## 3 Results and Discussion
### Isolated Strains Identification  
Gram-Farbung tests revealed that the majority of the strains were Gram-negative, with the exception of _BY1_ and _BY2_, which were Gram-positive (Table 3). Gram-negative bacteria are often harmful to humans' health as many exhibit pathogenic traits. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Isolates** & **BY1** & **BY2** & **BY3** & **BY4** & **BY5** & **BY6** & **BY7** \\ \hline Biodegradation Efficiency (\%) & 32.1 & 44.7 & 33.2 & 24.5 & 38.2 & 42.3 & 42.1 \\ Most Favored Temperature (\({}^{\circ}\)C) & 35 & 30 & 30 & 30 & 30 & 25 & 30 \\ Most Favored pH & 6.0 & 6.0 & 7.0 & 7.0 & 7.0 & 6.0 & 7.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The summarization of biodegradation efficiency of the isolates and its favored temperature and pH respectively. Figure 1: Biodegradation efficiency for the isolated strains in MS medium (**A**) and colony numbers under different growth conditions: incubation times (**B**), temperatures (**C**), and pH values (**D**). The isolated strains were identified using 16S rRNA gene sequencing (Figures 2 and 3). _BY1_ and _BY6_ were found to belong the genus _Bacillus_, while _BY4_ and _BY7_ were _Pseudomonas_ species. Both of these genera have been widely reported to contain bacteria that are capable of degrading compounds including polyvinyl chloride, phthalate ester, eugenol, endosulfan, and dibenzothiophene [20, 21, 22]. _BY1_ exhibited a 99.2% similarity to _Bacillus taivanensis_, which is a nitrate-ammoniuming bacterium and a partial denittirier. Previous studies have reported that _Bacillus vireti_ is able to degrade benzo[a]pyrene, a common cause of cancer, and lignocellulosic [23]. _BY6_ exhibited 100.0% similarity to _Bacillus viredmannii_, which has been reported to be able to degrade polyethylene after 120 days incubation with a 51.53% efficiency and also exhibits biomineralization potential and hydrocarbon-degrading ability [24]. _BY4_ was identified as _Pseudomonas mandelii_, which has been reported to contain a hcdABC gene cluster that is necessary for 7-hydroxycoumarin degradation [25]. _BY7_ exhibited a 99.9% similarity to _Pseudomonas freeriksbergensis_. Previous studies have revealed that _P. freeriksbergensis_ is an effective bioinoculant for enhancing cold stress tolerance in plants and could promote plant growth in soils with high saline levels [26]. However, it has not been previously reported to possess petroleum-degrading ability. \begin{table}
\begin{tabular}{c c c c} \hline
**Strains** & **Species** & **Description** & **Gram–Farbung Test (1)** \\ \hline _BY1_ & _Bacillus sp._ & 99.23\% similarity to _B. taivanensis_ & + \\ _BY2_ & _Acinetobactor sp._ & 100.00\% similarity to _A. junii_ & + \\ _BY3_ & _Sphingobium sp._ & 100.00\% similarity to _S. abikonense_ & - \\ _BY4_ & _Pseudomonas sp._ & 99.86\% similarity to _P. mandelii_ & - \\ _BY5_ & _Rhodococcus sp._ & 100.00\% similarity to _R. erythropolis_ & - \\ _BY6_ & _Bacillus sp._ & 100.00\% similarity to _B. viredmannii_ & - \\ _BY7_ & _Pseudomonas sp._ & 99.93\% similarity to _P. freeriksbergensis_ & - \\ \hline \end{tabular} (1) Symbols denoted the positive (+) and negative (-) in the Gram–Farbung tests.  
\end{table} 
Table 3: Species and Gram–Farbung tests for the isolated strains. Figure 2: Phylogenetic tree of the 16S rDNA gene sequence of _BY1_, _BY4_, _BY6_, and _BY7_ derived by MEGA 4.0 software. _BY2, BY3, and BY5_ were found to belong to the genera _Acinetobacter_, _Sphingomonas_, and _Rhodococcus_, respectively. _BY2_ exhibited a 100.0% similarity to _Acinetobacter junii_, which is a lead-resistant and surfactant-producing bacterium that is able to degrade crude oil and has a potential application in the bioremediation of oil pollution [27].