Abstract
One hundred eighty four strains belonging to the species Lactobacillus casei, L. paracasei and L. rhamnosus were screened for their ability to grow under aerobic conditions, in media containing heme and menaquinone and/or compounds generating reactive oxygen species (ROS), in order to identify respiratory and oxygen-tolerant phenotypes. Most strains were able to cope with aerobic conditions and for many strains aerobic growth and heme or heme/menaquinone supplementation increased biomass production compared to anaerobic cultivation. Only four L. casei strains showed a catalase-like activity under anaerobic, aerobic and respiratory conditions and were able to survive in presence of H2O2 (1 mM). Almost all L. casei and L. paracasei strains tolerated menadione (0.2 mM) and most tolerated pyrogallol (50 mM), while L. rhamnosus was usually resistant only to the latter compound. This is the first study in which an extensive screening of oxygen and oxidative stress tolerance of members of the L. casei group has been carried out. Results allowed the selection of strains showing the typical traits of aerobic and respiratory metabolism (increased pH and biomass under aerobic or respiratory conditions) and unique oxidative stress response properties. Aerobic growth and respiration may confer technological and physiological advantages in the L. casei group and oxygen-tolerant phenotypes could be exploited in several food industry applications.
Highlights
The Lactobacillus casei group includes three closely related species (Lactobacillus casei, L. paracasei and L. rhamnosus), involved in different food and health-related applications [1,2,3]
All strains of L. casei group were able to cope with aerobic conditions, even if a large variability in growth behaviour was found (Figures 1a and 1b)
All strains grown in heme-supplemented aerobiosis were tested for their tolerance of reactive oxygen species (ROS) generating compounds to evaluate if aerobic growth and heme improved tolerance of oxidative stresses
Summary
The Lactobacillus casei group includes three closely related species (Lactobacillus casei, L. paracasei and L. rhamnosus), involved in different food and health-related applications [1,2,3]. Their wide ecological distribution (human host, vegetable, meat and dairy products) and the potential role as probiotics makes these species interesting for the development of new functional foods and relevant for several genetic and physiological studies. The growth condition and the type of metabolism significantly affect the stress responses in LAB and, recently, several studies have demonstrated that conditions which promote aerobic and respiratory growth (presence of oxygen, heme and/or menaquinone in the substrate) induce in Lactococcus lactis and L. plantarum useful traits (improved biomass production and stress tolerance) for industrial and biotechnological applications [8], [9]
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