CO improves the anaerobic biodegradation intensity and selectivity of heterocyclic hydrocarbons in heavy oil.

Heterocyclic hydrocarbons pollution generated by oil spills and oilfield wastewater discharges threatens the ecological environment and human health. Here we described a strategy that combines the greenhouse gas CO reduction with microbial remediation. In the presence of nitrate, CO can improve the biodegradation efficiency of the resins and asphaltenes in heavy oil, particularly the biodegradation selectivity of the polar heterocyclic compounds by the newly isolated Klebsiella michiganensis. This strain encoded 80 genes for the xenobiotic biodegradation and metabolism, and can efficiently utilize CO when degrading heavy oil. The total abundance of resins and asphaltenes decreased significantly with CO, from 40.816% to 26.909%, to 28.873% with O, and to 36.985% with N. The transcripts per million (TPM) value of accA gene was 57.81 under CO condition, while respectively 8.86 and 21.23 under O and N conditions. Under CO condition, the total relative percentage of N1-type heterocyclic compounds was selectively decreased from 32.25% to 22.78%, resulting in the heavy oil viscosity decreased by 46.29%. These results demonstrated a novel anaerobic degradation mechanism that CO can promote the anaerobic biodegradation of heterocyclic hydrocarbons in heavy oil, which provides a promising biotreatment technology for the oil-contaminated water.