Respiration of Lactobacillus casei

Although Lactobacillus casei is generally considered to be "indifferent" to oxygen, several strains exhibited considerable respiratory activity with a number of substrates related to carbohydrate catabolism. In many cases this respiratory ability enables the organism to utilize energy sources that would be unavailable under anaerobic conditions. The chief features of respiration of L. casei strain 103 were fairly representative of those examined. [Formula: see text] (N) values of this strain on glucose ranged from 75 to 200 and with mannitol from 250 to 500. This respiration was insensitive to 1.7 mM KCN and the rate of oxygen consumption was independent of oxygen concentration from ca. 500 μM to ca. 6 μM with an apparent K s (O 2 ) of 3 μM. Enzymatic studies indicated that this respiration was mediated by flavin-linked reduced pyridine nucleotide oxidase(s) and peroxidase(s) and did not involve benzo- or naphtho-quinones. No H 2 O 2 accumulation occurred with glucose or mannitol as substrate. Growth yield coefficients of 21.7 and 24.4 with glucose and mannitol respectively as energy sources under aerobic growth conditions indicate that electron flow through these flavin respiratory enzymes was not coupled to any additional energy yielding.