Planococcus maritimus VITP21 synthesizes (2-acetamido-2-deoxy-α-d-glucopyranosyl)-(1→2)-β-d-fructofuranose under osmotic stress: a novel protein stabilizing sugar osmolyte.

A halotolerant bacterium, Planococcus maritimus VITP21 isolated from a saltern region in Kumta along the Arabian Sea Coast of India was found to have increased cellular levels of sugars (up to 2.3-fold) under osmotic stress when grown in minimal medium with glucose as the sole carbon and energy source supplemented with 10% w/v NaCl. The major sugar osmolyte which increased with the concentration of NaCl in the growth medium was purified and characterized using various nuclear magnetic resonance spectroscopy techniques. The sugar was found to be similar to sucrose but with the C-2 hydroxyl group of the glucose ring substituted with acetamido group, which is not previously reported for its natural synthesis by any other organism. This novel sugar, (2-acetamido-2-deoxy-α-d-glucopyranosyl)-(1→2)-β-d-fructofuranose, exhibited stabilizing effect on a model protein α-amylase by increasing the apparent midpoint transition, onset temperature of denaturation, and free energy of thermal unfolding.