Understanding the probiotic potential of Lactobacillus plantarum: Antioxidant capacity, non-specific immunity and intestinal microbiota improvement effects on Manila clam Ruditapes philippinarum.

Lactic acid bacteria (LAB) have beneficial effects on aquatic animals, improving their immune system and intestinal microbiota. Nevertheless, the probiotic effects of LAB on the Manila clam Ruditapes philippinarum remain poorly understood. Herein, the effects of administering Lactobacillus plantarum at final doses of 1 × 105 CFU/L (T5 group), 1 × 107 CFU/L (T7 group), and 1 × 109 CFU/L (T9 group) in the rearing water for eight weeks were evaluated for the antioxidant capacity, non-specific immunity, resistance to Vibrio parahaemolyticus infection, and intestinal microbiota of R. philippinarum. The rearing water without the addition of L. plantarum served as a control. The results showed that the T7 and T9 groups demonstrated a significant elevation in the disease resistance of clams against V. parahaemolyticus, in the activities of alkaline phosphatase and lysozyme in the hepatopancreas, and in the expression of antioxidant- and immune-related genes, including SOD, GPx, and GST. Meanwhile, the T7 group showed a significant enhancement in superoxide dismutase and catalase activities and CAT expression, while the T9 group experienced a remarkable elevation in reduced glutathione content. Only catalase activity was markedly elevated in the T5 group. The expression of SOD, CAT, GPx, and GST was significantly elevated in three treatment groups following the V. parahaemolyticus challenge. The T7 group exhibited a significant increase in intestinal microbiota richness. Significant increases were noted in Firmicutes abundance across all three treatment groups and in Actinobacteriota in the T5 and T7 groups. Additionally, the opportunistic pathogen Escherichia-Shigella abundance significantly decreased in three treatment groups. Furthermore, administration of 1 × 107 CFU/L L. plantarum enhanced the stability of the intestinal microecosystem, whereas a dose of 1 × 109 CFU/L might have a negative effect. The application of three doses of L. plantarum significantly enhanced intestinal microbiota functions related to the immune response and oxidative stress regulation, while a higher dose (1 × 109 CFU/L) might inhibit several functions. In conclusion, the application of L. plantarum in the rearing water exerted beneficial effects on the antioxidant capacity, non-specific immunity, resistance to V. parahaemolyticus, and the intestinal microbiota stability and functions of R. philippinarum. The beneficial effects of L. plantarum on R. philippinarum were dose-dependent, and the final dose of 1 × 107 CFU/L exhibited the optimal effects.

The Antibacterial Activities and Effects of Baicalin on Ampicillin Resistance of MRSA and Stenotrophomonas maltophilia.

The development of novel antibacterial agents from plant sources is emerging as a successful strategy to combat antibiotic resistance in pathogens. In this study, we systemically investigated the antibacterial activity and underlying mechanisms of baicalin against methicillin-resistant Staphylococcus aureus (MRSA) and Stenotrophomonas maltophilia. Our results showed that baicalin effectively restrained bacterial proliferation, compromised the integrity of cellular membranes, increased membrane permeability, and triggered oxidative stress within bacteria. Transcriptome profiling revealed that baicalin disrupted numerous biological pathways related to antibiotic resistance, biofilm formation, cellular membrane permeability, bacterial virulence, and so on. Furthermore, baicalin demonstrated a synergistic antibacterial effect when combined with ampicillin against both MRSA and S. maltophilia. In conclusion, baicalin proves to be a potent antibacterial agent with significant potential for addressing the challenge of antibiotic resistance in pathogens.

Assessment of Multifunctional Activity of a Postbiotic Preparation Derived from Lacticaseibacillus paracasei Postbiotic-P6.

Postbiotics possess various functional activities, closely linked to their source bacterial strains and preparation methods. Therefore, the functional activities of postbiotics need to be evaluated through in vitro and in vivo methods. This study aims to prepare a postbiotic and explore its antihemolytic, anti-inflammatory, antioxidant, and antibacterial activities. Specifically, a postbiotic preparation named PostbioP-6 was prepared by intercepting 1-5 kDa of Lacticaseibacillus paracasei Postbiotic-P6 fermentation broth. The results demonstrate that PostbioP-6 exhibited notable biological activities across multiple assays. It showed significant antihemolytic activity, with a 4.9-48.1% inhibition rate at 10-50% concentrations. Anti-inflammatory effects were observed both in vitro, where 8-40% PostbioP-6 was comparable to 259.1-645.4 µg/mL diclofenac sodium, and in vivo, where 3.5 and 4.0 µL/mL PostbioP-6 significantly reduced neutrophil counts in inflamed zebrafish (p < 0.05). Antioxidant properties were evident through increased reducing power (OD700 increased from 0.279 to 2.322 at 1.25-12.5% concentrations), DPPH radical scavenging activity (38.9-92.4% scavenging rate at 2.5-50% concentrations), and hydroxyl radical scavenging activity (4.66-10.38% scavenging rate at 0.5-4% concentrations). Additionally, PostbioP-6 demonstrated antimicrobial activity against two Gram-positive bacteria, eight Gram-negative bacteria, and one fungus. Furthermore, PostbioP-6 significantly inhibited the increase in peroxide value and malondialdehyde content in cookies, highlighting its potential application in food preservation. In conclusion, we prepared a novel postbiotic, termed PostbioP-6, which proved to have prominent anti-hemolytic, anti-inflammatory, antioxidant, and broad-spectrum antimicrobial activities. The multifunctional properties of PostbioP-6 position it as a potentially effective functional food supplement or preservative. In the future, further research is necessary to elucidate the precise mechanisms of action, identify the active components, and validate its biological activities in animal models or clinical trials.

Shellfish CO2 excretion is modulated by seawater carbonate chemistry but largely independent of pCO2.

Four species of shellfish, blue mussel (Mytilus galloprovincialis), Pacific abalone (Haliotis discus hannai), zhikong scallops (Chlamys farreri), and Pacific oyster (Crassostrea gigas), were exposed to decoupled carbonate system variables to investigate the impacts of different seawater carbonate parameters on the CO2 excretion process of mariculture shellfish. Six experimental groups with two levels of seawater pH (pH 8.1 and pH 7.7) and three levels of total alkalinity (TA = 1000, 2300, and 3600 µmol/kg, respectively) were established, while pH 8.1 and TA = 2300 µmol/kg was taken as control. Results showed that the CO2 excretion rates of these tested shellfish were significantly affected by the change in carbonate chemistry (P < 0.05). At the same TA level, animals incubated in the acidified group (pH 7.7) had a lower CO2 excretion rate than those in the control group (pH 8.1). In comparison, at the same pH level, the CO2 excretion rate increased when seawater TA level was elevated. No significant correlation between the CO2 excretion rate and seawater pCO2 levels (P > 0.05) was found; however, a significant correlation (P < 0.05) between CO2 excretion rate and TA-DIC (the difference between total alkalinity and dissolved inorganic carbon) was observed. Blue mussel has a significantly higher CO2 excretion rate than the other three species in the CO2 excretions per unit mass of soft parts, with no significant difference observed among these three species. However, in terms of CO2 excretion rate per unit mass of gills, abalone has the highest CO2 excretion rate, while significant differences were found between each species. Our studies indicate that the CO2 buffering capacity impacts the CO2 excretion rate of four shellfish species largely independent of pCO2. Since CO2 excretion is related to acid-base balancing, the results imply that the effects of other carbonate parameters, particularly the CO2 buffering capacity, should be studied to fully understand the mechanism of how acidification affects shellfish. Besides, the species difference in gill to soft parts proportion may contribute to the species difference in responding to ocean acidification.

The Application of the Generalized Additive Model to Represent Macrobenthos near Xiaoqing Estuary, Laizhou Bay.

Macrobenthos is widely used as an indicator of ecological health in marine monitoring and assessment. The present study aimed to characterize the interrelationships between the distribution of the macrobenthos community and environmental factors near Xiaoqing Estuary, Laizhou Bay. Responses of species richness to environmental factors were studied using the generalized additive model (GAM) and the Margalef diversity index (dM) as indicators of species diversity instead of individual indicator species. Six factors were selected in the optimal model by stepwise regression: sediment factors (organic matter, phosphate, nitrate nitrogen, and ammonium nitrogen) and water factors (salinity, and ammonium nitrogen). The response curves generated by the GAM showed a unimodal relationship among taxa diversity, salinity in water, and sediment organic matter. dM was positively correlated with ammonium nitrogen in water and was negatively correlated with phosphate in the sediment. The model optimized by forward stepwise optimization explained 92.6% of the Margalef diversity index with a small residual (2.67). The model showed good performance, with the measured dM strongly correlated with the predicted dM (Pearson R2 = 0.845, p < 0.05). The current study examined the combined influence of multiple eco-factors on macrobenthos, and the Margalef diversity index of macrobenthos was predicted by the GAM model in a salinity-stressed estuary.

Influences of Substrate Grain Size on the Burrowing Behavior of Juvenile Meretrix meretrix.

The substrate is the key environmental factor that affects the growth, survival, population and distribution of dwelling mollusks in mudflat settings. To clarify the effect of the substrate grain size on soft substrate preference, burrowing ability and behavior during the selection process of juvenile Meretrix meretrix, four different grain size substrates (coarse sand, medium sand, fine sand, and natural substrate) were set up for comparison. The results indicated that: (1) the burrowing ability of juvenile specimens in fine sand was the strongest; (2) the degree (from high to low) of the juvenile's preference for the four substrates was in the order of fine sand > natural substrate > medium sand > coarse sand; and (3) the selection process of the substrate by the juveniles could be divided into four stages: preparation, selection, burrowing and end stages. These stages showed the behavioral characteristics of a longer selection time and higher percentage of movement in coarse sand. Therefore, our results demonstrated that sea areas or ponds with fine sand as the main component are more suitable for stock enhancement with M. meretrix. These results provide basic data for habitat selection and suitability evaluations for the aquaculture of M. meretrix.