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Two novel species of bacteria isolated from oil wells

23.11.2004


Oilfields usually represent extreme environments, where physicochemical conditions appear at first sight to be generally unsuitable for living organisms to develop. However, these environments, usually poor in nitrates and oxygen, harbour a rich diverse community of microorganisms. The most widely represented and best-known types are sulfate-reducing, methanogenic and fermentative bacteria.



Nitrate-reducing bacteria, on the other hand, have received little research attention regarding their biology and role. Nevertheless some of their bacteria are known also to have the ability to oxidize sulfates. These components, which can result from metabolic activity of sulfate-reducing bacteria, prove dangerous for the environment and corrosive for drilling equipment. Nitrate injection is practised in some regions of the world in order to restrict the emission of sulfites produced during processes of exploitation of oil deposits. This input of nitrates stimulates nitrate-reducing bacteria, initially present in low quantities in the waters associated with oil reservoirs, to proliferate (2). They thus induce at once inhibition of the development of sulfate-reducing bacteria and oxidation of sulfides that such microorganisms produce.

The question remains of determining whether or not these nitrate inputs into the petroleum reservoir environment can favour the growth of populations of nitrate-reducing microorganisms different from those which oxidize the sulfides, in this way modifying the microbial ecology of oil wells. IRD scientists are therefore investigating in the laboratory the metabolism of novel nitrate-reducing bacteria, especially those able to oxidize organic acids. These acids are often present in the waters of oil reservoirs.


The IRD team surveyed oilfields in Australia and Mexico, along with their scientific partners in these countries (1). The group has succeeded in isolating and identifying two novel nitrate-reducing bacteria, Petrobacter succinatimandens and Garciella nitratireductens (3), which can be distinguished by their metabolic activities. The bacterium Petrobacter succinatimandens, extracted from an oil well located in Queensland, in the East of Australia, was shown to be capable of oxidizing the organic acids. It has an aerobic metabolism, which means that it develops in the presence of oxygen. Accidental introduction of oxygen, by means of an input of water from outside the oil deposit (rainwater infiltrations, common practice of water injection while oil is being extracted) could explain the presence of this bacterium and its survival in an anaerobic environment. However, Garciella nitratireductens, isolated from several oil wells in the Gulf of Mexico, has an anaerobic metabolism, like most microorganisms that live in these kinds of habitat.

This research work brings fundamental new information about oil reservoir ecosystems and the microorganisms which colonize there. In particular they offer the oil industry the means to gauge more accurately the biodiversity of nitrate-reducing microorganisms in the reservoirs and the impact of their metabolism on the biogeochemical cycles of matter, within these environments. Other research has been embarked upon in order to identify bacteria potentially useful for industry, characteristic of oil reservoir environments, which might be usefully deployed in aided recuperation of oil deposits by microorganism-based processes (production of acids, gases and surfactants…).

(1) The IRD worked with Griffith University, Brisbane, Australia in one investigation, and with the Autonomous Metropolitan University of Mexico City and the Mexican Petroleum Institute, in the other.

(2) In this case, development occurs entirely in an enclosed environment.

(3) They are two species, each representing a new genus. Petrobacter succinatimandens belongs to the b-Proteobacteria class and Garciella nitratireductens to the Clostridiales order.

Marie Guillaume | alfa
Further information:
http://www.ird.fr

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