Kotsakou Christina Agricultural University of Athens MSc Food Science and Technology and Human Nutrition Physiology of lactic acid bacteria under acid stress conditions Food Biochemistry
Lactococcus Lactobacillus Streptococcus Bifidobacterium Leuconostoc etc Uses of LAB
Uses of LAB
Streptococcus macedonicus
Acid stress Επίδραση του ρη επί των μικροοργανισμών δείκτης οξύτητας ή αλκαλικότητας Ολοι οι μικροοργανισμοί έχουν ένα εύρος ρη που μπορούν να αναπτυχθούν Τhe ρη του εξωτερικού, όχι του εσωτερικού, περιβάλλοντος θα πρέπει να παραμένει σταθερό για να μην καταστραφούν τα οξεο-αλκαλικά ασταθή μακρομόρια του κυττάρου Σε συνθήκες στρες μπορεί να επηρεαστεί το εσωτερικό ph
Microorganisms ph Fungi 3 to 5 Yeast 5 Lactobacilli 5,5 Streptococci 6 Propionic 6,5 Enterobactiria 7
Examples of acid stress response Leuconostoc mesenteroides ATCC 8293 - Sensitive to acid stress. - Acid-adapted cells at ph 5.0 exhibited maximum increase in tolerance. Streptococcus macedonicus - The exhibition of S. macedonicus cells in the average log phase at ph 4.0 had no effect on their survival. - The exhibition at ph 3.0 was lethal. - The exhibition of cells at ph 3,5 had as result the increase of the damaged cells. Lactococcus lactis Lactobacillus casei
Acid tolerance is presently under study in L. lactis The results with strain MG1363 show that it survives a lethal challenge at ph 4.0 if adapted briefly (5 to 15 minutes) at a ph between 4.5 and 6.5. These results show that L. lactis possesses an inducible response to acid stress in exponential phase.
Adaptive evolution was conducted for 70 days to generate acid-tolerant L. casei. The evolved mutant lb-2 exhibited more than a 60% increase in biomass as well as a 13.6 and 65.6% increase in concentrations of lactate and acetate, respectively, when cultured at ph 4.3 for 64 h. Lactic acid tolerances of the parental strain and the evolved mutant were determined. The evolved mutant showed a 318-fold higher survival rate than that of the parental strain. Physiological analysis showed that the evolved mutant exhibited higher intracellular ph, NH4+ concentration and lower inner membrane permeability than that of the parental strain during acid stress.
Μηχανισμοί Η μείωση του εξωκυττάριου PH οδηγεί σε απώλεια της κινητήριας δύναμης πρωτονίων(pmf)
Μηχανισμοί Τι συμβαίνει όταν το εξωτερικό ph ελαττώνεται Αλλοίωση στις ενζυματικές δραστηριότητες Αποσύνθεση πρωτεΐνης Καταστροφή των νουκλεϊκών οξέων
Μηχανισμοί FOF1 ATPase (connection of ATP Protion Motion Force) Pathway of Arginine Deiminase (ADI) arginine deiminase, ornithine cabamoyltransferaseand carbamate kinase Urease
The operation of F1F0 - ΑΤPase
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