Project description: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 µ 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.
Project description:We used a whole-genome microarray based on the sequenced strain Lactobacillus sakei 23K to study ribose catabolism in three Lactobacillus sakei strains by screening for differentially expressed genes when grown on ribose compared to glucose
Project description:Lactobacillus (L.) sakei belongs to the dominating lactic acid bacteria in indigenous meat fermentations, while diverse strains of this species have also been isolated from plant fermentations. We could recently show, that L. sakei TMW 1.411 produces a high molecular weight dextran from sucrose, indicating its potential use as a dextran forming starter culture. However, the general physiological response of L. sakei to sucrose as carbohydrate source has not been investigated yet, especially upon simultaneous dextran formation. To address this lack of knowledge, we sequenced the genome of L. sakei TMW 1.411 and performed a label-free, quantitative proteomics approach to investigate the sucrose-induced changes in the proteomic profile of this strain in comparison to its proteomic response to glucose. In total, 21 proteins were found to be differentially expressed at the applied significance criteria (FDR ≤ 0.01). Among these, 14 were associated with the carbohydrate metabolism including several enzymes, which enable sucrose and fructose uptake as well as their subsequent intracellular metabolization, respectively. The plasmid-encoded, extracellular dextransucrase of L. sakei TMW 1.411 was expressed at high levels irrespective of the present carbohydrate and was predominantly responsible for sucrose consumption in growth experiments using sucrose as sole carbohydrate source, while the released fructose from the dextransucrase reaction was more preferably taken up and intracellularly metabolized than sucrose. Genomic comparisons revealed, that operons coding for uptake and intracellular metabolism of sucrose and fructose are chromosomally conserved among L. sakei, while plasmid-located dextransucrase genes are present only in few strains. In accordance with these findings, all 59 different L. sakei strains of our strain collection were able to grow on sucrose as sole carbohydrate source, while eight of them exhibited a mucous phenotype on agar plates indicating dextran formation from sucrose. Our study therefore highlights the intrinsic adaption of L. sakei to plant environments, where sucrose is abundant, and provides fundamental knowledge regarding the use of L. sakei as starter culture for sucrose-based food fermentation processes with in-situ dextran formation.
