Enhanced Red Emission from Amorphous Silicon Carbide Films via Nitrogen Doping.

The enhanced red photoluminescence (PL) from Si-rich amorphous silicon carbide (a-SiCx) films was analyzed in this study using nitrogen doping. The increase in nitrogen doping concentration in films results in the significant enhancement of PL intensity by more than three times. The structure and bonding configuration of films were investigated using Raman and Fourier transform infrared absorption spectroscopies, respectively. The PL and analysis results of bonding configurations of films suggested that the enhancement of red PL is mainly caused by the reduction in nonradiative recombination centers as a result of the weak Si-Si bonds substituted by Si-N bonds.

Production of bacterial cellulose hydrogels with tailored crystallinity from Enterobacter sp. FY-07 by the controlled expression of colanic acid synthetic genes.

Hydrogels exhibit smart three-dimensional networks and extraordinary water-absorbing ability. To improve the water-holding capacity of bacterial cellulose hydrogels, the expression of a biosynthetic gene cluster of colanic acid, a water-soluble polysaccharide, was induced in Enterobacter sp. FY-07, which produces an abundance of bacterial cellulose hydrogel under aerobic and anaerobic fermentation conditions. The results indicated that in situ modified bacterial cellulose hydrogels with different crystallinities, rheological properties and water-holding capacities were produced by cultivating the engineered strain Enterobacter sp. FY-07::tac under different inducing conditions. The water-holding capacity of the modified bacterial cellulose hydrogel was enhanced by more than 1.7 fold compared to the hydrogel produced by Enterobacter sp. FY-07, and the networks of the modified bacterial cellulose hydrogel were densified but still clear. These results suggest that this in situ modification strategy endows bacterial cellulose hydrogels with improved properties and potentially expands their applications in biomedical fields and the food industry.

Bacterial cellulose synthesis mechanism of facultative anaerobe Enterobacter sp. FY-07.

Enterobacter sp. FY-07 can produce bacterial cellulose (BC) under aerobic and anaerobic conditions. Three potential BC synthesis gene clusters (bcsI, bcsII and bcsIII) of Enterobacter sp. FY-07 have been predicted using genome sequencing and comparative genome analysis, in which bcsIII was confirmed as the main contributor to BC synthesis by gene knockout and functional reconstitution methods. Protein homology, gene arrangement and gene constitution analysis indicated that bcsIII had high identity to the bcsI operon of Enterobacter sp. 638; however, its arrangement and composition were same as those of BC synthesizing operon of G. xylinum ATCC53582 except for the flanking sequences. According to the BC biosynthesizing process, oxygen is not directly involved in the reactions of BC synthesis, however, energy is required to activate intermediate metabolites and synthesize the activator, c-di-GMP. Comparative transcriptome and metabolite quantitative analysis demonstrated that under anaerobic conditions genes involved in the TCA cycle were downregulated, however, genes in the nitrate reduction and gluconeogenesis pathways were upregulated, especially, genes in three pyruvate metabolism pathways. These results suggested that Enterobacter sp. FY-07 could produce energy efficiently under anaerobic conditions to meet the requirement of BC biosynthesis.

The simultaneous production of sphingan Ss and poly(R-3-hydroxybutyrate) in Sphingomonas sanxanigenens NX02.

Sphingans and poly(R-3-hydroxybutyrate) (PHB) are both widely used biopolymers produced by bacteria. In the batch fermentation of Sphingomonas sanxanigenens NX02 in a 5L fermenter using glucose as carbon source, ivory colored sphingan Ss production was a growth-associated process with a maximum purified production of 14.88 ± 0.83 g/L, while 6.08 ± 0.23 g/L PHB was simultaneously produced. Sphingan Ss and PHB were separated by a simple dilution, heating and centrifugation or filtration process, and sphingan Ss can be cost-effectively extracted using a small amount of acid rather than multi-fold volumes of alcohols. From ultrathin sections of S. sanxanigenens NX02, we found that the interior space of the cells was filled with PHB granules, and the outside was surrounded by abundant Ss. The purified sphingan Ss can be used as an excellent gelling and emulsifying agent in biotechnology applications such as food, personal care and production processes. Proposed pathways of Ss and PHB biosynthesis from glucose are also presented.