Analysis of Leuconostoc citreum strains using multilocus sequence typing

Genomic insights into antibiotic resistance genes in Leuconostoc citreum strains isolated from artisanal buffalo milk curd in Bangladesh through whole-genome sequencing

We sequenced the genome of Leuconostoc citreum strains BSMRAU-M1L6 and BSMRAU-M1L13 isolated from artisanal buffalo milk curd in Bangladesh. The draft genomes of BSMRAU-M1L6 and BSMRAU-M1L13 are 1,869,891 and 1,890,611 bp, respectively, with 50.0× coverage (both) and 65 and 75 contigs, respectively.

Genetic Diversity of Leuconostoc mesenteroides Isolates from Traditional Montenegrin Brine Cheese

In many dairy products, Leuconostoc spp. is a natural part of non-starter lactic acid bacteria (NSLAB) accounting for flavor development. However, data on the genomic diversity of Leuconostoc spp. isolates obtained from cheese are still scarce. The focus of this study was the genomic characterization of Leuconostoc spp. obtained from different traditional Montenegrin brine cheeses with the aim to explore their diversity and provide genetic information as a basis for the selection of strains for future cheese production. In 2019, sixteen Leuconostoc spp. isolates were obtained from white brine cheeses from nine different producers located in three municipalities in the northern region of Montenegro. All isolates were identified as Ln. mesenteroides. Classical multilocus sequence tying (MLST) and core genome (cg) MLST revealed a high diversity of the Montenegrin Ln. mesenteroides cheese isolates. All isolates carried genes of the bacteriocin biosynthetic gene clusters, eight out of 16 strains carried the citCDEFG operon, 14 carried butA, and all 16 isolates carried alsS and ilv, genes involved in forming important aromas and flavor compounds. Safety evaluation indicated that isolates carried no pathogenic factors and no virulence factors. In conclusion, Ln. mesenteroides isolates from Montenegrin traditional cheeses displayed a high genetic diversity and were unrelated to strains deposited in GenBank.

Research on the role of LuxS/AI-2 quorum sensing in biofilm of Leuconostoc citreum 37 based on complete genome sequencing

Leuconostoc citreum, a type of food-grade probiotic bacteria, plays an important role in food fermentation and intestinal probiotics. Biofilms help bacteria survive under adverse conditions, and LuxS/AI-2-dependent quorum sensing (QS) plays an important role in the regulation of their biofilm-forming activities. L. citreum 37 was a biofilm-forming strain isolated from dairy products. The aim of this study was to analyze genes involved in the LuxS/AI-2 system based on genome sequencing and biofilm formation of L. citreum 37. Genome assembly yielded two contigs (one chromosome and one plasmid), and the complete genome contained 1,946,279 base pairs (bps) with a G + C content of 38.91%. The genome sequence analysis showed that there were several pathways such as the two-component system, QS, and seven other signal pathways, and 26 genes (including luxS, pfs, and 24 other genes) may participate in QS related to biofilm formation. All these results showed that the LuxS/AI-2 system is complete in the genome of L. citreum 37. The quantitative polymerase chain reaction (qPCR) of pfs, luxS genes, and AI-2 production of L. citreum 37 in planktonic state and biofilm state showed that the expression of pfs and luxS genes was consistent with the production of AI-2 and was positively correlated with biofilm formation. After luxS of L. citreum 37 expressed in Escherichia coli BL21, AI-2 production was detected, suggesting that the luxS gene played an important role in AI-2 synthesis, Therefore, luxS may regulate the biofilm formation of L. citreum 37 by participating in AI-2 synthesis. It is projected that results of this study could help facilitate further understanding and application of L. citreum 37.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02747-2.

Multilocus Sequence Typing of Leuconostoc mesenteroides Strains From the Qinghai-Tibet Plateau

Leuconostoc mesenteroides strains were a type of epiphytic bacterium widely used in fermented foods and products in the biochemical and pharmaceutical industries but data on its presence in foods from Qinghai-Tibet Plateau in China was scarce. In this study, molecular analysis based on multilocus sequence typing (MLST) with eight housekeeping genes (pyrG, groeL, rpoB, recA, uvrC, murC, carB, and pheS) was carried out on 45 L. mesenteroides strains isolated from different plants and dairy products from Qinghai-Tibet Plateau in China. The objective of this study was to perform genetic diversity analysis and explore the relationship between strains and isolate samples or separate regions. A total of 25 sequence types (STs) were identified with a diversity of up to 55.6%, which were grouped into one clonal complexes (CCs), 3 doublets and 17 singletons by eBURST. The results of minimum spanning tree and clustering analysis indicated these L. mesenteroides strains from the Qinghai-Tibet Plateau were relatively weakly related to the isolated region. However, there was a close relationship between the genotypes of L. mesenteroides strains and the type of the isolated sample, which was consistent with the results of API 50CH. The MLST scheme presented in this study provides a shareable and comparable sequence database and enhances our knowledge of the population diversity of L. mesenteroides strains which will be further used for the selection of industrial strains.

Molecular typing tools for identifying and characterizing lactic acid bacteria: a review

Identification and classification of beneficial microbes is of the highest significance in food science and related industries. Conventional phenotypic approaches pose many challenges, and they may misidentify a target, limiting their use. Genotyping tools show comparatively better prospects, and they are widely used for distinguishing microorganisms. The techniques already employed in genotyping of lactic acid bacteria (LAB) are slightly different from one another, and each tool has its own advantages and disadvantages. This review paper compiles the comprehensive details of several fingerprinting tools that have been used for identifying and characterizing LAB at the species, sub-species, and strain levels. Notably, most of these approaches are based on restriction digestion, amplification using polymerase chain reaction, and sequencing. Nowadays, DNA sequencing technologies have made considerable progress in terms of cost, throughput, and methodology. A research journey to develop improved versions of generally applicable and economically viable tools for fingerprinting analysis is ongoing globally.

Tracking of deliberately inoculated Leuconostoc mesenteroides and Lactobacillus brevis in kimchi

The objective of this study was to track intentionally inoculated Leuconostoc mesenteroides (11251) and Lactobacillus brevis (B151) strains in kimchi using random amplified polymorphic DNA (RAPD), repetitive element palindromic PCR (rep-PCR), and comparative housekeeping gene sequences analysis. The 16S rRNA gene provided species-level information for 30 colonies randomly picked from kimchi inoculated with strains 11251 and B151. Out of 30 colonies, one colony was matched to strain 11251, and two colonies were found identical to strain B151 reference strain in inoculated kimchi. Notably, among the three tools, strain 11251 was best tracked by comparative gene sequence analysis, while strain B151 tracked by all three tools. Our results suggest that the gene sequence analysis is a more reliable tool for tracking of desired strains than RAPD and rep-PCR. Based on the findings, it is recommended that gene sequence analysis could be used to avoid misuse of industrially useful strains within the growing food industry.

Tracking of Intentionally Inoculated Lactic Acid Bacteria Strains in Yogurt and Probiotic Powder

The present work aimed at tracking intentionally inoculated lactic acid bacteria (LAB) strains in yogurt and probiotic powder. Leuconostoc (Leu.) mesenteroides (11251), Lactobacillus (L.) brevis (B151), and Lactobacillus plantarum (LB41^K) strains were tracked in yogurt, and L. plantarum (LB41^P) was tracked in a commercial probiotic powder. The yogurt was intentionally inoculated with the selected bacterial strains. Two types of yogurt with known and unknown bacterial pools were utilized. The standard 16S rRNA gene sequencing was used to evaluate the initial screening. The molecular typing tools, random amplified polymorphic DNA (RAPD), repetitive element palindromic PCR (rep-PCR), and comparative gene sequence analysis of selected housekeeping loci were used to track the inoculated dubious strains. Out of 30 random selections for each inoculation, the developed method identified seven (11251), nine (B151), and five (LB41^K) colonies in the yogurt. The validation was performed by identifying 7 colonies (LB41^P) out of 30 in the probiotic powder. The DNA banding profiles and the gene sequence alignments led to the identification of the correct inoculated strains. Overall, the study summarizes the use of molecular tools to identify the deliberately inoculated LAB strains. In conclusion, the proposed polyphasic approach effectively tracked the intentionally inoculated strains: Leu. mesenteroides, L. brevis, and L. plantarum (LB41^K) in yogurt and L. plantarum (LB41^P) in probiotic powder. The study demonstrates how to track industrially relevant misused LAB strains in marketable food products.