A systematic survey for thermophilic fermentative bacteria and archaea in high temperature petroleum reservoirs

Abstract: Production waters from 36 high temperature petroleum reservoirs were examined for the presence of thermophilic, fermentative microorganisms. The direct supplementation of production waters with glucose and either yeast extract, peptone, tryptone or casamino acid resulted in the isolation of thermophilic, fermentative microorganisms from 47% of the petroleum reservoirs examined. Three distinctive morphological groups were isolated from the production waters of petroleum reservoirs with depths ranging from 396–3048 metres, temperatures ranging from 21–130°C, salinities ranging from 2.8–128 gl⁻¹ and pHs ranging from 6.0–8.5. Group 1 were pleomorphic rod-shaped bacteria, Group 2 were sheathed rod-shaped bacteria, and Group 3 were coccoid archaea. Partial characterisation of strains from one seawater-flooded petroleum reservoir and three non-waterflooded petroleum reservoirs tentatively identified some strains in Group 1 as members of the genera Thermoanaerobacter and Thermoanaerobacterium , Group 2 as members of the Thermotogales order, and Group 3 as members of the genus Thermococcus . Production water salinity determined the type of microorganisms that were isolated. Group 1 organisms were found primarily in petroleum reservoirs with salinities less than 30 g/l, while Group 2 and 3 organisms were found to dominate in more saline reservoirs. The successful isolation of thermophilic, fermentative microorganisms from petroleum reservoirs decreased significantly with increasing salinity and temperature. These findings support the existence of a deep biosphere where fermentative microorganisms are widespread.