Antibacterial action mode of quaternized carboxymethyl chitosan/poly(amidoamine) dendrimer core-shell nanoparticles against Escherichia coli correlated with molecular chain conformation.

The action mode of quaternized carboxymethyl chitosan/poly(amidoamine) dendrimer core-shell nanoparticles (CM-HTCC/PAMAM) against Escherichia coli (E. coli) was investigated via a combination of approaches including measurements of cell membrane integrity, outer membrane (OM) and inner membrane (IM) permeability, and scanning electron microscopy (SEM). CM-HTCC/PAMAM dendrimer nanoparticles likely acted in a sequent event-driven mechanism, beginning with the binding of positively charged groups from nanoparticle surface with negative cell surface, thereby causing the disorganization of cell membrane, and subsequent leakage of intracellular components which might ultimately lead to cell death. Moreover, the chain conformation of polymers was taken into account for a better understanding of the antibacterial action mode by means of viscosity and GPC measurements. High utilization ratio of positive charge and large specific surface area generated from a compacted conformation of CM-HTCC/PAMAM, significantly different from the extended conformation of HTCC, were proposed to be involved in the antibacterial action.

Effect of ferrous ion on ε-poly-L-lysine biosynthesis by Streptomyces diastatochromogenes CGMCC3145.

ε-Poly-L-lysine (ε-PL) is known as an amino acid homopolymer occurring in nature. It is mainly produced by bacteria belonging to the family of Streptomycetaceae. In this study, the effect of ferrous ion on the metabolic pathway such as key enzyme activities and substrate consumptions relating to ε-PL production were investigated. When 0.1 mM Fe(2+) was supplemented into the culture medium of Streptomyces diastatochromogenes CGMCC3145 for 72 h of cultivation, the yield of ε-PL and biomass were enhanced by 29.2 and 41.9%, respectively, compared with those of the control. Synchronously, consumptions of glucose, ammoniac nitrogen, and phosphorus were increased by 50, 67.6, and 35.7%, respectively. The enzyme activity measurements showed that the specific activities of proteinase, phosphatase, glutamate dehydrogenase, and aspartate aminotransferase activities were improved for 2.32, 3.68, 1.72, and 1.50 folds, respectively, however, aspartokinase and ε-PL synthetase were hardly affected by ferrous ion. These results manifested that Fe(2+) can improve the yield of ε-PL by promoting aspartate production, and the aspartate was further catalyzed to produce much more L-lysine, precursor for ε-PL biosynthesis.