Environmental adaptability and biosurfactant production of bacterial isolates from the Boca de Jaruco oil field (Cuba)

Environmental protection requirements and the need to increase the proportion of oil recovered by secondary methods have led to the rise in popularity of microbial enhanced oil recovery (MEOR) techniques. Usually, MEOR requires the use of indigenous strains of microorganisms residing in wells, as they are adapted to local conditions. However, for some wells and fields, such as the Boca de Jaruco field in Cuba, information about the oilfield microorganisms and their properties is extremely limited. One of the properties crucial for the successful implementation of MEOR in fields is the ability of indigenous strains to produce biosurfactants. The aim of the present study is to evaluate the ability of six bacterial isolates obtained from the Boca de Jaruco field in Cuba to produce biosurfactants. The isolates capable of utilizing oil as their sole carbon source were identified as Bacillus subtilis (strains CC21, CC23, CC31, and CC32), Bacillus licheniformis (strain CC33), and Aeromonas veronii (strain CC22). It was determined that all isolates can tolerate temperatures between 30 and 60 °C, salinity ranging from 0.5 to 10.0% NaCl, and pH levels between 6 and 9. Regarding their ability to produce biosurfactants, assessed using the drop collapse method, oil-spreading method, emulsification activity test, and surface tension measurement, the isolates ranked as follows: A. veronii CC22 > B. subtilis CC21 = B. subtilis CC31 > B. subtilis CC23 = B. subtilis CC32 > B. licheniformis CC33. The biosurfactants produced were stable in the presence of 1.7 to 20.0% NaCl, irrespective of temperature (30 or 70 °C). However, substituting 20% of the NaCl with CaCl₂ resulted in destabilization of the biosurfactants produced by all investigated isolates, with destabilization levels averaging up to 32% at 70 °C.