is rapidly processed within cells, the first task was to design a laboratory experiment to demonstrate that mRNA for dsrA could be detected and quantified in produced water samples. Produced water samples were spiked with a SRP culture grown from the produced water sample and the mRNA for dsrA was successfully detected and quantified.

For the field study, fresh produced water samples were obtained from two wells where direct seawater and nitrate breakthrough has occurred. DAPI, FISH & RT-qPCR analyses were performed directly on the water samples. This paper describes the use of RT-qPCR and detection of mRNA for dsrA as a tool for monitoring SRP activity in biogenic sulphide producing reservoirs. The technique can be used to ascertain the effects of nitrate injection on SRP populations, for instance, in the case of Desulfovibrio; do species of this bacterium preferentially reduce nitrate rather than sulphate? The technique may also be used to determine the recovery of SRP activity following nitrate or biocide dosing.