Depletion of reactive oxygen species induced by beetroot (Beta vulgaris) extract leads to apoptosis-like death in Cronobacter sakazakii.

This research aimed to disclose the antibacterial activity of beetroot extract (Beta vulgaris) against Cronobacter sakazakii and its possible mechanisms. We evaluated its antibacterial activity by measuring the minimum inhibitory concentration (MIC) and time-kill kinetics. We also evaluated the intracellular ATP levels, bacterial apoptosis-like death (ALD), and reactive oxygen species (ROS) levels to reveal the possible antibacterial mechanisms. Our results showed that the MIC of beetroot extract against C. sakazakii was 25 mg/mL and C. sakazakii (approximately 8 log cfu/mL) was completely inhibited after treatment with 2 MIC of beetroot extract for 3 h. Beetroot extract reduced intracellular ATP levels and facilitated characteristics of ALD in C. sakazakii, such as membrane depolarization, increased intracellular Ca2+ levels, phosphatidylserine externalization, caspase-like protein activation, and DNA fragmentation. Additionally, and different from most bacterial ALD caused by the accumulation of ROS, beetroot extract reduced the intracellular ROS levels in C. sakazakii. Our experimental data provide a rationale for further research of bacterial ALD and demonstrate that beetroot extract can inhibit C. sakazakii in food processing environments.

Physicochemical and transcriptomic responses of Lactobacillus brevis JLD715 to sodium selenite.

BACKGROUND: Elemental selenium, as a new type of selenium supplement, can be prepared by microorganisms reducing inorganic selenium. In this study, Lactobacillus brevis JLD715 was incubated in broth containing different concentrations of sodium selenite (Na2 SeO3 ). RESULTS: The results showed that the bacterial biomass of L. brevis JLD715 decreased due to the inhibition of Na2 SeO3 . The cell membrane of L. brevis JLD715 treated with Na2 SeO3 was damaged, as evidenced by the reduction of intracellular ATP concentration, depolarization of cell membrane, reduction of intracellular pH and impairment of membrane integrity. In addition, we investigated the metabolism mechanism of Na2 SeO3 by L. brevis JLD715 based on transcriptome sequencing. A total of 461 genes were significantly differentially expressed under Na2 SeO3 treatment, of which 231 genes were up-regulated and 230 genes were down-regulated. These genes were involved in pathways such as pyruvate metabolism, fatty acid biosynthesis, selenocompound metabolism and nucleotide-binding oligomerization domain-like (NOD-like) receptor signaling. Meanwhile, the genes related to sulfhydryl oxidoreductase, electron carrier proteins and transmembrane transport proteins synthesis were significantly up-regulated. CONCLUSION: To sum up, the findings of this research will contribute to providing support for the application of L. brevis JLD715 in selenium-enriched functional foods. © 2021 Society of Chemical Industry.

Determination of the transfer of lead and chromium from feed to raw milk in Holstein cows.

In this study, we aimed to determinate the transfer of lead (Pb) and chromium (Cr) from feed to raw milk in Holstein cows. Solutions of lead acetate and chromium (III) nicotinate were added together at different levels to individual portions of feed on a daily basis. Lead administration for the low-, middle- and high-dosage groups was controlled as 0.9, 1.8 and 3.6 g/day for 30, 30 and 25 days, while chromium was feed at 0.47, 1.5 and 4.7 g/d for 40, 40, and 40 days, respectively. A sensitive graphite furnace atomic absorption spectrometry (GFAAS) method was developed and optimised with a respective limit of detection of lead and chromium found to be 1 and 5 µg kg-1 raw milk. The optical wavelengths for detection of lead and chromium were 283.31 nm and 357.87 nm respectively. The results showed that the highest concentrations of lead in raw milk for the low-, middle- and high-dosage groups were 0.083 ± 0.021, 0.215 ± 0.064 and 0.232 ± 0.035 mg kg-1, which displayed a positive correlation with dosage levels. In addition, a high dosage level accompanied a greater rate of loss of lead contents after dosing withdrawal. However, chromium concentrations maintained a relatively stable range around 0.1 mg kg-1 raw milk for all dosing groups and showed little transfer from feed to raw milk through the whole experiment.

Transcriptomic response to GABA-producing Lactobacillus plantarum CGMCC 1.2437T induced by L-MSG.

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter found in the central nervous system of mammals. A range of bacterial species can synthesize GABA, including Lactobacillus plantarum of which L-monosodium glutamate (L-MSG) is an inducer of its production. In order to synthesize GABA in high concentrations, L-MSG was utilized as the single inducing factor, a chemically defined medium (CDM) was used as the fermentation substrate, with L. plantarum CGMCC 1.2437T cultured in medium supplemented with or without L-MSG. High-throughput transcriptome sequencing was used to explore the differential genes expression of bacterial cells at 36 h of fermentation, where the GABA concentration of CDM with L-MSG reached the peak value and was 7.7 times higher than that of medium without L-MSG at the same timepoint. A total of 87 genes showed significant differential expression induced by L-MSG: of these, 69 were up-regulated genes and 18 were down-regulated. The up-regulated genes were assigned to biological processes and molecular function, while the down-regulated genes covered biological process, cellular process and molecular function. Interrogation of results using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, indicated carbohydrate metabolism, fatty acid synthesis and amino acid metabolism were closely associated with GABA synthesis induced by L-MSG. This study provides insights into L. plantarum-mediated GABA fermentation at the molecular level and will provide a new approach for further studies related to GABA production by the other Lactic acid bacteria.