Comparative Genomic Analysis Determines the Functional Genes Related to Bile Salt Resistance in Lactobacillus salivarius

Lactobacillus salivarius has drawn attention because of its promising probiotic functions. Tolerance to the gastrointestinal tract condition is crucial for orally administrated probiotics to exert their functions. However, previous studies of L. salivarius have only focused on the bile salt resistance of particular strains, without uncovering the common molecular mechanisms of this species. Therefore, in this study, we expanded our research to 90 L. salivarius strains to explore their common functional genes for bile salt resistance. First, the survival rates of the 90 L. salivarius strains in 0.3% bile salt solutions were determined. Comparative genomics analysis was then performed to screen for the potential functional genes related to bile salt tolerance. Next, real-time polymerase chain reaction and gene knockout experiments were conducted to further verify the tolerance-related functional genes. The results indicated that the strain-dependent bile salt tolerance of L. salivarius was mainly associated with four peptidoglycan synthesis-related genes, seven phosphotransferase system-related genes, and one chaperone-encoding gene involved in the stress response. Among them, the GATase1-encoding gene showed the most significant association with bile salt tolerance. In addition, four genes related to DNA damage repair and substance transport were redundant in the strains with high bile salt tolerance. Besides, cluster analysis showed that bile salt hydrolases did not contribute to the bile salt tolerance of L. salivarius. In this study, we determined the global regulatory genes, including LSL_1568, LSL_1716 and LSL_1709, for bile salt tolerance in L. salivarius and provided a potential method for the rapid screening of bile salt-tolerant L. salivarius strains, based on PCR amplification of functional genes

Ag/AgX (X = Cl, Br, or I) Nanocomposite Loaded on Ag₃PO₄ Tetrapods as a Photocatalyst for the Degradation of Contaminants

A silver phosphate (Ag3PO4)/silver (Ag)/silver halide (AgX, X = Cl, Br, or I) ternary composite photocatalysts were prepared by loading Ag nanoparticles on Ag3PO4 tetrapods followed with in situ halogenation. The interface charge transfer behavior in the Ag3PO4/Ag/AgX nanocomposite was studied, and the photocatalytic performance was also evaluated. The results show that the Ag3PO4/Ag/AgI photocatalyst exhibits higher photocatalytic activity than the other two photocatalysts due to the more matched band structure between AgI and Ag3PO4. An internal electric field (IEF) from Ag3PO4 to AgI is formed at the heterogeneous interface, so the photogenerated electrons at the conduction band of AgI can rapidly transfer to the valence band of Ag3PO4 and recombine with photogenerated holes, which is consistent with the S-scheme charge transfer mechanism. Meanwhile, the photogenerated electrons left at the conduction band of Ag3PO4 can transfer to Ag nanoparticles due to the Schottky junction and react with oxygen to produce •O2–, which is proved to be the main active species in the photocatalytic procedure. This tandem junction modulated between the S-scheme heterojunction and Schottky junction promotes the efficient separation of photogenerated carriers, thus significantly increasing the average PL lifetime of electrons by 2.95 times. Therefore, the Ag3PO4/Ag/AgI photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene blue and norfloxacin. The seven consecutive cyclic tests prove the good stability of the photocatalyst, thus showing the application potential in the field of sewage treatment