Cold‐Adapted Lipid A from <i>Polaribacter</i> sp. SM1127: A Study of Structural Heterogeneity and Immunostimulatory Properties

Polaribacter sp. SM1127, a cold-adapted marine Gram-negative bacterium isolated from Laminaria in Arctic waters, plays a crucial role in nutrient cycling and biopolymer degradation in cold environments. Additionally, its exopolysaccharide (EPS) exhibits promising biotechnological potential, including antioxidant and wound-healing properties. This study focuses on the isolation and characterization of lipid A, the glycolipid component of Polaribacter sp. SM1127 lipopolysaccharide (LPS), by bypassing full LPS extraction and working directly with the ethanol precipitation product containing both EPS and bacterial cells. Mass spectrometry analysis reveals significant structural heterogeneity in the lipid A, with variations in fatty acid chain length, branching, saturation, and hydroxylation. These features likely enable the bacterium to fine-tune its response to fluctuating temperatures or other cold-related environmental stresses, contributing to resilience in the Arctic Ocean ecosystem. Furthermore, immunological assays demonstrate that both LPS and EPS produced by Polaribacter sp. SM1127 induce weak Toll-like receptor 4 activation and, in general, poorly stimulate the nuclear factor kappa-light-chain-enhancer of activated B cells pathway, compared to Escherichia coli LPS. These findings suggest their potential as immunomodulatory agents, like vaccine adjuvants.