Production and partial characterization of exopolysaccharide from a newly isolated halophilic strain Halomonas sp. DT-Z4

Halomonas sp. DT-Z4, a moderately halophilic strain isolated from saline and alkali soil in Qinghai Province, was used to characterize the structure and function of a novel extracellular polysaccharide (EPS-Z4). By optimizing the fermentation conditions (carbon source: sucrose 9% w/v; Nitrogen source: peptone 12 g/L; pH 9.0; 25°C), EPS production reached 3.09 g/L, indicating its adaptability to extreme salinity environment. Structural characterization showed that EPS-Z4 is a fructose-dominated heteropolysaccharide (97.6%) with small amounts of glucose (1.4%), glucuronic acid (0.5%) and amino sugar (0.1%). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to confirm its α-(1→6) linkage and high thermal stability (Td = 275.9°C). Scanning electron microscopy (SEM) showed that it had a dense lamellar network morphology and a zeta potential of -21.4 mV, indicating that it had moderate colloidal stability. Functional analysis showed that EPS-Z4 had excellent water solubility (WSI = 85.79%) and oil retention (OHC = 321%), which were better than most traditional microbial polysaccharides. EPS-Z4 could be used as a stabilizer for high-temperature food processing and as a biological agent for saline-alkali soil remediation.