Production of Lactobionic Acid by Pressure-Treated <i>Pseudomonas fluorescens</i> SK17.001 and the Mechanism of Pressure-Dependent Changes

In this work, lactobionic acid production by <i>Pseudomonas fluorescens</i> SK17.001 and the variation of the cell envelope were studied after high hydrostatic pressure treatment. The production of lactobionic acid by the resting cells of <i>P. fluorescens</i> SK17.001 reached its maximum value (7.5 g/L) at 200 MPa and was approximately 3.5 times that at 0.1 MPa (atmospheric pressure), although the cell viability and integrity were decreased by high-pressure treatment. A pressure of 300 MPa appeared to be the turning point, in which remarkable changes occurred in the bacteria. Cell injuries were observed at 200 MPa, where the activity of membrane-bound Na⁺/K⁺-ATPase was enhanced. Pressure-induced changes were observed in the Fourier-transform infrared spectra of the cell envelope. The β-sheet content reduced from 34% to 25% with the increase of pressure from 200 to 300 MPa. These results revealed that a high-pressure treatment induced physical alteration to proteins in the cell membrane, which might be associated with changes in lactobionic acid production.