Organic substrates and biochar are important in controlling arsenic release from sediments and soils; however, little is known about their impact on arsenic-reducing bacteria and genes during arsenic transformation in flooded paddy soils. In this study, microcosm experiments were established to profile transcriptional activity of As(V)-respiring gene (arrA) and arsenic resistance gene (arsC) as well as the associated bacteria regulated by lactate and/or biochar in anaerobic arsenic-contaminated paddy soils. Chemical analyses revealed that lactate as the organic substrate stimulated microbial reduction of As(V) and Fe(III), which was simultaneously promoted by lactate+biochar, due to biochar's electron shuttle function that facilitates electron transfer from bacteria to As(V)/Fe(III). Sequencing and phylogenetic analyses demonstrated that both arrA closely associated with Geobacter (>60%, number of identical sequences/number of the total sequences) and arsC related to Enterobacteriaceae (>99%) were selected by lactate and lactate+biochar. Compared with the lactate microcosms, transcriptions of the bacterial 16S rRNA gene, Geobacter spp., and Geobacter arrA and arsC genes were increased in the lactate+biochar microcosms, where transcript abundances of Geobacter and Geobacter arrA closely tracked with dissolved As(V) concentrations. Our findings indicated that lactate and biochar in flooded paddy soils can stimulate the active As(V)-respiring bacteria Geobacter species for arsenic reduction and release, which probably increases arsenic bioavailability to rice plants.
Organic
matter is important for controlling arsenic reduction and
release under anoxic conditions. Humic substances (HS) represent an
important fraction of natural organic matter, yet the manner in which
HS affect arsenic transformation in flooded paddy soil has not been
thoroughly elucidated. In this study, anaerobic microcosms were established
with arsenic-contaminated paddy soil and amended with three extracted
humic fractions (fulvic acid, FA; humic acid, HA; and humin, HM).
The HS substantially enhanced the extent of arsenic reduction and
release in the order FA > HA > HM. It was confirmed that microbially
reduced HS acted as an electron shuttle to promote arsenate reduction.
HS, particularly FA, provided labile carbon to stimulate microbial
activity and increase the relative abundances of Azoarcus, Anaeromyxobacter, and Pseudomonas, all of which may be involved in the
reduction of HS, Fe(III), and arsenate. HS also increased the abundance
of transcripts for an arsenate-respiring gene (arrA) and overall transcription in arsenate-respiring Geobacter spp. The increase in both abundances lagged
behind the increases in dissolved arsenate levels. These results help
to elucidate the pathways of arsenic reduction and release in the
presence of HS in flooded paddy soil.
Intestinal microbiota plays an important role in human health. The aim of this paper is to determine the impact of the phenolics and carbohydrate in buckwheat honey on human intestinal microbiota. We investigated the phenolics and carbohydrate compositions of eight buckwheat honey samples using high-performance liquid chromatography and ion chromatography. The human intestinal microbes were cultured in a medium supplemented with eight buckwheat honey samples or the same concentration of fructooligosaccharides. The bacterial 16S rDNA V4 region sequence of DNA extraction was determined by the Illumina MiSeq platform. 12 phenolics and 4 oligosaccharides were identified in almost all buckwheat honey samples, namely, protocatechuic acid, 4-hydroxy benzoic acid, vanillin, gallic acid, p-coumaric acid, benzoic acid, isoferulic acid, methyl syringate, trans,trans-abscisic acid, cis,trans-abscisic acid, ferulic acid, 4-hydroxybenzaldehyde, kestose, isomaltose, isomaltotriose, and panose. Most notably, this is the first study to reveal the presence of 4-hydroxybenzaldehyde in buckwheat honey. 4-Hydroxybenzaldehyde seems to be a land marker of buckwheat honey. Our results indicate that buckwheat honey can provide health benefits to the human gut by selectively supporting the growth of indigenous Bifidobacteria and restraining the pathogenic bacterium in the gut tract. We infer that buckwheat honey may be a type of natural intestinal-health products.
Honey
fraud has an extensive global magnitude and impacts both
honey price and beekeeper viability. This study aimed at investigating
the characteristic phytochemicals of rape, acacia, and linden honey
to verify honey authenticity. We discovered methyl syringate, phaseic
acid, and lindenin (4-(2-hydroxypropan-2-yl) cyclohexa-1,3-diene-1-carboxylic
acid) as particular or unique phytochemicals of rape, acacia, and
linden honey. Methyl syringate and lindenin were the most abundant
components in rape and linden honey; moreover, their average contents
reached up to 10.44 and 21.25 mg/kg, respectively. The average content
of phaseic acid was 0.63 mg/kg in acacia honey. To our knowledge,
the presence of phaseic acid in honey is a novel finding. Furthermore,
we established the HPLC fingerprints of three monofloral honeys. We
offered assessment criteria and combined characteristic components
with standard fingerprints to evaluate the authenticity of commercial
rape, acacia, and linden honeys. For uncertain commercial honey samples,
genuine pure honeys constituted nearly 70%. We differentiate the adulteration
of acacia and linden honeys with low-price rape honey. Our results
reveal that 10% of commercial honeys were pure syrups. Overall, we
seem to propose a novel and reliable solution to assess the authenticity
of monofloral honey.
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