Current Status of the Degradation of Aliphatic and Aromatic Petroleum Hydrocarbons by Thermophilic Microbes and Future Perspectives

Abstract

Contamination of the environment by petroleum products is a growing concern worldwide, and strategies to remove these contaminants have been evaluated. One of these strategies is biodegradation, which consists of the use of microorganisms. Biodegradation is significantly improved by increasing the temperature of the medium, thus, the use of thermophiles, microbes that thrive in high-temperature environments, will render this process more efficient. For instance, various thermophilic enzymes have been used in industrial biotechnology because of their unique catalytic properties. Biodegradation has been extensively studied in the context of mesophilic microbes, and the mechanisms of biodegradation of aliphatic and aromatic petroleum hydrocarbons have been elucidated. However, in comparison, little work has been carried out on the biodegradation of petroleum hydrocarbons by thermophiles. In this paper, a detailed review of the degradation of petroleum hydrocarbons (both aliphatic and aromatic) by thermophiles was carried out. This work has identified the characteristics of thermophiles, and unraveled specific catabolic pathways of petroleum products that are only found with thermophiles. Gaps that limit our understanding of the activity of these microbes have also been highlighted, and, finally, different strategies that can be used to improve the efficiency of degradation of petroleum hydrocarbons by thermophiles were proposed.

Keywords: aliphatics; aromatics; biodegradation; metabolites; petroleum hydrocarbons; thermophiles.

Figure 1

Various advantages of carrying out biodegradation reactions at higher temperatures (T°), thus, in the presence of thermophiles.

Figure 2

Distribution of genera of the 59 thermophilic strains degrading petroleum hydrocarbons summarized in Table 1.

Figure 3

Pathways of phenol degradation. So far, only the meta-cleavage pathway has been described in thermophilic bacteria, yet both pathways (meta- and ortho-) are present in mesophilic bacteria.

Figure 4

Possible pathways of naphthalene (NAPH) degradation by thermophilic microbes.

Figure 5

Biodegration pathways of phenanthrene in thermophilic bacteria. All these metabolites were identified from a strain of Nocardia otitidiscaviarum bacterium (ST29).

Figure 6

Biodegration pathways of anthracene in thermophilic bacteria. All these metabolites were identified from a strain of Nocardia otitidiscaviarum bacterium (ST29).