Lactate-enhanced production of a cyclic β-1,2-glucan in Acetobacter pasteurianus

Cyclic β-1,2-glucans (CβGs) are well documented in pathogenic and plant-associated α-proteobacteria, but their occurrence in food-relevant acetic acid bacteria (AAB) remains poorly understood. Here, we report a neutral CβG, designated CG-I, in the vinegar-fermenting strain Acetobacter pasteurianus CICC 22518. CG-I production increased under lactate supplementation. MALDI-TOF/MS, accurate-mass high-resolution ESI-MS, and reducing-end analysis are consistent with a cyclic topology and exclude a predominantly linear glucan structure. FTIR spectroscopy and ESI-CID-MS/MS indicate a β-configured, 1→2-linked glucan backbone, with dominant species observed at a degree of polymerization (DP) of 24-26. Lactate supplementation (5.0 g/L) increased CG-I production to approximately 10.4 mg/g dry cell weight, compared with 1.39 and 0.71 mg/g under ethanol and glucose conditions, respectively. This increase was accompanied by elevated expression of cgs (FCN51_RS25580), and deletion of cgs abolished detectable CG-I production. The Δcgs mutant showed reduced motility and growth under elevated lactate concentrations but no detectable defect in maximal biomass under the tested hypoosmotic conditions. CG-I was also detected in simulated grain vinegar fermentation. Together, these findings identify a CβG in a food-relevant AAB and support a link between lactate-rich conditions and increased cgs expression and CG-I production.