The blowout of the Deepwater Horizon in the Gulf of Mexico in 2010 occurred at a depth of 1500 m, corresponding to a hydrostatic pressure of 15 MPa. Up to now, knowledge about the impact of high pressure on oil-degrading bacteria has been scarce. To investigate how the biodegradation of crude oil and its components is influenced by high pressures, like those in deep-sea environments, hydrocarbon degradation and growth of two model strains were studied in high-pressure reactors. The alkane-degrading strain Rhodococcus qingshengii TUHH-12 grew well on n-hexadecane at 15 MPa at a rate of 0.16 h −1 , although slightly slower than at ambient pressure (0.36 h −1 ). In contrast, the growth of the aromatic hydrocarbon degrading strain Sphingobium yanoikuyae B1 was highly affected by elevated pressures. Pressures of up to 8.8 MPa had little effect on growth of this strain. However, above this pressure growth decreased and at 12 MPa or more no more growth was observed. Nevertheless, S. yanoikuyae continued to convert naphthalene at pressure >12 MPa, although at a lower rate than at 0.1 MPa. This suggests that certain metabolic functions of this bacterium were inhibited by pressure to a greater extent than the enzymes responsible for naphthalene degradation. These results show that high pressure has a strong influence on the biodegradation of crude oil components and that, contrary to previous assumptions, the role of pressure cannot be discounted when estimating the biodegradation and ultimate fate of deep-sea oil releases such as the Deepwater Horizon event.
Novel thermophilic and alkaliphilic bacteria for the processing of bast fibres were isolated using hemp pectin as substrate. The strain PB94A, which showed the highest growth rate (micro = 0.5/h) was identified as Geobacillus thermoglucosidasius (DSM 21625). The strain grew optimally at 60 degrees C and pH 8.5. During growth on citrus pectin, the strain produced pectinolytic lyases, which were excreted into the medium. In contrast to the commercially available pectinase Bioprep 3000 L, the enzymes from G. thermoglucosidasius PB94A converted pectin isolated from hemp fibres. In addition to hemp pectin, the culture supernatant also degraded citrus, sugar beet and apple pectin and polygalacturonic acid. When hemp fibres were incubated with the cell-free fermentation broth of G. thermoglucosidasius PB94A, the fineness of the fibres increased. The strain did not produce any cellulases, which is important in order to avoid damaging the fibres during incubation. Therefore, these bacteria or their enzymes can be used to produce fine high-quality hemp fibres.
A significant portion of oil released during the Deepwater Horizon disaster reached the Gulf of Mexico (GOM) seafloor. Predicting the long-term fate of this oil is hindered by a lack of data about the combined influences of pressure, temperature, and sediment composition on microbial hydrocarbon remineralization in deep-sea sediments. To investigate crude oil biodegradation by native GOM microbial communities, we incubated core-top sediments from 13 GOM sites at water depths from 60–1500 m with crude oil under simulated aerobic seafloor conditions. Biodegradation occurred in all samples and followed a predictable compound class sequence dictated by molecular weight and structure. 45 to ~100% of total n-alkane and 3 to 60% of total polycyclic aromatic hydrocarbons (PAH) were depleted. In reactors incubated at 4°C and at pressures of 6–15 MPa, the depletion in total n-alkane was inversely correlated to pressure (R2 ~ 0.85), equivalent to a 4% decrease in total n-alkane depletion for every 1 MPa increase. Our results indicated a modest inhibitory effect of pressure on biodegradation over our experimental range. However, the expansion of oil exploration to deeper waters (e.g., 5000 m) opens the risk of spills at conditions at which pressure might have a more pronounced effect.
We report here the draft genome sequence of Rhodococcus qingshengii strain TUHH-12. The ability of this piezotolerant bacterium to grow on crude oil and tetracosane as sole carbon sources at 150 × 105 Pa makes it useful in studies of hydrocarbon degradation under simulated deep-sea conditions.
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