High lactic acid and fructose production via Mn2+-mediated conversion of inulin by Lactobacillus paracasei

Isolation, antibacterial characterization, and alternating tangential flow-based preparation of viable cells of Lacticaseibacillus paracasei XLK 401: Potential application in milk preservation

It is desirable to obtain high levels of viable Lacticaseibacillus paracasei, a widely used food probiotic whose antibacterial activity and potential application in milk remain largely uninvestigated. Here, we isolated and purified the L. paracasei strain XLK 401 from food-grade blueberry ferments and found that it exhibited strong antibacterial activity against both gram-positive and gram-negative foodborne pathogens, including Staphylococcus aureus, Salmonella paratyphi B, Escherichia coli O157, and Shigella flexneri. Then, we applied alternating tangential flow (ATF) technology to produce viable L. paracasei XLK 401 cells and its cell-free supernatant (CFS). Compared with the conventional fed-batch method, 22 h of ATF-based processing markedly increased the number of viable cells of L. paracasei XLK 401 to 12.14 ± 0.13 log cfu/mL. Additionally, the CFS exhibited good thermal stability and pH tolerance, inhibiting biofilm formation in the abovementioned foodborne pathogens. According to liquid chromatography-mass spectrometry analysis, organic acids were the main antibacterial components of XLK 401 CFS, accounting for its inhibition activity. Moreover, the CFS of L. paracasei XLK 401 effectively inhibited the growth of multidrug-resistant gram-positive Staph. aureus and gram-negative E. coli O157 pathogens in milk, and caused a reduction in the pathogenic cell counts by 6 to 7 log cfu/mL compared with untreated control, thus considerably maintaining the safety of milk samples. For the first time to our knowledge, ATF-based technology was employed to obtain viable L. paracasei on a large scale, and its CFS could serve as a broad-spectrum biopreservative for potential application against foodborne pathogens in milk products.

Biofilm formation by agave epiphytic lactic acid bacteria fed with agave fructans

The aim of this work was to find out if biofilms can be made by lactic acid bacteria (LAB) isolated from agave plants using agave fructans as sole carbohydrate substrates or if it was necessary to use fructose as a breakdown product of such polymers. This is part of a research project geared to develop industrial lactic acid production from agave fructans, an abundant raw material in Mexico's agave plantations. Present results showed that nine strains of LAB isolated from Agave salmiana and belonging to genus Lacticaseibacillus and Enterococcus produced exopolysaccharides directly from agave fructans to a greater extent than with fructose. The best polysaccharide productions in planktonic cultures were Lacticaseibacillus paracasei strains DG2, DG3, DG4 and DG8. Furthermore, all nine LAB strains produced biofilms on polystyrene microplates, much better with agave fructans than with fructose. In most strains, biofilm formation was favored at pH from 6.0 to 6.5, except for strains DG7 and DG9 where pH 5.5 was optimal. Biofilm formation required between 3 and 5 days of incubation in all Lacticaseibacillus paracasei strains, whereas Enterococcus faecium required a little less of 3 days. Present results support the straight use of agave fructans to develop LAB biofilms using agave epiphytic bacteria. This finding simplifies upstream processing of agave fructans to be used for future lactic acid fermentation in LAB biofilm reactors.

Antimicrobial and Antibiofilm Effect of Inulin-Type Fructans, Used in Synbiotic Combination with Lactobacillus spp. Against Candida albicans

There is great interest in the search for new alternatives to antimicrobial drugs, and the use of prebiotics and probiotics is a promising approach to this problem. This study aimed to assess the effect of inulin-type fructans, used in synbiotic combinations with Lactobacillus paracasei or Lactobacillus plantarum, on the production of short-chain fatty acids and antimicrobial activity against Candida albicans. The inhibition assay using the L. paracasei and L. plantarum supernatants resulting from the metabolization of inulin-type fructans displayed growth inhibition and antibiofilm formation against C. albicans. Inhibition occurred at concentrations of 12.5, 25, and 50% of the L. paracasei supernatant and at a concentration of 50% of the L. plantarum supernatant. The analysis of short-chain fatty acids by gas chromatography showed that lactic acid was the dominating produced metabolite. However, acetic, propionic, and butyric acids were also detected in supernatants from both probiotics. Therefore, the synbiotic formulation of L. paracasei or L. plantarum in the presence of inulin-type fructans constitutes with anticandidal effect is a possible option to produce antifungal drugs or antimicrobial compounds.

Butanol Tolerance of Lactiplantibacillus plantarum: A Transcriptome Study

Biobutanol is a promising alternative fuel with impaired microbial production thanks to its toxicity. Lactiplantibacillus plantarum (L. plantarum) is among the few bacterial species that can naturally tolerate 3% (v/v) butanol. This study aims to identify the genetic factors involved in the butanol stress response of L. plantarum by comparing the differential gene expression in two strains with very different butanol tolerance: the highly resistant Ym1, and the relatively sensitive 8-1. During butanol stress, a total of 319 differentially expressed genes (DEGs) were found in Ym1, and 516 in 8-1. Fifty genes were upregulated and 54 were downregulated in both strains, revealing the common species-specific effects of butanol stress: upregulation of multidrug efflux transporters (SMR, MSF), toxin-antitoxin system, transcriptional regulators (TetR/AcrR, Crp/Fnr, and DeoR/GlpR), Hsp20, and genes involved in polysaccharide biosynthesis. Strong inhibition of the pyrimidine biosynthesis occurred in both strains. However, the strains differed greatly in DEGs responsible for the membrane transport, tryptophan synthesis, glycerol metabolism, tRNAs, and some important transcriptional regulators (Spx, LacI). Uniquely upregulated in the butanol-resistant strain Ym1 were the genes encoding GntR, GroEL, GroES, and foldase PrsA. The phosphoenolpyruvate flux and the phosphotransferase system (PTS) also appear to be major factors in butanol tolerance.

Carboxymethyl chitosan crosslinked ꞵ-cyclodextrin containing hydrogen bonded NC QDs nanocomposites to design fluorescence probes for manganese ion (II) sensing

The direct determination Mn²⁺ using carboxymethyl chitosan crosslinked with cyclodextrin containing hydrogen-bonded NC QDs (NC QD/CCSCD nanocomposites). The probable mechanism of the NC QD/CCSCD nanocomposites' fluorescence was quenched by Mn²⁺ could be interpreted as acyclic crown ether chelation. Mn²⁺ induced the NC QD/CCSCD clusters assembly to form large aggregates, which resulted in aggregation-caused quenching. The linear detection (I = 479.93-15.94C (R² = 0.9954)) can be established at Mn²⁺ concentrations from 0 to 21.11 × 10^-6 mol/L. Common metal ions, except iron and magnesium, showed minimal effect on detection. It could satisfy the standard range of Mn²⁺ in actual water samples. The method which using chelating assembly mechanism to build a novel sensor would provide a new model for the application of polymer materials in this field, but the precise assembly of polymer is an unsolved challenge.

Metagenomic reconstructions of gut microbial metabolism in weanling pigs

BACKGROUND

The piglets' transition from milk to solid feed induces a succession of bacterial communities, enhancing the hosts' ability to harvest energy from dietary carbohydrates. To reconstruct microbial carbohydrate metabolism in weanling pigs, this study combined 16S rRNA gene sequencing (n = 191) and shotgun metagenomics (n = 72).

RESULTS

Time and wheat content in feed explained most of the variation of the microbiota as assessed by 16S rRNA gene sequencing in weanling pigs. De novo metagenomic binning reconstructed 360 high-quality genomes that represented 11 prokaryotic and 1 archaeal phylum. Analysis of carbohydrate metabolism in these genomes revealed that starch fermentation is carried out by a consortium of Firmicutes expressing extracellular α-(1 → 4)-glucan branching enzyme (GH13) and Bacteroidetes expressing periplasmic neopullulanase (GH13) and α-glucosidase (GH97). Fructans were degraded by extracellular GH32 enzymes from Bacteriodetes and Lactobacillus. Lactose fermentation by β-galactosidases (GH2 and GH42) was identified in Firmicutes. In conclusion, the assembly of 360 high-quality genomes as the first metagenomic reference for swine intestinal microbiota allowed identification of key microbial contributors to degradation of starch, fructans, and lactose.

CONCLUSIONS

Microbial consortia that are responsible for degradation of these glycans differ substantially from the microbial consortia that degrade the same glycans in humans. Our study thus enables improvement of feeding models with higher feed efficiency and better pathogen control for weanling pigs.

Production of lactic acid from thermal pretreated food waste through the fermentation of waste activated sludge: Effects of substrate and thermal pretreatment temperature

Valorization of organic-rich waste stream to lactic acid by the mixed microbial consortium has attracted tremendous research interests in recent years. In this study, thermal pretreatment was involved in co-fermentation of food waste (FW) and waste activated sludge (WAS) to enhance lactic acid production. First, sole FW was observed as the most suitable substrate employing thermal pretreatment for the generation of lactic acid. The fermentation time for reaching the maximal plateau was significantly shortened at a corresponding thermal pretreatment temperature. The mechanism study found that the enhancement of lactic acid yield was in accordance with the acceleration of solubilization and hydrolysis. Furthermore, the physicochemical characteristics of fermentative substrate and surface morphology of the fermentation mixture varied with the pretreatment temperatures. Further investigations of microbial community structure also revealed that the proportions of key microorganisms such as Bacillus and Lactobacillus were changed by the thermal pretreatment.