## 3 Results and Discussion
### Microbial Community Analysis in Field Soil  
To monitor and identify the prominent bacteria affecting the major metabolites and the effect of toluene exposal on the fate of the microbial community, 16s rRNA analysis was conducted (Figure 7). The _Proteobacteria_ (34%), _Actinobacteria_ (29%) and _Chloroflexi_ (9%), _Acidobacteria_ (7%), and _Cyanobacteria_ (5%) were dominant bacteria phylums in control soil. This composition of phyla was slightly changed after the toluene exposure (Table 5). Cyanobacteria were decreased below 1% and another phylum composition was almost similar. _Actinobacteria_ and _Proteobacteria_ are well-known aerobic steroid-degrading bacteria [36]. These strains were mainly isolated from soil. _Arthobacter globiformis_, _Streptomyces cabiei_, _Sphingomonas lutea_, and _Sphingomonas sediminicola_ were major groups in control soil. These bacteria were decreased after toluene exposure, while _Bradyrhizobium japonicum_, _Mycobacterium farincogenes_, _Hamadaae flawa_, and _Sphingomonas pruni_ groups were increased after toluene exposure (Table 5). _Arthobacter globiformis_ can oxidize ammonium ions and biodegradable various pollutants [37; 38]. It was expected that _Arthobacter_ would break down the aromatic compound when contaminated with toluene. The _Streptomyces cabiei_ attend the steroid degradation pathway [39]. _Bradyrhizobium japonicum_ was reported as toluene degrader [40]. Consequently, the combination of soil microbiome and metabolome analysis can provide comprehensive insight into the ecological impact of the emerging contaminants. In this study, the majority of identified bacteria in field soil would affect the major metabolites discovered in field soil (Tables 4 and 5).  
To propose a relationship between toluene combustion products and detected metabolites in toluene-affected soils, it should be noted that streptomycin 6-phosphate and naphthyl-2-methyl-succinic acid degraded from naphthalene have a metabolic relationship with _Streptomyces cabiei_ group discovered in contaminated soil (Table 5) [41; 42]. In the control soil, DNA count of _Streptomyces cabiei_ group was about three times more than field soil (Table 5). It is expected that the population of _Streptomyces cabiei_ group in the field soil decreased instantly due to the acute toxicity of toluene and its combustion by-products in soil bacteria. Damage to the cytoplasmic membrane happens instantly to the bacteria cell membrane, resulting in the loss of the cations Mg\({}^{2+}\) and Ca\({}^{2+}\)[43]. Moreover, these aromatic compounds are so volatile and not easily soluble in water that toxicity duration can last due to chemicals adsorbed on clay minerals for a long term; even rainfall leaches  
Figure 6: The normalized peak intensity of proposed metabolites as the metabolite biomarkers in field soil (contaminated soil); raw peak intensity of LC–MS was normalized by statistical analysis using data filter (relative standard deviation, (RSD)), normalization by sum, and data scaling (Pareto scaling).  
into ground soil. However, the small number of _Streptomyces scabiei_ group that decomposes naphthalene appears to have barely survived for a while, as shown in Table 5.  
Figure 7: The 16s rRNA sequencing results of soil bacteria community in (a) control soil (b) field soil (contaminated).