Potential of crude oil-degrading bacteria to co-resist heavy metals in soil

The toxicity and adverse effects of crude oil pollution entail a quick clean-up using available competent technologies such as bioremediation. One factor affecting the bioremediation of crude oil is the presence of stressors such as heavy metals that halt the biodegradative potentials of the indigenous microbiota resulting in prolonged bioremediation and the accumulation of toxic hydrocarbons in the environment. Thus, it was considered sensible to investigate the potentials of the indigenous microbiota to resist the inhibitory effects of heavy metals (Al, Cd, Co, Hg and Ni) in soil. For this purpose, the tolerance of crude oil-degrading bacteria isolated from three different soils to heavy metals was investigated. Results demonstrated that bacteria isolated from the old crude oil-contaminated site and the recently heavy metal-contaminated construction sites that harbored high concentrations of heavy metals showed significantly (P0.05) higher tolerance to heavy metals compared to those isolated from pristine soil. Furthermore, longer co-existence of bacteria with heavy metals resulted in higher bacterial potentials to tolerate the inhibitory effects of heavy metals where the majority of the isolates exhibited multiple resistances to heavy metals especially to Co and Ni. However, all heavy metals tested, in particular, Hg, Co and Ni showed lethal effects at elevated concentrations.