Lean-rich combustion characteristics of methane and ammonia in the combined porous structures for carbon reduction and alternative fuel development.

Ammonia as a carbon-free alternative fuel has received much attention with the consumption of fossil fuels. In order to explore the mixed combustion of methane and ammonia, a combined porous media burner was designed with pellets embedded in annular ceramic foam. And the effects of operating parameters on combustion characteristics were investigated. The results showed that the ammonia addition increased the combustion temperature and reduced carbon dioxide emissions at the equivalence ratio of <1. And the ammonia promoted the conversion of CO2 to CO for an equivalence ratio of >1. With the increasing of the ammonia ratio, the CO selectivity increased but the CO2 selectivity decreased. In addition, the mixed combustion of ammonia and methane improved the hydrogen production. The fuel ratio of methane to ammonia (0.80: 0.20) resulted in higher syngas production and lower CO2 mole fraction. The flame propagated faster in ceramic foam with lower pore densities (20 PPI) so the preheating time was greatly reduced. Moreover, the 40 PPI ceramic foam was conducive to the stability of the flame position in the upstream zone, and the H2 mole fraction achieved 10.60 % at the inlet velocity of 14 cm/s.

Unraveling the significance of calcium as a biofilm promotion signal for Bacillus licheniformis strains isolated from dairy products.

Bacillus licheniformis, a quick and strong biofilm former, is served as a persistent microbial contamination in the dairy industry. Its biofilm formation process is usually regulated by environmental factors including the divalent cation Ca2+. This work aims to investigate how different concentrations of Ca2+ change biofilm-related phenotypes (bacterial motility, biofilm-forming capacity, biofilm structures, and EPS production) of dairy B. licheniformis strains. The Ca2+ ions dependent regulation mechanism for B. licheniformis biofilm formation was further investigated by RNA-sequencing analysis. Results revealed that supplementation of Ca2+ increased B. licheniformis biofilm formation in a dose-dependent way, and enhanced average coverage and thickness of biofilms with complex structures were observed by confocal laser scanning microscopy. Bacterial mobility of B. licheniformis was increased by the supplementation of Ca2+ except the swarming ability at 20 mM of Ca2+. The addition of Ca2+ decreased the contents of polysaccharides but promoted proteins production in EPS, and the ratio of proteins/polysaccharides content was significantly enhanced with increasing Ca2+ concentrations. RNA-sequencing results clearly indicated the variation in regulating biofilm formation under different Ca2+ concentrations, as 939 (671 upregulated and 268 downregulated) and 951 genes (581 upregulated and 370 downregulated) in B. licheniformis BL2-11 were induced by 10 and 20 mM of Ca2+, respectively. Differential genes were annotated in various KEGG pathways, including flagellar assembly, two-component system, quorum sensing, ABC transporters, and related carbohydrate and amino acid metabolism pathways. Collectively, the results unravel the significance of Ca2+ as a biofilm-promoting signal for B. licheniformis in the dairy industry.

Genotype-phenotype evaluation of the heterogeneity in biofilm formation by diverse Bacillus licheniformis strains isolated from dairy products.

The spoilage bacterium Bacillus licheniformis has been identified as a quick and strong biofilm former in the dairy industry. In our previous study, intra-species variation in bacterial biofilms has been observed in diverse B. licheniformis strains from different genetic backgrounds; however, the mechanisms driving the observed heterogeneity of biofilms remain to be determined. In this study, the genotype-phenotype evaluation of the heterogeneity in biofilm formation of four B. licheniformis strains were examined. The heterogeneity in biofilm phenotype was accessed in aspects of bacterial growth and motility, cell viability, biofilm matrix production, and biofilm architectures. The underlying mechanisms of the intra-species variability in biofilms were also explored by whole genome resequencing (WGR). Results from bacterial motility tests showed a diverse motility among the strains, but there was no clear correlation between bacterial motility and biofilm formation. The cell viability results showed a different number of live cells in biofilms at the intra-species level. Analysis of chemical components in biofilm matrix demonstrated the great intra-species differences regarding extracellular matrix composition, and a negative correlation between biofilm formation on stainless steel and the protein: carbohydrate ratio in biofilm matrix was observed. Confocal laser scanning microscopy analysis also revealed the intra-species variability by showing great differences in general properties of B. licheniformis biofilms. WGR results identified important pathways involved in biofilm formation, such as two-component systems, quorum sensing, starch and sucrose metabolism, ABC transporters, glyoxylate and dicarboxylate metabolism, purine metabolism, and a phosphotransferase system. Overall, the above results emphasize the necessity of exploring the intra-species variation in biofilms, and would provide in-depth knowledge for designing efficient biofilm control strategies in the dairy industry.

Invited review: Current perspectives for analyzing the dairy biofilms by integrated multiomics.

Biofilms formed by pathogenic or spoilage microorganisms have become serious issues in the dairy industry, as this mode of life renders such microorganisms highly resistant to cleaning-in-place (CIP) procedures, disinfectants, desiccation, and other control strategies. The advent of omics techniques, especially the integration of different omics tools, has greatly improved our understanding of the features of microbial biofilms, and provided in-depth knowledge on developing effective methods that are directly against deleterious biofilms. This review provides novel insights into the single use of each omics tool and the application of multiomics tools to unravel the mechanisms of biofilm formation, specific molecular phenotypes exhibited by biofilms, and biofilm control strategies. Challenges and future perspective on the integration of omics tools for biofilm studies are also addressed.

Multi-omics reveals the increased biofilm formation of Salmonella Typhimurium M3 by the induction of tetracycline at sub-inhibitory concentrations.

Exposure to sub-inhibitory concentrations (sub-MICs) of antibiotics could induce the biofilm formation of microorganisms, but its underlying mechanisms still remain elusive. In the present work, biofilm formation by Salmonella Typhimurium M3 was increased when in the presence of tetracycline at sub-MIC, and the highest induction was observed with tetracycline at 1/8 MIC. The integration of RNA-sequencing and untargeted metabolomics was applied in order to further decipher the potential mechanisms for this observation. In total, 439 genes and 144 metabolites of S. Typhimurium M3 were significantly expressed after its exposure to 1/8 MIC of tetracycline. In addition, the co-expression analysis revealed that 6 genes and 8 metabolites play a key role in response to 1/8 MIC of tetracycline. The differential genes and metabolites were represented in 12 KEGG pathways, including five pathways of amino acid metabolism (beta-alanine metabolism, tryptophan metabolism, arginine and proline metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, and glutathione metabolism), three lipid metabolism pathways (biosynthesis of unsaturated fatty acids, fatty acid degradation, and fatty acid biosynthesis), two nucleotide metabolism pathways (purine metabolism, and pyrimidine metabolism), pantothenate and CoA biosynthesis, and ABC transporters. Metabolites (anthranilate, indole, and putrescine) from amino acid metabolism may act as signaling molecules to promote the biofilm formation of S. Typhimurium M3. The results of this work highlight the importance of low antimicrobial concentrations on foodborne pathogens of environmental origin.