Evaluation of prokaryotic diversity by restrictase digestion of 16S rDNA directly amplified from hypersaline environments

Digestion profile, antioxidant, and antidiabetic capacity of Morchella esculenta exopolysaccharide: in vitro, in vivo and microbiota analysis

BACKGROUND

Novel functional polysaccharides from fungi are important nutraceuticals. An exopolysaccharide, Morchella esculenta exopolysaccharide (MEP 2), was extracted and purified from the fermentation liquor of M. esculenta. The aim of this study was to investigate its digestion profile, antioxidant capacity, and effect on the microbiota composition in diabetic mice.

RESULTS

The study found that MEP 2 was stable during in vitro saliva digestion but was partially degraded during gastric digestion. The digest enzymes exerted a negligible effect on the chemical structure of MEP 2. Molecular weight and atomic force microscope (AFM) images suggest that both smaller chains and larger aggregations were produced. Scanning electron microscope (SEM) images reveal that the surface morphology was much altered after intestinal digestion. After digestion, the antioxidant ability increased as revealed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. Both MEP 2 and its digested components showed strong α-amylase and moderate α-glucosidase inhibition activity, leading us to further investigate its ability to modulate the diabetic symptoms. The MEP 2 treatment ameliorated the inflammatory cell infiltration and increased the size of pancreas inlets. Serum concentration of HbA1c was significantly reduced. Blood glucose level during the oral glucose tolerance test (OGTT) was also slightly lower. The MEP 2 increased the diversity of the gut microbiota and modulated the abundance of several important bacteria including Alcaligenaceae, Caulobacteraceae, Prevotella, Brevundimonas, Demequina, and several Lachnospiraceae species.

CONCLUSION

It was found that MEP 2 was partially degraded during in vitro digestion. Its potential antidiabetic bioactivity may be associated with its α-amylase inhibition and gut microbiome modulation ability. © 2023 Society of Chemical Industry.

Antimicrobial Emulsifier-Glycerol Monolaurate Induces Metabolic Syndrome, Gut Microbiota Dysbiosis, and Systemic Low-Grade Inflammation in Low-Fat Diet Fed Mice

SCOPE

Glycerol monolaurate (GML) is widely consumed worldwide in the food industry and is considered safe, but for chronic diseases, supporting scientific data remain sparse. This study investigates whether dietary GML induces metabolic syndrome, gut microbiota dysbiosis, and systemic low-grade inflammation.

METHODS AND RESULTS

GML-induced occurrence of metabolic syndrome, gut microbiota alterations, and systemic low-grade inflammation are investigated. The results demonstrate that GML induced metabolic syndrome by significantly increasing the body weight, weight gain, food intake, body fat, fat droplet size and percentage of epididymal fat, serum triglycerides (TG), LDL, and atherogenic index, and decreasing the body muscle ratio, liver weight, and HDL, compared to the control (CON) group. Meanwhile, GML significantly changed the β-diversity and composition of gut microbiota and upregulated the circulating levels of serum LPS, IL-1β, IL-6, and TNF-α. Importantly, GML significantly decreased Akkermansia muciniphila and Lupinus luteus, and increased Bacteroides acidifaciens, Escherichia coli and the microbial DNA abundance of the ten predicated metabolism pathways involved in carbohydrate, amino acid, and lipid metabolism.

CONCLUSION

Our results indicate that relatively low-dose GML consumption promotes metabolic syndrome, gut microbiota dysbiosis, and systemic low-grade inflammation, thereby calling for a reassessment of GML usage.

Kalkipyrone B, a marine cyanobacterial γ-pyrone possessing cytotoxic and anti-fungal activities

Bioassay-guided fractionation of two marine cyanobacterial extracts using the H-460 human lung cancer cell line and the OVC-5 human ovarian cancer cell line led to the isolation of three related α-methoxy-β, β'-dimethyl-γ-pyrones each containing a modified alkyl chain, one of which was identified as the previously reported kalkipyrone and designated kalkipyrone A. The second compound was an analog designated kalkipyrone B. The third was identified as the recently reported yoshinone A, also isolated from a marine cyanobacterium. Kalkipyrone A and B were obtained from a field-collection of the cyanobacterium Leptolyngbya sp. from Fagasa Bay, American Samoa, while yoshinone A was isolated from a field-collection of cyanobacteria (cf. Schizothrix sp.) from Panama. One-dimensional and two-dimensional NMR experiments were used to determine the overall structures and relative configurations of the kalkipyrones, and the absolute configuration of kalkipyrone B was determined by (1)H NMR analysis of diastereomeric Mosher's esters. Kalkipyrone A showed good cytotoxicity to H-460 human lung cancer cells (EC50=0.9μM), while kalkipyrone B and yoshinone A were less active (EC50=9.0μM and >10μM, respectively). Both kalkipyrone A and B showed moderate toxicity to Saccharomyces cerevisiae ABC16-Monster strain (IC50=14.6 and 13.4μM, respectively), whereas yoshinone A was of low toxicity to this yeast strain (IC50=63.8μM).

Intraspecific Variation in Microbial Symbiont Communities of the Sun Sponge, Hymeniacidon heliophila, from Intertidal and Subtidal Habitats

Sponges host diverse and complex communities of microbial symbionts that display a high degree of host specificity. The microbiomes of conspecific sponges are relatively constant, even across distant locations, yet few studies have directly examined the influence of abiotic factors on intraspecific variation in sponge microbial community structure. The contrast between intertidal and subtidal environments is an ideal system to assess the effect of environmental variation on sponge-microbe symbioses, producing two drastically different environments on a small spatial scale. Here, we characterized the microbial communities of individual intertidal and subtidal Hymeniacidon heliophila sponges, ambient seawater, and sediment from a North Carolina oyster reef habitat by partial (Illumina sequencing) and nearly full-length (clone libraries) 16S rRNA gene sequence analyses. Clone library sequences were compared to H. heliophila symbiont communities from the Gulf of Mexico and Brazil, revealing strong host specificity of dominant symbiont taxa across expansive geographic distances. Sediment and seawater samples yielded clearly distinct microbial communities from those found in H. heliophila. Despite the close proximity of the sponges sampled, significant differences between subtidal and intertidal sponges in the diversity, structure, and composition of their microbial communities were detected. Differences were driven by changes in the relative abundance of a few dominant microbial symbiont taxa, as well as the presence or absence of numerous rare microbial taxa. These findings suggest that extreme abiotic fluctuations, such as periodic air exposure in intertidal habitats, can drive intraspecific differences in complex host-microbe symbioses.

Survival of extremely and moderately halophilic isolates of Tunisian solar salterns after UV-B or oxidative stress

Adaptation to a solar saltern environment requires mechanisms providing tolerance not only to salinity but also to UV radiation (UVR) and to reactive oxygen species (ROS). We cultivated prokaryote halophiles from two different salinity ponds: the concentrator M1 pond (240 g·L(-1) NaCl) and the crystallizer TS pond (380 g·L(-1) NaCl). We then estimated UV-B and hydrogen peroxide resistance according to the optimal salt concentration for growth of the isolates. We observed a higher biodiversity of bacterial isolates in M1 than in TS. All strains isolated from TS appeared to be extremely halophilic Archaea from the genus Halorubrum. Culturable strains isolated from M1 included extremely halophilic Archaea (genera Haloferax, Halobacterium, Haloterrigena, and Halorubrum) and moderately halophilic Bacteria (genera Halovibrio and Salicola). We also found that archaeal strains were more resistant than bacterial strains to exposure to ROS and UV-B. All organisms tested were more resistant to UV-B exposure at the optimum NaCl concentration for their growth, which is not always the case for H(2)O(2). Finally, if these results are extended to other prokaryotes present in a solar saltern, we could speculate that UVR has greater impact than ROS on the control of prokaryote biodiversity in a solar saltern.

Evaluations of different hypervariable regions of archaeal 16S rRNA genes in profiling of methanogens by Archaea-specific PCR and denaturing gradient gel electrophoresis

Different hypervariable (V) regions of the archaeal 16S rRNA gene (rrs) were compared systematically to establish a preferred V region(s) for use in Archaea-specific PCR-denaturing gradient gel electrophoresis (DGGE). The PCR products of the V3 region produced the most informative DGGE profiles and permitted identification of common methanogens from rumen samples from sheep. This study also showed that different methanogens might be detected when different V regions are targeted by PCR-DGGE. Dietary fat appeared to transiently stimulate Methanosphaera stadtmanae but inhibit Methanobrevibacter sp. strain AbM4 in rumen samples.

Microbial diversity in Maras salterns, a hypersaline environment in the Peruvian Andes

Maras salterns are located 3,380 m above sea level in the Peruvian Andes. These salterns consist of more than 3,000 little ponds which are not interconnected and act as crystallizers where salt precipitates. These ponds are fed by hypersaline spring water rich in sodium and chloride. The microbiota inhabiting these salterns was examined by fluorescence in situ hybridization (FISH), 16S rRNA gene clone library analysis, and cultivation techniques. The total counts per milliliter in the ponds were around 2 x 10(6) to 3 x 10(6) cells/ml, while the spring water contained less than 100 cells/ml and did not yield any detectable FISH signal. The microbiota inhabiting the ponds was dominated (80 to 86% of the total counts) by Archaea, while Bacteria accounted for 10 to 13% of the 4',6'-diamidino-2-phenylindole (DAPI) counts. A total of 239 16S rRNA gene clones were analyzed (132 Archaea clones and 107 Bacteria clones). According to the clone libraries, the archaeal assemblage was dominated by microorganisms related to the cosmopolitan square archaeon "Haloquadra walsbyi," although a substantial number of the sequences in the libraries (31% of the 16S rRNA gene archaeal clones) were related to Halobacterium sp., which is not normally found in clone libraries from solar salterns. All the bacterial clones were closely related to each other and to the gamma-proteobacterium "Pseudomonas halophila" DSM 3050. FISH analysis with a probe specific for this bacterial assemblage revealed that it accounted for 69 to 76% of the total bacterial counts detected with a Bacteria-specific probe. When pond water was used to inoculate solid media containing 25% total salts, both extremely halophilic Archaea and Bacteria were isolated. Archaeal isolates were not related to the isolates in clone libraries, although several bacterial isolates were very closely related to the "P. halophila" cluster found in the libraries. As observed for other hypersaline environments, extremely halophilic bacteria that had ecological relevance seemed to be easier to culture than their archaeal counterparts.

Population dynamics within a microbial consortium during growth on diesel fuel in saline environments

The diversity and dynamics of a bacterial community extracted from an exploited oil field with high natural soil salinity near Comodoro Rivadavia in Patagonia (Argentina) were investigated. Community shifts during long-term incubation with diesel fuel at four salinities between 0 and 20% NaCl were monitored by single-strand conformation polymorphism community fingerprinting of the PCR-amplified V4-V5 region of the 16S rRNA genes. Information obtained by this qualitative approach was extended by flow cytometric analysis to follow quantitatively the dynamics of community structures at different salinities. Dominant and newly developing clusters of individuals visualized via their DNA patterns versus cell sizes were used to identify the subcommunities primarily involved in the degradation process. To determine the most active species, subcommunities were separated physically by high-resolution cell sorting and subsequent phylogenetic identification by 16S rRNA gene sequencing. Reduced salinity favored the dominance of Sphingomonas spp., whereas at elevated salinities, Ralstonia spp. and a number of halophilic genera, including Halomonas, Dietzia, and Alcanivorax, were identified. The combination of cytometric sorting with molecular characterization allowed us to monitor community adaptation and to identify active and proliferating subcommunities.