Metal-reducing microorganisms reduce a variety of metals in metabolic processes
coupled to the oxidation of organic compounds. These bacteria play an important role
in the biogeochemical cycling of metals and organic matter in anaerobic aquatic and
sediment ecosystems. It has been proposed recently that metal-reducing
microorganisms also are active in deep subsurface environments such as petroleum
reservoirs. Only two metal-reducing bacteria have been isolated from petroleum
reservoir fluids, Shewanella putrefaciens and Deferribacter thermophilus. This project
studied the occurrence and distribution of metal-reducing microorganisms in petroleum
reservoirs. The research focused on the isolation, characterisation and identification of
anaerobic bacteria from petroleum reservoirs that were capable of reducing metals and
the potential roles of these isolates in the microbial ecology and biogeochemical cycling
of petroleum reservoirs.
Petroleum reservoirs were selected for this study on the basis of physio-chemical
conditions such as temperature, salinity, pH and the presence of organic and inorganic
compounds, that were likely to provide a suitable environment for anaerobic bacteria
capable of reducing metals. Factors such as the stratigraphic features of the
sedimentary basin, age of reservoir and past oil field practices also were considered in
choosing the reservoir for study. Seven petroleum reservoirs in the USA and
Azerbaijan were chosen for extensive investigations. The physico-chemical conditions
in these reservoirs varied substantially.
A systematic study of the production water from these petroleum reservoirs revealed a
consistent presence of iron- and manganese-reducing microorganisms. It was found
that salinity and temperature play a significant and defining role in the occurrence and
distribution of these metal-reducing microorganisms. Biotic metal reduction was
detected from production waters from all but one of the oil wells sampled. It was
significant that the water from this well (Neftcala #1074) was the most saline (78 g/l
NaCI). Metal-reducing activity was detected at temperatures up to 70°C.
Two pure cultures, strains RED1 for Redwash petroleum reservoir (USA) and NEF1
from the Neftcala petroleum reservoir (Azerbaijan) were isolated and characterized.
The strains had diverse physiological and metabolic properties including the ability to
oxidize a wide range of carbon compounds and reduce a variety of metals. Their
temperature, salinity and pH optima varied markedly. Phylogenetic analyses of the 16S
rRNA of strain RED1 showed that the strain represented a new species of a new genus
in the domain Bacteria. The bacterium most closely related to strain RED1 is the
fermentative Fe(III)-reducer, Pelobacter acetylenicus (similarity value, 92.8%). Strain
NEF1 possesses a unique combination of phenotypic traits and a low mol % G+C.
From preliminary analyses and comparative biochemistry, NEF1 appears to be a novel
metal-reducing bacterium of the Flexistipes group.
The bacteria isolated in this study were able to grow at temperatures and salinities
consistent with the reservoir from which they were isolated. This indicated that
petroleum reservoirs are a new source of physiologically diverse, novel, metal-reducing
microorganisms. The bacteria isolated also demonstrated a number of characteristics
that would enable them to survive and persist in extreme subsurface conditions and
develop a selective ecological advantage in petroleum reservoir environments.
Significantly, the metal-reducing bacteria isolated were able to utilize an array of
metabolic products produced by bacteria indigenous to petroleum reservoirs. This has
resulted in a new proposed model for the ecological succession of bacteria in petroleum
reservoirs.
| Identifer | oai:union.ndltd.org:ADTP/219483 |
| Date | January 2000 |
| Creators | Yacob, Shahrakbah, n/a |
| Publisher | University of Canberra. Resource & Environmental Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Shahrakbah Yacob |
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