Effect of the absence of the CcpA gene on growth, metabolic production, and stress tolerance in Lactobacillus delbrueckii ssp. bulgaricus.

ABSTRACT

The catabolite control protein A (CcpA) is a kind of multi-effect regulatory protein. In the study, the effect of the inactivation of CcpA and aerobic conditions on the growth, metabolic production, and stress tolerance to heat, oxidative, and cold stresses in Lactobacillus delbrueckii ssp. bulgaricus was investigated. Results showed that inactivation of CcpA distinctly hindered growth. Total lactic acid concentration was significantly lower in aerobiosis for both strains and was lower for the mutant strain than L. bulgaricus. Acetic acid production from the mutant strain was higher than L. bulgaricus in aerobiosis compared with anaerobiosis. Enzyme activities, lactate dehydrogenase (LDH), phosphate fructose kinase (PFK), pyruvate kinase (PK), and pyruvic dehydrogenase (PDH), were significantly lower in the mutant strain than L. bulgaricus. The diameters of inhibition zone were 13.59 ± 0.02 mm and 9.76 ± 0.02 mm for L. bulgaricus in anaerobiosis and aerobiosis, respectively; and 8.12 ± 0.02 mm and 7.38 ± 0.02 mm for the mutant in anaerobiosis and aerobiosis, respectively. For both strains, cells grown under aerobic environment possess more stress tolerance. This is the first study in which the CcpA-negative mutant of L. bulgaricus is constructed and the effect of aerobic growth on stress tolerance of L. bulgaricus is evaluated. Although aerobic cultivation does not significantly improve growth, it does improve stress tolerance.