The impact of nutrients on microbial Hydrocarbon degradation at deep-sea Temperature and Hydrostatic Pressure

Currently available physical and chemical remediation technologies are not effective in the deep sea, where ultimate fate of oil is strongly dependent on degradation by microorganisms. In order to setup an efficient bioremediation strategy, the effect of the environmental constraints on oil degrading communities’ metabolism needs to be assessed. In this work, natural surface seawater communities were incubated under different T, P and in different dilutions of the medium ONR7a. Then, after 1 day, 1 week and 3 weeks, cell number, SO4, NH4 and DIC concentration were assessed. When only one environmental stress (low T or high HP) is applied, a positive effect of nutrients’ concentration is highlighted, with increased growth rates and DIC production; at 23 °C and 20 MPa, a lower cell growth is observed with respect to atmospheric pressure samples, but a relatively high value of oil degradation is mostly sustained by respiration to DIC: this result evidence the possibility to setup an effective biostimulation strategy in deep seas characterized by milder temperatures (Sulu, Mediterranean, Red Sea). High Ammonium concentrations are needed to sustain large production of proteins for cell maintenance process required for adaptation to HP. Moreover, at 23 °C and 20 MPa, significant Sulphate uptake occurs, whose role in HP adaptation needs to be clarified. Also at low T and atmospheric pressure oil biodegradation mostly relies on respiration to DIC, however biodegradation rates seems to be more affected by T reduction than HP increase. When both low T and high HP are applied, cellular metabolism is still active but any growth is observed, drastically reducing the oil biodegradation, that relies only on respiration to DIC. Surface communities subject to combination of 2 stresses may need more than 3 weeks to adapt to the deep sea environment and start a growth phase.