11.8.5 Salinity
Some oleophilic microorganisms may have certain salinity requirements. P
aeruginosa NCIM 5541 isolated from a petroleum oil well and demonstrated to
efficiently utilize both glycerol and crude oil (Varjani and Upasani 2017) has been
shown to grow in PH medium only when supplemented with 5% (w/v) NaCl. This
halotolerant nature of this strain will find use in bioremediation of marine oil spills.
In general, it has been reported that hydrocarbon degradation increases with increasing salinity (Varjani 2017); however, extreme salinity is expected to be inhibitory to
microbes.
11.9 Conclusion
Petroleum or crude oil, as it is naturally found, is derived from buried fossils which
have undergone natural weathering processes over millions of years. Today, crude
oil is used to produce a multitude of products including diesel and petrol. Its
extensive use world over has led to an increase in accidental spillage during storage
and transport. Contamination of pristine environments by crude oil or its derivatives
has detrimental effects on the ecological balance due to the toxicity and recalcitrant
nature of these chemicals. Both aquatic and terrestrial habitats can be affected
through accidental exposures, affecting organisms from microbes to larger animals,
either causing direct mortality or affecting the food chain through bioaccumulation.
Thus, methods to tackle such accidental spills are continuously being developed
and improved. While physical and chemical methods have been used as remedial
measures, bioremediation through the use of microbes is being increasingly seen as
the most ecologically and economically viable solution. As such, identification of
newer and more efficient organisms with the ability to degrade petroleum hydrocarbons and the development of microbial bioremediation techniques are currently
extensively researched.
Due to the hydrophobic nature of petroleum hydrocarbons, bioavailability of the
carbon source to the microbes is often a limiting factor. The use of surfactants to
increase bioavailability is thus a commonly observed practice. Biosurfactant secretion by certain microbes has been found to increase efficiency and proved to be more
suitable than the use of chemical dispersants in improving bioavailability of the
hydrocarbons. As such, exploration for biosurfactant-secreting organisms is an
important area of research. Hydrocarbonoclastic microbes tend to increase at sites
of contamination and thus serve as the ideal source for isolating new organisms.
It has been observed that bioremediation rates at contamination sites often reduce
with time as a result of limiting inorganic nutrients such as nitrogen and phosphate
and/or reduction in microbial population. Biostimulation (introduction of suitable
microbes) and bioaugmentation (provision of required nutrients) are strategies that
11 Microbial Bioremediation of Petroleum Hydrocarbons
285
Some oleophilic microorganisms may have certain salinity requirements. P
aeruginosa NCIM 5541 isolated from a petroleum oil well and demonstrated to
efficiently utilize both glycerol and crude oil (Varjani and Upasani 2017) has been
shown to grow in PH medium only when supplemented with 5% (w/v) NaCl. This
halotolerant nature of this strain will find use in bioremediation of marine oil spills.
In general, it has been reported that hydrocarbon degradation increases with increasing salinity (Varjani 2017); however, extreme salinity is expected to be inhibitory to
microbes.
11.9 Conclusion
Petroleum or crude oil, as it is naturally found, is derived from buried fossils which
have undergone natural weathering processes over millions of years. Today, crude
oil is used to produce a multitude of products including diesel and petrol. Its
extensive use world over has led to an increase in accidental spillage during storage
and transport. Contamination of pristine environments by crude oil or its derivatives
has detrimental effects on the ecological balance due to the toxicity and recalcitrant
nature of these chemicals. Both aquatic and terrestrial habitats can be affected
through accidental exposures, affecting organisms from microbes to larger animals,
either causing direct mortality or affecting the food chain through bioaccumulation.
Thus, methods to tackle such accidental spills are continuously being developed
and improved. While physical and chemical methods have been used as remedial
measures, bioremediation through the use of microbes is being increasingly seen as
the most ecologically and economically viable solution. As such, identification of
newer and more efficient organisms with the ability to degrade petroleum hydrocarbons and the development of microbial bioremediation techniques are currently
extensively researched.
Due to the hydrophobic nature of petroleum hydrocarbons, bioavailability of the
carbon source to the microbes is often a limiting factor. The use of surfactants to
increase bioavailability is thus a commonly observed practice. Biosurfactant secretion by certain microbes has been found to increase efficiency and proved to be more
suitable than the use of chemical dispersants in improving bioavailability of the
hydrocarbons. As such, exploration for biosurfactant-secreting organisms is an
important area of research. Hydrocarbonoclastic microbes tend to increase at sites
of contamination and thus serve as the ideal source for isolating new organisms.
It has been observed that bioremediation rates at contamination sites often reduce
with time as a result of limiting inorganic nutrients such as nitrogen and phosphate
and/or reduction in microbial population. Biostimulation (introduction of suitable
microbes) and bioaugmentation (provision of required nutrients) are strategies that
11 Microbial Bioremediation of Petroleum Hydrocarbons
285