Direct visualization of oil degradation and biofilm formation for the screening of crude oil-degrading bacteria

Abstract

A simple procedure has provided detection and screening of oil-degrading bacteria using optical microscopy. A 100 µm crude-oil droplet was injected at the bottom of and attached onto a transparent Petri dish pre-filled with mineral salt medium. After pipetting microbes into the Petri dish, we observed the interactions between the bacteria and the oil drops. As oil-degrading-bacteria (UltraTech microbes) were consuming components of the oil drops and forming biofilms, the original perfectally spherical shaped oil drop became irregular and the size of the oil drop also varied, whereas non-oil-degrading bacteria changed neither the size nor shape of the oil drops. The surface hydrophobicity and the initial motility of bacteria play essential roles in microbial oil degradation, as the oil-degrading bacteria are more surface hydrophobic than the non-oil-degraders, and high initial motilities were accompanied with high degradation rates. This assay provided direct visualizations of the interactions between oil-degrading bacteria and oil drops, and can be used as a quick screening assay when processing a large number of bacteria strains for potential oil degraders.