AimsThis study evaluated the aerobic and respiratory metabolism in Lactobacillus reuteri and Lactobacillus spicheri, two heterofermentative species used in sourdough fermentation. Methods and ResultsIn silico genome analysis, production of metabolites and gene expression of pyruvate oxidase, pyruvate dehydrogenase and cytochrome oxidase were assessed in anaerobic and aerobic cultures of Lact.reuteri and Lact.spicheri. Respiring homofermentative Lactobacillus casei N87 and Lact.rhamnosus N132 were used for comparison. Aerobiosis and respiration increased the biomass production of heterofermentative strains compared to anaerobic cultivation. Respiration led to acetoin production by Lact.rhamnosus and Lact.casei, but not in heterofermentative strains, in which lactate and acetate were the major end-products. Lactobacillus spicheri LP38 showed the highest oxygen uptake. Pyruvate oxidase, respiratory cytochromes, NADH oxidase and NADH peroxidase were present in the genome of Lact.spicheri LP38. Both Lact.spicheri LP38 and Lact.rhamnosus N132 overexpressed pox in aerobic cultures, while cydA was up-regulated only when haeme was supplied; pdh was repressed during aerobic growth. ConclusionsAerobic and respiratory growth provided physiological and metabolic advantages also in heterofermentative lactobacilli. Significance and Impact of the StudyThe exploitation of oxygen-tolerant phenotypes of Lact.spicheri may be useful for the development of improved starter cultures.