RESUMO
The biofilm (BF) provides favorable growth conditions to cells, which has been exploited in the field of industrial biotechnology. Based on our previous research works on type I fimbriae for the biosynthesis of L-threonine (LT) in Escherichia coli, in this study, a fimA-overexpressing strain was engineered, which improved BF formation under industrial fermentation conditions. The morphological observation and characterization of BF formation were conducted to verify the function of the subunit FimA. However, it was not suitable for repeated-batch immobilized fermentation as the LT titer was not elevated significantly. The underlying molecular mechanisms of BF formation and the LT carbon flux were explored by transcriptomic analysis. The results showed that fimA regulated E. coli BF formation but affected LT carbon distribution. This study will stimulate thoughts about how the fimbriae gene regulated biofilms and amino acid excretion and will bring some consideration and provide a reference for the development of BF-based biomanufacturing processes in E. coli.
RESUMO
Almost all reported salts of nucleotides crystallized from solutions are in the form of hydrate. Layered hydrates often occur in crystals with more than five water molecules per host molecule. In the present report, five single-crystal structures of uridine-5'-monophosphate (UMP) series hydrates of acid or salts (UMPNa x ·yH2O, x = 0-2) were determined and analysed. It was found that all crystal hydrates were orthorhombic with a C2221 space group but with mere variation in the plane angle of adjacent bases and the distance between phosphate arms. The packing arrangements of UMPNa x ·yH2O hydrates present typical layered sandwich structures and show that the UMP molecular layers alternate with water molecular layers parallel to the ac plane, linked by hydrogen bonds or coupled with coordinate bonds besides ionic electrostatic interaction. Metal ions were located in water molecular layers as a form of hydration. In addition, we tried to deduce and give insights into the formation of UMPNa x ·yH2O hydrates. The effect of water molecules and metal ions on the crystal structure and stability was investigated. It was found that the coexistence of relatively rigid architectures constructed by host molecules and flexible interlayer regions was a key factor to the formation of these hydrates. Excessive loss of lattice water would give rise to the irreversible collapse of the host structure and loss of ability to recover to the initial state under humidity. Approximately seven crystal-water molecules were the balance point of sodium salt hydrates at room temperature under 43-76% RH conditions. The number of sodium ions in the crystal lattice is positively correlated with their thermal stability.
RESUMO
A novel adsorbent lignin-calcium was fabricated by a simple flocculation-sedimentation approach to remove methylene blue. The structure and morphology of the well-prepared sample were analyzed by multiple characterization methods. Lignin-calcium microspheres demonstrated a mesoporous and inserted layer structure with a coarse surface. Methylene blue (MB) adsorption by lignin-calcium complied with the Langmuir model, showing a maximum adsorption amount of 803.9 mg/g, exceeding that reported in the literature by 3-22-fold. The adsorption kinetics matched the pseudo-second-order model well. The pore volume diffusion model was technically applied to evaluate the mass transfer mechanisms. The effective pore volume diffusion coefficient was 6.28 × 10-12 m2/s. Furthermore, lignin-calcium exhibited excellent adsorbability for methylene blue across a pH range from 3 to 11 and could be regenerated by hydrochloric acid with an elution efficiency of 62.44%. Multiple mechanisms may support the adsorption. Altogether, the tailor-made lignin-calcium is promising as an efficient and sustainable adsorbent for scavenging cationic dyes from dyestuff effluent.
