Antagonistic Effects and the Underlying Mechanisms of Bacillus velezensis and its Antibacterial Peptide LCI Against Aeromonas hydrophila Infection in Largemouth Bass.

Aeromonas hydrophila is one of the most prevalent pathogenic bacteria in largemouth bass. The use of antibiotics to inhibit A. hydrophila poses a significant threat to fish and environmental safety. Bacillus velezensis, a safe bacterium with probiotic and antibacterial characteristics, is an ideal candidate for antagonizing A. hydrophila. This study explored the antagonistic effects of B. velezensis FLU-1 on A. hydrophila in vivo and in vitro. In addition, we explored the antimicrobial peptides (AMPs) produced by strain FLU-1 and clarified the underlying antibacterial mechanisms. The results showed that strain FLU-1 could inhibit a variety of fish pathogens, including A. hydrophila. The challenge test showed that dietary supplementation with B. velezensis FLU-1 significantly improved the survival rate of largemouth bass and reduced the bacterial load in liver. Subsequently, the AMP LCI was isolated from B. velezensis FLU-1 and was found to be effective against A. hydrophila in vitro and in vivo. Transcriptomic analysis revealed that LCI downregulated the genes associated with flagellar assembly and peptidoglycan synthesis in A. hydrophila. Phenotypic test results showed that LCI disrupted the membrane integrity, markedly reduced the biofilm biomass and diminished the swimming motility of A. hydrophila. Furthermore, the results showed that LCI bound to the genomic DNA of A. hydrophila and destroyed the DNA structures. Overall, these findings elucidated the mechanism of action of LCI against A. hydrophila at the phenotypic and physiological levels. This study suggests that B. velezensis FLU-1 and its AMP LCI could serve as antibiotic alternatives for controlling pathogens in aquaculture.

Antipsychotic drug-induced behavioral abnormalities in common carp: The potential involvement of the gut microbiota-brain axis.

The effects of antipsychotic drugs on aquatic organisms have received widespread attention owing to their widespread use and continued release in aquatic environments. The toxicological effects of antipsychotics on aquatic organisms, particularly fish, are unexplored, and the underlying mechanisms remain unelucidated. This study aimed to use common carp to explore the effects of antipsychotics (olanzapine [OLA] and risperidone [RIS]) on behavior and the potential mechanisms driving these effects. The fish were exposed to OLA (0.1 and 10 µg/L) and RIS (0.03 and 3 µg/L) for 60 days. Behavioral tests and neurological indicators showed that exposure to antipsychotics could cause behavioral abnormalities and neurotoxicity in common carp. Further, 16 S rRNA sequencing revealed gut microbiota alteration and decreased relative abundance of some strains related to SCFA production after OLA and RIS exposure. Subsequently, a pseudo-sterile common carp model was successfully constructed, and transplantation of the gut microbiota from antipsychotic-exposed fish caused behavioral abnormalities and neurotoxicity in pseudo-sterile fish. Further, SCFA supplementation demonstrated that SCFAs ameliorated the behavioral abnormalities and neurological damage caused by antipsychotic exposure. To our knowledge, the present study is the first to investigate the effects of antipsychotics on various complex behaviors (swimming performance and social behavior) in common carp, highlighting the potential health risks associated with antipsychotic drug-induced neurotoxicity in fish. Although these results do not fully elucidate the mechanisms underlying the effects of antipsychotic drugs on fish behavior, they serve as a valuable initial investigation and form the basis for future research.

Omics data analysis reveals the system-level constraint on cellular amino acid composition.

Proteins play a pivotal role in coordinating the functions of organisms, essentially governing their traits, as the dynamic arrangement of diverse amino acids leads to a multitude of folded configurations within peptide chains. Despite dynamic changes in amino acid composition of an individual protein (referred to as AAP) and great variance in protein expression levels under different conditions, our study, utilizing transcriptomics data from four model organisms uncovers surprising stability in the overall amino acid composition of the total cellular proteins (referred to as AACell). Although this value may vary between different species, we observed no significant differences among distinct strains of the same species. This indicates that organisms enforce system-level constraints to maintain a consistent AACell, even amid fluctuations in AAP and protein expression. Further exploration of this phenomenon promises insights into the intricate mechanisms orchestrating cellular protein expression and adaptation to varying environmental challenges.

Dietary Bacillus velezensis R-71003 and sodium gluconate improve antioxidant capacity, immune response and resistance against Aeromonas hydrophila in common carp.

This study aimed to evaluate the effects of dietary supplementation with Bacillus velezensis R-71003 combined with sodium gluconate on antioxidant capacity, immune response and resistance against Aeromonas hydrophila in common carp. In addition, the biocontrol potential of the secondary metabolites of B. velezensis R-71003 was also evaluated to analyze the possible mechanism of B. velezensis R-71003 against A. hydrophila. The results indicated that the antibacterial crude extract of B. velezensis R-71003 can destroy the cell wall of A. hydrophila. Moreover, the results showed that dietary B. velezensis R-71003 could promote antioxidant capacity, which significantly increased the activities of CAT and SOD and decreased the content of MDA. Additionally, B. velezensis R-71003 supplementation significantly enhanced the immunity of common carp, as measured by the mRNA expression levels of cytokine-related genes (TNF-α, TGF-ß, IL-1ß and IL-10). In addition, dietary B. velezensis R-71003 exhibited an upregulation of IL-10 and a downregulation of IL-1ß, coupled with higher survival rates when challenged with A. hydrophila compared to the positive group. Furthermore, compared to prechallenge, the mRNA expression levels of TLR-4, MyD88, IRAK1, TRAF6, TRIF and NF-κB in the head kidney of common carp were significantly increased after challenge. The fish fed the B. velezensis R-71003 diet showed lower expression of TLR-4, MyD88, IRAK1, TRAF6, TRIF and NF-κB after the challenge than those fed the control diet. Thus, this study revealed that B. velezensis R-71003 can improve the resistance of common carp to pathogenic bacteria by destroying bacterial cell walls and improving fish immunity by activating the TLR4 signaling pathway. Importantly, this study indicated that sodium gluconate has a positive effect on B. velezensis R-71003 in enhancing the anti-infection ability of common carp. The results of this study will lay the foundation for the application of B. velezensis R-71003 in combination with sodium gluconate as an alternative to antibiotics in aquaculture.

ecBSU1: A Genome-Scale Enzyme-Constrained Model of Bacillus subtilis Based on the ECMpy Workflow.

Genome-scale metabolic models (GEMs) play an important role in the phenotype prediction of microorganisms, and their accuracy can be further improved by integrating other types of biological data such as enzyme concentrations and kinetic coefficients. Enzyme-constrained models (ecModels) have been constructed for several species and were successfully applied to increase the production of commodity chemicals. However, there was still no genome-scale ecModel for the important model organism Bacillus subtilis prior to this study. Here, we integrated enzyme kinetic and proteomic data to construct the first genome-scale ecModel of B. subtilis (ecBSU1) using the ECMpy workflow. We first used ecBSU1 to simulate overflow metabolism and explore the trade-off between biomass yield and enzyme usage efficiency. Next, we simulated the growth rate on eight previously published substrates and found that the simulation results of ecBSU1 were in good agreement with the literature. Finally, we identified target genes that enhance the yield of commodity chemicals using ecBSU1, most of which were consistent with the experimental data, and some of which may be potential novel targets for metabolic engineering. This work demonstrates that the integration of enzymatic constraints is an effective method to improve the performance of GEMs. The ecModel can predict overflow metabolism more precisely and can be used for the identification of target genes to guide the rational design of microbial cell factories.

The antipsychotic drug olanzapine altered lipid metabolism in the common carp (Cyprinus carpio L.): Insight from the gut microbiota-SCFAs-liver axis.

Olanzapine (OLA) is a common drug used to treat schizophrenia and has recently come under increasing scrutiny as an emerging contaminant. However, its impact on lipid metabolism in fish and its mechanisms of action are not well understood. In this study, common carp were exposed to 0, 10, 100, and 250 µM OLA for 60 days. The results indicated that OLA exposure increased weight gain, total cholesterol (TC), low-density lipoprotein (LDL), and triglycerides (TG) and decreased high-density lipoprotein (HDL). In addition, lipids accumulated in the liver of the common carp. To explore the underlying mechanisms of action, gut microbiota, short-chain fatty acids (SCFAs), liver transcripts, and genes related to lipid metabolism were measured. It was discovered that OLA exposure altered the common carp gut microbiota composition and increased the abundance of SCFA-producing bacteria. Correspondingly, this study showed that OLA exposure increased the levels of SCFAs, which are highly relevant to the development of lipid accumulation. Transcriptome sequencing results indicated that OLA exposure could change lipid metabolism signalling pathways, including steroid biosynthesis, the PPAR signalling pathway, asglycerophospholipid metabolism, glycerolipid metabolism, and fatty acid metabolic pathways of the common carp. Additionally, OLA exposure interrupted lipid metabolism by means of significant upregulation of lipid synthesis-related genes, including pparγ, srebp1, and fas. OLA exposure also resulted in significant lipolysis-related gene downregulation, including cpt, lpl, hsl, and pparα. The results of this study indicated that contamination of aquatic environments with OLA alters lipid metabolism in common carp. In addition, the underlying mechanism might be due in part to the modulation of the gut microbiota-SCFA-PPAR signalling pathway.

Bacillus coagulans SCC-19 maintains intestinal health in cadmium-exposed common carp (Cyprinus carpio L.) by strengthening the gut barriers, relieving oxidative stress and modulating the intestinal microflora.

Heavy metal cadmium (Cd) pollution is a serious problem affecting the sustainable development of aquaculture and the safety of aquatic foods. Research about the use of probiotics to attenuate toxic damage caused by Cd2+ in aquatic animals has received widespread attention. Bacillus coagulans (B. coagulans), a kind of probiotics commonly used in aquaculture, has been shown to adsorb Cd2+ both in vivo and vitro. Here, we aimed to determine the effects of B. coagulans on Cd2+ bioaccumulation, gut barrier function, oxidative stress and gut microbiota in common carp following Cd2+ exposure. The fish were exposure to Cd2+ at 0 and 0.5 mg/L and/or fed a B. coagulans-containing diet at 107, 108 and 109 CFU/g for 8 weeks. The results indicated that B. coagulans can maintain gut barrier function in Cd2+-exposed fish by reducing Cd2+ bioaccumulation, increasing the mRNA levels of tight junction protein genes (occludin, claudin-2 and zonula occludens-1), and decreasing the levels of diamine oxidase and D-lactic acid. In addition, B. coagulans could relieve oxidative stress in Cd2+-exposed fish by restoring the activities of glutathione peroxidase, catalase and superoxide dismutase. Moreover, Cd2+ exposure decreased the intestinal microbiota diversity and changed the intestinal microbiota compositions in common carp. However, supplementation with B. coagulans could reverse the altered intestinal microbiota diversity and composition after Cd2+ exposure, decrease the abundance of some pathogens (Shewanella and Vibrio), and increase the abundance of probiotics (Bacillus and Lactobacillus). These results indicate that B. coagulans may serve as a potential antidote for alleviating Cd2+ toxicity.

[Responses of radial growth of Quercus mongolica to stand density and climatic factors in a mountainous area of eastern Liaoning Province, China]. / è¾½ä¸œå±±åŒºè’™å¤æ Žå¾„å‘ç”Ÿé•¿å¯¹æž—åˆ†å¯†åº¦å’Œæ°”å€™å› å­çš„å“åº”.

To explore the effects of stand density and climatic factors on radial growth of Quercus mongolica, we used tree ring chronology to examine the radial growth changes in a secondary Q. mongolica forest under different levels of stand density (thinning). The meteorological data combined with the driving factors of Q. mongolica growth were analyzed. The results showed that the radial growth of Q. mongolica was significantly affected by stand density. The mean annual radial growth of Q. mongolica was 3.12 mm in low-density virgin forest, 1.55 and 1.42 mm in the two medium-density secondary forests, respectively, and 0.96 mm in high-density secondary forest. The thinning intensity of 20% had a limited effect on promoting the radial growth recovery of high-density forest (1900 trees·hm-2), but had a significant effect on medium-density forest (1600 trees·hm-2). The radial growth of Q. mongolica was sensitive to the precipitation changes in January and February of the current year. Thinning reduced the sensitivity of Q. mongolica radial growth to climate. Under scenarios of climate warming and drying, density regulation could be beneficial in mitigating the adverse effects of climate change on the growth of Q. mongolica.