TY - JOUR
T1 - Influence of extracellular pH on growth, viability, cell size, acidification activity, and intracellular pH of Lactococcus lactis in batch fermentations
AU - Hansen, Gunda
AU - Johansen, Claus Lindvald
AU - Marten, Gunvor
AU - Wilmes, Jacqueline
AU - Jespersen, Lene
AU - Arneborg, Nils
PY - 2016/7/1
Y1 - 2016/7/1
N2 - In this study, we investigated the influence of three extracellular pH (pHex) values (i.e., 5.5, 6.5, and 7.5) on the growth, viability, cell size, acidification activity in milk, and intracellular pH (pHi) of Lactococcus lactis subsp. lactis DGCC1212 during pH-controlled batch fermentations. A universal parameter (e.g., linked to pHi) for the description or prediction of viability, specific acidification activity, or growth behavior at a given pHexwas not identified. We found viability as determined by flow cytometry to remain high during all growth phases and irrespectively of the pH set point. Furthermore, regardless of the pHex, the acidification activity per cell decreased over time which seemed to be linked to cell shrinkage. Flow cytometric pHidetermination demonstrated an increase of the averaged pHilevel for higher pH set points, while the pH gradient (pHi–pHex) and the extent of pHiheterogeneity decreased. Cells maintained positive pH gradients at a low pHexof 5.5 and even during substrate limitation at the more widely used pHex6.5. Moreover, the strain proved able to grow despite small negative or even absent pH gradients at a high pHexof 7.5. The larger pHiheterogeneity at pHex5.5 and 6.5 was associated with more stressful conditions resulting, e.g., from higher concentrations of non-dissociated lactic acid, while the low pHiheterogeneity at pHex7.5 most probably corresponded to lower concentrations of non-dissociated lactic acid which facilitated the cells to reach the highest maximum active cell counts of the three pH set points.
AB - In this study, we investigated the influence of three extracellular pH (pHex) values (i.e., 5.5, 6.5, and 7.5) on the growth, viability, cell size, acidification activity in milk, and intracellular pH (pHi) of Lactococcus lactis subsp. lactis DGCC1212 during pH-controlled batch fermentations. A universal parameter (e.g., linked to pHi) for the description or prediction of viability, specific acidification activity, or growth behavior at a given pHexwas not identified. We found viability as determined by flow cytometry to remain high during all growth phases and irrespectively of the pH set point. Furthermore, regardless of the pHex, the acidification activity per cell decreased over time which seemed to be linked to cell shrinkage. Flow cytometric pHidetermination demonstrated an increase of the averaged pHilevel for higher pH set points, while the pH gradient (pHi–pHex) and the extent of pHiheterogeneity decreased. Cells maintained positive pH gradients at a low pHexof 5.5 and even during substrate limitation at the more widely used pHex6.5. Moreover, the strain proved able to grow despite small negative or even absent pH gradients at a high pHexof 7.5. The larger pHiheterogeneity at pHex5.5 and 6.5 was associated with more stressful conditions resulting, e.g., from higher concentrations of non-dissociated lactic acid, while the low pHiheterogeneity at pHex7.5 most probably corresponded to lower concentrations of non-dissociated lactic acid which facilitated the cells to reach the highest maximum active cell counts of the three pH set points.
U2 - 10.1007/s00253-016-7454-3
DO - 10.1007/s00253-016-7454-3
M3 - Journal article
C2 - 27020293
SN - 0175-7598
VL - 100
SP - 5965
EP - 5976
JO - Applied Microbiology and Biotechnology
JF - Applied Microbiology and Biotechnology
IS - 13
ER -