No abstract

Although metal-organic frameworks (MOFs) or porous coordination polymers have been widely studied, their antimicrobial activities have not yet been fully investigated. In this work, antifungal activity of copper-based benzene-tricarboxylate MOF (Cu-BTC MOF), which is water stable and industrially interesting, is investigated against Candida albicans, Aspergillus niger, Aspergillus oryzae and Fusarium oxysporum. The Cu-BTC MOF can effectively inhibit the growth rate of C. albicans and remarkably inhibit the spore growth of A. niger, A. oryzae and F. oxysporum. This finding shows the potential of using Cu-BTC MOF as a strong biocidal material against representative yeasts and moulds that are commonly found in the food and agricultural industries.

Bacillus circulans No.4.1 produced a high level of chitinase when cells were grown in tryptic soy broth supplemented with 0.3% colloidal chitin at 35 degrees C for 5 days. Purification was carried out by protein precipitation with 80% saturation ammonium sulfate, anion-exchange chromatography with DEAE-Sephacel, and gel filtration with Sephadex G-100, sequentially. The purified enzyme could be demonstrated as a single band on SDS-PAGE, estimated to be 45 kDa. This enzyme could hydrolyze colloidal chitin, purified chitin, glycol chitin, carboxymethyl-chitin (CM-chitin), and 4-methylumbelliferyl-beta-D-N,N'-diacetylchitobioside [4-MU-(GlcNAc)(2)]. The optimal conditions for this chitinase were pH 8.0 and 40 degrees C. The isoelectric point of the chitinase was 5.1. The amino acid composition of the purified chitinase was determined. The initial 20 amino acid residues of the N-terminal were found to be alanine (A), proline (P), tryptophan (W), asparagine (N), serine (S), lysine (K), glycine (G), asparagine (N), tyrosine (Y), alanine (A), leucine (L), proline (P), tyrosine (Y), tyrosine (Y), arginine (R), glycine (G), alanine (A), tryptophan (W), alanine (A), and valine (V). Knowledge of these properties of chitinase from B. circulans No. 4.1 should be useful in the development of genetically engineered Bacillus sp. as biopesticides.

Dual-function silica-silver core-shell (SiO 2 @Ag) nanoparticles (NPs) with the core diameter of 17 6 2 nm and the shell thickness of about 1.5 nm were produced using a green chemistry. The SiO 2 @Ag NPs were tested in vitro against gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli), both of which are human pathogens. Minimal inhibitory concentrations of the SiO 2 @Ag NPs based on Ag content are 4 and 10 lg mL À1 against S. aureus and E. coli, respectively. These values are similar to those of Ag NPs. SiO 2 @Ag NPs were for the first time incorporated to a commodity polypropylene (PP) polymer. This yielded an advanced multifunctional polymer using current compounding technologies i.e., melt blending by twin-screw extruder and solvent (toluene) blending. The composite containing 5 wt % SiO 2 @Ag NPs (0.05 wt % Ag) exhibited efficient bactericidal activity with over 99.99% reduction in bacterial cell viability and significantly improved the flexural modulus of the PP. Anodic stripping voltammetry, used to investigate the antibacterial mechanism of the composite, indicated that a bactericidal Ag þ agent was released from the composite in an aqueous environment.

A chitinase encoding gene from Bacillus circulans No. 4.1 was cloned in Escherichia coli by using pBluescript II SK. The recombinant plasmid containing the 2.6-kb chitinase gene was designated as pCHIB43. The nucleotide sequence revealed a single open reading frame containing 1794 bp and encoding 598 amino acids with a molecular mass of 65.78 kDa. The gene was sequentially deleted; the deletion clones were designated as pC66, pC6S, pSS6, and pEVS. The clones pC6S, pSS6, and pEVS hydrolyzed soluble chitin, but the ability to hydrolyze colloidal chitin was lost. The deduced amino acid sequence was investigated and found to be a chitin-binding domain and a catalytic domain containing 40 and 57 amino acid residues, respectively. A HindIII-SacI fragment of pSS6 was subcloned into pBluescript SK to reverse the orientation of the gene, and the resulting plasmid pSK43 did produce chitinase. Thus, the cloned gene was expressed under the control of a self-promoter.