"Author's personal copy"Microbial Enhanced Oil Recovery (MEOR) is potentially useful to increment oil recovery from a reservoir
beyond primary and secondary recovery operations using microorganisms and their metabolites. Stimulation
of bacterial growth for biosurfactant production and degradation of heavy oil fractions by indigenous
microorganisms can enhance the fluidity and reduce the capillary forces that retain the oil into the
reservoir. MEOR offers major advantages over conventional EOR, namely low energy consumption and
independence of the price of crude oil. In this work, the isolation and identification of microorganisms
capable of producing biosurfactants and promote degradation of long-chain n-alkanes under conditions
existent in oil reservoirs were addressed. Among the isolated microorganisms, five Bacillus strains were
able to produce extracellular biosurfactants at 40 C under anaerobic conditions in medium supplemented
with hydrocarbons. Three isolates were selected as the higher biosurfactant producers. The obtained
biosurfactants reduced the surface tension of water from 72 to 30 mN/m, exhibited emulsifying activity
and were not affected by exposure to high temperatures (121 C). These characteristics make them good
candidates for use at conditions usually existing in oil reservoirs. Furthermore, it was here shown for the
first time that Bacillus strains were able to degrade large alkyl chains and reduce the viscosity of hydrocarbon
mixtures under anaerobic conditions. The results obtained show that the isolated microorganisms
are promising candidates for the development of enhanced oil recovery processes.This work was supported by PARTEX OIL AND GAS. Jorge F. B. Pereira acknowledges the financial support from Fundacao para a Ciencia e a Tecnologia through doctoral research grant SFRH/BD/60228/2009
