Common components of industrial metal-working fluids as sources of carbon for bacterial growth

Water-based metal-working fluids used in large-scale industrial operations consist of many components, but in the most commonly used formulations only three classes of components are present in high enough concentrations that they could, in principle, provide enough carbon to support the high bacterial densities (10 CFU/ml) often observed in contaminated factory fluids. These components are petroleum oil (1 to 5%), petroleum sulfonates (0.1 to 0.5%), and fatty acids (less than 0.1%, mainly linoleic and oleic acids supplied as tall oils). We isolated pure strains of predominating bacteria from contaminated reservoirs of two metal-working systems and randomly selected 12 strains which we tested in liquid culture for growth with each of the metal-working fluid components as the sole source of carbon. Of the 12 strains, 7 reached high density (10 CFU/ml from an initial inoculum of less than 2 x 10) in 24 h, and 1 strain did the same in 48 h with 0.05% oleic or linoleic acid as the carbon source. These same strains also grew on 1% naphthenic petroleum oil but required up to 72 h to reach densities near 10 CFU/ml. One strain grew slightly and the others not at all on the petroleum sulfonates. The four remaining strains did not grow on any of the components, even though they were among the predominating bacteria in the contaminated system. Of the seven strains that grew best on the fatty acids and on the naphthenic petroleum oil, five were tentatively identified as Acinetobacter species and two were identified as Pseudomonas species. Four of the bacteria that did not grow were tentatively identified as species of Pseudomonas, and one could not be identified.