This study evaluated the probiotic potential of B. velezensis JW through experimental and genomic analysis approaches. Strain JW showed antimicrobial activity against a broad range of fish pathogenic bacteria including Aeromonas hydrophila, Aeromonas salmonicida, Lactococcus garvieae, Streptococcus agalactiae, and Vibrio Parahemolyticus. Fish (Carassius auratus) were fed with the diets containing 0 (control), 10, and 10 cfu/g of B. velezensis JW for 4 weeks. Various immune parameters were examined at 1, 2, 3, and 4 weeks of post-feeding. Results showed that JW supplemented diets significantly increased acid phosphatase (ACP), alkaline phosphatase (AKP), and glutathione peroxidase (GSH-PX) activity. The mRNA expression of immune-related genes in the head kidney of C. auratus was measured. Among them, the interferon gamma gene (IFN- γ) and tumor necrosis factor-α (TNF-α) showed higher expression after 3 and 4 weeks of feeding (P < 0.05). The expression of interleukin-1 (IL-1) only being significantly upregulated by 10 cfu/g of JW after 1 week of feeding (P < 0.05). The upregulation of interleukin-4 (IL-4) increased over time from 1st to 4th week. The expression of interleukin-10 (IL-10) and interleukin-12 (IL-12) showed an opposite expression pattern with IL-10 significantly upregulated and IL-12 significantly downregulated by JW containing diets at 2, 3, and 4 weeks of post-feeding (P < 0.05). Moreover, fish fed with JW supplemented diets showed significantly improved survival rate after A. hydrophila infection. The analysis of the genome of JW revealed several features aiding host health and being relevant to the GIT adaptation. Four bacteriocins, three Polyketide Synthetase (PKS), and five Nonribosomal Peptide-Synthetase (NRPS) gene clusters were identified in the genome. In summary, the above results clearly proved that B. velezensis JW has the potential to be developed as a probiotic agent in aquaculture.
The stability of gut microbiota is essential for the host health. Parabacteroides spp., core members of the human gut microbiota, have average abundance of 1.27% in the human of 12 populations. Parabacteroides has been recently reported to have a close relationship with host health (E.g., metabolic syndrome, inflammatory bowel disease and obesity). Parabacteroides have the physiological characteristics of carbohydrate metabolism and secreting SCFAs. However, antimicrobial resistance of Parabacteroides to antibiotic (such as clindamycin, moxifloxacin and cefoxitin) should not be ignored. In this review, we primarily focused on Parabacteroides distasoniss, Parabacteroides goldsteinii, Parabacteroides johnsonii and Parabacteroides merdae and discussed their relationships with host disease, diet and the prevention or induction of diseases. P. distasonis and P. goldsteinii may be viewed as the potential next generation probiotics (NGP) candidate due to their protective effects on inflammation and obesity in mice. We also discussed the potential therapeutic application of Parabacteroides spp. in maintaining host-intestine homeostasis.
Ichthyophthiriasis is a widespread disease in aquaculture and causes mass mortalities of fish. The development of new antiprotozoal agents for the treatment of Ichthyophthirius multifiliis infections is of increasing interest. The aim of the present study was to investigate the efficacy of 30 medicinal plants against I. multifiliis. The results showed that the methanol extracts of Magnolia officinalis and Sophora alopecuroides displayed the highest antiprotozoal activity against theronts, with 4-h LC(50) values estimated to be 2.45 and 3.43 mg L(-1), respectively. Concentrations of 2.5, 5.0, 10.0, and 20.0 mg L(-1) of M. officinalis extracts resulted in tomont mortality of 9.7, 43.7, 91.3, and 100% at 20 h, respectively. From 40 to 320 mg L(-1) of S. alopecuroides extracts, tomont mortality increased from 29.7 to 100%. Antiprotozoal efficacy against settled tomonts (2 and 10 h) was also applied; the results indicated that encysted I. multifiliis tomonts were less susceptible to these plant extract treatments. In vivo experiments demonstrated that high concentrations of M. officinalis and S. alopecuroides extracts could kill tomonts, and M. officinalis significantly reduced its reproduction (P < 0.05). These results suggested that the methanol extracts of M. officinalis and S. alopecuroides have the potential to be used as an eco-friendly approach for the control of I. multifiliis.
Plant root secreted compounds alter the gene expression of associated microorganisms by acting as signal molecules that either stimulate or repel the interaction with beneficial or harmful species, respectively. However, it is still unclear whether two distinct groups of beneficial bacteria, non-plant-associated (soil) strains and plant-associated (endophytic) strains, respond uniformly or variably to the exposure with root exudates. Therefore, Bacillus mycoides, a potential biocontrol agent and plant growth-promoting bacterium, was isolated from the endosphere of potatoes and from soil of the same geographical region. Confocal fluorescence microscopy of plants inoculated with GFP-tagged B. mycoides strains showed that the endosphere isolate EC18 had a stronger plant colonization ability and competed more successfully for the colonization sites than the soil isolate SB8. To dissect these phenotypic differences, the genomes of the two strains were sequenced and the transcriptome response to potato root exudates was compared. The global transcriptome profiles evidenced that the endophytic isolate responded more pronounced than the soil-derived isolate and a higher number of significant differentially expressed genes were detected. Both isolates responded with the alteration of expression of an overlapping set of genes, which had previously been reported to be involved in plant–microbe interactions; including organic substance metabolism, oxidative reduction, and transmembrane transport. Notably, several genes were specifically upregulated in the endosphere isolate EC18, while being oppositely downregulated in the soil isolate SB8. These genes mainly encoded membrane proteins, transcriptional regulators or were involved in amino acid metabolism and biosynthesis. By contrast, several genes upregulated in the soil isolate SB8 and downregulated in the endosphere isolate EC18 were related to sugar transport, which might coincide with the different nutrient availability in the two environments. Altogether, the presented transcriptome profiles provide highly improved insights into the life strategies of plant-associated endophytes and soil isolates of B. mycoides.
Background
Plant growth-promoting rhizobacteria (PGPR) are good alternatives for chemical fertilizers and pesticides, which cause severe environmental problems worldwide. Even though many studies focus on PGPR, most of them are limited in plant-microbe interaction studies and neglect the pathogens affecting ruminants that consume plants. In this study, we expand the view to the food chain of grass-ruminant-human. We aimed to find biocontrol strains that can antagonize grass pathogens and mammalian pathogens originated from grass, thus protecting this food chain. Furthermore, we deeply mined into bacterial genomes for novel biosynthetic gene clusters (BGCs) that can contribute to biocontrol.
Results
We screened 90 bacterial strains from the rhizosphere of healthy Dutch perennial ryegrass and characterized seven strains (B. subtilis subsp. subtilis MG27, B. velezensis MG33 and MG43, B. pumilus MG52 and MG84, B. altitudinis MG75, and B. laterosporus MG64) that showed a stimulatory effect on grass growth and pathogen antagonism on both phytopathogens and mammalian pathogens. Genome-mining of the seven strains discovered abundant BGCs, with some known, but also several potential novel ones. Further analysis revealed potential intact and novel BGCs, including two NRPSs, four NRPS-PKS hybrids, and five bacteriocins.
Conclusion
Abundant potential novel BGCs were discovered in functional protective isolates, especially in B. pumilus, B. altitudinis and Brevibacillus strains, indicating their great potential for the production of novel secondary metabolites. Our report serves as a basis to further identify and characterize these compounds and study their antagonistic effects against plant and mammalian pathogens.
Bacteriocins are generally considered as low‐molecular‐weight ribosomal peptides or proteins synthesized by G+ and G− bacteria that inhibit or kill other related or unrelated microorganisms. However, low yield is an important factor restricting the application of bacteriocins. This paper reviews mining methods, heterologous expression in different systems, the purification technologies applied to bacteriocins, and identification methods, as well as the antibacterial mechanism and applications in three different food systems. Bioinformatics improves the efficiency of bacteriocins mining. Bacteriocins can be heterologously expressed in different expression systems (e.g., Escherichia coli, Lactobacillus, and yeast). Ammonium sulfate precipitation, dialysis membrane, pH‐mediated cell adsorption/desorption, solvent extraction, macroporous resin column, and chromatography are always used as purification methods for bacteriocins. The bacteriocins are identified through electrophoresis and mass spectrum. Cell envelope (e.g., cell permeabilization and pore formation) and inhibition of gene expression are common antibacterial mechanisms of bacteriocins. Bacteriocins can be added to protect meat products (e.g., beef and sausages), dairy products (e.g., cheese, milk, and yogurt), and vegetables and fruits (e.g., salad, apple juice, and soybean sprouts). The future research directions are also prospected.
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