Degradation of benzo[a]pyrene by halophilic bacterial strain Staphylococcus haemoliticus strain 10SBZ1A

Abstract

The exploitation of petroleum oil generates a considerable amount of "produced water or petroleum waste effluent (PWE)" that is contaminated with polycyclic aromatic hydrocarbons (PAHs), including Benzo[a]pyrene (BaP). PWE is characterised by its high salinity, which can be as high as 30% NaCl, thus the exploitation of biodegradation to remove PAHs necessitates the use of active halophilic microbes. The strain 10SBZ1A was isolated from oil contaminated soils, by enrichment experiment in medium containing 10% NaCl (w/v). Homology analyses of 16S rRNA sequences identified 10SBZ1A as a Staphylococcus haemoliticus species, based on 99.99% homology (NCBI, accession number GI: MN388897). The strain could grow in the presence of 4-200 μmol l-1 of BaP as the sole source of carbon, with a doubling time of 17-42 h. This strain optimum conditions for growth were 37 oC, 10% NaCl (w/v) and pH 7, and under these conditions, it degraded BaP at a rate of 0.8 μmol l-1 per day. The strain 10SBZ1A actively degraded PAHs of lower molecular weights than that of BaP, including pyrene, phenanthrene, anthracene. This strain was also capable of removing 80% of BaP in the context of soil spiked with BaP (10 μmol l-1 in 100 g of soil) within 30 days. Finally, a metabolic pathway of BaP was proposed, based on the identified metabolites using liquid chromatography-high resolution tandem mass spectrometry. To the best of our knowledge, this is the first report of a halophilic BaP degrading bacterial strain at salinity > 5% NaCl.

Fig 1. Growth profile of Staphylococcus haemoliticus 1OSBZ1A strain in the presence of various concentrations of benzo(a)pyrene (BaP).

CFU represents colony forming unit.

Fig 2. Doubling time (dt, in hours) of culture of Staphylococcus heamolysis strain 10SBZ1A in the presence of various concentrations of Benzo(a)pyrene (BaP).

Fig 3. Doubling time (dt, in hours) of a culture of Staphylococcus haemoliticus strain 10SBZ1A in the presence of benzo(a)pyrene (BaP), along with various aromatic substrates.

All substrates were used at 40 μmole.l^-1.

Fig 4. Quantification of the remaining benzo[a]pyrene (BaP) in a culture of Staphylococcus haemoliticus strain 10SBZ1A.

Open circles represent the bacterial growth, and closed squares and closed triangles represent the control and the BaP degradation profiles, respectively.

Fig 5. Values of degradation rates of benzo[a]pyrene (BaP) reported in various studies.

Studies A were cultures of single strains, in minimum mineral media (MM); studies B consisted of consortia of bacteria in MM or rich medium, or single bacterial strain but in rich media. References are listed in the text, in the Results/Discussions section.

Fig 6. Propose pathways for the degradation of BaP by Staphylococcus haemoliticus strain 10SBZ1A.

*Compounds with identical exact molar mass. ** Compounds with identical exact molar mass.