Mechanisms Underlying the Virulence Regulation of Vibrio alginolyticus ND-01 pstS and pstB with a Transcriptomic Analysis

Bacterium-Phage Symbiosis Facilitates the Enrichment of Bacterial Pathogens and Antibiotic-Resistant Bacteria in the Plastisphere

The plastisphere, defined as the ecological niche for microbial colonization of plastic debris, has been recognized as a hotspot of pathogenic and antibiotic-resistant bacteria. However, the interactions between bacteria and phages facilitated by the plastisphere, as well as their impact on microbial risks to public health, remain unclear. Here, we analyzed public metagenomic data from 180 plastisphere and environmental samples, stemming from four different habitats and two plastic types (biodegradable and nonbiodegradable plastics) and obtained 611 nonredundant metagenome-assembled genomes (MAGs) and 4061 nonredundant phage contigs. The plastisphere phage community exhibited decreased diversity and virulent proportion compared to those found in environments. Indexes of phage-host interaction networks indicated significant associations of phages with pathogenic and antibiotic-resistant bacteria (ARB), particularly for biodegradable plastics. Known phage-encoded auxiliary metabolic genes (AMGs) were involved in nutrient metabolism, antibiotic production, quorum sensing, and biofilm formation in the plastisphere, which contributed to enhanced competition and survival of pathogens and ARB hosts. Phages also carried transcriptionally active virulence factor genes (VFGs) and antibiotic resistance genes (ARGs), and could mediate their horizontal transfer in microbial communities. Overall, these discoveries suggest that plastisphere phages form symbiotic relationships with their hosts, and that phages encoding AMGs and mediating horizontal gene transfer (HGT) could increase the source of pathogens and antibiotic resistance from the plastisphere.

Transcriptomic analysis of Vibrio alginolyticus challenged by Rhizoma coptidis reveals mechanisms of virulence genes

Rhizoma coptidis, a Chinese herbal medicine widely used to treat various bacterial infections, has the potential to develop antibiotic substitutes to overcome the drug resistance of Vibrio alginolyticus. To study the inhibitory effect of R. coptidis on V. alginolyticus, we sequenced the transcriptomes of three groups of samples of wild-type V. alginolyticus (CK) and V. alginolyticus, which were stressed by 5 mg/mL R. coptidis for 2 h (RC_2 h) and 4 h (RC_4 h). CK was compared with RC_2 h and RC_4 h, respectively, and a total of 1565 differentially expressed genes (DEGs) (988 up-regulated and 577 down-regulated) and 1737 DEGs (1152 up-regulated and 585 down-regulated) were identified. Comparing RC_2 h with RC_4 h, 156 DEGs (114 up-regulated and 42 down-regulated) were identified. The ability of biofilm formation and motility of V. alginolyticus altered upon with different concentrations of R. coptidis. Interestingly, relative expression patterns of virulence genes appeared statistically significantly varied, upon different concentrations of R. coptidis extract. DEGs were annotated to the Gene Ontology (GO) database for function enrichment analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, the results showed that the main enriched pathways, was those related to the virulence of V. alginolyticus. This study provides a new perspective for understanding the complex pathogenic mechanism of V. alginolyticus. R. coptidis could potnetially be used as alternative or complimnetary to antibiotics to treat infections after further research.

The involvement of the T6SS vgrG gene in the pathogenicity of Pseudomonas plecoglossicida

Pseudomonas plecoglossicida, the causative agent of white spot disease of large yellow croaker, has caused serious economic losses to the aquaculture industry. The type VI secretion system (T6SS) is a significant virulence system widely distributed among Gram-negative bacteria. VgrG, a structural and core component of T6SS, is crucial to the function of T6SS. To explore the biological profiles mediated by vgrG gene and its effects on the pathogenicity of P. plecoglossicida, the vgrG gene deletion (ΔvgrG) strain and complementary (C-ΔvgrG) strain were constructed and the differences in pathogenicity and virulence-related characteristics between different strains were analysed. The results showed that vgrG gene deletion significantly affected the virulence-related characteristics of P. plecoglossicida, including chemotaxis, adhesion, and biofilm formation. In addition, the LD50 of ΔvgrG strain was nearly 50-fold higher than that of the NZBD9 strain. Transcriptome data analysis suggested that the vgrG gene may affect the virulence of P. plecoglossicida by regulating the quorum sensing pathway to inhibit the secretion of virulence factors and affect biofilm formation. Besides, deletion of the vgrG gene may reduce bacterial pathogenicity by affecting bacterial signal transduction processes and the ability to adapt to chemotactic substances.

Genetic analysis of Vibrio alginolyticus challenged by Fructus schisandrae reveals the mechanism of virulence genes

Due to the abusive use of antibiotics, bacterial resistance has become a global problem and poses severe threats to aquaculture. The drug-resistant diseases caused by Vibrio alginolyticus have caused significant economic losses to cultured marine fish. Fructus schisandrae is used to treat inflammatory diseases in China and Japan. There have been no reports of bacterial molecular mechanisms associated with F. schisandrae stress. In this study, the inhibiting effect of F. schisandrae on the growth of V. alginolyticus was detected to understand response mechanisms at the molecular level. The antibacterial tests were analyzed via next-generation deep sequencing technology (RNA sequencing, RNA-seq). Wild V. alginolyticus (CK) was compared with V. alginolyticus, F. schisandrae incubated for 2 h, and V. alginolyticus, F. schisandrae incubated for 4 h. Our results revealed that there were 582 genes (236 upregulated and 346 downregulated) and 1068 genes (376 upregulated and 692 downregulated), respectively. Differentially expressed genes (DEGs) were involved in the following functional categories: metabolic process, single-organism process, catalytic activity, cellular process, binding, membrane, cell part, cell, and localization. FS_2 h was compared with FS_4 h, and 21 genes (14 upregulated and 7 downregulated) were obtained. The RNA-seq results were validated by detecting the expression levels of 13 genes using quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR results matched those of the sequencing, which reinforced the reliability of the RNA-seq. The results revealed the transcriptional response of V. alginolyticus to F. schisandrae, which will provide new ideas for studying V. alginolyticus' complex virulence molecular mechanism and the possibility of developing Schisandra to prevent and treat drug-resistant diseases.