Sessile culture as a strategy to enhance the production of emulsifying exopolysaccharides by Glutamicibacter sp. XHA18

Abstract

Pristine environments harbor diverse microbial communities with unique and underexplored metabolic capabilities, including the production of exopolysaccharides (EPS) with bioemulsifying properties. These polymers have increasing biotechnological relevance in food, pharmaceutical, and environmental sectors. This study evaluated the effect of two contrasting growth modes—sessile and planktonic—on the production and stability of an emulsifying EPS synthesized by the halotolerant strain Glutamicibacter sp. XHA18, isolated from a pristine cenote in the Yucatan Peninsula, Mexico. Emulsifying activity and 24-h stability were assessed using the emulsification index (EI₂₄), while physicochemical parameters such as carbon and nitrogen sources, pH, agitation, and salinity were optimized in both culture systems. EPS extraction and purification protocols were designed to recovery both high- and low-molecular-weight fractions. The purified EPS was characterized by FTIR, UV–Vis spectroscopy, SEM-EDS, and zeta potential analysis. Sessile cultivation promoted earlier and higher emulsifying activity (EI₂₄ = 62.09 % at 24 h), whereas planktonic culture required 96 h to reach comparable levels (EI₂₄ = 60.09 %). In both systems, dextrose and alkaline pH significantly enhanced EPS production, whereas high salinity impaired its emulsifying performance. EPS yield was higher under sessile conditions (2.8 g/L) than in planktonic culture (1.8 g/L). FTIR and zeta potential analysis confirmed the polysaccharidic nature and negative surface charge of the EPS, supporting its ability to form stable emulsions with various hydrophobic substrates, even under salinity levels of 5–10 %. Toxicity assays with Artemia salina and Cucumis sativus confirmed the low toxicity of the EPS, with only minor effects at elevated concentration. Genomic analysis revealed that strain XHA18 belongs to the genus Glutamicibacter but differs in G + C content and metabolic features from known species, suggesting it may represent a novel taxon. Overall, this study provides new insights into the biosynthesis and functional stability of bioemulsifying EPS under sessile conditions and highlights Glutamicibacter sp. XHA18 as a promising biotechnological resource for industrial and environmental applications.