Optimization and characterization of pullulan production by a newly isolated high-yielding strain Aureobasidium melanogenum.

Pullulan is an extracellular water-soluble polysaccharide with wide applications. In this study, we screened strains that could selectively produce high molecular weight pullulan for application in industrial pullulan production. A new fungus strain A4 was isolated from soil and identified as Aureobasidium melanogenum based on colony characteristics, morphology, and internally transcribed spacer analysis. Thin-layer chromatography, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance analysis suggested that the dominant exopolysaccharide produced by this strain, which presented a molecular weight of 1.384 × 106 Dalton in in-gel permeation chromatography, was pullulan. The culture conditions for A. melanogenum A4 were optimized at 30 °C and 180 rpm: carbon source, 50 g/L maltose; initial pH 7; and 8 g/L Tween 80. Subsequently, batch fermentation was performed under the optimized conditions in a 5-L stirred-tank fermentor with a working volume of 3 L. The fermentation broth contained 303 g/L maltose, which produced 122.34 g/L pullulan with an average productivity of 1.0195 g/L/h and 82.32 g/L dry biomass within 120 h. The conversion efficiency of maltose to pullulan (Y%) and specific production rate (g/h/g dry cells) (Qs) reached 40.3% and 0.0251 g/L/g dry cells, respectively. The results showed strain A4 could be a good candidate for industrial production.

Effect of electronic cigarette and tobacco smoking on the human saliva microbial community.

Increasing evidence demonstrated the oral microbial community profile characteristics affected by conventional cigarettes smoking, but few studies focus on oral microbiome in response to electronic cigarettes (E-cigarettes). This study aimed to investigate the effect of E-cigarettes on the oral microbiome and to describe the difference of oral community profiles between E-cigarette smokers and tobacco smokers. 16S rRNA V4 gene sequencing was performed to investigate the oral microbial profiles of 5 E-cigarette smokers, 14 tobacco smokers, 8 quitting tobacco smokers, and 6 nonsmokers. The Chao1, ACE, and Shannon diversity indexes increased significantly in saliva samples collected from E-cigarette smokers and tobacco smokers compared to the non-smokers, and no significant difference was found in alpha diversity between E-cigarette smokers and tobacco smokers. The main phyla Proteobacteria, Firmicutes, Bacteroidetes, and Fusobacteria and major genera Neisseria, Streptococcus, Prevotellaceae, Fusobacterium, and Porphyromonas dominated in the smoking groups, while Actinobacteria, Proteobacteria, Firmicutes, Bacteroidetes, and Fusobacteria became the dominant phyla along with the genera Corynebacterium, Neisseria, Streptococcus, Actinomyces, and Porphyromonas in the nonsmokers. The differences in the phylum Actinobacteria and genus Corynebacterium contributed to various functional differences between smokers and nonsmokers. The difference on oral microbial and composition between E-cigarettes and common tobacco were associated with increased Prevotellaceae and decreased Neisseria. Additionally, smoking cessation could lead to re-establishment of the oral microbiome to that of nonsmokers. Our data demonstrate that E-cigarette smoking had different effects on the structure and composition of the oral microbial community compared to tobacco smoking. However, the short- and long-term impact of E-cigarette smoking on microbiome composition and function needs further exploration.

Autophagy and Hsp70 activation alleviate oral epithelial cell death induced by food-derived hypertonicity.

Stable intracellular and intercellular osmolarity is vital for all physiological processes. Although it is the first organ that receives food, the osmolarity around the mouth epithelium has never been systematically investigated. We found that oral epithelial cells are a population of ignored cells routinely exposed to hypertonic environments mainly composed of saline, glucose, etc. in vivo after chewing food. By using cultured oral epithelial cells as an in vitro model, we found that the hypotonic environments caused by both high NaCl and high glucose induced cell death in a dose- and time-dependent manner. Transcriptomics revealed similar expression profiles after high NaCl and high glucose stimulation. Most of the common differentially expressed genes were enriched in "mitophagy" and "autophagy" according to KEGG pathway enrichment analysis. Hypertonic stimulation for 1 to 6 h resulted in autophagosome formation. The activation of autophagy protected cells from high osmolarity-induced cell death. The activation of Hsp70 by the pharmacological activator handelin significantly improved the cell survival rate after hypertonic stimulation. The protective role of Hsp70 activation was partially dependent on autophagy activation, indicating a crosstalk between Hsp70 and autophagy in hypertonic stress response. The extract of the handelin-containing herb Chrysanthemum indicum significantly protected oral epithelial cells from hypertonic-induced death, providing an inexpensive way to protect against hypertonic-induced oral epithelial damage. In conclusion, the present study emphasized the importance of changes in osmolarity in oral health for the first time. The identification of novel compounds or herbal plant extracts that can activate autophagy or HSPs may contribute to oral health and the food industry.