Differential anti-microbial properties between the burying beetle Nicrophorus quadripunctatus and the short sexton beetle Necrodes littoralis.

Molecular Characterization, Gene Expression and Antibacterial Activity Analysis of a Novel Piscidin (Piscidin-4) of Largemouth Bass (Micropterus Salmoides)

Piscidins, fish-specific antimicrobial peptides (AMPs), play important roles in the innate immunity of fish against invading bacteria. In this study, a novel piscidin was identified in largemouth bass (Micropterus salmoides) (MSPiscidin-4), which contained an active peptide of 25 aa with an amphipathic helix possessing distinct hydrophobic and positively charged regions. MSPiscidin-4 belongs to the Group I piscidins as determined by sequence identity, homology modeling and phylogenetic tree analysis. MSPiscidin-4 was constitutively expressed in all seven selected tissues, with the highest transcript level in the gill and the lowest in the brain and spleen. Furthermore, MSPiscidin-4 was significantly up-regulated in spleen from 6 h to 24 h post-lipopolysaccharide (LPS) stimulation. A synthetic MSPiscidin-4 peptide was produced by the Fmoc solid-phase synthesis method and exhibited antibacterial activity against several aquatic bacterial strains, with the strongest against Aeromonas hydrophila, followed by Vibrio splendidus, Staphylococcus aureus, Edwardsiella tarda, and the weakest against E. coli and A. veronii. MSPiscidin-4 is the fourth piscidin reported in largemouth bass, showing distinct sequence identity (35.0–68.0% with previously reported MSPiscidins), physicochemical properties (net charge +5, pI 12.48), tissue distribution (highest expression in gill), and antibacterial potency (particularly strong against A. hydrophila). Our results enrich the piscidin components and deepen the understanding of piscidins against invading bacteria in largemouth bass.

Comparative Phenotypic and Transcriptomic Analysis Reveals Distinct Yet Partially Convergent Mechanisms of Daphnetin and 6-Methylcoumarin Against Eucalyptus-Derived Ralstonia pseudosolanacearum

Eucalyptus bacterial wilt in China, caused predominantly by Ralstonia pseudosolanacearum, severely threatens Eucalyptus plantation management in China and demands plant-derived alternatives to conventional bactericides. This study evaluated the in vitro antibacterial activities and underlying molecular mechanisms of two differentially substituted coumarin derivatives, daphnetin (DAP) and 6-methylcoumarin (MC), against a eucalyptus-derived R. pseudosolanacearum strain. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using broth microdilution assays. Quantitative phenotypic assays were conducted to evaluate the effects of sub-lethal concentrations on biofilm formation, swimming motility, and extracellular polysaccharide (EPS) accumulation. Furthermore, high-throughput RNA sequencing integrated with GO and KEGG enrichment analyses was employed to characterize the genome-wide transcriptomic responses. Antimicrobial susceptibility testing demonstrated that DAP possessed superior bactericidal efficacy, yielding lower MIC (62.5 μg/mL) and MBC (250 μg/mL) values than MC. Conversely, sub-lethal MC exhibited a more pronounced, early-stage suppression of flagellum-dependent swimming motility and biofilm maturation. Both compounds consistently attenuated EPS production. Transcriptomic analysis revealed distinct yet partially convergent regulatory networks: DAP primarily exerted metabolic strangulation by downregulating genes governing aerobic respiratory chains and peripheral carbon/nitrogen pathways, whereas MC targeted collective behavior and active pathogenesis, systematically downregulating the expression of genes associated with flagellar assembly, quorum sensing, and Type III and VI secretion systems. Notably, both pathways converged downstream to repress the master virulence regulator xpsR and the epsA-P operon. These findings provide valuable insights into the potential molecular pathways affected by DAP and MC, offering a useful reference for future exploration of botanical formulations for ecologically responsible forest disease control.

Isolation and characterization of an entomopathogenic Serratia strain against rice delphacid planthoppers.

BACKGROUND Delphacid planthoppers (Hemiptera: Delphacidae), including the brown planthopper (Nilaparvata lugens), pose a significant threat to global rice production, highlighting the urgent need for sustainable and effective biological control agents. Here, we isolated a virulent strain of Serratia nematodiphila named BPH1 from diseased N. lugens and characterized its insecticidal activity, genomic features, and virulence-associated phenotypes. RESULTS S. nematodiphila BPH1 exhibited median lethal concentrations (LC50) of 5.5 × 104 and 2.4 × 108 CFU/mL for N. lugens adults and nymphs, respectively. At a concentration of 108 CFU/mL, the median lethal time (LT50) was approximately 15 h for adults and 45 h for nymphs. Whole-genome sequencing revealed a 5.15 Mb draft genome assembly containing a complete prodigiosin biosynthetic gene cluster and multiple serralysin metalloprotease genes, representing candidate virulence-associated genomic features. The strain exhibited extracellular protease activity and swimming and swarming motility in vitro, which are commonly associated with bacterial entomopathogenicity. In insecticidal-spectrum assays, the strain caused mortality in two additional delphacid planthoppers, Laodelphax striatellus and Sogatella furcifera, and in the mosquito Aedes albopictus, whereas it showed no pathogenicity toward the green peach aphid Myzus persicae under the tested conditions. CONCLUSION These results reveal a virulent Serratia strain with strong insecticidal activity against rice planthoppers, and highlight genomic and phenotypic features potentially associated with pathogenicity. © 2026 Society of Chemical Industry.

Medlar (Mespilus germanica) as a new natural host of Pelamoviroid latenspruni (PLMVd): effects on phenology and fruit quality

Hepatincolaceae (Alphaproteobacteria) Symbionts of Snapping Shrimp Alpheus brevicristatus: Genomic Capacity for Functions Beyond Nutrient Scavenging

Candidatus Hepatincolaceae is a poorly characterized family of obligate Alphaproteobacterial symbionts that are widely detected in ecdysozoans. They were previously assumed to play a nutrient-scavenging role in the gut lumen. In this study, two high-quality metagenome-assembled genomes (MAGs, 1.39 Mb and 1.48 Mb in size) were recovered from the gut of the snapping shrimp Alpheus brevicristatus via metagenomic sequencing. Phylogenetic and whole-genome similarity analyses confirm that these two MAGs represent two novel, undescribed genera within the family Ca. Hepatincolaceae. Metabolic reconstruction reveals that they not only retain the canonical nutrient-scavenging pathways conserved across all Hepatincolaceae members, but also encode previously undocumented functional modules for antioxidant defense, vitamin B1 and B2 biosynthesis, and short-chain fatty acid production. They maintain a high oxygen-affinity cytochrome bd terminal oxidase to thrive in the anoxic gut microenvironment. Consistent with their symbiotic lifestyle, their genomes exhibit typical signatures of reductive evolution, such as reduced genome size, low GC content, and gene loss in amino acid and nucleotide de novo biosynthesis pathways. This study presents the first reported high-quality genomes of marine Ca. Hepatincolaceae symbionts, which are predicted to possess multiple metabolic functions extending beyond nutritional mutualism.

Comparative characterization of six teleost piscidins reveals distinct antimicrobial, antibiofilm and stability profiles.