Guangdong Ocean University

Studying the salt tolerance mechanisms of rice under a single substrate has certain limitations. The salt tolerance strategies of rice may differ under different substrate conditions. This study established three substrate types by adjusting the proportions of laterite, peat moss, and river sand: S1 (high sand; low nutrient), S2 (medium sand; medium nutrient), and S3 (low sand; high nutrient). Compared with the respective fresh water control, the magnitude of dry weight reduction in each substrate gradually decreased (S1-S3), indicating that the salt stress was effectively alleviated. KEGG enrichment analysis of differentially expressed genes (DEGs) showed that Xiangliangyou900 may be more dependent on the remodeling of carbon metabolism pathway (compared to nitrogen metabolism) in S1, but the nitrogen metabolism pathway were more significant in S3. In S3, differential metabolites were significantly enriched in carbon and nitrogen metabolism pathways, but no such enrichment was found in S1, indicating that the S3 substrate, with its high nutrient and low river sand content, is more likely to trigger carbon and nitrogen metabolism remodeling. Under salt stress, the methylation level of C bases in the CHH type increased in S1 and decreased in S3. The methylation level of CHH-type C bases in the whole genome was more strongly correlated with the physicochemical parameters of the substrate (compared to CG and CHG types).This study speculated that rice may optimize its ability to adapt to salt stress by specifically regulating the methylation of CHH-type C bases to mediate gene expression. The results of this study help enrich the theoretical system of the rice salt stress response mechanism.

The global rise of antimicrobial resistance has intensified the demand for novel antimicrobial agents with broad-spectrum efficacy and unique mechanisms of action. Herein, a marine-derived strain, Bacillus velezensis (B. velezensis) AM12, exhibiting clear inhibitory activity against eight major foodborne pathogens, was isolated from coastal seawater near Zhanjiang, China. Whole-genome sequencing revealed a 3,992,266 bp circular chromosome with a GC content of 46%, and functional annotation indicated extensive metabolic potential. Genome mining using the antiSMASH platform identified 14 secondary metabolite biosynthetic gene clusters, including those encoding surfactin, macrolactin H, bacillaene, fengycin, difficidin, bacillibactin, and bacilysin, as well as several additional clusters potentially responsible for the biosynthesis of novel antimicrobial compounds. Analysis using the BAGEL4 database further detected four bacteriocin/RiPP biosynthetic loci, corresponding to Competence/ComX, Amylocyclicin, LCI, and a Lichenicidin-like cluster. These collectively explain the broad-spectrum antibacterial activity of AM12 and suggest potential antifungal capability. Notably, the core genes of ComX and LCI exhibited relatively low similarity (46.67% and 73.91%, respectively) to known references, and B. velezensis AM12-origin lichenicidin component 2 showed no detectable homology, suggesting that AM12 may encode structurally and functionally distinct novel bacteriocins. Comparative genomic analysis with closely related terrestrial B. velezensis strains revealed that AM12-specific genes are predominantly enriched in functions associated with marine environmental adaptation and antimicrobial activity. Furthermore, machine learning-based prediction using the AM12-specific gene set identified seven high-confidence antimicrobial peptide candidates characterized by cationic charge, amphipathicity, and structural stability. This study elucidates the genomic and molecular basis of the broad-spectrum antibacterial activity pertaining to B. velezensis AM12, and establishes a systematic framework for the identification of novel antimicrobial peptides, offering candidate genes for subsequent functional characterization.

Marine heatwaves (MHWs) have increased in frequency, intensity, and duration in this era of unprecedented climate change, posing significant threats to bivalves. Yet, the consequences of MHWs for bivalves during reproductive conditioning, which are vital for the recruitment success and population maintenance, remain largely unknown. Here, we assessed the impact of intensifying MHWs on economically and ecologically significant clams (Ruditapes philippinarum) during gonadal maturation. The survival of clams significantly decreased to 56 % following repeated exposure to the most severe thermal scenario of MHWs (22 °C-32 °C for 5 days and then recovery at 22 °C for 5 days for each event). Qualitative evidence suggests that intensifying MHWs resulted in irreversible gonadal impairments in both female and male clams even after two recovery periods. With increasing frequency and intensify of MHWs, activities of energy-metabolizing enzymes (NKA, CMA, and T-ATP) decreased initially and then increased significantly. This pattern agreed well with changes in enzyme performances (e.g., SOD, CAT, MDA, AKP, ACP) and associated gene expressions in the gill antioxidant and immune defence system. Our, our findings demonstrate that R. philippinarum exhibits physiological plasticity in response to MHWs. However, significant increases in mortality and irreversible impairments in gonads underscore the profound impact of intensifying MHWs on bivalves during reproduction, which can affect recruitment success and population maintenance.