Identification of Salt Stress Responsive Protein in Lactobacillus Paracasei LN-1 Using SDS-PAGE

bglG Regulates the Heterogeneity Driven by the Acid Tolerance Response in Lacticaseibacillus paracasei L9

The acid tolerance of lactic acid bacteria is crucial for their fermentation and probiotic functions. Acid adaption significantly enhances the acid tolerance of strains, and the phenotypic heterogeneity driven by the acid tolerance response (ATR) contributes to this process by providing a selective advantage in harsh environments. The mechanism of heterogeneity under the ATR is not yet clear, but individual gene expression differences are recognized as the cause. In this study, we observed four heterogeneous subpopulations (viable, injured, dead, and unstained) of Lacticaseibacillus paracasei L9 (L9) induced by acid adaption (pH 5.0, 40 min) using flow cytometry. The viable subpopulation represented a significantly superior acid tolerance to the injured subpopulation or total population. Different subpopulations were sorted and transcriptomic analysis was performed. Five genes were found to be upregulated in the viable subpopulation and downregulated in the injured subpopulation, and bglG (LPL9_RS14735) was identified as having a key role in this process. Using salicin (glucoside)-inducing gene expression and gene insertion mutagenesis, we verified that bglG regulated the heterogeneity of the acid stress response and that the relevant mechanisms might be related to activating hsp20. This study provides new evidence for the mechanism of the ATR and may contribute to the theoretical basis of improving the acid tolerance of Lacticaseibacillus paracasei L9.

Comparative proteomic analysis of three Lactobacillus plantarum strains under salt stress by iTRAQ

BACKGROUND

Lactobacillus plantarum, a common species of lactic acid bacteria, is used to improve the flavor of traditional fermented food. Under salt stress, different strains of L. plantarum can respond differently. In this work, proteomics and bioinformatics analysis of L. plantarum strains (ATCC14917, FS5-5, and 208) grown under salt stress (240 g L^-1 sodium chloride (NaCl)) were investigated based on the isobaric tags for relative and absolute quantitation method.

RESULTS

Although 171 differentially expressed proteins (DEPs) were observed, only 44, 57, and 112 DEPs were identified in the strains ATCC14917, FS5-5, and 208 respectively. There were 33, 191, and 179 specific DEPs in ATCC14917 versus FS5-5, in 208 versus FS5-5, and in strain 208 versus ATCC14917 in 240 g L^-1 NaCl. These DEPs indicate that the three strains, from pickles, fermented soybean paste, and fermented milk, may have different salt stress responses. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes analysis showed that most DEPs observed were involved in protein biosynthesis, nucleotide metabolism, and sugar metabolism. Twenty-six significantly different DEPs that were possibly associated with salt response were selected and further analyzed for gene expression level and pattern by quantitative reverse transcription polymerase chain reaction. Pyruvate kinase and cysteine desulfurase had similar expression patterns in all three strains; glutamate decarboxylase expression was upregulated in FS5-5 and significantly upregulated in strain 208; RNA polymerase subunit alpha was downregulated in FS5-5 but upregulated in strain 208.

CONCLUSIONS

These results also showed that the salt stress response of strain 208 may involve higher numbers of genes than the other strains. This research provides a theoretical basis for improvement of salt tolerance of L. plantarum in industrial production. © 2020 Society of Chemical Industry.

Evaluation and Application of Different Cholesterol-Lowering Lactic Acid Bacteria as Potential Meat Starters

ABSTRACT

A total of 115 isolates of lactic acid bacteria were screened from traditional fermented foods in Guizhou Province, People's Republic of China. The cholesterol removal rates of 86 isolates ranged from 7.29 to 25.66%, and 18 isolates showed a cholesterol removal rate of more than 15%. According to the results of physiological and biological tests, 13 isolates were selected to determine the fermentation performance; 9 isolates-MT-4, MT-2, PJ-15, SR2-2, SQ-4, SQ-7, ST2-2, ST2-6, and NR1-7-had high tolerance of bile salt and acid and had a survival rate of more than 96% under pH 3.0 and 0.3% bile salt. ST2-2, SR2-2, NR1-7, SQ-4, and MT-4 had high survival rate in different concentrations of NaCl and NaNO2 under different temperatures. According to BLAST comparison results of the 16S rRNA sequence in the GenBank database and the genetic distance of the 16S rRNA sequence with an ortho-connected algorithm, SR2-2, NR1-7, and ST2-2 were identified as Lactobacillus plantarum, MT-4 was identified as Lactobacillus pentosus, and SQ-4 was identified as Lactobacillus paraplantarum. Moreover, strains SQ-4 and MT-4 were added to fermented beef. Results showed that the fermented beef had delicious taste and was popular to consumers because of its proper pH, pleasant colors, high viable cell count, and suitable content of bound and immobilized water. These results provide a basis for the development of new starter formulation for the production of high-quality fermented meat products.

HIGHLIGHTS

Honey as a functional additive in yoghurt – a review

Purpose

Recent societal interest in healthful foods has led to the development of functional dairy products that basically provide health benefits in addition to their fundamental nutrients. Yoghurt being most popular fermented milk product due to its healthy image can be an excellent carrier for probiotics. Functional properties of yoghurt can be enhanced with the inclusion of functional ingredients such as probiotics and its conjugate application with prebiotics may be advantageous as it favors probiotic growth. Nutritional and medicinal value of honey coupled with presence of oligosaccharides has projected honey as a functional additive in yoghurt.

Design/methodology/approach

Attempt has been made to review the literature on the biochemical activities of yoghurt cultures and probiotics in presence of honey. Both review and research papers related to biochemical activities and functional properties of yoghurt cultures and probiotics in presence of honey and their health benefits published in diverse journals under Pub Med and Science Direct have been considered. Keywords used for data search included functional foods, yoghurt, probiotic, health benefits, honey, etc.

Findings

Functional properties of yoghurt can be further enhanced with the inclusion of probiotic cultures and honey. Honey can be safely used in association with different probiotic cultures during yoghurt manufacture for augmenting functional properties of yoghurt to extend health benefits. Honey may not be equally a suitable matrix for all yoghurt cultures or probiotic cultures.

Research limitations/implications

Reviewed literature indicated that limited research on animal or human feeding trials with honey containing yoghurt has been done. Clinical trials with honey containing yoghurt are emerging prior to its marketing as functional food.

Originality/value

Application of honey as a functional additive during the manufacture of probiotic yoghurt is suggested to extend the functional properties of normal yoghurt.

Viability and Stress Response of Putative Probiotic Lactobacillus plantarum Strains in Honey Environment

Due to problem of preservation of dairy products which serve as a matrix for probiotics, it is challenging to use these probiotics as food supplements in many developing countries. To determine the suitability of the Lactobacillus strains for exploitation as probiotics in honey, we investigated the effect of their storage on the viability, functionality, and the mechanism associated with their protective effect. Three isolates obtained from our laboratory collection were identified through amplification of the 16S rRNA gene. The viability of the strains in honey at different storage conditions was studied. Three genes (hdc, gtf, and clpL) responsible for the resistance of bacteria in acidic environments were screened. SDS-PAGE analysis of total protein was performed to observe protein profile changes of the strains after exposure to honey. All the three isolates, namely, GGU, GLA51, and GLP56, were identified as Lactobacillus plantarum strains. After 28 days of storage in honey at 4 °C, viable cell concentrations of the three strains were higher than 2.04 × 10⁶ CFU/ml. During the same period at room temperature, only the Lactobacillus plantarum GLP56 strain remained viable with a cell concentration of 1.86 × 10⁴ CFU/ml. The clpL gene coding for ATPase was detected in all the three strains. The protein of molecular weight ~ 50 kDa was absent in the protein profile of Lactobacillus plantarum GGU after 60 days of storage in honey at 4 °C. The Lactobacillus plantarum GLP56, Lactobacillus plantarum GLA51, and Lactobacillus plantarum GGU strains exposed to honey can withstand acidic environmental stress but their viability declines over time.