Defined inoculum for the investigation of microbial contaminations of liquid fuels

Microbial contamination of hydrocarbons, especially fuels, has been intensively investigated, as the contamination leads to quality losses of the fuel or damage and even destruction of storage equipment. Researchers use different microbes for these investigations. Alternative inocula include pure cultures, low diversity mixed cultures or samples from (contaminated) storage tanks. In contrast to chemical investigations, no standards exist regarding the composition and use of the organisms; hence, the results may differ widely. Here, a defined mixture for the investigation of microbial contamination of stored fuels, especially middle distillates under standardized conditions, is presented. The organisms represent genera and species commonly found in fuel storage systems. The mixture includes 27 individual species, consisting of bacteria, yeast, and molds. The microbes use heating oil as well as biodiesel as sole carbon source and produce acids and surfactants during growth. The defined mixture is diverse enough to cover all aspects of fuel contamination but defined enough for easy handling during experiments including analytics. The defined microbe mix could contribute to greater reproducibility of experiments, resulting in faster development of technical solutions to minimize or avoid microbial contamination and its negative results during fuel storage.