## 4 Discussion  
We previously reported that emergence of _Rhodococcus_ was a consequence of the 1-week incubation of _Mollic Gleysol_ with petrol and diesel [19]. The current study evaluated the effect of longer (6-week) soil exposition to petroleum substances applied to test the resistance of bacteria to long-lasting PH pollution. [PERSON] et al. [33] reported that the effect of hydrocarbon toxicity is affected by the hydrocarbon type. PHs can enter the soil environment with falling dust and they are usually strongly absorbed by the soil surface and thus hardly biodegradable [34]. The fact that diesel is a less toxic source of carbon than other automobile oils was noted by [PERSON] et al. [2] and [PERSON] et al. [19]. This was also proved in the current study by the Biolog EcoPlate analysis via which functional diversity was estimated. Community level physiological profiling (CLPP) yields the metabolic fingerprint of bacteria present in the soil environment and indicates the numbers of defined substrates that are oxidized by autochthonic microflora [4]. We found that the metabolic activity of bacteria inhabiting soil contaminated with diesel fuel was higher than those from the petrol-treated soil, where the functional diversity was activated only at 168 h of the incubation period. Similarly, the biodiversity of bacteria was higher in the diesel-contaminated soil in comparison to the petrol treatment (Table 3). Also, [PERSON] et al. [7] confirmed that soil contaminated with diesel was characterized by higher dehydrogenase activity than the control, whilst petrol was found to act as a dehydrogenase inhibitor [12]. Figure 3: Agarose gel electrophoresis of PCR products (gene fragment 16S rRNA): Line 1—molecular mass marker DNA 100–10,000 bp, 2–4 control samples, 5–9 samples contaminated with unleaded 95-octane petrol, 10–13 samples contaminated with diesel. It should be mentioned here that dehydrogenases are intracellular enzymes present in viable microbial cells only that indicate soil biological activity [12; 35]. They are considered to be pollution indicators, as they have no ability to accumulate in the extracellular environment [12]. [PERSON] and [PERSON] [14] noted that, besides dehydrogenases, alkaline and acid phosphatases displayed higher activity in chernozem and rendzina polluted with PHs. However, a study reported that soil contamination with diesel and petrol inhibited the nitrification process and that diesel oil was a much more powerful inhibitor of nitrification than petrol [5]. The experiment also lasted 42 days and at the last day nitrification was reduced by 99% and 88% for diesel and petrol contamination, respectively [5]. Many bacteria and fungi have been described as being able to utilize PHs via cometabolism [1; 36; 3]. Microorganisms that have the ability to degrade PHs are referred to as hydrocarbonoclastic or oleophilic microflora [8]. Environments contaminated with PHs are home for many phylogenetically and metabolically diverse groups of microorganisms [8], which was also evidenced in our study. The most common groups summarized by [PERSON] et al. [1] were represented by the following bacterial genera, i.e., _Achromobacter_, _Acidovorax_, _Aeromonas_, _Ataligenes_, _Arthrobacter_, _Bacillus_, _Burkholderia_, _Cellulomonas_, _Flavobacterium_, _Methylomonas_, _Pseudomonas_, _Paraococcus_, _Ralstonia_, _Rhizobium_, _Rhodococcus_, _Shingomonas_, _Shewanella_, and _Staphylococcus_. Some of these genera were also identified in our study as _Bacillus_, _Rhodococcus_, _Pseudomonas_, and _Arthrobacter_. _[PERSON] et al. [22] indicated that _Rhodococcus_-like populations were involved in PH degradation in a majority of soils, whilst the presence of _Bacillus_ was noted by [PERSON] et al. [37], [PERSON] et al. [38], [PERSON] et al. [39], and [PERSON] et al. [40]. Also, the current study confirmed this fact, as we identified the presence of _Rhodococcus_ in soils contaminated with unleaded 95-octane petrol and with diesel.