Application of response surface methodology to optimize the production of antimicrobial metabolites by Micromonospora Y15

Optimizing postbiotic production through solid-state fermentation with Bacillus amyloliquefaciens J and Lactiplantibacillus plantarum SN4 enhances antibacterial, antioxidant, and anti-inflammatory activities

Background

Postbiotics are an emerging research interest in recent years and are fairly advanced compared to prebiotics and probiotics. The composition and function of postbiotics are closely related to fermentation conditions.

Methods

In this study, we developed a solid-state fermentation preparation method for postbiotics with antimicrobial, antioxidant, and anti-inflammatory activities. The antibacterial activity was improved 3.62 times compared to initial fermentation conditions by using optimization techniques such as single factor experiments, Plackett-Burman design (PBD), steepest ascent method (SAM), and central composite design (CCD) methods. The optimized conditions were carried out with an initial water content of 50% for 8 days at 37°C and fermentation strains of Bacillus amyloliquefaciens J and Lactiplantibacillus plantarum SN4 at a ratio of 1:1 with a total inoculum size of 8%. The optimized SSF medium content ratios of peptide powder, wheat bran, corn flour, and soybean meal were 4, 37.4, 30, and 28.6%, respectively.

Results

Under these optimized conditions, postbiotics with a concentration of 25 mg/mL showed significant broad-spectrum antibacterial capabilities against Escherichia coli, Salmonella, and Staphylococcus aureus and strong antioxidant activity against ABTS, DPPH, and OH radicals. Moreover, the optimized postbiotics exhibited good anti-inflammatory ability for reducing nitric oxide (NO) secretion in RAW 264.7 macrophage cells in response to LPS-induced inflammation. Furthermore, the postbiotics significantly improved intestinal epithelial wound healing capabilities after mechanical injury, such as cell scratches in IPEC-J2 cells (p < 0.05).

Conclusion

In brief, we developed postbiotics through optimized solid-state fermentation with potential benefits for gut health. Therefore, our findings suggested that the novel postbiotics could be used as potential functional food products for improving body health.

Optimizing total ammonia-nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.

Optimization of Bacillus amyloliquefaciens BLB369 Culture Medium by Response Surface Methodology for Low Cost Production of Antifungal Activity

Bacillus amyloliquefaciens BLB369 is an important plant growth-promoting bacterium, which produces antifungal compounds. A statistics-based experimental design was used to optimize a liquid culture medium using inexpensive substrates for increasing its antifungal activity. A Plackett–Burman design was first applied to elucidate medium components having significant effects on antifungal production. Then the steepest ascent method was employed to approach the experimental design space, followed by an application of central composite design. Three factors were retained (candy waste, peptone, and sodium chloride), and polynomial and original trigonometric models fitted the antifungal activity. The trigonometric model ensured a better fit. The contour and surface plots showed concentric increasing levels pointing out an optimized activity. Hence, the polynomial and trigonometric models showed a maximal antifungal activity of 251.9 (AU/mL) and 255.5 (AU/mL) for (19.17, 19.88, 3.75) (g/L) and (19.61, 20, 3.7) (g/L) of candy waste, peptone, and NaCl, respectively. This study provides a potential strategy for improving the fermentation of B. amyloliquefaciens BLB369 in low-cost media for large-scale industrial production.

Use of a model to understand the synergies underlying the antibacterial mechanism of H2O2-producing honeys

Honey has been valued as a powerful antimicrobial since ancient times. However, the understanding of the underlying antibacterial mechanism is incomplete. The complexity and variability of honey composition represent a challenge to this scope. In this study, a simple model system was used to investigate the antibacterial effect of, and possible synergies between, the three main stressors present in honey: sugars, gluconic acid, and hydrogen peroxide (H₂O₂), which result from the enzymatic conversion of glucose on honey dilution. Our results demonstrated that the synergy of H₂O₂ and gluconic acid is essential for the antibacterial activity of honey. This synergy caused membrane depolarization, destruction of the cell wall, and eventually growth inhibition of E. coli K-12. The presence of H₂O₂ stimulated the generation of other long-lived ROS in a dose-dependent manner. Sugars caused osmosis-related morphological changes, however, decreased the toxicity of the H₂O₂/gluconic acid. The susceptibility of catalase and general stress response sigma factor mutants confirmed the synergy of the three stressors, which is enhanced at higher H₂O₂ concentrations. By monitoring cellular phenotypic changes caused by model honey, we explained how this can be bactericidal even though the antimicrobial compounds which it contains are at non-inhibitory concentrations.

Extending the "One Strain Many Compounds" (OSMAC) Principle to Marine Microorganisms

Genomic data often highlights an inconsistency between the number of gene clusters identified using bioinformatic approaches as potentially producing secondary metabolites and the actual number of chemically characterized secondary metabolites produced by any given microorganism. Such gene clusters are generally considered as “silent”, meaning that they are not expressed under laboratory conditions. Triggering expression of these “silent” clusters could result in unlocking the chemical diversity they control, allowing the discovery of novel molecules of both medical and biotechnological interest. Therefore, both genetic and cultivation-based techniques have been developed aimed at stimulating expression of these “silent” genes. The principles behind the cultivation based approaches have been conceptualized in the “one strain many compounds” (OSMAC) framework, which underlines how a single strain can produce different molecules when grown under different environmental conditions. Parameters such as, nutrient content, temperature, and rate of aeration can be easily changed, altering the global physiology of a microbial strain and in turn significantly affecting its secondary metabolism. As a direct extension of such approaches, co-cultivation strategies and the addition of chemical elicitors have also been used as cues to activate “silent” clusters. In this review, we aim to provide a focused and comprehensive overview of these strategies as they pertain to marine microbes. Moreover, we underline how changes in some parameters which have provided important results in terrestrial microbes, but which have rarely been considered in marine microorganisms, may represent additional strategies to awaken “silent” gene clusters in marine microbes. Unfortunately, the empirical nature of the OSMAC approach forces scientists to perform extensive laboratory experiments. Nevertheless, we believe that some computation and experimental based techniques which are used in other disciplines, and which we discuss; could be effectively employed to help streamline the OSMAC based approaches. We believe that natural products discovery in marine microorganisms would be greatly aided through the integration of basic microbiological approaches, computational methods, and technological innovations, thereby helping unearth much of the as yet untapped potential of these microorganisms.