Biodegradation of diesel fuel by two psychrotolerant strains isolated from Southern Victoria Island, Antarctica
Hydrocarbon contamination in Antarctica poses a great threat to the delicate and unique ecosystems of this continent. Bioremediation of hydrocarbon pollutants via utilisation of the indigenous hydrocarbon-degrading bacteria, has been proposed as an environmentally friendly method to clean-up c...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/75710/1/FBSB%202018%2041%20IR.pdf |
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| Summary: | Hydrocarbon contamination in Antarctica poses a great threat to the delicate and unique
ecosystems of this continent. Bioremediation of hydrocarbon pollutants via utilisation of
the indigenous hydrocarbon-degrading bacteria, has been proposed as an
environmentally friendly method to clean-up contaminated soils in Antarctica. This
study focused on diesel-degrading Pseudomonas and Rhodococcus species isolated from
pristine soils located at the Southern Victoria Island, Antarctica. Isolates were assessed
for their ability to grow on diesel as a sole carbon source on solid media at 4°C. Nine
isolates showed significant growth in enriched agar after 14 days of incubation. Isolates
were then screened to obtain the most promising diesel-degrading strains through
colourimetric assay. Two potent isolates that possess rapid utilisation of 0.5% (v/v) diesel
were selected and identified as Pseudomonas sp. strain ADL15 and Rhodococcus sp.
strain ADL36. The factors that contribute to the growth of both strains were characterised
initially using the conventional ‘one-factor-at-a-time’ approach. During this stage, the
optimal condition for the growth of both ADL15 and ADL36 were at pH 7.0, 20°C, 1.0%
(w/v) NaCl, and 1.0 g/L NH4NO3. However, strain ADL36 favoured a higher amount of
diesel (2.0% (v/v)) for bacterial growth by comparison to ADL15 (1.0% (v/v)).
Percentage of dodecane mineralisation was used as the mean to indicate diesel reduction
through gas chromatographic analysis. While strain ADL36 showed 83.75% of dodecane
mineralisation, the reduction of dodecane by AD15 is merely at 22.39%. Response
surface methodology (RSM) based on central composite design (CCD) was used to
improve and optimise the effect of significant factors toward the biodegradation of
diesel. RSM proved to enhance the reduction of experimented hydrocarbon (dodecane)
with a 15% and 16% increment of mineralisation for isolate ADL15 (38.32%) and
ADL36 (99.89%), respectively. The results also demonstrated that addition of salt to
culture media was the limiting factor in hydrocarbon degradation. Whole genome
sequencing showed that ADL15 and ADL36 were closely related to the Pseudomonas
fluorescens and Rhodococcus erythropolis grouping, respectively. Metagenomic
analyses revealed the presence of alkane hydroxylases systems which was responsible
for alkane degradation in ADL36 but not in ADL15. This founding corresponds to the gas chromatographic analysis in which ADL36 proved to be a better alkane degrader
than ADL15. Detection of the complete pathway of aromatic compound degradation in
the latter strain indicates a stronger inclination of the strain to utilise aromatic
components in diesel as the carbon source. The presence of putative monooxygenases
may also suggest that this strain may utilise specific alkane for their growth. The results
from this study showed that strain ADL15 and ADL36 have an excellent potential in
bioremediation of aromatics and aliphatics, respectively. |
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