Real-Time PCR Applied to Quantification of SRB in Bottom Water from Fuel Tanks

Microorganisms can grow in different types of fuels. The presence of water in the fuel is crucial for the growth of bacteria, fungi and yeasts. Microorganisms may grow in the presence of oxygen (aerobic) or in its absence (anaerobic), feeding primarily on hydrocarbon fuel, minerals and other impurities in the water. The amount of water required for microbial growth is very small. A fuel containing only 1% of water presents favorable conditions for the development of microbial colonies and spores can survive in the presence of only 5 -80 ppm of water. In practice, the bottom of storage tanks of fuel or even tanks of buses and trucks have enough water for microbial growth. Microbial growth results in the production of biomass (fouling), which is deposited at the bottom of the tank. Moreover, the microbial oxidation of hydrocarbons produces corrosive metabolites, such as organic and inorganic acids. Biomass, metabolic products and corrosion products result in problems such as filter and pipelines clogging, production of emulsion, change in fuel quality and corrosion of metal tanks. The detection and quantification of microorganisms in industrial samples are traditionally based on culture techniques such as the most probable number (MPN) and colony forming units (CFU). However, the slow growth of strictly anaerobic sulfate-reducing bacteria (SRB) complicates the detection and isolation of these microorganisms in culture media. The cultivation of SRB requires a long incubation period (28 days) to obtain the results. In some cases, the extended time for the detection of microorganisms retards the preventive and corrective actions which aggravate the corrosive process. In this work, the results of SRB quantification in bottom water from fuel tanks analyzed by real time PCR and traditional MPN technique were compared.