Biology subjects

Duncan, S. H.

Publications and source records attributed to Duncan, S. H..

4 recordsLinked to original sources

bioRxiv2023

Simulated digestion, uptake and colonic fermentation of Gorse (Ulex europeaus) suggests safe use as a source of protein concentrates and potential bioactives.

BackgroundInvasive plants such as Gorse (Ulex europeaus) may serve as a potentially sustainable source of edible proteins and bioactives through the production of leaf protein concentrates (GLPC). The digestion, uptake and safety of phytochemicals from GLPC and the protein depleted but bioactive rich fraction (PDF) from Gorse was studied using an in vitro simulated digestion model. ResultsBoth the Gorse fractions and their digesta maintained the viability of cultured (Caco-2) intestinal cells above the 80% threshold, suggesting a lack of overt toxicity. In the digestion model, most of the plant metabolites in the digesta were largely confined to the apical fraction of the Caco-2 monolayer (representing the lumen) and were subsequently expected to be delivered to the colon. Food matrix had a significant but marginal effect on the permeability of metabolites across the Caco-2 monolayer. Lastly, in vitro intestinal microbial action appeared to produce beneficial compounds such as enterolactones, and equol. ConclusionThe Gorse fractions lack general overt toxicity to Caco-2 cells. GLPC and PDF provide metabolic substrates for the colonic microbes to produce secondary compounds that are associated with positive health outcomes.

biochemistry↗

bioRxiv2023

Gorse (Ulex europeaus) wastes with 5,6-dimethyl benzimidazole supplementation can support growth of vitamin B12 producing commensal gut microbes

Many commensal gut microbes are recognized for their potential to synthesize vitamin B12, offering a promising avenue to address deficiencies through probiotic supplementation. While bioinformatics tools aid in predicting B12 biosynthetic potential, empirical validation remains crucial to confirm production, identify cobalamin vitamers, and establish biosynthetic yields. This study investigates vitamin B12 production in three human colonic bacterial species: Anaerobu-tyricum hallii DSM 3353, Roseburia faecis DSM 16840, and Anaerostipes caccae DSM 14662, along with Propionibacterium freudenreichii DSM 4902 as a positive control. These strains were selected for their potential use as probiotics, based on speculated B12 production from prior bioinformatic analyses. Cultures were grown in M2GSC, chemically defined media (CDM), and Gorse extract medium (GEM). The composition of GEM was similar to CDM, expect that the carbon and nitrogen source was replaced with protein-depleted liquid wastes obtained after subjecting Gorse to a leaf protein extraction process. B12 yields were quantified using liquid chromatography with tandem mass spectrophotometry. The results suggest that the three butyrate-producing strains could indeed produce B12, although the yields were notably low, and with no B12 being detected in the extracellular media. Next, GEM outperformed the conventional M2GSC growth medium in enhancing B12 production. The positive control, P. freudenreichii DSM 4902 produced B12 at concentrations ranging from 7 ng{middle dot}mL-1 to 12 ng{middle dot}mL-1. Univariate-scaled Principal Component Analysis of data from previous publications investigating B12 production in P. freudenreichii revealed that B12 yields diminished when the carbon source concentration was[≤] 30 g{middle dot}L-1. In conclusion, the protein-depleted wastes from the leaf protein extraction process from Gorse can be valorised as a viable substrate for culturing B12-producing colonic gut microbes. Furthermore, this is the first report attesting to the ability of A. hallii, R. faecis, and A. caccae to produce B12. However, these microbes seem unsuitable for industrial applications owing to low B12 yields.

microbiology↗

bioRxiv2021

Human gut bifidobacteria inhibit the growth of the opportunistic fungal pathogen Candida albicans

The human gut microbiota protects the host from invading pathogens and the overgrowth of indigenous opportunistic species via mechanisms such as competition for nutrients and by production of antimicrobial compounds. Here, we investigated the antagonist activity of human gut bacteria towards Candida albicans, an opportunistic fungal pathogen that can cause severe infections and mortality in susceptible patients. Co-culture batch incubations of C. albicans in the presence of faecal microbiota from six different healthy individuals revealed varying levels of inhibitory activity against C. albicans. 16S rRNA gene sequence profiling of these faecal co-culture bacterial communities showed that the Bifidobacteriaceae family, and Bifidobacterium adolescentis in particular, were most correlated with antagonistic activity against C. albicans. Follow up mechanistic studies confirmed that culture supernatants of Bifidobacterium species, particularly B. adolescentis, inhibited C. albicans in vitro under both aerobic and anaerobic conditions. Production of the fermentation acids acetate and lactate, together with the concomitant decrease in pH, were strong drivers of the inhibitory activity. Bifidobacteria may therefore represent attractive targets for the development of probiotics and prebiotic interventions tailored to enhance inhibitory activity against C. albicans in vivo.

microbiology↗

bioRxiv2021

Distribution, organization and expression of genes concerned with anaerobic lactate-utilization in human intestinal bacteria

Lactate accumulation in the human gut is linked to a range of deleterious health impacts. However, lactate is consumed and converted to the beneficial short chain fatty acids butyrate and propionate by indigenous lactate-utilizing bacteria. To better understand the underlying genetic basis for lactate utilization, transcriptomic analysis was performed for two prominent lactate-utilizing species from the human gut, Anaerobutyricum soehngenii and Coprococcus catus, during growth on lactate, hexose sugar, or hexose plus lactate. In A. soehngenii L2-7, six genes of the lct cluster including NAD-independent D-lactate dehydrogenase (i-LDH) were co-ordinately upregulated during growth on equimolar D and L-lactate (DL-lactate). Upregulated genes included an acyl-CoA dehydrogenase related to butyryl-CoA dehydrogenase, which may play a role in transferring reducing equivalents between reduction of crotonyl-CoA and oxidation of lactate. Genes upregulated in C. catus GD/7 included a six-gene cluster (lap) encoding propionyl CoA-transferase, a putative lactoyl-CoA epimerase, lactoyl-CoA dehydratase and lactate permease, and two unlinked acyl-CoA dehydrogenase genes that are candidates for acryloyl-CoA reductase. An i-LDH homolog in C. catus is encoded by a separate, partial lct, gene cluster, but not upregulated on lactate. While C. catus converts three mols of DL-lactate via the acrylate pathway to two mols propionate and one mol acetate, some of the acetate can be re-used with additional lactate to produce butyrate. A key regulatory difference is that while glucose partially repressed lct cluster expression in A. soehngenii, there was no repression of lactate utilization genes by fructose in the non-glucose utilizer C. catus. This implies that bacteria such as C. catus might be more important in curtailing lactate accumulation in the gut. Impact statementLactate can be produced as a fermentation by-product by many gut bacteria but has the potential to perturb intestinal microbial communities by lowering luminal pH, and its accumulation has been linked to a range of deleterious health outcomes. Fortunately, in healthy individuals, lactate tends not to accumulate as it is consumed by cross-feeding lactate-utilizing bacteria, which can convert it into the beneficial short chain fatty acids butyrate and propionate. Lactate-utilizing gut bacteria are therefore promising candidates for potential development as novel probiotics. However, lactate-utilizers are taxonomically diverse, and the genes that underpin utilization of lactate by these specialized gut bacteria are not fully understood. In this study we used transcriptomics to compare gene expression profiles of Anaerobutyricum soehngenii and Coprococcus catus, two prominent lactate-utilizing species in the human gut, during growth on lactate alone, sugar alone, or sugar plus lactate. The results revealed strong upregulation of key, but distinct, gene clusters that appear to be responsible for lactate utilization by these, and other, gut bacterial species. Our results therefore increase mechanistic understanding of different lactate utilization pathways used by gut bacteria, which may help to inform selection of optimal lactate-utilizing species for development as novel therapeutics against colonic microbiota perturbations. Data summaryNovel draft genomes generated for this study have been made available from GenBank (https://www.ncbi.nlm.nih.gov/bioproject/) under BioProject number PRJNA701799. RNA-seq data have been deposited in the ArrayExpress database at EMBL-EBI (www.ebi.ac.uk/arrayexpress) under accession number E-MTAB-10136. Further details of additional existing genomic data that were analyzed in this project are given in Table 1 and Table S2. O_TBL View this table: org.highwire.dtl.DTLVardef@13fd07borg.highwire.dtl.DTLVardef@90796dorg.highwire.dtl.DTLVardef@1140a60org.highwire.dtl.DTLVardef@b53597org.highwire.dtl.DTLVardef@d16268_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1.C_FLOATNO O_TABLECAPTIONNew and existing strains used for in vitro cultivation studies in this work, and their corresponding genomes. "N/A" indicates no genome available for this strain, which was used for in vitro work only. The full list of strains used for genomic-based analyses is shown in Table S2. C_TABLECAPTION C_TBL

microbiology↗