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The amount and biodegradability of oil-degrading bacteria in seawater should be augmented to improve the biodegradation of marine petroleum hydrocarbons. This study investigated the degradation of petroleum-degrading bacteria (P1) with biosurfactant-producing bacteria (B2) and its mechanism. Two groups of experiments that consist of P1 with and without B2 were designed. The degradation performance and surface characteristics of the bacteria and the degradation path of diesel were studied. The degradation rate in the group of P1 with B2 was 82.65%, which was higher than that without B2, after 12 days. The analysis of surface characteristics showed that a high hydrophobicity enabled diesel to be accessible to cells. Meanwhile, the addition of B2 increased the contact area between bacteria and diesel, which was favorable to bioaugmentation degradation. The diesel degradation paths included surface adsorption, cell uptake, and biodegradation. The first step of diesel degradation was a rapid surface adsorption followed by cell uptake. The velocities of the removal rate of diesel by biodegradation and cell uptake in the group of P1 with B2 were higher than those without B2.

At present, improvement in the degradation effect of diesel-degrading bacteria by combining them with surfactant-producing bacteria is an important way to efficiently repair the ecology of oil-contaminated areas. Among the 14 bacterial isolates, three diesel-degrading bacteria showed better degradation performance, with degradation rates of diesel of 50.52% (HDMP1), 42.70% (HDMP2), and 36.46% (HDMP3). Three biosurfactant-producing bacteria showed better emulsifying ability. The (E 24) values of the biosurfactant against diesel were determined to be 55% (HDMB1), 81% (HDMB2), and 73% (HDMB3). The best surfactant-producing bacteria (HDMB2) produce lipopeptide biosurfactants that can be observed by the presence of peptide and carboxyl groups using Fourier transform infrared spectroscopy. In addition, the interaction between the diesel-degrading bacteria and biosurfactant-producing bacteria was evaluated and we found that the combination of HDMP1 and HDMB2 had significant performance for oil removal (the degradation rate of diesel was 67.38%), which indicated its future application in a microbial enhanced oil recovery process.

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