Interspecies assertiveness of Lactobacillus curvatus and Lactobacillus sakei in sausage fermentations

Lactobacillus (L.) curvatus and L. sakei contain strains, which are assertive in sausage fermentation. Previous work has demonstrated differences in assertiveness at strain level within one species, and revealed either exclusion of competitors by complementary partner strains or their inhibition by single strains. This work addresses interspecies differences in the assertiveness of L. curvatus and L. sakei. Strain sets of L. curvatus and L. sakei were employed as starters in a fermented sausage model and their abundancy upon fermentation was determined by strain-specific MALDI-TOF MS identification. Generally, single or groups of L. sakei strains outcompeted L. curvatus strains. In multiple growth tests employing mMRS and mMSM it could be shown that assertive L. sakei strains can be predicted along their mu max in mMSM. Still, L. curvatus TMW 1.624 could suppress all L. curvatus and most L. sakei strains in competitive settings. This could be referred to its expression of several bacteriocins, which are active against all of the L. curvatus strains. Strain specific differences could be demonstrated in the susceptibility of L. sakei to bacteriocins, and in oxidative stress tolerance, which is higher in co-existing L. sakei strains than in the bacteriocin producer. This suggests that tolerance to bacteriocins and oxidative stress represent additional determinants for assertiveness, above previously reported bacteriocin production versus metabolic complementarism of partner strains.