Transcriptional analysis of galactomannooligosaccharides utilization by Lactobacillus plantarum WCFS1

Complex alpha and beta mannan foraging by the human gut bacteria

The human gut microbiota (HGM), a community of trillions of microbes, underscores its contribution by impacting many facets of host health and disease. In the HGM, Bacteroidota and Bacillota represent dominant bacterial phyla, which mainly rely on the glycans recalcitrant to host digestion to meet their energy requirements. Accordingly, the impact of dietary and host-derived glycans in the assembly and operation of these dominant microbial communities continues to be an area of active research. Among various glycans, mannans represent an integral component of the human diet. Apart from their health effects, the diverse and complex mannan structures bears molecular signatures that alter the expression of specific gene clusters in selected Bacteroidota and Bacillota species. Both the phyla possess variable and sophisticated loci of mannan recognition proteins, hydrolytic enzymes, transporters, and other metabolic proteins to sense, capture and utilize mannans as an energy source. The current review summarizes mannan structural diversity, and strategies adopted by select species of the HGM bacteria to forage mannans by focusing primarily on glycoside hydrolases and their effects on host health and metabolism.

Anti-cariogenic Properties of Lactobacillus plantarum in the Utilization of Galacto-Oligosaccharide

Ecological approaches can help to correct oral microbial dysbiosis and drive the advent and persistence of a symbiotic oral microbiome, which benefits long-term dental caries control. The aim of this study was to investigate the impact of the prebiotic Galacto-oligosaccharide (GOS) on the growth of probiotics L. plantarum 14,917 and its effect on the inhibitory ability of L. plantarum 14,917 against the growth of Streptococcus mutans and Candida albicans in an in vitro model. Single-species growth screenings were conducted in TSBYE broth with 1% glucose and 1–5% GOS. Interaction experiments were performed using duo- and multi-species models with inoculation of 10⁵ CFU/mL S. mutans, 10³ CFU/mL C. albicans, and 10⁸ CFU/mL L. plantarum 14,917 under 1%, 5% GOS or 1% glucose. Viable cells and pH changes were measured. Real-time PCR was utilized to assess expression of C. albicans and S. mutans virulence genes. Six replicates were used for each group. Student’s t-test, one-way ANOVA, and Kruskal-Wallis were employed to compare the outcomes of different groups. GOS significantly inhibited the growth of C. albicans and S. mutans in terms of growth quantity and speed when the two strains were grown individually. However, GOS did not affect the growth of L. plantarum 14,917. Moreover, 1% and 5% GOS enhanced the anti-fungal performance of L. plantarum 14,917 in comparison to 1% glucose. GOS as the carbon source resulted in a less acidic environment in the C. albicans and S. mutans duo-species model and multispecies model where L. plantarum 14,917 was added. When GOS was utilized as the carbohydrate substrate, S. mutans and C. albicans had a significant reduction in the expression of the HWP1, ECE1, atpD, and eno genes (p < 0.05). To our knowledge, this is the first study that reported the ability of GOS to neutralize S. mutans-C. albicans high caries of medium pH and to disrupt virulence gene expression. Moreover, as a prebiotic, GOS augmented the inhibitory ability of L. plantarum against C. albicans in vitro. The current study revealed the anti-caries potential of prebiotics GOS and shed light on novel caries prevention strategies from the perspective of prebiotics and probiotics. These findings provide a rationale for future biofilm or clinical studies to elucidate the effect of GOS on modulating oral microbiota and caries control.

An α type gluco-oligosaccharide from brown algae Laminaria japonica stimulated the growth of lactic acid bacteria encoding specific ABC transport system components

Glucan is the most widely distributed glycan. Many probiotics such as lactic acid bacteria (LAB) encoded corresponding hydrolytic enzymes, which could use these glucans as energy substances. Brown alga is rich in glucan and has high edible and medicinal value, but research on its regulation to probiotics is not detailed enough. In this study, we determined a novel neutral α type gluco-oligosaccharide from the brown alga Laminaria japonica with a degree of polymerization (DP) of 2-8 and a structure that mainly consists of α-(1→4)-linked glycosidic bonds called Laminaria japonica gluco-oligosaccharide (LJGO). Fermentation in vitro and gene-phenotype correlation analyses revealed that LJGO selectively stimulated the growth of the LAB strain encoding a specific ATP-binding cassette (ABC) transport system in a GH13 gene cluster, with apparent differences among 14 tested species. Comparative genomics further revealed that this transport system is species-specific, implying a potential contribution to species evolution. Transcriptomic analysis based on LAB strains cultured on LJGO and 1H-NMR findings of LJGO residues after strain utilization showed that the GH13 gene cluster contains functional LAB genes involved in LJGO utilization. Further verification by gene knockout studies is needed to expand our findings.

Characterization, High-Density Fermentation, and the Production of a Directed Vat Set Starter of Lactobacilli Used in the Food Industry: A Review

Lactobacilli have been widely concerned for decades. Bacteria of the genus Lactobacillus have been commonly employed in fermented food to improve the appearance, smell, and taste of food or prolong its shelf-life. They comprise 261 species (by March 2020) that are highly diverse at the phenotypic, ecological, and genotypic levels. Some Lactobacilli strains have been documented to be essential probiotics, which are defined as a group of living microorganisms that are beneficial to the health of the host when ingested in sufficiency. However, the characterization, high-density fermentation, and the production of a directed vat set (DVS) starter of Lactobacilli strains used in the food industry have not been systematically reported. This paper mainly focuses on reviewing Lactobacilli as functional starter cultures in the food industry, including different molecular techniques for identification at the species and strain levels, methods for evaluating Lactobacilli properties, enhancing their performance and improving the cell density of Lactobacilli, and the production techniques of DVS starter of Lactobacilli strains. Moreover, this review further discussed the existing problems and future development prospects of Lactobacilli in the food industry. The viability and stability of Lactobacilli in the food industry and gastrointestinal environment are critical challenges at the industrial scale. The new production equipment and technology of DVS starter of Lactobacilli strains will have the potential for large-scale application, for example, developing low-temperature spray drying, freezing granulation drying, and spray freeze-drying.

Comparative transcriptome analysis for the biosynthesis of antioxidant exopolysaccharide in Streptococcus thermophilus CS6

BACKGROUND

Food grade Streptococcus thermophilus produces biological exopolysaccharides (EPSs) with great potential with respect to catering for higher health-promoting demands; however, how S. thermophilus regulates the biosynthesis of EPS is not completely understood, decelerating the application of these polymers. In our previous study, maltose, soy peptone and initial pH were three key factors of enhancing EPS yield in S. thermophilus CS6. Therefore, we aimed to investigate the regulating mechanisms of EPS biosynthesis in S. thermophilus CS6 via the method of comparative transcriptome and differential carbohydrate metabolism.

RESULTS

Soy peptone addition (58.6 g L^-1 ) and a moderate pH (6.5) contributed to a high bacterial biomass and a high EPS yield (407 mg L^-1 ). Maltose, soy peptone and initial pH greatly influenced lactose utilization in CS6. Soy peptone addition induced a high accumulation of mannose and arabinose in intracellular CS6, differential monosaccharide composition (mannose, glucose and arabinose) in EPS and high radical [2,2-diphenyl-1-picrylhydrazyl, superoxide and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] scavenging activities. Carbohydrate transportation, sugar activation and eps cluster-associated genes were differentially expressed to regulate EPS biosynthesis. Correlation analysis indicated high production of EPSs depended on high expression of lacS, galPMKUTE, pgm, gt2-5&4-1 and epsLM.

CONCLUSION

The production of antioxidant EPS in S. thermophilus CS6 depended on the regulation of galactose metabolism cluster and eps cluster. The present study recommends a new approach for enhancing EPS production by transcriptomic regulation for further food and health application of EPS. © 2022 Society of Chemical Industry.

Unraveling the mechanism of raffinose utilization in Ligilactobacillus salivarius Ren by transcriptomic analysis

In the gastrointestinal tract, some dietary carbohydrates, such as xylose, raffinose and arabinose, are able to stimulate the growth of Lactobacillus and Bifidobacterium. In this study, the growth rate of Ligilactobacillus salivarius Ren in raffinose was 0.91 ± 0.03 h-1, which was higher than that in glucose (0.83 ± 0.01 h-1). However, limited information is available on specific transporters and glycoside hydrolases responsible for raffinose uptake and catabolism in L. salivarius. Transcriptomic analysis revealed the differential expression of 236 genes (∣log2FoldChange∣ > 0.8) in response to raffinose, which were mainly associated with raffinose transport, raffinose hydrolysis, galactose metabolism and pyruvate metabolism. Notably, gene rafP encoding lactose/raffinose permease was 101.86-fold up-regulated. Two α-galactosidase gene galA1 and galA2 were 117.82-fold and 2.66-fold up-regulated, respectively. To further investigate the role of these genes in raffinose utilization, insertional inactivation was performed using the pORI28-pTRK669 system. The growth assay of these mutants in modified MRS containing 2% (w/v) raffinose indicated that RafP played an important role in raffinose transport and GalA1 was the primary enzyme involved in raffinose hydrolysis. To our knowledge, this is the first report on the molecular mechanism of raffinose utilization in L. salivarius.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03280-6.

Cellobiose inhibits the release of deoxynivalenol from transformed deoxynivalenol-3-glucoside from Lactiplantibacillus plantarum

The masked mycotoxin deoxynivalenol-3-glucoside (D3G) has been reported to be a detoxification product in plants, but can be hydrolyzed into its toxic precursor, deoxynivalenol (DON). Herein, we reported that Lactiplantibacillus plantarum (L. plantarum) NMM.1, isolated from Inner Mongolia raw milk, can efficiently transform D3G to DON in a short time. The global transcriptome microarray profiling of L. plantarum NMM.1 revealed differential expression of genes related to the phosphotransferase system (PTS) when D3G was used as the sole carbohydrate source. By adding an exogenous carbon source, we found that cellobiose efficiently inhibited the conversion of D3G into its precursor toxin by L. plantarum NMM.1. Overall, substrate depletion studies, transcriptome analysis, and carbohydrate intervention studies of L. plantarum NMM.1 suggested that cellobiose could be used to prevent the transformation of D3G into its free native DON by L. plantarum, thereby preventing harm to the human body.

Short-chain β-manno-oligosaccharides from copra meal: structural characterization, prebiotic potential and anti-glycation activity

Size-exclusion chromatography, HR-ESI-MS and FT-IR of copra meal hydrolyzed by ManB-1601 showed the presence of oligosaccharides (CM-β-MOS) having a degree of polymerisation (DP) between 2 and 4. Thermal decomposition studies of the purified CM-β-MOS (DP 2, 3 and 4) showed mass loss at high temperatures (135.8 °C to 600 °C). DP2, DP3 and DP4 CM-β-MOS were adjudged as un-substituted Manβ-4Man, Manβ-4Manβ-4Man and Manβ-4Manβ-4Manβ-4Man, respectively, using NMR (¹H and ¹³C) studies. During fermentation, purified CM-β-MOS supported the growth of Lactobacillus sp. and inhibited enteropathogens (Escherichia coli, Listeria monocytogenes and Salmonella typhi). Acetate was the predominant short-chain fatty acid produced by Lactobacillus sp. RT-PCR studies of L. plantarum WCFS1 fed with CM-β-MOS showed up-regulation (up to 6.7-fold) of the cellobiose utilization operon (pts23C and pbg6) and oligo-sucrose utilization loci (pts1BCA and agl2). Biochemical (free amino groups, carbonyl and fructosamine content), fluorescence (AGEs-specific and intrinsic) and molecular docking studies suggested the anti-glycation potential of CM-β-MOS.

Recent progress on n-butanol production by lactic acid bacteria

n-Butanol is an essential chemical intermediate produced through microbial fermentation. However, its toxicity to microbial cells has limited its production to a great extent. The anaerobe lactic acid bacteria (LAB) are the most resistant to n-butanol, so it should be the first choice for improving n-butanol production. The present article aims to review the following aspects of n-butanol production by LAB: (1) the tolerance of LAB to n-butanol, including its tolerance level and potential tolerance mechanisms; (2) genome editing tools in the n-butanol-resistant LAB; (3) methods of LAB modification for n-butanol production and the production levels after modification. This review will provide a theoretical basis for further research on n-butanol production by LAB.

The beneficial effects of polysaccharide obtained from persimmon (Diospyros kaki L.) on the proliferation of Lactobacillus and gut microbiota

The objective of this study was to investigate the effect of polysaccharide extracts from persimmon (PPE) on the proliferation of Lactobacillus and the gut microbiota of mice. Lactobacillus strains were cultured in medium containing PPE, and differential gene expression was evaluated using transcriptomics. In addition, 16S rDNA was employed to analyze the abundance and diversity of fecal colonies in mice, and the influence of PPE on the intestinal flora in mice was further examined. The results showed that Lactobacillus acidophilus NCFM and Lactobacillus acidophilus CICC 6075 could proliferate in PPE medium. Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomics (KEGG) pathway analysis indicated that glucose metabolism-related genes, such as phosphoyruvate hydratase (eno) and PTS mannose transporter subunit IIAB (manX), were up-regulated. The metabolic pathways of fructose and mannose were also significantly up-regulated. After gavage of mice with PPE, 16S rDNA sequencing of mouse feces indicated that the beneficial bacteria in the intestines proliferated and the abundance of harmful bacteria was reduced. PPE can maintain the balance of intestinal microorganisms in mice. Therefore, PPE has a significant positive effect on both Lactobacillus proliferation and gut microbiota of mice.

Microbiota-directed fibre activates both targeted and secondary metabolic shifts in the distal gut

Beneficial modulation of the gut microbiome has high-impact implications not only in humans, but also in livestock that sustain our current societal needs. In this context, we have tailored an acetylated galactoglucomannan (AcGGM) fibre to match unique enzymatic capabilities of Roseburia and Faecalibacterium species, both renowned butyrate-producing gut commensals. Here, we test the accuracy of AcGGM within the complex endogenous gut microbiome of pigs, wherein we resolve 355 metagenome-assembled genomes together with quantitative metaproteomes. In AcGGM-fed pigs, both target populations differentially express AcGGM-specific polysaccharide utilization loci, including novel, mannan-specific esterases that are critical to its deconstruction. However, AcGGM-inclusion also manifests a “butterfly effect”, whereby numerous metabolic changes and interdependent cross-feeding pathways occur in neighboring non-mannanolytic populations that produce short-chain fatty acids. Our findings show how intricate structural features and acetylation patterns of dietary fibre can be customized to specific bacterial populations, with potential to create greater modulatory effects at large.

Here, the authors tailor an acetylated galactoglucomannan (AcGGM) fibre from spruce wood to specifically enrich Roseburia and Faecalibacterium - beneficial species which have the enzymatic machinery to breakdown the fibre and generate butyrate. They subsequently perform a piglet feeding trial, metagenomics and metaproteomics, together showing that AcGGM-fed pigs exhibit not only increased Roseburia and Faecalibacterium populations with AcGGM-specific mannan-specific esterases, but also secondary metabolic pathways.

Molecular advancements on over-expression, stability and catalytic aspects of endo-β-mannanases

The hydrolysis of mannans by endo-β-mannanases continues to gather significance as exemplified by its commercial applications in food, feed, and a rekindled interest in biorefineries. The present review provides a comprehensive account of fundamental research and fascinating insights in the field of endo-β-mannanase engineering in order to improve over-expression and to decipher molecular determinants governing activity-stability during harsh conditions, substrate recognition, polysaccharide specificity, endo/exo mode of action and multi-functional activities in the modular polypeptide. In-depth analysis of the available literature has also been made on rational and directed evolution approaches, which have translated native endo-β-mannanases into superior biocatalysts for satisfying industrial requirements.

The local transcriptional regulators SacR1 and SacR2 act as repressors of fructooligosaccharides metabolism in Lactobacillus plantarum

Background

In Lactobacillus plantarum, fructooligosaccharides (FOS) metabolism is controlled by both global and local regulatory mechanisms. Although catabolite control protein A has been identified as a global regulator of FOS metabolism, the functions of local regulators remain unclear. This study aimed to elucidate the roles of two local regulators, SacR1 and SacR2, in the regulation of FOS metabolism in L. plantarum both in vitro and in vivo.

Results

The inactivation of sacR1 and sacR2 affected the growth and production of metabolites for strains grown on FOS or glucose, respectively. A reverse transcription-quantitative PCR analysis of one wild-type and two mutant strains (ΔsacR1 and ΔsacR2) of L. plantarum identified SacR1 and SacR2 as repressors of genes relevant to FOS metabolism in the absence of FOS, and these genes could be induced or derepressed by the addition of FOS. The analysis predicted four potential transcription factor binding sites (TFBSs) in the putative promoter regions of two FOS-related clusters. The binding of SacR1 and SacR2 to these TFBSs both in vitro and in vivo was verified using electrophoretic mobility shift assays and chromatin immunoprecipitation, respectively. A consensus sequence of WNNNNNAACGNNTTNNNNNW was deduced for the TFBSs of SacR1 and SacR2.

Conclusion

Our results identified SacR1 and SacR2 as local repressors for FOS metabolism in L. plantarum. The regulation is achieved by the binding of SacR1 and SacR2 to TFBSs in the promoter regions of FOS-related clusters. The results provide new insights into the complex network regulating oligosaccharide metabolism by lactic acid bacteria.