Research Articles (Microbiology)

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    Molecular insights into probiotic mechanisms of action employed against intestinal pathogenic bacteria
    (Taylor & Francis, 2020-10) van Zyl, Winschau F.; Deane, Shelly M.; Dicks, Leon M. T.
    Gastrointestinal (GI) diseases, and in particular those caused by bacterial infections, are a major cause of morbidity and mortality worldwide. Treatment is becoming increasingly difficult due to the increase in number of species that have developed resistance to antibiotics. Probiotic lactic acid bacteria (LAB) have considerable potential as alternatives to antibiotics, both in prophylactic and therapeutic applications. Several studies have documented a reduction, or prevention, of GI diseases by probiotic bacteria. Since the activities of probiotic bacteria are closely linked with conditions in the host’s GI-tract (GIT) and changes in the population of enteric microorganisms, a deeper understanding of gut-microbial interactions is required in the selection of the most suitable probiotic. This necessitates a deeper understanding of the molecular capabilities of probiotic bacteria. In this review, we explore how probiotic microorganisms interact with enteric pathogens in the GIT. The significance of probiotic colonization and persistence in the GIT is also addressed.
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    Soymilk bio-enrichment by indigenously isolated riboflavin-producing strains of Lactobacillus plantarum
    (Elsevier, 2019-11) Bhushan, Bharat; Kumkum, C. R.; Kumari, Mamta; Ahire, Jayesh J.; Dicks, Leon M. T.; Mishra, Vijendra
    Lactobacilli (n = 68) isolated from human feces and fermented milk products were screened for the production of riboflavin (vitamin B2) by culturing into riboflavin assay medium (RAM). Cell-free culture supernatants from positive isolates (BBC32A, BBC32B, BBC33 and BIF43) were transferred onto RAM agar pre-seeded with Enterococcus faecalis MTCC2729 (a riboflavin auxotroph). The enhanced growth of B2-auxotroph confirmed the bioavailability of produced vitamin. Isolate BBC32B produced the highest riboflavin (319 ± 36 μg/l), followed by BBC33 (304 ± 91 μg/l), BBC32A (276 ± 8 μg/l) and BIF43 (257 ± 91 μg/l). All four isolates contained riboflavin genes ribG, ribB, ribA and ribH. Sequencing of DNA fragments amplified from the 16S–23S rRNA intergenic spacer region and areas flanking the 23S rRNA gene grouped these isolates within the species Lactobacillus plantarum. Identifications were confirmed by sequencing 1300-bp of amplified 16S rDNA fragments. Fermentation of soymilk by single cultures of L. plantarum BBC32B, BBC33 and BIF43 yielded 49.05%, 38.97% and 35.94% riboflavin enrichment respectively, which is more than 18.75% recorded in literature for Lactobacillus fermentum MTCC8711. Maximum levels of riboflavin were obtained within 12 h of fermentation in soymilk. Lactobacillus plantarum BBC32B may be used as starter culture for developing of riboflavin-enriched soymilk.
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    Disinfectant, Soap or Probiotic Cleaning? Surface Microbiome Diversity and Biofilm Competitive Exclusion
    (MDPI [Commercial Publisher], 2020-11-04) Stone, Wendy; Tolmay, Janke; Tucker, Keira; Wolfaardt, Gideon M.
    This study extends probiotic cleaning research to a built environment. Through an eight-month cleaning trial, we compared the e ect of three cleaning products (disinfectant, plain soap, and a probiotic cleaner containing a patented Bacillus spore consortium), and tap water as the control, on the resident microbiome of three common hospital surfaces (linoleum, ceramic, and stainless steel). Pathogens, Escherichia coli and Staphylococcus aureus, were deposited and desiccated, and competitive exclusion was assessed for each microbiome. Cell survival was shown to be an incomplete tool for measuring microbial competitive exclusion. Biofilm competition offered a fuller understanding of competitive dynamics. A test for culturable cell survival showed that both plain soap and probiotic cleaner regimes established a surface microbiome that outcompeted the two pathogens. A different picture emerged when observing biofilms with a deposited and desiccated GFP-labeled pathogen, Pseudomonas aeruginosa. Competitive exclusion was again demonstrated. On surfaces cleaned with disinfectant the pathogen outcompeted the microbiomes. On surfaces cleaned with plain soap, the microbiomes outcompeted the pathogen. However, on surfaces cleaned with probiotic cleaner, despite the exponentially higher surface microbial loads, the microbiome did not completely outcompete the pathogen. Thus, the standard culturable cell test for survival on a surface confirmed the competitive advantage that is typically reported for probiotic cleaners. However, observation of competition in biofilms showed that the more diverse microbiome (according to alpha and beta indices) established on a surface cleaned with plain soap had a better competitive advantage than the monoculture established by the probiotic cleaner. Therefore, microbial diversity appears to be as critical to the competitive exclusion principle as cell numbers. The study showed that both plain soap and probiotic cleaner fostered competitive exclusion far more effectively than disinfectant. Probiotic cleaners with microbial diversity could be worth considering for hospital cleaning.
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    Seasonal and Agricultural Response of Acidobacteria Present in Two Fynbos Rhizosphere Soils
    (MDPI, 2020-07-10) Conradie, Tersia; Jacobs, Karin
    The Acidobacteria is one of the most abundant phyla in most soil types. Fynbos plants are endemic to South Africa, and these soils provide the ideal habitat for Acidobacteria, because of its low pH and oligotrophic properties. However, little is known about their distribution in the fynbos biome and the impact of cultivation of plants on Acidobacterial diversity. Therefore, the aim of this study was to determine the effect of seasonal changes and cultivation on the relative abundance and diversity of Acidobacteria associated with Aspalathus linearis (rooibos) and Cyclopia spp. (honeybush). This study was based on rhizosphere soil. A total of 32 and 31 operational taxonomic units (OTUs) were identified for honeybush and rooibos, respectively. The majority of these were classified as representatives of subdivisions 1, 2, 3, and 10. Significant differences in community compositions were observed between seasons for both honeybush and rooibos, as well as between the cultivated and uncultivated honeybush. Acidobacteria had a significantly positive correlation with pH, C, Ca2+, and P. In this study, we have shown the effect of seasonal changes, in summer and winter, and cultivation farming on the relative abundance and diversity of Acidobacteria present in the soil of rooibos and honeybush.
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    Enzymatic Hydrolysis of Softwood Derived Paper Sludge by an In Vitro Recombinant Cellulase Cocktail for the Production of Fermentable Sugars
    (2020) Malgas, Samkelo; Rose, Shaunita H; van Zyl, Willem H; Pletschke, Brett I
    Abstract: Paper sludge is an attractive biomass feedstock for bioconversion to ethanol due to its low cost and the lack of pretreatment required for its bioprocessing. This study assessed the use of a recombinant cellulase cocktail (mono-components: S. cerevisiae-derived PcBGL1B (BGL), TeCel7A (CBHI), ClCel6A (CBHII) and TrCel5A (EGII) mono-component cellulase enzymes) for the efficient saccharification of softwood-derived paper sludge to produce fermentable sugars. The paper sludge mainly contained 74.3% moisture and 89.7% (per dry mass (DM)) glucan with a crystallinity index of 91.5%. The optimal protein ratio for paper sludge hydrolysis was observed at 9.4: 30.2: 30.2: 30.2% for BGL: CBHI: CBHII: EGII. At a protein loading of 7.5 mg/g DW paper sludge, the yield from hydrolysis was approximately 80%, based on glucan, with scanning electron microscopy micrographs indicating a significant alteration in the microfibril size (length reduced from ≥ 2 mm to 93 µm) of the paper sludge. The paper sludge hydrolysis potential of the Opt CelMix (formulated cellulase cocktail) was similar to the commercial Cellic CTec2® and Celluclast® 1.5 L cellulase preparations and better than Viscozyme® L. Low enzyme loadings (15 mg/g paper sludge) of the Opt CelMix and solid loadings ranging between 1 to 10% (w/v) rendered over 80% glucan conversion. The high glucose yields attained on the paper sludge by the low enzyme loading of the Opt CelMix demonstrated the value of enzyme cocktail optimisation on specific substrates for efficient cellulose conversion to fermentable sugars.