## 1 Introduction  
Intensive exploitation of liquid fossil fuels, and the migration of hydrocarbon compounds to the natural environment, have a highly negative influence on terrestrial and aquatic ecosystems. Due to the high resistance to biodegradation, and the potential for biomagnification, this pollution is considered to be one of the most serious environmental threats [1, 2, 3]. Due to the complexity of the chemical structure, and the diversity of physical and chemical properties, individual groups of hydrocarbons differ in bioavailability, toxicity, and the potential for biological decomposition [3, 4]. Many biotic and abiotic factors affect the biological decomposition rate of hydrocarbon compounds [3, 4, 5, 6, 7, 8]. The abiotic factor, i.e., the supply of microelements such as nitrogen, phosphorus, sulfur, calcium, magnesium, and potassium, is crucial in the functioning of the cellular metabolism of microorganisms that perform biodegradation processes [9]. In contaminated areas, deficiencies in biogenic elements and inhibition of bioremediation processes may occur very quickly, as a result of an excessive supply of carbon compounds, and the activity of microorganisms [10]. Research suggests that the share of nutrients, including the C:N ratio, should be at a level similar to that in live cells. The optimal values for the C:N ratio are in the range from 100:5 to 100:15 [9,11]. The wide range of the optimal ratio of these elements may result from the different rates of decomposition of individual hydrocarbon groups, and the limited bioavailability of biogenic elements, depending on abiotic and biotic environmental factors [9]. One of the most popular bioremediation technologies, based on the knowledge of the influence of nutrient supply, is the biostimulation technique. Targeted compensation of deficiencies in the environmental niche results in metabolic activation of indigenous microflora, and the improvement of the biodegradation efficiency of xenobiotics. This compensation may consist of the application of deficient nutrients and electron acceptors, in the form of both organic and inorganic compounds [12,13]. Many studies prove that biostimulation is beneficial for effective hydrocarbon degradation [14, 15, 16]. A popular strategy is also to combine bioaugmentation and biostimulation techniques, in order to maximize remediation effects [12, 17, 18]. Despite the many advantages of bioremediation technologies, and their widespread social acceptability, they have a number of limitations. These include the differentiation of the metabolic potential of microorganisms living in different environments, problems related to the optimization of the scale of necessary implementations, and the difficulties in extrapolating the results of tests carried out on a laboratory scale [19, 20]. It is emphasized that, in the case of biostimulation with nitrogen compounds, the excessive supply of nutrient may negatively affect the efficiency of biological decomposition [21, 22, 23]. An innovative context in the improvement and understanding of the mechanisms of bioremediation processes is the approach to the issues within the field of synthetic microbiology, assuming a multitude of biotic and abiotic interactions in the microbial community. According to the assumptions of the synthetic approach, simple interactions between genotypically different microorganisms may contribute to the creation of properties that are difficult to predict at the consortium level [20, 24, 25]. Therefore, there is a need to acquire and analyze data on the molecular mechanisms of the microbial transformation of hydrocarbon compounds, and the influence of environmental factors and degradation processes. The aim of this study was to comprehensively assess the effect of nitrogen compounds on an environmental consortium with high hydrocarbon degradation potential. Both the enzymatic efficiency and metabolic activity, as well as the overall genetic potential of individual members of the metapopulation, were taken into account.