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.

The exopolysaccharides produced by rhizobia play an important role in their biotechnological and bioremediation properties. The characteristics and properties of an exopolysaccharide produced by Rhizobium sp. L01 were investigated. Strain Rhizobium sp. L01 was identified as Rhizobium tropici and produced a high yield of exopolysaccharides (REPS-L01), reaching 22.8 g/L after 63 h of fermentation in a 5 L bioreactor with glucose as the carbon source. REPS-L01 was composed of glucose and galactose in a ratio of 2.95:1, carrying pyruvate, acetate, and succinate groups. REPS-L01 had good shear-thinning properties in aqueous solutions at various concentrations and revealed typical non-crosslinked polymer properties. REPS-L01 revealed thermal stability up to 275 °C. REPS-L01 had the potential to be thicker, being suitable for use under conditions ranging from 4 to 60 °C, pH between 2 and 12, and salt concentrations up to 20,000 mg/L. REPS-L01 showed strong emulsifying activity, particularly with n-hexane; even at concentrations as low as 0.25 wt%, the emulsification index could reach more than 50%. Even more impressively, stable n-hexane emulsion gel was formed with 2 wt% REPS-L01 solution. Rheological studies showed that the solid-like emulsion gel had a high storage modulus, and the SEM studies of the emulsion gel indicated that n-hexane could fill the pores of REPS-L01.

The characterization and flocculation mechanism of a biopolymer flocculant produced by Sphingomonas sp. HL-1, were investigated. The bio-flocculant HL1 was identified as an acidic polysaccharide, mainly composed of glucose, and also contained a small amount of mannose, galacturonic acid and guluronic acid. The flocculating activity of the purified HL1 polysaccharide could be activated by trivalent cations, and its flocculation mechanism was mainly charge neutralization and bridging. The working concentration of fermentation broth HL1 in a kaolin suspension was only 1/10,000 (v/v), in which the polysaccharide concentration was about 2 mg/L. The bio-flocculant HL1 maintained high efficiency at a wide range of pH (pH 3–10). It also exhibited good flocculating activity at a temperature range of 20–40 °C; it could even tolerate high salinity and kept activity at a mineralization degree of 50,000 mg/L. Therefore, the bio-flocculant HL1 has a good application prospect in the treatment of wastewater over a broad pH range and in high salinity.

In this study, it is shown that the strain Sphingomonas sp. HL-1 can utilize glucose, xylose and mixed sugars to produce high yields (28.7 g/L) of HL gum, which has a high molecular weight of 2.03 × 10⁶ Da. HL gum is a novel sphingan uniquely enriched in guluronic acid (16.74%) and galacturonic acid, with low rhamnose content, distinguishing it from conventional sphingans. It exhibits good solubility in water at 25 °C and 60 °C, pronounced shear-thinning behavior, and concentration-dependent, heat-activated gelation. Remarkably, even at a low concentration of 1% (w/v), HL gum forms a resilient hydrogel upon heating to 90 °C, achieving a gel strength of 2950 ± 130 g/cm², and maintains gel stability under high salinity (up to 50 g/L). SEM micrographs revealed a clear temperature-dependent morphological transition: from fibrous structures at 20 °C to curled aggregates at 60 °C and finally to a porous fibrous network at 90 °C, consistent with a sol–gel transition. Combined with its ability to efficiently utilize mixed sugars in a short fermentation cycle, HL gum’s unique chemical composition and superior gelation properties distinguish it from conventional sphingans, highlighting its potential for food, biomedical, and industrial hydrogel applications.