Comparative Genomics of Leuconostoc carnosum

Abstract

Leuconostoc carnosum is a known colonizer of meat-related food matrices. It reaches remarkably high loads during the shelf life in packaged meat products and plays a role in spoilage, although preservative effects have been proposed for some strains. In this study, the draft genomes of 17 strains of L. carnosum (i.e., all the strains that have been sequenced so far) were compared to decipher their metabolic and functional potential and to determine their role in food transformations. Genome comparison and pathway reconstruction indicated that L. carnosum is a compact group of closely related heterofermentative bacteria sharing most of the metabolic features. Adaptation to a nitrogen-rich environment, such as meat, is evidenced by 23 peptidase genes identified in the core genome and by the autotrophy for nitrogen compounds including several amino acids, vitamins, and cofactors. Genes encoding the decarboxylases yielding biogenic amines were not present. All the strains harbored 1–4 of 32 different plasmids, bearing functions associated to proteins hydrolysis, transport of amino acids and oligopeptides, exopolysaccharides, and various resistances (e.g., to environmental stresses, bacteriophages, and heavy metals). Functions associated to bacteriocin synthesis, secretion, and immunity were also found in plasmids. While genes for lactococcin were found in most plasmids, only three harbored the genes for leucocin B, a class IIa antilisterial bacteriocin. Determinants of antibiotic resistances were absent in both plasmids and chromosomes.

Phenotypic Traits and Immunomodulatory Properties of Leuconostoc carnosum Isolated From Meat Products

“…The spectrum of sugars fermented by the strains was limited to few mono- and disaccharides but consistent with the main isolation sources of the species, i.e., meat products and fermented vegetables ( Jung et al, 2014 ; Ishii et al, 2017 ; Raimondi et al, 2018 ). All the strains fermented glucose, sucrose, and ribose, coherently with the equipment of genes encoding the transporters for these sugars (i.e., specific phosphotransferase systems for glucose and sucrose, and ABC transporters for ribose) ( Candeliere et al, 2021 ). In meat matrices, glucose derives from the hydrolysis of glycogen, while sucrose is present in plants or in fermented meat products where it may be supplemented to accelerate the fermentation rate.…”

“…Unlike Latilactobacillus sakei (former Lactobacillus sakei , Zheng et al, 2020 ) and other LAB that thrive in meat products gaining energy from arginine through the arginine deiminase pathway, L. carnosum did not catabolize arginine. Differently from other Leuconostoc species, L. carnosum was unable to catabolize citrate, coherently with the lack of the genes encoding citrate transporter, citrate lyase, and oxaloacetate decarboxylase, and thus relied only on carbohydrate fermentation for energy supply ( Özcan et al, 2019 ; Candeliere et al, 2021 ).…”

“…Twelve strains of Leuconostoc carnosum , the genome of which has been recently subjected to comparative analysis ( Candeliere et al, 2021 ), were investigated in terms of biochemical, physiological, and functional properties. The spectrum of sugars fermented by the strains was limited to few mono- and disaccharides but consistent with the main isolation sources of the species, i.e., meat products and fermented vegetables ( Jung et al, 2014 ; Ishii et al, 2017 ; Raimondi et al, 2018 ).…”

“…The genus Leuconostoc encompasses heterofermentative Lactobacillales sharing facultative anaerobiosis, intrinsic vancomycin resistance, catalase negativity, ovococcoid morphology, and dextran production ( Björkroth et al, 2014 ). Carbohydrates are catabolized through pentose phosphate and phosphoketolase pathway, yielding lactic acid, CO 2 , and ethanol and/or acetic acid ( Candeliere et al, 2021 ). The ratio between the amounts of ethanol and acetic acid depends on the ability of the microorganism to re-oxidize the NADH generated in the early stages of the process along with the energy requirements.…”

“…Based on genomic annotation, most of the strains of Leuconostoc carnosum have the genes for bacteriocin synthesis, secretion, and immunity, including the production of leucocin B, a class IIc bacteriocin effective against L. monocytogenes ( Felix et al, 1994 ; Candeliere et al, 2021 ). Comparative genomics revealed that L. carnosum consist of a compact group of closely related bacteria sharing most of the metabolic features ( Candeliere et al, 2021 ). Adaptation to a nitrogen-rich environment such as meat is consistent with a number of peptidase genes in the core genome and by the auxotrophy for nitrogen compounds including some amino acids, vitamins, and cofactors.…”