The biodegradation of petroleum hydrocarbons has many potential applications and has attracted much attention recently. The hydrocarbon-degrading bacterium BL-27 was isolated from petroleum-polluted soil and was compounded with surfactants to improve biodegradation. Its 16S rDNA and rpoD gene sequences indicated that it was a strain of Bacillus subtilis. Strain BL-27 had extensive adaptability and degradability within a broad range of temperatures (25–50 °C), pH (4.0–10.0) and salinity (0–50 g/L NaCl). Under optimal conditions (45 °C, pH 7.0, 1% NaCl), the strain was able to degrade 65% of crude oil (0.3%, w/v) within 5 days using GC-MS analysis. Notably, strain BL-27 had weak cell surface hydrophobicity. The adherence rate of BL-27 to n-hexadecane was 29.6% with sucrose as carbon source and slightly increased to 33.5% with diesel oil (0.3%, w/v) as the sole carbon source, indicating that the cell surface of BL-27 is relatively hydrophilic. The strain was tolerant to SDS, Tween 80, surfactin, and rhamnolipids at a concentration of 500 mg/L. The cell surface hydrophobicity reduced more with the addition of surfactants, while the chemical dispersants, SDS (50–100 mg/L) and Tween 80 (200–500 mg/L), significantly increased the strain’s ability to biodegrade, reaching 75–80%. These results indicated that BL-27 has the potential to be used for the bioremediation of hydrocarbon pollutants and could have promising applications in the petrochemical industry.

Rhamnolipids are a mixture of the homologs species due to variations in the rhamnose units and β-hydroxy fatty acid moieties, mainly including Rha-C₁₀-C₁₀, Rha-Rha-C₁₀-C₁₀, and Rha-C₁₀. In this study, strain P. aeruginosa YM4 was selected for its capacity to efficiently produce di-rhamnolipid (Rha-Rha-C₁₀-C₁₀) as the predominant component with soybean oil and glycerol as carbon source, accounting for 64.8% and 85.7% of total products, respectively. The critical micelle concentration (CMC) of rhamnolipid products varies with the content of di-rhamnolipid, whereby lower CMC values corresponding to higher di-rhamnolipid contents. The rhamnolipids containing 85.7% di-rhamnolipid had the lowest CMC value of 50 mg/L. Accordingly the viscosity-reducing efficiency and oil-washing efficiency of rhamnolipids increased with higher di-rhamnolipid component. At a concentration of 500 mg/L, the rhamnolipids containing 85.7% di-rhamnolipid worked best and showed 82.5% oil-washing efficiency, which offered great promise for applications in enhanced oil recovery. The results showed the variation of structure and composition of rhamnolipids had a significant effect on their application.

The genus Sphingomonas was established by Yabuuchi et al. in 1990, and has attracted much attention in recent years due to its unique ability to degrade environmental pollutants. Some Sphingomonas species can secrete high-molecular-weight extracellular polymers called sphingans, most of which are acidic heteropolysaccharides. Typical sphingans include welan gum, gellan gum, and diutan gum. Most sphingans have a typical, conserved main chain structure, and differences of side chain groups lead to different rheological characteristics, such as shear thinning, temperature or salt resistance, and viscoelasticity. In petroleum production applications, sphingans, and their structurally modified derivatives can replace partially hydrolyzed polyacrylamide (HPAM) for enhanced oil recovery (EOR) in high-temperature and high-salt reservoirs, while also being able to replace guar gum as a fracturing fluid thickener. This paper focuses on the applications of sphingans and their derivatives in EOR.

Enhanced oil recovery (EOR) is a crucial technology for improving crude oil recovery; it extracts residual oil from reservoirs through chemical, physical, or biological methods, thereby further increasing recovery rates after secondary recovery. Biosurfactants, particularly lipopeptides, have become a research focus in the field of EOR due to their excellent properties. However, existing studies have mainly concentrated on their production and characterization, while systematic investigation into their deactivation mechanisms and stability limits remains lacking at the molecular level. This study integrates density functional theory (DFT), ab initio molecular dynamics (AIMD), and classical molecular dynamics (MD) simulations to systematically reveal the hydrolysis mechanisms and stability boundaries of lipopeptide model molecules under high-temperature and high-salinity reservoir conditions from a multiscale perspective. DFT calculations show significant differences in the energy barriers among different hydrolysis sites in lipopeptide molecules, with side-chain structure being a key factor influencing amide bond hydrolysis. Metal ions present in reservoir environments (Na⁺, K⁺, Ca²⁺, Mg²⁺), particularly divalent ones (Ca²⁺, Mg²⁺), can act as catalysts to reduce the hydrolysis energy barrier. Electronic structure analysis reveals that the catalytic effect originates from the polarization of the carbonyl oxygen by metal ions, weakening the covalent character of the C=O bond. AIMD simulations reveal that only Ca²⁺ can specifically activate the hydrolysis of lipopeptide molecules at certain distances (critical distance), while other cations (e.g., Mg²⁺, K⁺, Na⁺) do not exhibit similar catalytic activity. MD simulations further demonstrate that Ca²⁺ ion concentration and temperature are the dominant factors influencing Ca²⁺ permeation toward hydrolysis sites (limit distance), with other ions having a weaker effect. By systematically simulating lipopeptide behavior under varying temperature and ion concentration conditions, a catalytic hydrolysis criterion based on the effective distance of Ca²⁺ interaction (i.e., limit distance ≤ critical distance) is established through multiscale simulation, and the performance boundaries of its temperature and salt tolerance are preliminarily defined. This study provides a theoretical basis and quantitative design guidance for the applicability of lipopeptide-based biosurfactants in high-temperature and high-salinity reservoirs.