No abstract

No abstract

No abstract

Background: Lactobacillus species are used as probiotics and play an important role in fermented food production. However, use of 16S rRNA gene sequences as standard markers for the differentiation of Lactobacillus species offers a very limited scope, as several species of Lactobacillus share similar 16S rRNA gene sequences. In this study, we developed a rapid and accurate method based on comparative genomic analysis for the identification of 37 Lactobacillus species that are commonly used in probiotics and fermented foods. Results: To select species-specific sequences or genes, a total of 180 Lactobacillus genome sequences were compared using Python scripts. In 14 out of 37 species, species-specific sequences could not be found due to the similarity of the 16S-23S rRNA gene. Selected unique genes were obtained using comparative genomic analysis and all genes were confirmed to be specific for 52,478,804 genomes via in silico analysis; they were found not to be strain-specific, but to exist in all strains of the same species. Species-specific primer pairs were designed from the selected 16S-23S rRNA gene sequences or unique genes of species. The specificity of the species-specific primer pairs was confirmed using reference strains, and the accuracy and efficiency of the polymerase chain reaction (PCR) with the standard curve were confirmed. The PCR method developed in this study is able to accurately differentiate species that were not distinguishable using the 16S rRNA gene alone. This PCR assays were designed to detect and identify 37 Lactobacillus species. The developed method was then applied in the monitoring of 19 probiotics and 12 dairy products. The applied tests confirmed that the species detected in 17 products matched those indicated on their labels, whereas the remaining products contained species other than those appearing on the label. Conclusions: The method developed in this study is able to rapidly and accurately distinguish different species of Lactobacillus, and can be used to monitor specific Lactobacillus species in foods such as probiotics and dairy products.

Gochujang is a Korean fermented hot pepper paste beneficial to human health by providing various nutrients. In this study, its physicochemical characteristics were identified, and its microbial communities were analyzed by high-throughput sequencing. The interrelationship between physicochemical characteristics and microbial composition was investigated to reveal the properties of gochujang before and after fermentation. After fermentation, all samples showed decreased salt concentration, pH, and reducing sugar content, while the acidity and amino-type nitrogen increased. The water content, salt concentration, amino-type nitrogen, and reducing sugar differed according to the batches of samples. Bacillus, Aerosakkonema, and Enterococcus were identified as the predominant bacterial genera. Furthermore, Aerosakkonema was the most abundant genus before fermentation; however, it was replaced by Bacillus as it decreased after fermentation. For the fungi, Aspergillus dominated before fermentation, whereas Zygosaccharomyces and Millerozyma dominated after fermentation. The high level of amino-type nitrogen in gochujang was related to the relative abundance of B. haynesii/B. licheniformis before fermentation. Additionally, the high abundance of Z. rouxii after fermentation was related to the flavor of gochujang. This comprehensive analysis of the microbial community associated with the physicochemical properties of gochujang could help in understanding the factors affecting the quality of the product.