## 4 Discussion  
We have presented the variation in performance of two bacterial strains, Kp and Pa in the degradation of PHs [1]. We found that the Pa strain was able to reduce diesel (a common form of PHs) by 58%, while the Kp strain degraded 45% of diesel within 14 days. This difference in degradation efficacy for given PHs was even greater in previous studies where one bacterial strain (_Burkholderia fungorum_ T3A13001) could degrade pyrene by 59-62% while the other strain (_Caulobacter_ sp. T2A12002) only did so by 21-24% over an 18-day incubation. This difference was also reported for two bacterial strains (_Pseudomonas_ (22.39-38.32%) and _Rhodococcus_ sp. (87.35-99.89%)) in the degradation of diesel and its component _n_-alkane [66]. Additionally, this difference was found for extreme halophilic bacterial strains: one strain could degrade up to 47% of crude oil while another degraded 13% [67]. From two petroleum-contaminated soils, ten strains were screened out and were able to produce biosurfactant and degrade oil. These strains could produce glycolipid biosurfactants, which ranged from 1.93 to 3.7 g L\({}^{-1}\). The results showed that four isolates could effectively degrade crude oil in saline mineral broth, with the highest removal efficacy of 39%. Gas chromatography analysis revealed that both lighter and heavier PHs were degraded by microbial cells. It was also demonstrated that branched alkanes as well as linear alkanes were degraded by the isolates. Based on 16S rDNA sequencing, all four isolates were identified as _Pseudomonas aeruginosa_[68]. A hydrocarbon-degrading, biosurfactant-producing, and plant-growth-promoting endophytic bacterium, _Pseudomonas aeruginosa_ L10, was isolated from the roots of a reed, Phragmites australis, in the Yellow River Delta, Shandong, China. _P. aeruginosa_ L10 effectively degraded C\({}_{10}\)-C\({}_{26}\) n-alkanes from diesel, as well as common PAHs such as naphthalene, phenanthrene, and pyrene. In addition, _P. aeruginosa_ L10 could produce biosurfactant. Moreover, they identified genes related to PHs degradation, such as putative genes encoding monooxygenase, dioxygenase, alcohol dehydrogenase, and aldehyde dehydrogenase. Genome annotation revealed that _P. aeruginosa_ L10 contained a gene cluster involving in the biosynthesis of rhamnolipids, rhlABRI, which could be responsible for the observed biosurfactant activity [69]. There are also many applications of bacterial communities. An in vitro experiment was performed by taking petrol pump soils and diesel in flasks with micronutrient and macronutrient supplements. The bioreactor was inoculated with bacterial communities containing _Moraxella saccharolytica_, _Aletomonas putrefaciens_, _Klebsiella pneumoniae_ subsp. aerogenes and _Pseudomonas fragi_ along with soil and diesel. The ability of the bacterial inoculum to degrade diesel was analyzed through GC-MS. Smaller chain compounds were obtained after the experimental period of 30 days. The diesel degradation rate was better with the bacterial consortium than with individual bacteria. The bacterial consortium can be a better choice for faster and complete remediation of soils contaminated by hydrocarbons [70]. Together with these previous studies, our study provided strong evidence that PHs degradation capacity is species-specific and a comprehensive understanding of the contributing factors to this species-specific degradation capacity is of importance to enhance microbial remediation of a PHs polluted environment. Different species have different capacities to utilize given diesel constituents as a sole source of carbon and energy. For example, the _Dietzia_ strain DQ12-45-1b was reported to utilize a wide range of _n_-alkanes (C\({}_{6}\)-C\({}_{40}\)) and aromatic compounds of crude oil as a sole carbon source while other strains only use some of these compounds (\(\leq\)C\({}_{25}\)) [71]. Similarly, [PERSON] et al.