Production of LactobionicAcid by Pressure-Treated Pseudomonas fluorescens SK17.001 and the Mechanismof Pressure-Dependent Changes

In this work, lactobionic acid production by Pseudomonas fluorescens 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 P. fluorescens 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.