Characterization of the respiratory physiology of Lactococcus lactis for starter culture production with improved acidification capacity
Conference contribution, 2015
Commercial freeze-dried starter cultures for cheese making are produced mainly via anaerobic batch processes. A recent discovery has shown that some lactic acid bacteria (LAB) are able to sustain respiration under aerobic conditions when hemin is added to the growth medium, since it completes the electron transport chain for respiration, which is otherwise defective . Respiration is energetically beneficial: compared to fermentation, under respiratory conditions the biomass yield is higher and a different by-product pattern is observed. However, it is also important to consider whether the different metabolism can affect the performance of the starter culture. Thus, this project investigates LAB respiratory physiology, aiming to clarify the molecular reasons behind the milk acidification capacity of the respiratory culture. Our bioreactor results demonstrate that with hemin addition, cells switch from the fermentation to respiration only in the late exponential phase of growth. Although presence of oxygen is an additional stress for LAB, in the presence of hemin under aerobic conditions cells have surprisingly better fermentation behaviour, i.e. higher lactate yield before the respiratory switch. Therefore, we hypothesize that with improved fermentation a certain energy threshold is achieved for the respiratory switch. This energy requirement might be related to the intake of the hemin, however this aspect needs further investigation, as hemin transport into the cells has not been characterized yet.
Reference:  Lechardeur D et al Curr Opin Biotechnol 2011,22(2):143