The effect of water isotopic composition on concentration of oil-oxidizing actinobacteria Rhodococcus erythropolis VKM Ac-2017D cellular biomass is observed during cultivation in liquid nutrient media. The value for the effect was determined by experimental conditions, including consecutive use of hydrophilic and hydrophobic nutritious substrates--saccharose and hexadecane. It is shown, that when Rhodococcus erythropolis VKM Ac-2017D cells, cultivated in media with sucrose and 71 and 98 ppm deuterium content in water were inoculated into the similar in mineral and isotopic composition media with hexadecane, a considerable increase in cellular biomass production is observed if compared to a control sample in which water with 150 ppm deuterium concentration was used.