Assessment of bioremediation potential of <i>Stutzerimonas stutzeri NL3</i> and <i>Enterobacter cloacae NL4</i> isolates from an Algerian oilfield

<b>ABSTRACT</b>Heavy metals (HM) and hydrocarbons rank as highly hazardous pollutants. For their remediation, it is advisable to employ eco-friendly green technologies. This study aims to evaluate the bioremediation potential of two bacterial strains isolated from oilfield and identified by 16S rRNA as <i>Stutzerimonas stutzeri NL3</i> and <i>Enterobacter cloacae</i> strain NL4. Their application to treat a polluted water sample was also tested. Within a short period of 7 days, <i>E. cloacae</i> NL4 was able to degrade 80.04% of crude oil (50%, (v/v)) under alkaline (pH 12) and halophilic (50 g/L NaCl) conditions. Whereas <i>S. stutzeri</i> NL3 degraded 77.9% of crude oil in a medium containing 50% (v/v) crude oil, 10 g L^-1 NaCl and pH 8. These strains can reduce 89.83% of barium and 85.65% of mercury using up to 50% petroleum as the sole carbon source. In addition, these strains were found to be resistant to 10 different HMs, tolerating high concentrations up to 50 mM. The addition of these strains to a water sample from a chemically polluted river induced a significant reduction in the concentration of different HMs such as Cr by 93.67%, Ni by 88.31%, Fe by 79.34% and others all simultaneously within a short span of 10 days. Finally, these strains were also shown to form biofilms and produce biosurfactants in response to stressful conditions as a mechanism of resistance. These promising results indicate that these bacteria could be utilized in more complex polluted environments, positioning them as strong candidates for future bioremediation endeavours.