Abstract
The oil-producing Arabian Gulf states have hot summer seasons of about 7-month in length. Therefore, environmental oil spills should be bioremediated by the activity of indigenous, hydrocarbonoclastic (hydrocarbon-degrading) microorganisms with optimum growth at about 50 °C. Soils in such arid countries harbor thermophilic bacteria, whose oil-consumption potential is enhanced by calcium (II) - and dipicolinic acid (DPA)-supplement. Those organisms are, however, subjected to additional stresses including toxic effects of heavy metals that may be associated with the spilled oil. Our study highlighted the resistance of indigenous, thermophilic isolates to the heavy metals, mercury (II), cadmium (II), arsenic (II) and lead (II) at 50 °C. We also detected the uptake of heavy metals by 15 isolates at 50 °C, and identified the merA genes coding for Hg2+-resistance in 4 of the studied Hg2+-resistant isolates. Hg2+ was the most toxic metal and the metal toxicity was commonly higher in the presence of oil. The addition of Ca2+ and DPA enhanced the Hg2+-resistance among most of the isolates at 50 °C. Crude oil consumption at 50 °C by 4 selected isolates was inhibited by the tested heavy metals. However, Ca2+ and DPA limited this inhibition and enhanced oil-consumption, which exceeded by far the values in the control cultures.
Highlights
Calcium (II) - and dipicolinic acid mediated-biostimulation of oilbioremediation under multiple stresses by heat, oil and heavy metals
Summer temperatures of about 50 °C and higher are usual in the Gulf region, leading to minimized activities of indigenous, mesophilic microorganisms that are responsible for oil bioremediation world-wide[1,2,3,4]
We have investigated the probable roles of Ca2+-and dipicolinic acid (DPA)-amendment in resisting the toxic effects of heavy metals that lead to reduced growth and hydrocarbon consumption activity of those thermophiles at 50 °C
Summary
A new finding of that survey was that growth and hydrocarbonoclastic activities of all the tested organisms were enhanced in response to treating the cultures with Ca2+ and dipicolinic acid (DPA) Both substances are long known to accumulate in cells of Bacillus spp during endospore formation, and are believed to be involved in the heat-resistance mechanisms of the spores, probably by stabilizing DNA at elevated temperatures[15, 16]. These facts indicate that Ca2+- and DPA-amendment may enhance microbial tolerance to heat, and may stimulate their potential for spilled-oil bioremediation in the thermophilic range. The results are expected to be useful in designing biotechnologies for bioremediating environmental oil spills in hot countries
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
