Oxygen Relieves the CO₂ and Acetate Dependency of <em>Lactobacillus johnsonii</em> NCC 533

<div><p>Oxygen relieves the CO₂ and acetate dependency of <i>Lactobacillus johnsonii</i> NCC 533. The probiotic <i>Lactobacillus johnsonii</i> NCC 533 is relatively sensitive to oxidative stress; the presence of oxygen causes a lower biomass yield due to early growth stagnation. We show however that oxygen can also be beneficial to this organism as it relieves the requirement for acetate and CO₂ during growth. Both on agar- and liquid-media, anaerobic growth of <i>L. johnsonii</i> NCC 533 requires CO₂ supplementation of the gas phase. Switching off the CO₂ supply induces growth arrest and cell death. The presence of molecular oxygen overcomes the CO₂ dependency. Analogously, <i>L. johnsonii</i> NCC 533 strictly requires media with acetate to sustain anaerobic growth, although supplementation at a level that is 100-fold lower (120 microM) than the concentration in regular growth medium for lactobacilli already suffices for normal growth. Analogous to the CO₂ requirement, oxygen supply relieves this acetate-dependency for growth. The <i>L. johnsonii</i> NCC 533 genome indicates that this organism lacks genes coding for pyruvate formate lyase (PFL) and pyruvate dehydrogenase (PDH), both CO₂ and acetyl-CoA producing systems. Therefore, C1- and C2- compound production is predicted to largely depend on pyruvate oxidase activity (POX). This proposed role of POX in C2/C1-generation is corroborated by the observation that in a POX deficient mutant of <i>L. johnsonii</i> NCC 533, oxygen is not able to overcome acetate dependency nor does it relieve the CO₂ dependency.</p>